Small Nuclear Power Reactors

(Updated September 2020)

There is strong interest in small and simpler units for generating electricity from nuclear power, and for process heat.

This interest in small and medium nuclear power reactors is driven both by a desire to reduce the impact of capital costs and to provide power away from large grid systems.

The technologies involved are numerous and very diverse.

As nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MWe to more than 1600 MWe, with corresponding economies of scale in operation. At the same time there have been many hundreds of smaller power reactors built for naval use (up to 190 MW thermal) and as neutron sourcesa, yielding enormous expertise in the engineering of small power units. The International Atomic Energy Agency (IAEA) defines 'small' as under 300 MWe, and up to about 700 MWe as 'medium' – including many operational units from the 20th century. Together they have been referred to by the IAEA as small and medium reactors (SMRs). However, 'SMR' is used more commonly as an acronym for 'small modular reactor', designed for serial construction and collectively to comprise a large nuclear power plant. (In this paper the use of diverse pre-fabricated modules to expedite the construction of a single large reactor is not relevant.) A subcategory of very small reactors – vSMRs – is proposed for units under about 15 MWe, especially for remote communities.

Today, due partly to the high capital cost of large power reactors generating electricity via the steam cycle and partly to the need to service small electricity grids under about 4 GWe,b there is a move to develop smaller units. These may be built independently or as modules in a larger complex, with capacity added incrementally as required (see section below on Modular construction using small reactor units). Economies of scale are envisaged due to the numbers produced. There are also moves to develop independent small units for remote sites. Small units are seen as a much more manageable investment than big ones whose cost often rivals the capitalization of the utilities concerned.

An additional reason for interest in SMRs is that they can more readily slot into brownfield sites in place of decommissioned coal-fired plants, the units of which are seldom very large – more than 90% are under 500 MWe, and some are under 50 MWe. In the USA coal-fired units retired over 2010-12 averaged 97 MWe, and those expected to retire over 2015-25 average 145 MWe.

Small modular reactors (SMRs) are defined as nuclear reactors generally 300MWe equivalent or less, designed with modular technology using module factory fabrication, pursuing economies of series production and short construction times. This definition, from the World Nuclear Association, is closely based on those from the IAEA and the US Nuclear Energy Institute. Some of the already-operating small reactors mentioned or tabulated below do not fit this definition, but most of those described do fit it.

This paper focuses on advanced designs in the small category, i.e. those now being built for the first time or still on the drawing board, and some larger ones which are outside the mainstream categories dealt with in the Advanced Nuclear Power Reactors information paper. Note that many of the designs described here are not yet actually taking shape. Four main options are being pursued: light water reactors, fast neutron reactors, graphite-moderated high temperature reactors and various kinds of molten salt reactors (MSRs). The first has the lowest technological risk, but the second (FNR) can be smaller, simpler and with longer operation before refuelling. Some MSRs are fast-spectrum.

SMR development is proceeding in Western countries with a lot of private investment, including small companies. The involvement of these new investors indicates a profound shift taking place from government-led and -funded nuclear R&D to that led by the private sector and people with strong entrepreneurial goals, often linked to a social purpose. That purpose is often deployment of affordable clean energy, without carbon dioxide emissions.

A 2011 report for the US Department of Energy by the University of Chicago Energy Policy Institute18 said that small reactors could significantly mitigate the financial risk associated with full‐scale plants, potentially allowing small reactors to compete effectively with other energy sources.

Generally, modern small reactors for power generation, and especially SMRs, are expected to have greater simplicity of design, economy of series production largely in factories, short construction times, and reduced siting costs. Most are also designed for a high level of passive or inherent safety in the event of malfunctionc. Also many are designed to be emplaced below ground level, giving a high resistance to terrorist threats. A 2010 report by a special committee convened by the American Nuclear Society showed that many safety provisions necessary, or at least prudent, in large reactors are not necessary in the small designs forthcoming. This is largely due to their higher surface area to volume (and core heat) ratio compared with large units. It means that a lot of the engineering for safety including heat removal in large reactors is not needed in the small reactorsd. Since small reactors are envisaged as replacing fossil fuel plants in many situations, the emergency planning zone required is designed to be no more than about 300 m radius. The combined tables from this report are appended, along with notes of some early small water-, gas-, and liquid metal-cooled reactors.

Licensing is potentially a challenge for SMRs, as design certification, construction and operation licence costs are not necessarily less than for large reactors. Several developers have engaged with the Canadian Nuclear Safety Commission's (CNSC's) pre-licensing vendor design review process, which identifies fundamental barriers to licensing a new design in Canada and assures that a resolution path exists. The pre-licensing review is essentially a technical discussion, phase 1 of which involves about 5000 hours of staff time, considering the conceptual design and charged to the developer. Phase 2 is twice that, addressing system-level design.

A World Nuclear Association 2015 report on SMR standardization of licensing and harmonization of regulatory requirements17 said that the enormous potential of SMRs rests on a number of factors:

Because of their small size and modularity, SMRs could almost be completely built in a controlled factory setting and installed module by module, improving the level of construction quality and efficiency.

Their small size and passive safety features lend them to countries with smaller grids and less experience of nuclear power.

Size, construction efficiency and passive safety systems (requiring less redundancy) can lead to easier financing compared to that for larger plants.

Moreover, achieving ‘economies of series production’ for a specific SMR design will reduce costs further.

The World Nuclear Association lists the features of an SMR, including:

Small power and compact architecture and usually (at least for nuclear steam supply system and associated safety systems) employment of passive concepts. Therefore there is less reliance on active safety systems and additional pumps, as well as AC power for accident mitigation.

The compact architecture enables modularity of fabrication (in-factory), which can also facilitate implementation of higher quality standards.

Lower power leading to reduction of the source term as well as smaller radioactive inventory in a reactor (smaller reactors).

Potential for sub-grade (underground or underwater) location of the reactor unit providing more protection from natural (e.g. seismic or tsunami according to the location) or man-made (e.g. aircraft impact) hazards.

The modular design and small size lends itself to having multiple units on the same site.

Lower requirement for access to cooling water – therefore suitable for remote regions and for specific applications such as mining or desalination.

Ability to remove reactor module or in-situ decommissioning at the end of the lifetime.

A 2009 assessment by the IAEA under its Innovative Nuclear Power Reactors & Fuel Cycle (INPRO) programme concluded that there could be 96 small modular reactors (SMRs) in operation around the world by 2030 in its 'high' case, and 43 units in the 'low' case, none of them in the USA. (In 2011 there were 125 small and medium units – up to 700 MWe – in operation and 17 under construction, in 28 countries, totaling 57 GWe capacity.) The IAEA has a programme assessing a conceptual multi-application small light water reactor (MASLWR) design with integral steam generators, focused on natural circulation of coolant, and in 2003 the US DOE published a report on this MASLWR conceptual design. Several of the integral PWR designs below have some similarities.

There are a number of small modular reactors coming forward requiring fuel enriched at the top end of what is defined as low-enriched uranium (LEU) – 20% U-235. The US Nuclear Infrastructure Council (NIC) has called for some of the downblending of military HEU to be only to about 19.75% U-235, so as to provide a small stockpile of fuel which would otherwise be very difficult to obtain (since civil enrichment plants normally cannot go above 5%). A reserve of 20 tonnes of high-assay low-enriched uranium (HALEU) has been suggested. The NIC said that the only supply of fuel for many advanced reactors under development would otherwise be foreign-enriched uranium. “Without a readily available domestic supply of higher enriched LEU in the USA, it will be extremely difficult to conduct research on advanced reactors, potentially driving American innovators overseas.” In 2019 the DOE contracted with Centrus Energy to deploy a cascade of large centrifuges to produce HALEU fuel for advanced reactors. Urenco USA has announced its readiness to supply HALEU from a dedicated production line at its New Mexico plant.

US support for SMRs

In January 2012 the DOE called for applications from industry to support the development of one or two US light-water reactor designs, allocating $452 million over five years through the SMR Licensing Technical Support (LTS) programme. Four applications were made, from Westinghouse, Babcock & Wilcox, Holtec, and NuScale Power, the units ranging from 225 down to 45 MWe. The DOE announced its decision in November 2012 to support the B&W 180 MWe mPower design, to be developed with Bechtel and TVA. Through the five-year cost-share agreement, the DOE would invest up to half of the total project cost, with the project's industry partners at least matching this. The total would be negotiated between DOE and B&W, and DOE had paid $111 million by the end of 2014 before announcing that funds were cut off due to B&W shelving the project. However B&W is not required to repay any of the DOE money, and the project, capped at $15 million per year, is now under BWX Technologies. The company had spent more than $375 million on the mPower programme to February 2016.

In March 2012 the DOE signed agreements with three companies interested in constructing demonstration small reactors at its Savannah River site in South Carolina. The three companies and reactors are: Hyperion (now Gen4 Energy) with a 25 MWe fast reactor, Holtec with a 160 MWe PWR, and NuScale with its 45 MWe PWR (since increased to 60 MWe). The agreements concerned the provision of land but not finance. The DOE was in discussion with four further small reactor developers regarding similar arrangements, aiming to have in 10-15 years a suite of small reactors providing power for the DOE complex. (Over 1953-1991, Savannah River was where a number of production reactors for weapons plutonium and tritium were built and run.)

In March 2013 the DOE called for applications for second-round funding, and proposals were made by Westinghouse, Holtec, NuScale, General Atomics, and Hybrid Power Technologies, the last two being for EM2 and Hybrid SMR, not PWRs. Other (non-PWR) small reactor designs will have modest support through the Reactor Concepts RD&D programme. A late application "from left field" was from National Project Management Corporation (NPMC) which includes a cluster of regional partners in the state of New York, South Africa’s PBMR company, and National Grid, the UK-based grid operator with 3.3 million customers in New York, Massachusetts and Rhode Island.*

* The project is for an HTR of 165 MWe, apparently the earlier direct-cycle version of the shelved PBMR, emphasising its ‘deep burn’ attributes in destroying actinides and achieving high burn-up at high temperatures. The PBMR design was a contender with Westinghouse backing for the US Next-Generation Nuclear Power (NGNP) project, which has stalled since about 2010.

In December 2013 the DOE announced that a further grant would be made to NuScale on a 50-50 cost-share basis, for up to $217 million over five years, to support design development and NRC certification and licensing of its initially 45 MWe small reactor design, subsequently increased to 60 MWe. In mid-2013 NuScale launched the Western Initiative for Nuclear (WIN) – a broad, multi-western state collaboration – to study the demonstration and deployment of multi-module NuScale SMR plants in the western USA. WIN includes Energy Northwest (ENW) in Washington and Utah Associated Municipal Power Systems (UAMPS). It is now called the Carbon-Free Power Project. A demonstration NuScale SMR built as part of Project WIN is projected to be operational by 2024, at the DOE’s Idaho National Laboratory (INL), with UAMPS as the owner and ENW the operator. This would be followed by a full-scale 12-module plant (720 MWe) there owned by UAMPS, run by Energy Northwest, and costing $5000/kW on an overnight basis, hence about $3.0 billion.

In January 2014 Westinghouse announced that was suspending work on its small modular reactors in the light of inadequate prospects for multiple deployment. The company said that it could not justify the economics of its SMR without government subsidies, unless it could supply 30 to 50 of them. It was therefore delaying its plans, though small reactors remain on its agenda. In 2016 however, the company was much more positive about SMRs. See also UK Support subsection below. However, in March 2017 BWXT suspended work on the mPower design, after Bechtel withdrew from the project.

The Small Modular Reactor Research and Education Consortium (SmrREC) has been set up by Missouri University of Science and Technology to investigate the economics of deploying multiple SMRs in the country. SmrREC has constructed a comprehensive model of the business, manufacturing and supply chain needs for a new SMR-centric nuclear industry.

A mid-2015 article sets out US SMR developments.

Early in 2016 developers and potential customers for SMRs set up the SMR Start consortium to advance the commercialization of SMR reactor designs. Members of the consortium include Bechtel, BWX Technologies, Dominion, Duke Energy, Energy Northwest, Fluor, GE Hitachi Nuclear Energy, Holtec, NuScale, Ontario Power, PSEG Nuclear, Southern Nuclear, Tennessee Valley Authority (TVA) and UAMPS. The organization will represent the companies in interactions with the US Nuclear Regulatory Commission (NRC), Congress and the executive branch on small reactor issues. US industry body the Nuclear Energy Institute (NEI) is assisting in the formation of the consortium, and is to work closely with the organization on policies and priorities relating to small reactor technology.

SMR Start has called for the DOE’s LTS programme for SMRs to be extended to 2025 with an increase in funding. It pointed out: "Private companies and DOE have invested over $1 billion in the development of SMRs. However, more investment, through public-private partnerships is needed in order to assure that SMRs are a viable option in the mid-2020s. In addition to accomplishing the public benefit from SMR deployment, the federal government would receive a return on investment through taxes associated with investment, job creation and economic output over the lifetime of the SMR facilities that would otherwise not exist without the US government's investment.”

In February 2016 TVA said it was still developing a site at Oak Ridge for a SMR and would apply for an early site permit (ESP, with no technology identified) for Clinch River in May with a view to building up to 800 MWe of capacity there. TVA has expanded discussions from B&W to include three other light-water SMR vendors. The DOE is supporting this ESP application financially from its SMR Licensing Technical Support Program, and in February 2016 DOE said it was committed to provide $36.3 million on cost-share basis to TVA.

Another area of small reactor development is being promoted by the DOE’s Advanced Research Projects Agency – Energy (ARPA-E) set up under a 2007 act. This focuses on high-potential, high-impact energy technologies that are too early for private-sector investment. ARPA-E is now beginning a new fission programme to examine microreactor technologies, below 10 MWe. This will solicit R&D project proposals for such reactors, which must have very high safety and security margins (including autonomous operations), be proliferation resistant, affordable, mobile, and modular. Targeted applications include remote sites, backup power, maritime shipping, military instillations, and space missions.

The DOE in 2015 established the Gateway for Accelerated Innovation in Nuclear (GAIN) initiative led by Idaho National Laboratory (INL) "to provide the new nuclear energy community with access to the technical, regulatory and financial support necessary to move new nuclear reactor designs toward commercialization. GAIN is based on feedback from the nuclear community and provides a single point of access to the broad range of capabilities – people, facilities, infrastructure, materials and data – across the Energy Department and its national laboratories." In January 2016 the DOE made grants of up to $40 million to X-energy for its Xe-100 pebble-bed HTR and to Southern for its molten chloride fast reactor (MCFR), being developed with TerraPower and Oak Ridge National Laboratory (ORNL).

In mid-2016 the DOE made GAIN grants of nuclear energy vouchers totalling $2 million including to Terrestrial Energy with Argonne National Laboratory, Transatomic Power with ORNL, and Oklo Inc with Argonne and INL for their respective reactor designs. A second round of GAIN voucher grants totalling $4.2 million was made in mid-2017, including to Terrestrial and Transatomic Power both with Argonne, Holtec’s SMR Inventec for the SMR-160 at ORNL, Oklo Inc with Sandia and Argonne, and Elysium with INL and Argonne.

In April 2018, the DOE selected 13 projects to receive $60 million of cost-shared R&D funding for advance nuclear technologies, including the first awards under the US Industry Opportunities for Advance Nuclear Technology Development initiative.

In September 2018 the Nuclear Energy Innovation Capabilities Act and the Department of Energy Research and Innovation Act passed Congress. The first enables private and public institutions to carry out civilian research and development of advanced nuclear energy technologies. Specifically, the Act established the National Reactor Innovation Center to facilitate the siting of privately=funded advanced reactor prototypes at DOE sites through partnerships between the DOE and private industry. The second Act combines seven previously passed science bills to provide policy direction to the DOE on nuclear energy research and development.

In October 2018 the DOE announced that it was proposing to convert metallic high-assay low-enriched uranium (HALEU), with enrichment levels between 5% and 20% U-235, into fuel for research and development purposes. This would be at Idaho National Laboratory's Materials and Fuels Complex and/or the Idaho Nuclear Technology and Engineering Center, to support the development of new reactor technologies with higher efficiencies and longer core lifetimes.

The US Nuclear Regulatory Commission (NRC) has released a draft white paper on its strategy for reviewing licensing applications for advanced non-light water reactor technologies. The NRC said it expects to finalise the draft paper by November, with submission of the first non-LWR application expected by December 2019. By mid-2019 the NRC had been formally notified by six reactor designers of their intention to seek design approval. These included three MSRs, one HTR, one FNR, and the Westinghouse eVinci heatpipe reactor. In December 2019 the Canadian Nuclear Safety Commission (CNSC) and the US NRC selected Terrestrial Energy's Integral Molten Salt Reactor (IMSR) for the first joint technical review of an advanced, non-light water nuclear reactor.

In May 2020 the DOE launched the Advanced Reactor Demonstration Program (ARDP) offering funds, initially $160 million, on a cost-share basis for the construction of two advanced reactors that could be operational within seven years. The ARDP will concentrate resources on designs that are "affordable" to build and operate. The programme would also extend to risk reduction for future demonstrations, and include support under the Advanced Reactor Concepts 2020 pathway for innovative and diverse designs with the potential to be commercial in the mid-2030s. Testing and assessing advanced technologies would be carried out at the Idaho National Laboratory's National Reactor Innovation Center (NRIC). The NRIC started up in August 2019 as part of the DOE's Gateway for Accelerated Innovation in Nuclear (GAIN) initiative, which aims to accelerate the development and commercialisation of advanced nuclear technologies.

UK support for SMRs

The UK government in 2014 published a report on SMR concepts, feasibility and potential in the UK. It was produced by a consortium led by the National Nuclear Laboratory (NNL). Following this, a second phase of work is intended to provide the technical, financial and economic evidence base required to support a policy decision on SMRs. If a future decision was to proceed with UK development and deployment of SMRs, then further work on the policy and commercial approach to delivering them would need to be undertaken, which could lead to a technology selection process for UK generic design assessment (GDA).

In March 2016 the UK Department of Energy & Climate Change (DECC) called for expressions of interest in a competition to identify the best value SMR for the UK. This relates to a government announcement in November 2015 that it would invest at least £250 million over five years in nuclear R&D including SMRs. DECC said the objective of the initial phase was "to gauge market interest among technology developers, utilities, potential investors and funders in developing, commercializing and financing SMRs in the UK." It said the initial stage would be a "structured dialogue" between the government and participants, using a published set of criteria, including that the SMR design must “be designed for manufacture and assembly, and … able to achieve in-factory production of modular components or systems amounting to a minimum of 40% of the total plant cost.”

In December 2017, the Department for Business, Energy & Industrial Strategy (BEIS), DECC's successor department, announced that the SMR competition had been closed. Instead, a new two-phase advanced modular reactor competition was launched, designed to incorporate a wider range of reactor types. Total funding for the Advanced Modular Reactor (AMR) Feasibility and Development (F&D) project is up to £44 million, and 20 bids had been received by the initial deadline of 7 February 2018. In September 2018 it was announced that the following eight organisations were awarded contracts up to £300,000 to produce feasibility studies for the first phase of the AMR F&D project: Advanced Reactor Concepts (ARC-100); DBD (representing China's Institute of Nuclear and New Energy Technology's HTR-PM); LeadCold (SEALER-UK); Moltex Energy (Stable Salt Reactor); Tokamak Energy (compact spherical modular fusion reactor); U-Battery Developments (U-Battery); Ultra Safe Nuclear (Micro-Modular Reactor); and Westinghouse (Westinghouse LFR).

In July 2020, under its AMR programme, BEIS awarded £10 million to each of: Westinghouse, for its 450 MWe LFR; U-Battery consortium for its 4 MWe HTR; and Tokamak Energy for its compact fusion reactor project. A further £5 million will be for British companies and start-ups to develop new ways of manufacturing advanced nuclear parts for modular reactor projects both at home and abroad. Another £5 million is to strengthen the country’s nuclear regulatory regime as it engages with advanced nuclear technologies such as these.

In March 2019 BEIS released a 2016 report on microreactors that defined them as having a capacity up to 100 MWt/30 MWe, and projecting a global market for around 570 units of an average 5 MWe by 2030, total 2850 MWe. It notes that they are generally not water-moderated or water cooled, but "use a compact reactor and heat exchange arrangement, frequently integrated in a single reactor vessel." Most are HTRs.

In 2015 Westinghouse had presented a proposal for a “shared design and development model" under which the company would contribute its SMR conceptual design and then partner with UK government and industry to complete, license and deploy it. The partnership would be structured as a UK-based enterprise jointly owned by Westinghouse, the UK government and UK industry. In October 2016 the company said it would work with UK shipbuilder Cammell Laird as well as the UK’s Nuclear Advanced Manufacturing Research Centre (NAMRC) on a study to explore potential design efficiencies to reduce the lead times of its SMR.

NuScale has said that it aims to deploy its SMR technology in the UK with UK partners, so that the first of its 60 MWe units could be in operation by the mid-2020s. In September 2017 the company released its five-point UK SMR action plan. Rolls Royce has submitted a detailed design to the government for a 220 MWe SMR unit.

Canadian support for SMRs

A June 2016 report for the Ontario Ministry of Energy focused on nine designs under 25 MWe for off-grid remote sites. All had a medium level of technology readiness and were expected to be competitive against diesel. Two designs were integral PWRs of 6.4 and 9 MWe, three were HTRs of 5, 8 and 16 MWe, two were sodium-cooled fast reactors (SFRs) of 1.5/2.8 and 10 MWe, one was a lead-cooled fast reactor (LFR) of 3-10 MWe, and one was an MSR of 32.5 MWe. Four were under 5 MWe (an SFR, LFR, and two HTRs). Ontario distinguishes ‘grid scale’ SMRs above 25 MWe from these (very) small-scale reactors.

The Canadian Nuclear Safety Commission (CNSC) has been conducting pre-licensing vendor design reviews – an optional service to assess a nuclear power plant design based on a vendor's reactor technology – for eight small reactors with capacities in the range of 3-300 MWe. Three further agreements for design review are being negotiated, including GE Hitachi’s BWRX-300, StarCore's HTR and Westinghouse's eVinci. In November 2017 CNSC completed phase 1 for Terrestrial Energy’s IMSR-400. In February 2019 it completed phase 1 for the Ultra-Safe Nuclear Corporation 5 MWe HTR, called a 'micro modular reactor' (MMR), and in March Global First Power submitted a site preparation licence application for an MMR at Chalk River. In October 2019 it completed phase 1 pre-licensing vendor design review for ARC Nuclear Canada’s ARC-100 design. In January 2020 NuScale Power submitted its 60 MWe SMR for pre-licensing vendor design review, and in August 2020 X-energy submitted its 75 MWe Xe-100 HTR design.

In June 2017 Canadian Nuclear Laboratories (CNL) invited expressions of interest in SMRs. This resulted in many responses, including 19 for siting a demonstration or prototype reactor at a CNL-managed site. CNL aims to have a new SMR at its Chalk River site by 2026. Global First Power with its partners Ontario Power Generation and Ultra-Safe Nuclear Corporation was the first to get to the third stage of CNL’s siting evaluation, with its MMR, a 5 MWe HTR. In February 2019 CNL announced that StarCore Nuclear and Terrestrial Energy had qualified to enter the due diligence (second) stage of its siting evaluation for their 14 MWe HTR and 195 MWe IMSR respectively.

In November 2019 CNL announced that Kairos Power, Moltex Canada, Terrestrial Energy and Ultrasafe Nuclear Corporation (UNC) had been selected as the first recipients of support under its Canadian Nuclear Research Initiative (CNRI). This is designed to accelerate SMR deployment by enabling research and development on particular projects and connecting global vendors of SMR technology with the facilities and expertise within Canada's national nuclear laboratories. Recipients are expected to match the value contributed by CNL either in monetary or in-kind contributions.

In November 2018 the Canadian government released its SMR Roadmap, a 10-month nationwide study of SMR technology. The report concludes that Generation IV SMR development is a response to market forces for "smaller, simpler and cheaper" nuclear energy, and the large global market for this technology will be "driven not just by climate change and clean energy policies, but also by the imperatives of energy security and access."

In December 2019 Saskatchewan and New Brunswick agreed to work with Ontario in promoting SMRs to "unlock economic potential across Canada, including rural and remote regions" in line with the national SMR Roadmap. In August 2020 Alberta joined in, flagging the potential for SMRs to be used for the province's northern oil sands industry. The agreement is to also address key issues for SMR deployment including technological readiness, regulatory frameworks, economics and financing, nuclear waste management and public and indigenous engagement.

Chinese support for SMRs

The most advanced small modular reactor project is in China, where Chinergy is starting to build the 210 MWe HTR-PM, which consists of twin 250 MWt high-temperature gas-cooled reactors (HTRs) which build on the experience of several innovative reactors in the 1960s to 1980s.

CNNC New Energy Corporation, a joint venture of CNNC (51%) and China Guodian Corp, is promoting the ACP100 reactor. A preliminary safety analysis report for a single unit demonstration plant at Changjiang was approved in April 2020.

However, China is also developing small district heating reactors of 100 to 200 MWt capacity which may have a strong potential evaluated at around 400 units. The heat market is very large in northern China, now almost exclusively served by coal, causing serious pollution, particularly by dust, particulates, sulfur, and nitrogen oxides.

Overall SMR research and development in China is very active, with vigorous competition among companies encouraging innovation.

Other countries

Urenco has called for European development of very small – 4 MWe – 'plug and play' inherently-safe reactors based on graphite-moderated HTR concepts. It is seeking government support for a prototype "U-Battery" which would run for 5-10 years before requiring refuelling or servicing.

Already operating in a remote corner of Siberia are four small units at the Bilibino co-generation plant. These four 62 MWt (thermal) units are an unusual graphite-moderated boiling water design with water/steam channels through the moderator. They produce steam for district heating and 11 MWe (net) electricity each, remote from any grid. They are the world’s smallest commercial power reactors and have performed well since 1976, much more cheaply than fossil fuel alternatives in the severe climate of this Arctic region, but are due to be retired by 2023.

Looking ahead, and apart from its barge-mounted ones, Rosatom is not positive about small reactors generally.

Also in the small reactor category are the Indian 220 MWe pressurised heavy water reactors (PHWRs) based on Canadian technology, and the Chinese 300-325 MWe PWR such as built at Qinshan Phase I and at Chashma in Pakistan, and now called CNP-300. The Nuclear Power Corporation of India (NPCIL) is now focusing on 540 MWe and 700 MWe versions of its PHWR, and is offering both 220 and 540 MWe versions internationally. These small established designs are relevant to situations requiring small to medium units, though they are not state of the art technology.

Another significant line of development is in very small fast reactors of under 50 MWe. Some are conceived for areas away from transmission grids and with small loads; others are designed to operate in clusters in competition with large units.

Other, mostly larger new designs are described in the information page on Advanced Nuclear Power Reactors.

In December 2019 CEZ in the Czech Republic said it was focusing on 11 SMR designs including these seven: Rosatom's RITM-200, GE Hitachi Nuclear Energy's BWRX-300, NuScale Power's SMR, China National Nuclear Corporation's ACP100, Argentina's CAREM, the South Korean SMART, and Holtec International's SMR-160.

Small reactors operating

Name Capacity Type Developer CNP-300 300 MWe PWR SNERDI/CNNC, Pakistan & China PHWR-220 220 MWe PHWR NPCIL, India EGP-6 11 MWe LWGR at Bilibino, Siberia (cogen, soon to retire) KLT-40S 35 MWe PWR OKBM, Russia RITM-200 50 MWe Integral PWR, civil marine OKBM, Russia

Small reactor designs under construction

Name Capacity Type Developer CAREM-25 27 MWe Integral PWR CNEA & INVAP, Argentina HTR-PM 210 MWe Twin HTR INET, CNEC & Huaneng, China ACPR50S 60 MWe PWR CGN, China

Small reactors for near-term deployment – development well advanced

Name Capacity Type Developer VBER-300 300 MWe PWR OKBM, Russia NuScale 60 MWe Integral PWR NuScale Power + Fluor, USA SMR-160 160 MWe PWR Holtec, USA + SNC-Lavalin, Canada ACP100/Linglong One 125 MWe Integral PWR NPIC/CNPE/CNNC, China SMART 100 MWe Integral PWR KAERI, South Korea BWRX-300 300 MWe BWR GE Hitachi, USA PRISM 311 MWe Sodium FNR GE Hitachi, USA ARC-100 100 MWe Sodium FNR ARC with GE Hitachi, USA Integral MSR 192 MWe MSR Terrestrial Energy, Canada BREST 300 MWe Lead FNR RDIPE, Russia RITM-200M 50 MWe Integral PWR OKBM, Russia

Small reactor designs at earlier stages (or shelved)

Name Capacity Type Developer EM2 240 MWe HTR, FNR General Atomics (USA) VK-300 300 MWe BWR NIKIET, Russia AHWR-300 LEU 300 MWe PHWR BARC, India CAP200 LandStar-V 220 MWe PWR SNERDI/SPIC, China SNP350 350 MWe PWR SNERDI, China ACPR100 140 MWe Integral PWR CGN, China IMR 350 MWe Integral PWR Mitsubishi Heavy Ind, Japan Westinghouse SMR 225 MWe Integral PWR Westinghouse, USA* mPower 195 MWe Integral PWR BWXT, USA* Rolls-Royce SMR 220+ MWe PWR Rolls-Royce, UK PBMR 165 MWe HTR PBMR, South Africa* HTMR-100 35 MWe HTR HTMR Ltd, South Africa Xe-100 75 MWe HTR X-energy, USA MCFR large? MSR/FNR Southern Co, TerraPower, USA SVBR-100 100 MWe Lead-Bi FNR AKME-Engineering, Russia* Westinghouse LFR 300 MWe Lead FNR Westinghouse, USA TMSR-SF 100 MWt MSR SINAP, China PB-FHR 100 MWe MSR UC Berkeley, USA Integral MSR 192 MWe MSR Terrestrial Energy, Canada Moltex SSR-U 150 MWe MSR/FNR Moltex, UK Moltex SSR-W global 150 MWe MSR Moltex, UK Thorcon TMSR 250 MWe MSR Martingale, USA Leadir-PS100 36 MWe Lead-cooled Northern Nuclear, Canada

Very small reactor designs being developed (up to 25 MWe)

Name Capacity Type Developer U-battery 4 MWe HTR Urenco-led consortium, UK Starcore 10-20 MWe HTR Starcore, Quebec MMR-5 5 MWe HTR UltraSafe Nuclear, USA Holos Quad 3-13 MWe HTR HolosGen, USA Gen4 module 25 MWe Lead-bismuth FNR Gen4 (Hyperion), USA Sealer 3-10 MWe Lead FNR LeadCold, Sweden eVinci 0.2-5 MWe Heatpipe FNR Westinghouse, USA Aurora 1.5 MWe Heatpipe FNR Oklo, USA NuScale micro 1-10 MWe Heatpipe NuScale, USA

See also IAEA webpage on Small and Medium Sized Reactors (SMRs) Development, Assessment and Deployment and also UxC listing of SMRs.

* Well-advanced designs understood to be on hold or abandoned.

Military developments of small power reactors from 1950s

US experience and plans

About five decades ago the US Army built eight reactors, five of them portable or mobile. PM1 successfully powered a remote air/missile defence radar station on a mountain top near Sundance, Wyoming for six years to 1968, providing 1 MWe. At Camp Century in northern Greenland the 10 MWt, 1.56 MWe plus 1.05 GJ/hr PM-2A was assembled from prefabricated components, and ran from 1960-64 on high-enriched uranium fuel. Another was the 9 MWt, 1.5 MWe (net) PM-3A reactor which operated at McMurdo Sound in Antarctica from 1962-72, generating a total of 78 million kWh and providing heat. It used high-enriched uranium fuel and was refuelled once, in 1970. MH-1A was the first floating nuclear power plant operating in the Panama Canal Zone from 1968-77 on a converted Liberty ship. It had a 45 MWt/10 MWe (net) single-loop PWR which used low-enriched uranium (4-7%). It used 541 kg of U-235 over ten years and provided power for nine years at 54% capacity factor.

ML-1 was a smaller and more innovative 0.3 MWe mobile power plant with a water-moderated HTR using pressurised nitrogen at 650°C to drive a Brayton closed cycle gas turbine. It used HEU in a cluster of 19 pins, the core being 56 cm high and 56 cm diameter. It was tested over 1962-66 in Idaho. It was about the size of a standard shipping container and was truck-mobile and air-transportable, with 12-hour set-up. The control unit was separate, to be located 150 m away.

All these were outcomes of the Army Nuclear Power Program (ANPP) for small reactor development – 0.1 to 40 MWe – which ran from 1954-77. ANPP became the Army Reactor Office (ARO) in 1992. More recently (2010) the DEER (Deployable Electric Energy Reactor) was being commercialised by Radix Power & Energy for forward military bases or remote mining sites. See later subsection.

A 2018 report from the US Army analysed the potential benefits and challenges of mobile nuclear power plants (MNPPs) with very small modular reactor (vSMR) technology. This followed a 2016 report on Energy Systems for Forward/Remote Operating Bases. The purpose is to reduce supply vulnerabilities and operating costs while providing a sustainable option for reducing petroleum demand and consequent vulnerability. MNPPs would be portable by truck or large aircraft and returned to the USA for refuelling after 10-20 years. They would load-follow and run on low-enriched uranium (<20%), probably as TRISO (tristructural-isotropic) fuel in high-temperature gas-cooled reactors (HTRs).

In January 2019 the Department of Defense (DOD) solicited proposals for a 'small mobile reactor' design which could address electrical power needs in rapid response scenarios – Project Pele. These would make domestic infrastructure resilient to an electrical grid attack and change the logistics of forward operating bases, both by making more energy available and by simplifying fuel logistics needed to support existing, mostly diesel-powered, generators. They would also enable a more rapid response during humanitarian assistance and disaster relief operations. "Small mobile nuclear reactors have the potential to be an across-the-board strategic game changer for the DOD by saving lives, saving money, and giving soldiers in the field a prime power source with increased flexibility and functionality."

Each reactor should be an HTR with high-assay low-enriched uranium (HALEU) TRISO fuel and produce a threshold power of 1-10 MWe for at least three years without refuelling. It must weigh less than 40 tonnes and be sized for transportability by truck, ship, and C-17 aircraft. Designs must be "inherently safe", ensuring that a meltdown is "physically impossible" in various complete failure scenarios such as loss of power or cooling, and must use ambient air as their ultimate heat sink, as well as being capable of passive cooling. The reactor must be capable of being installed to the point of "adding heat" within 72 hours and of completing a planned shutdown, cool down, disconnect and removal of transport in under seven days. The DOD announced its preparation of an environmental impact statement for the reactor in March 2020, and awarded contracts to BWX Technologies, X-energy and Westinghouse for design work over two years, after which a design would be selected. Westinghouse said it would develop the defense-eVinci (DeVinci) mobile design. A prototype microreactor would be built at Idaho National Laboratory or Oak Ridge National Laboratory.

Russian experience

The Joint Institute for Power Engineering and Nuclear Research (Sosny) in Belarus built two Pamir-630D truck-mounted small air-cooled nuclear reactors in 1976, during the Soviet era. The entire plant required several trucks. This was a 0.6 MWe HTR reactor using 45% enriched fuel and driving a gas turbine with nitrogen tetraoxide through the Brayton cycle. After some operational experience the Pamir project was scrapped in 1986. It had been preceded by the 1.5 MWe TES-3, a PWR mounted on four heavy tank chassis, each self-propelled, with the modules (reactor, steam generator, turbine, control) coupled at site. The prototype started up in 1961 at Obninsk, operated to 1965, and was abandoned in 1969.

Since 2010 Sosny has been involved with Luch Scientific Production Association (SRI SIA Luch) and Russia's N.A. Dollezhal Research and Development Institute of Power Engineering (NIKIET or RDIPE) to design a small transportable nuclear reactor. The new design will be an HTR concept similar to Pamir but about 2.5 MWe.

A small Russian HTR which was being developed by NIKIET is the Modular Transportable Small Power Nuclear Reactor (MTSPNR) for heat and electricity supply of remote regions. It is described as a single circuit air-cooled HTR with closed cycle gas turbine. It uses 20% enriched fuel and is designed to run for 25 years without refuelling. A twin unit plant delivers 2 MWe and/or 8 GJ/h. It is also known as GREM. No recent information is available, but an antecedent is the Pamir, from Belarus. More recently NIKIET has described the ATGOR – a transportable HTR with up to six parallel commercial gas-turbine engines with two independent heat sources (a nuclear reactor and a start-up diesel fuelled combustor).

Another NIKIET project is the 6 MWt, 1 MWe Vityaz modular integral light water reactor with two turbine generators, which is transportable as four modules of up to 60 tonnes.

In 2015 it was reported that the Russian defence ministry had commissioned the development of small mobile nuclear power plants for military installations in the Arctic. A pilot project being undertaken by Innovation Projects Engineering Company (IPEC) is a mobile low-power nuclear unit to be mounted on a large truck, tracked vehicle or a sledged platform. Production models will need to be capable of being transported by military cargo jets and heavy cargo helicopters, such as the Mil Mi-26. They need to be fully autonomous and designed for years-long operation without refuelling, with a small number of personnel, and remote control centre. It is assumed but not confirmed that these reactors will be the MTSPNR.

Light water reactors

These are moderated and cooled by ordinary water and have the lowest technologicalrisk, being similar to most operating power and naval reactors today. They mostly use fuel enriched to less than 5% U-235 with no more than a six-year refuelling interval, and regulatory hurdles are likely least of any small reactors.

US experience of small light water reactors (LWRs) has been of small military power plants, mostly PWRs – see above.

Some successful small reactors from the main national programme commenced in the 1950s. One was the Big Rock Point BWR of 67 MWe which operated for 35 years to 1997.

The US Nuclear Regulatory Commission is starting to focus on small light-water reactors using conventional fuel, such as B&W, Westinghouse, NuScale, and Holtec designs including integral types (B&W, Westinghouse, NuScale). Beyond these in time and scope, “the NRC intends to take full advantage of the experience and expertise” of other nations which have moved forward with non light-water designs, and it envisages “having a key role in future international regulatory initiatives.”

Of the following designs, the KLT, VBER and Holtec SMR have conventional pressure vessels plus external steam generators (PV/loop design). The others mostly have the steam supply system inside the reactor pressure vessel ('integral' PWR design). All have enhanced safety features relative to current LWRs. All require conventional cooling of the steam condenser.

In the USA major engineering and construction companies have taken active shares in two projects: Fluor in NuScale, and Bechtel in B&W mPower.

Three new concepts are alternatives to conventional land-based nuclear power plants. Russia's floating nuclear power plant (FNPP) with a pair of PWRs derived from icebreakers is well on the way to commissioning, with the KLT-40S reactors described below and in the Nuclear Power in Russia paper. The next generation is expected to use RITM-200M reactors. China has a similar project for its ACP100 SMR as a FNPP, whilst MIT is developing a floating plant moored offshore with a reactor of about 200 MWe in the bottom part of a cylindrical platform. France's submerged Flexblue power plant, using a 50-250 MWe reactor, was an early concept but is now cancelled.

KLT-40S

Russia's KLT-40S from OKBM Afrikantov is derived from the KLT-40 reactor well proven in icebreakers and now – with low-enriched fuel – on a barge, for remote area power supply. Here a 150 MWt unit produces 35 MWe (gross) as well as up to 35 MW of heat for desalination or district heating (or 38.5 MWe gross if power only). Burn-up is 45 GWd/t. Units are designed to run 3-4 years between refuelling with on-board refuelling capability and used fuel storage. All fuel assemblies are replaced in each such refuelling. At the end of a 12-year operating cycle the whole plant is taken to a central facility for overhaul and storage of used fuel. Operating plant lifetime is 40 years. Two units will be mounted on a 20,000 tonne barge to allow for outages (70% capacity factor). It may also be used in Kaliningrad.

Although the reactor core is normally cooled by forced circulation (four-loop), the design relies on convection for emergency cooling. Fuel is uranium aluminium silicide with enrichment levels of up to 20%, giving up to four-year refuelling intervals. A variant of this is the KLT-20, specifically designed for floating nuclear plants. It is a two-loop version with the same enrichment but with a ten-year refuelling interval.

The first floating nuclear power plant, the Akademik Lomonosov, commenced construction in 2007, and was grid connected in December 2019. (See also Floating nuclear power plants section in the information page on Nuclear Power in Russia.)

RITM-200M

OKBM Afrikantov has developed a compact reactor – RITM-200M – to replace the KLT reactors and to serve in floating nuclear power plants or optimised floating power units (OFPUs) as they are now called by OKBM. It is derived from the RITM-200 power plants in the LK-60 icebreakers, and is an integral 175 MWt/50 MWe PWR with four coolant loops and external main circulation pumps. It has inherent safety features, using low-enriched (<20%) fuel in 199 fuel assemblies. OFPUs will be returned to base for servicing every 10-12 years and no onboard used fuel storage is required. Operational lifetime is 40 years, with possible extension to 60 years. Twin reactor plants in containment have a mass of 2600 tonnes and occupy 6.8 m × 14.6 m × 16.0 m high, requiring a much smaller barge than the KLT-40S units. It is derived from the RITM-200 power plants in the LK-60 icebreakers. A major challenge is the reliability of steam generators and associated equipment which are much less accessible when inside the reactor pressure vessel.

Onshore installation of the RITM-200M is envisaged, with two or more modules of 175 MWt/50 MWe, fuel enriched to almost 20% and 5-7 year fuel cycle.

CNP-300

This is based on the early Qinshan 1 reactor in China as a two-loop PWR, with four operating in Pakistan. It is 1000 MWt, 325 MWe with a design operating lifetime of 40 years. Fuel enrichment is 2.4-3.0%, with refuelling at 12-month intervals. It was designed by Shanghai Nuclear Energy Research & Design Institute (SNERDI).

SNP350

The SNP350 is SNERDI's development of the CNP-300, upgraded in many respects to meet latest performance, economy, and safety requirements. It is 1035 MWt, 350 MWe gross, with design operating lifetime of 60 years and digital I&C systems.

NuScale

A smaller unit is the NuScale Power Module, a 200 MWt, 60 MWe gross integral PWR with natural circulation. In December 2013 the US Department of Energy (DOE) announced that it would support accelerated development of the design for early deployment on a 50-50 cost share basis. An agreement for $217 million over five years was signed in May 2014 by NuScale Power. In September 2017, following acceptance of the company's design certification application (DCA) by the US Nuclear Regulatory Commission (NRC) earlier in the year, NuScale applied for the second part of its loan guarantee with the US DOE.

It will be factory-built with a three-metre diameter pressure vessel and convection cooling, with the only moving parts being the control rod drives. It uses standard PWR fuel enriched to 4.95% in normal PWR fuel assemblies (but which are only 2 m long), with 24-month refuelling cycle. Installed in a water-filled pool below ground level, the 4.6 m diameter, 22 m high cylindrical containment vessel module weighs 650 tonnes and contains the reactor with steam generator above it. A standard power plant would have 12 modules together giving about 720 MWe. An overhead crane would hoist each module from its pool to a separate part of the plant for refuelling. Design operational lifetime is 60 years. It has full passive cooling in operation and after shutdown for an indefinite period, without even DC battery requirement. The NRC concluded in January 2018 that NuScale's design eliminated the need for class 1E backup power – a current requirement for all US nuclear plants. It claims good load-following capability, in line with EPRI requirements and also black start capability.

The UK’s National Nuclear Laboratory (NNL) has confirmed that the reactor can run on MOX fuel. It also said that a 12-module NuScale plant with full MOX cores could consume 100 tonnes of reactor-grade plutonium in about 40 years, generating 200 TWh from it. This would be in line with Areva’s proposal for using the UK plutonium stockpile, especially since Areva is already contracted to make fuel for the NuScale reactor.

NuScale Power Module (NuScale)

The company had estimated in 2010 that overnight capital cost for a 12-module, 540 MWe NuScale plant would be about $4000 per kilowatt, this in 2014 had risen to $5078/kWe net, with LCOE expected to be $100/MWh for first unit (or $90 for NOAK). In June 2018, the company announced that its reactor can generate 20% more power than originally planned. Subject to NRC approval, this would lower the overnight capital cost to about $4200 per kilowatt, and lower the LCOE by 18%.

The NuScale Power company was spun out of Oregon State University in 2007, though the original development was funded by the US Department of Energy. After NuScale experienced problems in funding its development, Fluor Corporation paid over $30 million for 55% of NuScale in October 2011. With the support of Fluor, NuScale expects to bring its technology to market in a timely manner. The DOE sees this as a "near-term LWR design." In August 2013 Rolls-Royce joined the venture to support an application for DOE funding, and in March 2014 Enercon Services took undisclosed equity to become a partner and assist with design certification and COL applications.

NuScale lodged an application for US design certification in January 2017, and in July 2017 the NRC confirmed that its highly integrated protection system (HIPS) architecture was approved. NuScale has been engaged with the NRC since 2008, having spent some $130 million on licensing to November 2013. The NRC certified the design in August 2020 – the first SMR to receive NRC design certification. A COL application is planned. In September 2018 NuScale selected BWX Technologies as the first manufacturer of its SMR after an 18-month selection process. The demonstration unit in Idaho will have dry cooling for the condenser circuit, with a 90% water saving while sacrificing about 5% of its power output to drive the cooling.

In December 2019 NuScale submitted its 60 MWe SMR to the Canadian Nuclear Safety Commission (CNSC) for pre-licensing vendor design review. Phase 2 of this commenced in January 2020.

Earlier in March 2012 the DOE signed an agreement with NuScale regarding constructing a demonstration unit at its Savannah River Site in South Carolina.

In mid-2013 NuScale launched the Western Initiative for Nuclear (WIN) – a broad, multi-western state collaboration* – to study the demonstration and deployment of a multi-module NuScale SMR plant in western USA. WIN includes Energy Northwest (ENW) in Washington and Utah Associated Municipal Power Systems (UAMPS). A demonstration NuScale SMR built as part of Project WIN is projected to be operational in 2029, at the DOE’s Idaho National Laboratory (INL), with UAMPS as the owner and ENW the operator. This would be followed by a full-scale 12-module plant (720 MWe) owned by UAMPS and run by Energy Northwest and costing $5000/kW on overnight basis, hence about $3.0 billion. Energy Northwest comprises 27 public utilities, and had examined small reactor possibilities before choosing NuScale and becoming part of the UAMPS Carbon-Free Power Project.

* Washington, Oregon, Idaho, Wyoming, Utah and Arizona.

NuScale is investigating cogeneration options including desalination (with Aquatech), oil recovery from tar sands and refinery power (with Fluor), hydrogen production by high-temperature steam electrolysis (with INL) and flexible back-up for a wind farm (with UAMPS and Energy Northwest).

Holtec SMR-160

Holtec International has a subsidiary – SMR-160 LLC – to commercialize a 160 MWe factory-built reactor concept called the Holtec Inherently Safe Modular Underground Reactor (HI-SMUR). This has two external horizontal steam generators, and uses PWR fuel assemblies, including MOX. The 32 full-length fuel assemblies are in a fuel cartridge, which is loaded and unloaded as a single unit from the 31-metre high pressure vessel. Holtec claims a one-week refuelling outage every 42 months. It has full passive cooling in operation and after shutdown for an indefinite period, and also a negative temperature coefficient so that it shuts down at high temperatures. The reactor will be offered with optional heat sink to atmosphere, using dry cooling. The whole reactor system will be installed below ground level, with used fuel storage. A 24-month construction period is envisaged for each $800 million unit ($5000/kW). Operational lifetime claimed is 80 years.

Licensing of the SMR-160 in the USA will initially use an NRC process which involves a construction permit followed by an operating licence, and later continuing to design certification under other licensing rules. Holtec submitted its design for pre-application review in 2017. The detailed design phase was from August 2012, and in August 2015 Mitsubishi Electric Power Products and its Japanese parent became a partner in the project, to undertake the digital I&C design* and help with licensing. This was formalised in September 2016 and the cooperation was boosted in mid-2017. In July 2017 a partner agreement with SNC-Lavalin based in Ontario was formalised, involving engineering support and licensing. The design has passed phase 1 of pre-licensing vendor design review with the CNSC.

* all of Japan’s PWRs and 14 Chinese PWRs use Mitsubishi Electric’s I&C technology.

In March 2012 the US DOE signed an agreement with Holtec regarding constructing a demonstration SMR-160 unit at its Savannah River Site in South Carolina. In 2013 NuHub, a South Carolina economic development project, and the state itself supported Holtec's bid for DOE funding for the SMR-160, as did partners PSEG and SCE&G – which would operate the demonstration plant. Apart from the SCE&G demonstration plant, Holtec was negotiating to supply an SMR-160 to PSEG for its Hope Creek/Salem site in New Jersey, for which PSEG has sought an early site permit (ESP). After failing to get DOE funding, both PSEG and SCE&G reaffirmed their support for the SMR-160. In January 2016 Holtec said that development continued with support from Mitsubishi and PSEG Power. In October 2016 Holtec said it was considering standardizing on a 160 MWe steam turbine from Turboatom in Ukraine. Electrical components will be from Mitsubishi Electric.

In February 2018, GE Hitachi Nuclear Energy, Global Nuclear Fuel, Holtec and SMR Inventec signed a memorandum of understanding, with the initial focus on fuel development and control rod drive mechanisms for the SMR-160. In April 2020 Holtec selected Framatome to supply its GAIA fuel assemblies to the reactor.

In February 2019 Holtec announced new agreements with Exelon – to join the support team with Mitsubishi and SNC-Lavalin – and Ukraine’s Energoatom, with which it had signed an agreement in 2018 with a view to building the SMR-160 in Ukraine. In June 2019 Holtec signed a partnership agreement with Energoatom and Ukraine's national nuclear consultant, State Scientific and Technical Centre for Nuclear and Radiation Safety (SSTC-NRS), to establish a consortium to explore the environmental and technical feasibility of qualifying a 'generic' SMR-160 system that can be built and operated at any candidate site in the country. This would establish a reactor design capability in Ukraine, with a view to it becoming a regional hub for selling such reactors in Europe, Asia and Africa.

mPower

In mid-2009, Babcock & Wilcox (B&W) announced its mPower reactor, a 500 MWt, 180 MWe integral PWR designed to be factory-made and railed to sitei. It was a deliberately conservative design, to more readily gain acceptance and licensing. In November 2012 the US Department of Energy (DOE) announced that it would support accelerated development of the design for early deployment, with up to $226 million, and it paid $111 million of this.

The reactor pressure vessel containing core of 2x2 metres and steam generator is thus only 3.6 metres diameter and 22 m high, and the whole unit 4.5 m diameter and 23 m high. It would be installed below ground level, have an air-cooled condenser giving 31% thermal efficiencyp, and passive safety systems. The power was originally 125 MWe, but by about 2014, 195 MWe was quoted when water-cooled. A 155 MWe air-cooled version was also planned. The integral steam generator is derived from marine designs, as is the control rod set-up. Convection would be assisted by eight small canned-motor coolant pumps. It has a "conventional core and standard fuel" (69 fuel assemblies, each standard 17x17, < 20 t)j enriched to almost 5%, with burnable poisons, to give a four-year operating cycle between refuelling, which will involve replacing the entire core as a single cartridge. Core power density is lower than in a large PWR, and burn-up is about 35 GWd/t. (B&W draws upon over 50 years of experience in manufacturing nuclear propulsion systems for the US Navy, involving compact reactors with long core life.) A 60-year service life is envisaged, as sufficient used fuel storage would be built onsite for this.

The mPower reactor is modular in the sense that each unit is a factory-made module and several units would be combined into a power station of any size, but most likely a 380 MWe twin-unit plant and using approx 200 MWe turbine generators (also shipped as complete modules), constructed in three years. BWXT Nuclear Energy's present manufacturing capability in North America could produce these units.

B&W Nuclear Energy Inc set up B&W Modular Nuclear Energy LLC (now BWXT mPower Inc) to market the design, in collaboration with Bechtel which joined the project as a 10% equity partner to design, license and deploy it. The company expects both design certification and construction permit in 2018, and commercial operation of the first two units in 2022. Overnight cost for a twin-unit plant was put by B&W at about $5000/kW.

In November 2013 B&W said it would seek to bring in further equity partners by mid-2014 to take forward the licensing and construction of an initial plant.* B&W said it had invested $360 million in Generation mPower with Bechtel, and wanted to sell up to 70% of its stake in the joint venture, leaving it with about 20% and Bechtel 10%. In April 2014 B&W announced that it was cutting back funding on the project to about $15 million per year, having failed to find customers or investors. DOE then terminated further funding. B&W planned to retain the rights to manufacture the reactor module and nuclear fuel for the mPower plant. In December 2014 B&W finished laying off staff working on the project, and early in 2016 reduced funding further.

With more than $375 million having been spent on the mPower program, in March 2016 BWXT and Bechtel reached agreement on “accelerated development” of the mPower project, so that Bechtel would take over leadership of the project and attempt for a year to secure funding for SMR development from third parties, including the DOE. If Bechtel succeeded in this, then BWXT and Bechtel would negotiate and execute a new agreement, with Bechtel taking over management of the mPower program from BWXT. If Bechtel decided to terminate the project, it would be paid $30 million by BWXT, which is what happened in March 2017. The project was then shelved, leaving both BWXT and Bechtel free to be involved in the supply chain or management of other SMR projects.

* When B&W launched the mPower design in 2009, it said that Tennessee Valley Authority (TVA) would begin the process of evaluating Clinch River at Oak Ridge as a potential lead site for the mPower reactor, and that a memorandum of understanding had been signed by B&W, TVA and a consortium of regional municipal and cooperative utilities to explore the construction of a small fleet of mPower reactors. It was later reported that the other signatories of the agreement were FirstEnergy and Oglethorpe Power3. In February 2013 B&W signed an agreement with TVA to build up to four units at Clinch River, with design certification and construction permit application to be submitted to NRC in 2015. In August 2014 the TVA said it would file an early site permit (ESP) application instead of a construction permit application for one or more small modular reactors at Clinch River, possibly by the end of 2015. In February 2016 TVA said it was still developing a site at Oak Ridge for a SMR and would apply for an early site permit (ESP, with no technology identified) in May with a view to building up to 800 MWe of capacity there.

BWRX-300

GE Hitachi Nuclear Energy has a 300 MWe small BWR design, envisaged as single units. GEH has announced this as the BWRX-300 “which further simplifies the NRC-licensed ESBWR” from which it is derived. The BWRX-300 incorporates a range of cost-saving features, including natural circulation systems, smaller, dry containment, and more passive operational control systems. The estimated capital cost is $2250/kWe for series production after initial units are built. The design aims to limit onsite operational staff numbers to 75 employees to achieve an estimated O&M cost of $16/MWh. In May 2018 the US utility Dominion Energy agreed to help fund the project.

In July 2018 GEH announced $1.9 million in funding from the US Department of Energy to lead a team including Bechtel, Exelon, Hitachi-GE Nuclear Energy and the Massachusetts Institute of Technology to examine ways to simplify the reactor design, reduce plant construction costs, and lower operation and maintenance costs for the BWRX-300. In particular the team aims to identify ways to reduce plant completion costs by 40-60% compared with other SMR designs in development and to be competitive with gas. "As the tenth evolution of the boiling water reactor, the BWRX-300 represents the simplest, yet most innovative BWR design since GE began developing nuclear reactors in 1955." In May 2019 the BWRX-300 was submitted to Canada’s CNSC for a pre-licensing vendor design review. Phase 2 of this commenced in January 2020. After initiating discussion with the US Nuclear Regulatory Commission early in 2019, in January 2020 GE-Hitachi announced it had submitted the first licensing topical report for the BWRX-300 SMR to the NRC.

In October 2019 GEH signed an agreement with Estonia’s Fermi Energia and another agreement with Synthos SA in Poland to examine the economic feasibility of constructing a single BWRX-300 reactor in each country.

IRIS

Westinghouse's IRIS (International Reactor Innovative & Secure) is a reactor design which was developed over more than two decades. A 1000 MWt, 335 MWe capacity was proposed, although it could be scaled down to 100 MWe. IRIS is a modular pressurised water reactor with integral primary coolant system and circulation by convection. Fuel is similar to present LWRs and (at least for the 335 MWe version) fuel assemblies would be identical to those in AP1000. Enrichment is 5% with burnable poison and fuelling interval of up to four years (or longer with higher enrichment and MOX fuel). US design certification was at the pre-application stage, but is now listed as 'inactive', and the concept has evolved into the Westinghouse SMR.

Westinghouse SMR

The Westinghouse small modular reactor is an 800 MWt/225 MWe class integral PWR with passive safety systems and reactor internals including fuel assemblies based closely on those in the AP1000 (89 assemblies 2.44m active length, <5% enrichment). The steam generator is above the core fed by eight horizontally-mounted axial-flow coolant pumps. The reactor vessel will be factory-made and shipped to site by rail, then installed below ground level in a containment vessel 9.8 m diameter and 27 m high. The reactor vessel module is 25 metres high and 3.5 metres diameter. It has a 24-month refueling cycle and 60-year service life. Passive safety means no operator intervention is required for seven days in the event of an accident. Daily load following can be performed from 100% to 20% power at a rate of 5% change per minute; in continuous load following, the plant can perform load changes of ±10% power at a rate of 2% per minute.

In May 2012 Westinghouse teamed up with General Dynamics Electric Boat to assist in the design and Burns & McDonnell to provide architectural and engineering support. A design certification application was expected by NRC in September 2013, but the company has stepped back from lodging one while it re-assesses the market for small reactors. The company has started fabricating prototype fuel assemblies.

The DOE earlier saw this as a "near-term LWR design". In March 2015 Westinghouse announced that the NRC had approved its safety evaluation report for the SMR design, which it said was a significant step towards design certification. However, while the company continues efforts to seek customer interest, it is not proceeding with the NRC yet.

In April 2012 Westinghouse set up a project with Ameren Missouri to seek DOE funds for developing the design, with a view to obtaining design certification and a combined construction and operation licence (COL) from the Nuclear Regulatory Commission (NRC) for up to five SMRs at Ameren's Callaway site, instead of an earlier proposed large EPR there. The initiative – NexStart SMR Alliance – had the support of other state utilities and the state governor, as well as Savannah River, Exelon and Dominion. However, this agreement expired about the end of 2013, and both companies stepped back from the project as DOE funds went to other SMR projects.

In May 2013 Westinghouse announced that it would work with China’s State Nuclear Power Technology Corporation (SNPTC) to accelerate design development and licensing in the USA and China of its SMR. SNPTC would ensure that the Westinghouse SMR design met standards for licensing in China and would lead the licensing effort in that country. The status of this collaboration is uncertain.

In October 2015 Westinghouse presented a proposal for a “shared design and development model" under which the company would contribute its SMR conceptual design and then partner with UK government and industry to complete, license and deploy it. This would engage UK companies such as Sheffield Forgemasters in the reactor supply chain.

VVER-300 (V-478)

This is a 850 MWt, 300 MWe two-loop PWR design from Gidropress, based on the VVER-640 (V-407) design. It is little reported.

VBER-150, VBER-300

A larger Russian factory-built and barge-mounted unit (requiring a 12,000 tonne vessel) is the VBER-150, of 350 MWt, 110 MWe. It is modular and is derived by OKBM from naval designs, with two steam generators. Uranium oxide fuel enriched to 4.7% has burnable poison; it has low burn-up (31 GWd/t average, 41.6 GWd/t maximum) and eight-year refuelling interval.

OKBM Afrikantov's larger VBER-300 PWR is a 917 MWt, 325 MWe unit, the first of which is planned to be built in Kazakhstan. It was originally envisaged in pairs as a floating nuclear power plant, displacing 49,000 tonnes. As a cogeneration plant it is rated at 200 MWe and 1900 GJ/hr. The reactor is designed for 60-year life and 90% capacity factor. It has four external steam generators and a cassette core with 85 standard VVER fuel assemblies enriched to 4.95% and 50 GWd/tU burn-up with a 72-month fuel cycle. Versions with three and two steam generators are also envisaged, of 230 and 150 MWe respectively. Also, with more sophisticated and higher-enriched (18%) fuel in the core, the refuelling interval can be pushed from two years out to five years (6 to 15 years fuel cycle) with burn-up to 125 GWd/tU. A 2006 joint venture between Atomstroyexport and Kazatomprom set this up for development as a basic power source in Kazakhstan, then for exporte. It is also envisaged for use in Russia, mainly as cogeneration unit. It is considered likely for near-term deployment.

The company also offers 200-600 MWe designs based on a standard 100 MWe module and explicitly based on naval units.

VK-300

Another larger Russian reactor with completed detailed design is NIKIET’s VK-300 integral boiling water reactor of 750 MWt, 250 MWe, being developed specifically for cogeneration of both power and district heating or heat for desalination (150 MWe plus 1675 GJ/hr) by the N.A. Dollezhal Research and Development Institute of Power Engineering (RDIPE or NIKIET) together with several major research and engineering institutes. It has evolved from the 50 MWe (net) VK-50 BWR at Dimitrovgradf, but uses standard components wherever possible, and has 313 fuel elements similar to the VVER. Cooling is passive, by convection, and all safety systems are passive. Fuel enrichment is 4% and burn-up is 41 GWd/tU with a 72-month refuelling interval. It is capable of producing 250 MWe if solely electrical. Design operating lifetime is 60 years.

In September 2007 it was announced that six would be built at Kola or Archangelsk and at Primorskaya in the far east, to start operating 2017-20,4 but no more has been heard of this plan. A feasibility study was undertaken for Arkhangelsk nuclear cogeneration plant with four units. As a cogeneration plant it was intended for the Mining & Chemical Combine at Zheleznogorsk, but MCC is reported to prefer the VBER-300. The design was completed in 2013.

VKT-12

A smaller Russian BWR design is the 12 MWe transportable VKT-12, described as similar to the VK-50 prototype BWR at Dimitrovgrad, with one loop. It has a ceramic-metal core with uranium enriched to 2.4-4.8%, and 10-year refuelling interval. The reactor vessel is 2.4m inside diameter and 4.9 m high. This is reported to be shelved.

ABV, ABV-6M

A smaller Russian PWR unit under development by OKBM Afrikantov is the ABV multipurpose power source. It is readily transported to the site, with rapid assembly and operation for 10-12 years between refuelling, which is carried out offsite at special facilities. There is a range of sizes from 45 MWt (ABV-6M ) down to 18 MWt (ABV-3), giving 4-18 MWe outputs. (The IAEA 2011 write-up of the ABV-6M quotes 14 MWt or 6 MWe in cogeneration mode.) The units are compact, with integral steam generator and natural circulation in the primary circuit. They will be factory-produced and designed as a universal power source for floating nuclear plants – the ABV-6M would require a 3500 tonne barge; the ABV-3, 1600 tonne for twin units. The Volnolom FNPP consists of a pair of reactors (12 MWe in total) mounted on a 97-metre, 8700 tonne barge plus a second barge for reverse osmosis desalination (over 40,000 m3/day of potable water).

The smallest land-based version has reactor module 13 m long and 8.5 m diameter, with a mass of 600 t. The land-based ABV-6M module is 44 m long, 10 m diameter and with mass of 3000 t. The core is similar to that of the KLT-40 except that enrichment is 16.5% or 19.7% and average burn-up 95 GWd/t. It would initially be fuelled in the factory. The service lifetime is about 40 years.

CAREM

The CAREM-25 reactor prototype being built by the Argentine National Atomic Energy Commission (CNEA), with considerable input from INVAPg, is an older design modular 100 MWt (27 MWe gross) integral pressurized water reactor, first announced in 1984. It has 12 steam generators within the pressure vessel and is designed to be used for electricity generation or as a research reactor or for water desalination (with 8 MWe in cogeneration configuration). CAREM has its entire primary coolant system within the reactor pressure vessel (11m high, 3.5m diameter), self-pressurized and relying entirely on convection (for modules less than 150 MWe). The final full-sized export version will be 100 MWe or more, with axial coolant pumps driven electrically. Fuel is standard 3.1 or 3.4% enriched PWR fuel in hexagonal fuel assemblies, with burnable poison, and is refuelled annually.

How a CAREM plant would look (CNEA)

The 25 MWe prototype unit is being built next to Atucha, on the Parana River in Lima, 110 km northwest of Buenos Aires, and the first larger version (probably 100 MWe) is planned in the northern Formosa province, 500 km north of Buenos Aries, once the design is proven. Some 70% of CAREM-25 components will be local manufacture. The pressure vessel is being manufactured by Industrias Metalurgicas Pescarmona SA (IMPSA).

The IAEA lists it as a research reactor under construction since April 2013, though first concrete was poured in February 2014. It is proceeding slowly and was originally due online in 2019.

In March 2015 Argentina’s INVAP and state-owned Saudi technology innovation company Taqnia set up a joint venture company, Invania, to develop nuclear technology for Saudi Arabia's nuclear power programme, apparently focused on CAREM for desalination.

SMART from KAERI

On a larger scale, South Korea's SMART (System-integrated Modular Advanced Reactor) is a 330 MWt pressurised water reactor with integral steam generators and advanced safety features. It is designed by the Korea Atomic Energy Research Institute (KAERI) for generating electricity (up to 100 MWe) and/or thermal applications such as seawater desalination. Design operating lifetime is 60 years, fuel enrichment 4.8%, with a three-year refuelling cycle. It has 57 fuel assemblies very similar to normal PWR ones but shorter, and it operates with a 36-month fuel cycle. All the active safety features of the original design were substituted by early 2016 with passive versions. Residual heat removal is passive. It received standard design approval (SDA) from the Korean regulator in mid-2012. A single unit can produce 90 MWe plus 40,000 m3/day of desalinated water.

In March 2015 KAERI signed an agreement with Saudi Arabia’s King Abdullah City for Atomic and Renewable Energy (KA-CARE) to assess the potential for building SMART reactors in that country, and in September 2015 further contracts were signed to that end. The cost of building the first SMART unit in Saudi Arabia was estimated at $1 billion. Through to November 2018 pre-project engineering will be undertaken jointly including FOAK engineering design and preparations for building two units.

MRX

The Japan Atomic Energy Research Institute (JAERI) designed the MRX, a small (50-300 MWt) integral PWR reactor for marine propulsion or local energy supply (30 MWe). The entire plant would be factory-built. It has conventional 4.3% enriched PWR uranium oxide fuel with a 3.5-year refuelling interval and has a water-filled containment to enhance safety. Little has been heard of it since the start of the Millennium.

Nuward NP-300

TechnicAtome with Naval Group and CEA in France have developed the NP-300 PWR design from submarine power plants and aimed it at export markets for power, heat and desalination. It has passive safety systems and could be built for applications of 100 to 300 MWe or more with up to 500,000 m3/day desalination. As of mid-2018, a 570 MWt/170 MWe version was proposed as SMR to be in a metallic compact containment submerged in water, each module in a separate pool. In September 2019 twin 170 MWe units were proposed to comprise a 340 MWe power plant.

TechnicAtome makes the K15 naval reactor of 150 MWt, running on low-enriched fuel. A land-based equivalent – Réacteur d’essais à terre (RES) – was built at Cadarache from 2003 with several delays and achieved criticality in October 2018. It is essentially a PWR test reactor for the Navy.

It earlier seemed that some version of this reactor might be used in the Flexblue submerged nuclear power plant being proposed by DCNS in France, but now cancelled. The concept eliminates the need for civil engineering, and refuelling or major service can be undertaken by refloating it and returning to the shipyard.

The Chinese NHR-200 (Nuclear Heating Reactor), developed by Tsingua University's Institute of Nuclear Energy Technology (now the Institute of Nuclear and New Energy Technology), is a simple 200 MWt integral PWR design for district heating or desalination. It is based on the NHR-5 which was commissioned in 1989, and runs at lower temperature than the above designsh. Used fuel is stored around the core in the pressure vessel.

In 2008, the Chinese government was reported to have agreed to build a multi-effect distillation (MED) desalination plant using this on the Shandong peninsula, but no more has been heard of that project, and INET is focused on the HTR-PM being built in Shandong.

ACP100/Linglong One

The Nuclear Power Institute of China (NPIC), under China National Nuclear Corporation (CNNC), has designed a multi-purpose small modular reactor, the ACP100 or Linglong One. China Nuclear Power Engineering Co (CNPE) is also promoting it. It has passive safety features, notably decay heat removal, and will be installed underground. It has 57 fuel assemblies 2.15m tall and integral steam generators (287°C), so that the whole steam supply system is produced and shipped a single reactor module. Its 385 MWt produces about 125 MWe, and power plants comprising two to six of these are envisaged, with 60-year design operating lifetime and 24-month refuelling. Or each module can supply 1000 GJ/hr, giving 12,000 m3/day desalination (with MED). Industrial and district heat uses are also envisaged, as well as floating nuclear power plant (FNPP) applications. Capacity of up to 150 MWe is envisaged. In April 2016 the IAEA presented CNNC with its report from the Generic Reactor Safety Review process.

In October 2015 the Nuclear Power Institute of China (NPIC) signed an agreement with UK-based Lloyd's Register to support the development of a floating nuclear power plant (FNPP) using the ACP100S reactor, a marine version of the ACP100. Following approval as part of the 13th Five-Year Plan for innovative energy technologies, CNNC signed an agreement in July 2016 with China Shipbuilding Industry Corporation (CSIC) to prepare for building its ACP100S demonstration floating nuclear plant, for 2019 operation.

CNNC New Energy Corporation, a joint venture of CNNC (51%) and China Guodian Corp, was planning to build two ACP100 units in Putian county, Zhangzhou city, at the south of Fujian province, near Xiamen, as a demonstration plant. This would be the CNY 5 billion ($788 million) phase 1 of a larger project. Preliminary design was completed in 2014, based on larger ACP/CNP units. Construction time is expected to be 36-40 months. Early in 2017 the site for the first ACP100 units was changed to Changjiang, on Hainan, with a larger reactor to be built at Putian. Preliminary work began in July 2019, with first concrete expected 2019/2020. It involves a joint venture of three companies for the pilot plant: CNNC as owner and operator; the Nuclear Power Institute of China (NPIC) as the reactor designer; and China Nuclear Engineering Group being responsible for plant construction. The preliminary safety analysis report for a single unit demonstration plant was approved in April 2020.

The company signed a second ACP100 agreement with Hengfeng county, Shangrao city in Jiangxi province, and a third with Ningdu county, Ganzhou city in Jiangxi province in July 2013 for another ACP100 project costing CNY 16 billion. Further inland units are planned in Hunan and possibly Jilin provinces. Export potential is considered to be high, with full IP rights. In 2016 China Nuclear Engineering & Construction Corporation (CNEC) submitted an expression of interest to the UK government based on its ACP100+ design.

CAP200/LandStar-V, CAP150, CAP50

CAP200 or LandStar-V multiple application SMR is a PWR, with SNPTC provenance, being developed from the CAP1000 in parallel with the CAP1400 by SNERDI, using proven fuel and core design. It is 660 MWt/220 MWe and has two external steam generators (301°C). It is pitched to replace coal plants and supply process heat and district heating, with a design operating lifetime of 60 years. With 24-month refuelling, burn-up of 42 GWd/t is expected, the 89 fuel assemblies being the same as those of the CAP1400 but shorter. It has both active and passive cooling, and natural circulation is effective for up to 20% power. In an accident scenario, no operator intervention is required for seven days. It will be installed below grade in a 32 m deep caisson structure, with seismic design basis 600 Gal, even in soft ground. In 2017 the first-of-a-kind cost was estimated at $5000/kW and $160/MWh, dropping to $4000/kW in series.

The OceanStar-V version would be on a barge, as a floating nuclear power plant.

The CAP150 is an earlier version, 450 MWt/150 MWe, with eight integral steam generators. It is claimed to have “a more simplified system and more safety than current third generation reactors.” Seismic design basis is 300 Gal. In mid-2013 SNPTC quoted approximately $5000/kW capital cost and 9 c/kWh, so significantly more than the CAP1400.

A related SNERDI project is the CAP50 reactor for floating nuclear power plants. This is to be 200 MWt and relatively low-temperature (250°C), so only about 40 MWe with two external steam generators and five-year refuelling.

ACPR100, ACPR50S

China General Nuclear Group (CGN) has two small ACPR designs: an ACPR100 and ACPR50S, both with passive cooling for decay heat and 60-year design life. Both have standard type fuel assemblies and fuel enriched to <5% with burnable poison giving 30-month refueling. The ACPR100 is an integral PWR, 450 MWt, 140 MWe, having 69 fuel assemblies. Reactor pressure vessel is 17m high and 4.4 m inside diameter, operating at 310°C. It is designed as a module in larger plant and would be installed underground. The applications for these are similar to those for the ACP100.

CGN's floating reactor concept

The offshore ACPR50S is 200 MWt, 60 MWe with 37 fuel assemblies and four external steam generators. Reactor pressure vessel is 7.4m high and 2.5 m inside diameter, operating at 310°C. It is designed for mounting on a barge as floating nuclear power plant (FNPP). Following approval as part of the 13th Five-Year Plan for innovative energy technologies, CGN announced construction start on the first FNPP at Bohai shipyard in November 2016 for trial operation in 2019, supplying power and desalination.

Flexblue

This was a conceptual design from DCNS (now Naval Group, state-owned), Areva, EdF and CEA from France. It is designed to be submerged, 60-100 metres deep on the sea bed up to 15 km offshore, and returned to a dry dock for servicing. The reactor, steam generators and turbine-generator would be housed in a submerged 12,000 tonne cylindrical hull about 100 metres long and 12-15 metres diameter. Each hull and power plant would be transportable using a purpose-built vessel. Reactor capacity ranged 50-250 MWe, derived from DCNS's latest naval designs, but with details not announced. In 2011 DCNS said it could start building a prototype Flexblue unit in 2013 in its shipyard at Cherbourg for launch and deployment in 2016, possibly off Flamanville, but the project has been cancelled.

UNITHERM

This is an integral 30 MWt, 6.6 MWe PWR conceptual design from Russia’s Research and Development Institute of Power Engineering (RDIPE or NIKIET). It has three coolant loops, with natural circulation, and claims self-regulation with burnable poisons in unusual metal-ceramic fuel design, so needs no more than an annual maintenance campaign and no refueling during a 25-year life. The mass of one unit with shielding is 180 tonnes, so it can be shipped complete from the factory to site.

SHELF

This is a Russian 6 MWe, 28 MWt PWR concept with turbogenerator in a cylindrical pod about 15 m long and 8 m diameter, sitting on the sea bed like Flexblue. The SHELF module uses an integral reactor with forced and natural circulation in the primary circuit, in which the core, steam generator, motor-driven circulation pump and control and protection system drive are housed in a cylindrical pressure vessel. It uses low-enriched fuel of UO 2 in aluminium alloy matrix. Fuel cycle is 56 months. The reactor is based on operating prototypes, and would be serviced infrequently. It is intended as energy supply for oil and gas developments in Arctic seas, and land-based versions have been envisaged. It is at concept design stage with NIKIET which estimates that a further five years would be required in order to finalise the design, licensing, construction and commissioning.

KARAT-45

This is a 45 MWe tank-type BWR as a stand-alone cogeneration plant. The design includes natural circulation in its core cooling system for heat removal in all operational modes and incorporates passive safety systems. A larger version is 100 MWe.

IMR

Mitsubishi Heavy Industries has a conceptual design of the Integral Modular Reactor (IMR), a PWR of 1000 MWt, 350 MWe. It has design operating lifetime of 60 years, 4.8% fuel enrichment and fuel cycle of 26 months. It has natural circulation for primary cooling. The project has involved Kyoto University, the Central Research Institute of the Electric Power Industry (CRIEPI), and the Japan Atomic Power Company (JAPC), with funding from METI. The target year to start licensing is 2020 at the earliest.

Rolls-Royce SMR

Rolls-Royce has been working since 2015 on a small reactor of 220 to 440 MWe, the output “depending on configuration”. It is to be factory-built, transportable to site (11.3 m high, 4.5 m diameter or 16 m high and 3 m diameter pressure vessel)*, with 60-year design operating lifetime. It is a three-loop PWR with close-coupled external steam generators. It would use 4.95% enriched fuel with 55-60 GWd/t burn-up in standard PWR fuel assemblies and the refuelling cycle would be 18-24 months.

* Both figures given in 2017 company factsheets.

Ten UK companies have been collaborating on the project, including Amec Foster Wheeler, Nuvia and Arup, together with the Nuclear Advanced Manufacturing Research Centre. Early in 2016 Rolls-Royce submitted a detailed design to the UK government for a 220 MWe SMR unit and also a paper to the Department of Business, Energy and Industrial Strategy, outlining its plan to develop a fleet of 7 GWe of SMRs in the UK with a new consortium, plus 9 GWe of exported units. In late 2019 the consortium comprised: Assystem, Atkins, BAM Nuttall, Laing O'Rourke, National Nuclear Laboratory, Nuclear AMRC, Rolls-Royce, Jacobs and The Welding Institute. Its focus is on existing licenced nuclear sites in the UK. It is hoping to have the first unit operating in 2030.

In January 2020 the company estimated that a 440 MWe unit would cost £1.75 billion (around $2.3 billion) on a brownfield site and produce power below £60/MWh ($78/MWh).

Rolls-Royce has designed three generations of naval reactors since the 1950s and also operates a small test reactor. It led the development of a small integral reactor (SIR) of 330 MWe in the 1980s.

TRIGA

The TRIGA Power System is a PWR concept based on General Atomics' well-proven research reactor design. It is conceived as a 64 MWt, 16.4 MWe pool-type system operating at a relatively low temperature. The secondary coolant is perfluorocarbon. The fuel is uranium-zirconium hydride enriched to 20% and with a little burnable poison and requiring refuelling every 18 months. Used fuel is stored inside the reactor vessel.

FBNR

The Fixed Bed Nuclear Reactor (FBNR) is an early conceptual design from the Federal University of Rio Grande do Sul, Brazil. It is a PWR with pebble fuel, 134 MWt, 70 MWe, with “flexible fuel cycle”. Other reports have it as 40 MWe.

SMART from Dunedin

The SMART (Small Modular Adaptable Reactor Technology) from Dunedin Energy Systems in Canada is a 30 MWt, 6 MWe battery-type unit, installed below grade. It is replaced by a new one when it is returned to a processing facility for refuelling; at 83% capacity factor this would be every 20 years. It drives a steam turbine. Emergency cooling is by convection. Cost is about 29c/kWh, according to Dunedin.

DEER from Radix

The DEER (Deployable Electric Energy Reactor) was being developed by Radix Power & Energy Corporation in the USA, in collaboration with Brookhaven Technology Group, Brookhaven National Laboratory, Parsons Corporation, Dunedin Energy Systems, and University of California, Berkeley. The DEER is a PWR and would be portable and sealed, able to operate in the range of 10-50 MWe. DEER-1 was to use fuel based on that in Triga research reactors, with a ten-year cycle, and DEER-2 was to use TRISO fuel, for forward military bases or remote mining sites. No recent information is available.

Chinese district heat reactors

Three Chinese designs are solely for district heat at 90-110°C, for northern provinces, especially Heilongjiang. Reducing winter air pollution is the main driver of their development. CGN’s NHR-200 passed regulatory review in the 1990s; CNNC’s DHR-400 or 'Yanlong' is a 400 MWt pool-type reactor; and SPIC’s LandStar-1 is similar to the Yanlong but 200 MWt.

Heavy water reactors

PHWR-220

These are the oldest and smallest of the Indian pressurized heavy water reactor (PHWR) range, with a total of 16 now on line, 800 MWt, 220 MWe gross typically. Rajasthan 1 was built as a collaborative venture between Atomic Energy of Canada Ltd (AECL) and the Nuclear Power Corporation of India (NPCIL), starting up in 1972. Subsequent indigenous PHWR development has been based on these units, though several stages of evolution can be identified: PHWRs with dousing and single containment at Rajasthan 1-2, PHWRs with suppression pool and partial double containment at Madras, and later standardized PHWRs from Narora onwards having double containment, suppression pool, and calandria filled with heavy water, housed in a water-filled calandria vault. They are moderated and cooled by heavy water, and the natural uranium oxide fuel is in horizontal pressure tubes, allowing refueling on line (maintenance outages are scheduled after 24 months). Burn-up is about 15 GWd/t.

AHWR-300 LEU

The Advanced Heavy Water Reactor developed by the Bhaba Atomic Research Centre (BARC) is designed to make extensive use of India’s abundant thorium as fuel, but a low-enriched uranium fuelled version is pitched for export. This will use low-enriched uranium plus thorium as a fuel, largely dispensing with the plutonium input of the version for domestic use. About 39% of the power will come from thorium (via in situ conversion to U-233, cf two thirds in domestic AHWR), and burn-up will be 64 GWd/t. Uranium enrichment level will be 19.75%, giving 4.21% average fissile content of the U-Th fuel. It will have vertical pressure tubes in which the light water coolant under high pressure will boil, circulation being by convection. Nominal 300 MWe, 284 MWe net. It is at the basic design stage.

High-temperature gas-cooled reactors

These use graphite as moderator (unless fast neutron type) and either helium, carbon dioxide or nitrogen as primary coolant. The experience of several innovative reactors built in the 1960s and 1970sk, notably those in Germany, has been analyzed, especially in the light of US plans for its Next Generation Nuclear Plant (NGNP) and China's launching its HTR-PM project in 2011. Lessons learned and documented for NGNP include the use of TRISO fuel, use of a reactor pressure vessel, and use of helium cooling (UK AGRs are the only HTRs to use CO2 as primary coolant). However US government funding for NGNP has now virtually ceased, and the technology lead has passed to China.

New high-temperature gas-cooled reactors (HTRs) are being developed which will be capable of delivering high temperature (700-950ºC and eventually up to about 1000°C) helium either for industrial application via a heat exchanger, or to make steam conventionally in a secondary circuit via a steam generator, or directly to drive a Brayton cycle* gas turbine for electricity with almost 50% thermal efficiency possible (efficiency increases around 1.5% with each 50°C increment). One design uses the helium to drive an air compressor to supercharge a CCGT unit. Improved metallurgy and technology developed in the last decade makes HTRs more practical than in the past, though the direct cycle means that there must be high integrity of fuel and reactor components. All but one of those described below have neutron moderation by graphite, one is a fast neutron reactor.

* There is little interest in pursuing the direct Brayton cycle for helium at present due to higher technological risk. Attrition of fuel tends to give rise to graphite dust with radioactivity in the coolant circuit.

Fuel for these reactors is in the form of TRISO (tristructural-isotropic) particles less than a millimetre in diameter. Each has a kernel (ca. 0.5 mm) of uranium oxycarbide (or uranium dioxide), with the uranium enriched up to 20% U-235, though normally less. This is surrounded by layers of carbon and silicon carbide, giving a containment for fission products which is stable to over 1600°C.

There are two ways in which these particles are arranged: in blocks – hexagonal 'prisms' of graphite, or in billiard ball-sized pebbles of graphite, each with about 15,000 fuel particles and 9g uranium. There is a greater volume of used fuel (20 times) than from the same capacity in a light water reactor, due to the fact that the fuel pebbles are mainly graphite – less than one percent is uranium. However, the used fuel is overall less radiotoxic and produces less decay heat due to higher burn-up. The HTR moderator is graphite.

HTRs can potentially use thorium-based fuels, such as highly-enriched or low-enriched uranium with Th, U-233 with Th, and Pu with Th. Most of the experience with thorium fuels has been in HTRs (see information paper on Thorium).

With negative temperature coefficient of reactivity (the fission reaction slows as temperature increases) and passive decay heat removal, the reactors are inherently safe. HTRs therefore are put forward as not requiring any containment building for safety. They are sufficiently small to allow factory fabrication, and will usually be installed below ground level.

Three HTR designs in particular – PBMR, GT-MHR and Areva's SC-HTGR – were contenders for the Next Generation Nuclear Plant (NGNP) project in the USA (see Next Generation Nuclear Plant section in the information page on US Nuclear Power Policy). In 2012 Areva's HTR was chosen. However, the only HTR project currently proceeding is the Chinese HTR-PM.

Hybrid Power Technologies have a hybrid-nuclear Small Modular Reactor (SMR) coupled to a fossil-fuel powered gas turbine.

HTTR, GTHTR

Japan Atomic Energy Research Institute's (JAERI's) High-Temperature Test Reactor (HTTR) of 30 MWt started up at the end of 1998 and first reached full power with a reactor outlet coolant temperature of 850°C in December 2001. In 2004 it achieved 950°C outlet temperature, and in 2009 it ran at 950°C for 50 days. Its fuel is in prisms and its main purpose is to develop thermochemical means of producing hydrogen from water.

Based on the HTTR, JAERI is developing the Gas Turbine High Temperature Reactor (GTHTR) of up to 600 MWt and 275 MWe per module. It uses improved HTTR fuel elements with 14% enriched uranium achieving high burn-up (112 GWd/t). Helium at 850°C drives a horizontal turbine at 47% efficiency to produce up to 300 MWe. The core consists of 90 hexagonal fuel columns 8 metres high arranged in a ring, with reflectors. Each column consists of eight one-metre high elements 0.4 m across and holding 57 fuel pins made up of fuel particles with 0.55 mm diameter kernels and 0.14 mm buffer layer. In each two-yearly refuelling, alternate layers of elements are replaced so that each remains for four years.

Early in 2019 the Japan Atomic Energy Agency (JAEA) formed a joint venture with Penultimate Power UK to build a 10 MWe SMR there based on the HTTR, for power and process heat. Plans include scaling up the design to 100 MWe and building a factory in the UK for multiple plants.

HTR-10

China's HTR-10, a 10 MWt high-temperature gas-cooled experimental reactor at the Institute of Nuclear & New Energy Technology (INET) at Tsinghua University north of Beijing started up in 2000 and reached full power in 2003. It has its fuel as a 'pebble bed' (27,000 elements) of oxide fuel with average burn-up of 80 GWday/t U. Each pebble fuel element has 5g of uranium enriched to 17% in around 8300 TRISO-coated particles. The reactor operates at 700°C (potentially 900°C) and has broad research purposes. Eventually it will be coupled to a gas turbine, but meanwhile it has been driving a steam turbine.

In 2004, the small HTR-10 reactor was subject to an extreme test of its safety when the helium circulator was deliberately shut off without the reactor being shut down. The temperature increased steadily, but the physics of the fuel meant that the re