WHEN the two big nuclear reactors under construction at Flamanville in France and Olkiluoto in Finland come on stream, each will boast enough electricity-generating capacity to light up a city of 1.5m. But despite the best efforts of EDF and Areva, which are building the reactors, both are behind schedule and, at over $5 billion apiece, well over budget. With results like these, it is little wonder that the vaunted “nuclear renaissance” has failed to materialise. In fact, the number of operating reactors is in decline, spurring the nuclear-power industry to look for new approaches. Rather than relying on huge, traditional reactors costing billions, it is turning to small, inexpensive ones, many of which are based on proven designs from nuclear submarines or warships.

A global race is under way to develop small-reactor designs, says Paul Genoa of the Nuclear Energy Institute, an industry body in Washington, DC. He estimates that more than 20 countries have expressed serious interest in buying mini-reactors.

At least eight different approaches are being developed, mainly in America and Asia, by an army of 3,000 nuclear engineers, according to Ron Moleschi of SNC-Lavalin Nuclear, an engineering firm based in Montreal. Regulatory and licensing procedures are lengthy, so little will be built until around 2017, he says. But after that the industry is expected to take off. The International Atomic Energy Agency (IAEA) estimates that by 2030 at least 40 (and possibly more than 90) small reactors will be in operation. It reckons that more than half of the countries that will build nuclear plants in coming years will plump for these smaller, simpler designs.

Nuclear deliveries

Russia is an early adopter. Rosatom, the state nuclear-energy giant, is building a floating, towable power station in a St Petersburg shipyard. The Akademik Lomonosov, due to set sail in 2012 for waters near Russia's far-east town of Vilyuchinsk, will be followed by at least four other floating nuclear plants for the country's Arctic regions. Such power stations are less prone to earthquakes and avoid the difficulties of erecting nuclear facilities on frozen land, which can melt, jeopardising foundations, says Vladimir Kuznetsov of the IAEA. And at a mere $550m a pop they cost a fraction of what a traditional reactor does (though they also provide less power).

Rosatom hopes its plants will appeal to energy-hungry coastal or river cities all over the world. By manufacturing in Russia, the firm sidesteps some of the regulatory controls a client country would impose on a plant built and installed on its own soil. Another selling point is Russia's willingness to bring home the nuclear waste. Demand for floating plants may also help Russia broaden, or at least retain, its nuclear expertise, which has suffered as engineers have gone abroad or retired.

“Engineers of small reactors stress their similarity to proven, existing designs such as those found in nuclear-powered ships and submarines.”

Similar concerns are driving efforts to develop small reactors elsewhere. No new nuclear plant has come on stream in America since 1996. The industry was dealt a blow in October, when Constellation Energy, a utility, dropped a joint plan with EDF to build a large nuclear plant in Maryland. In spite of strong political support and a reported $7.5 billion in government loan guarantees, Constellation balked at the initial capital outlay. Steven Chu, America's energy secretary, sees miniaturisation as a way to revive the country's once-mighty nuclear industry.

One advantage of small reactors is their modularity. Extra units can be added to a plant over the years, incrementally boosting output as capital becomes available and electricity demand rises. NuScale, of Corvallis, Oregon, offers “scalable” nuclear plants with reactors delivered by truck. A plant with 12 reactors, each with its own electricity-generating turbine, would cost about $2.2 billion and produce roughly a third as much power as a big facility. Since large plants can cost roughly three times as much, the cost of electricity would be about the same. Moreover, a modular facility would generate revenue as soon as the first reactor is fired up, after a few years of construction. A big reactor traditionally takes a decade to erect.

Hyperion Power Generation, a firm based in Santa Fe, New Mexico, is building components for what it calls a “nuclear battery”. The refrigerator-sized Hyperion Power Module (HPM) reactor will shift much of the building from field to factory, where a controlled environment reduces costs. Also, fewer workers and families must be moved, at great expense, to distant building sites. HPMs would be delivered by truck with enough uranium to run for about ten years. They would be constructed in batches with interchangeable parts and cost about $100m each. And they need little human oversight to operate. “Forget huge—let's make a hand-held version of a power plant,” says John Deal, the firm's boss. Five companies, located in America, Britain, Canada, China and India, have put down deposits for an HPM.

Engineers of small reactors stress their similarity to proven, existing designs such as those found in nuclear-powered ships and submarines, or, in Rosatom's case, icebreakers. And some small-reactor designs have an important advantage over bigger reactors. Because less heat is generated, small water-cooled reactors can use simpler designs relying not on pumps, but on natural convection. And eliminating moving parts should make the new small reactors both safer and cheaper. For instance, Hyperion's HPM dispenses with elaborate valve systems by using a molten metal as a coolant because, unlike water, it doesn't need to be kept under pressure to absorb large amounts of heat.

Christofer Mowry, who heads civilian power at Babcock & Wilcox, a maker of nuclear-propulsion systems for the US Navy, says the company's small reactor offers another source of savings. Because it can use existing power-transmission lines without overloading them, the mPower can act as a “drop-in replacement” for ageing coal furnaces without the need for costly refurbishment. The Tennessee Valley Authority, America's biggest public utility, hopes to put two of the firm's reactors into an old coal plant. Five other American utilities are also considering replacing coal furnaces with nuclear reactors, according to Philip Moor of the American Nuclear Society, an industry group. He estimates that in America alone perhaps 100 old coal plants could be converted to nuclear within a decade—a trice by the industry's standards.

Not all nuclear nations have entered the fray. France has studied micro-reactors' potential in spaceship propulsion, but for generating power on Earth, big reactors are best, says Christophe Béhar, in charge of nuclear energy at the country's Atomic Energy Commission. New markets for large plants are opening up as developing countries strengthen their grids to cope with the huge amounts of power they produce. China is building two small helium-cooled reactors, but the electricity they produce will never be as cheap as that from big reactors, according to Mr Béhar. Just in case, the Chinese have also commissioned French firms to build two large nuclear plants.

In Japan, too, utilities' interest in small reactors appears scant for now. Tatsujiro Suzuki, the vice-chairman of the Atomic Energy Commission in Tokyo, hopes it will grow. Today's broad trend to loosen government controls on electricity prices may do the trick. Utilities are more willing to make massive investments if they can accurately predict future income. As prices are allowed to fluctuate more widely, shorter-term investments for smaller reactors will become more attractive. At least one Japanese engineering giant sees promise in the market for such devices. Toshiba says its 4S (“super-safe, small and simple”) reactor is capable of running for three decades without refuelling.

Small comfort

Sceptics fear that these small, cheap reactors will not be enough to revive the nuclear industry. Mycle Schneider, a nuclear-energy expert who is an external lecturer at École des Mines, an engineering school in France, and also an adviser to Germany's environment ministry, says licensing and building small plants will take far too long to be profitable. As the costs of solar, wind and biogas power continue to fall, investors will increasingly favour household energy-producing kit and transmission technologies that let consumers sell excess production to neighbours and utilities, he says. South Africa's decision in September to abort construction of a small reactor, even though about $1.3 billion had been spent, illustrates the sort of financial risk the sector faces.

Others fret that lots of small reactors, rather than a few big ones, will be more vulnerable to a terrorist attack. Hyperion's Mr Deal insists that neither a rocket-propelled grenade nor a tank round could smash a small reactor. Small reactors can be shielded by a heavy layer of concrete and buried, in effect making them safer than big ones, whose protective concrete domes can only be so thick, lest they collapse under their own weight.

What if a rogue government tries to take advantage of an affordable reactor to acquire nuclear expertise or materials for weapons work? Henry Sokolski, a former Pentagon official who heads the Nonproliferation Policy Education Centre, a think-tank near Washington, DC, says that Western intelligence agencies have overestimated their ability to monitor the spread of nuclear equipment and know-how. If new enrichment facilities are built to supply a slew of small nuclear reactors, materials and expertise useful in bomb-making may spread as a result.

TerraPower, an American firm backed by Bill Gates, thinks it has the solution. It is working with Toshiba to design a small reactor based on a “travelling wave” design. Once kick-started with a tiny amount of enriched uranium, it would run for decades on non-enriched, depleted uranium, a widely available material. This will be possible because the nuclear reaction, eating its way through the core at the rate of about one centimetre a year, would gradually convert the depleted uranium into fissionable plutonium—in effect “breeding” high-grade fuel and then consuming it.

Mr Gates points out that nuclear power has historically been dogged by five worries: safety, proliferation, waste, cost and fuel availability. “This thing is a miracle that solves all five,” he says. John Gilleland, TerraPower's boss, says that a single enrichment plant would then suffice to produce all the enriched uranium needed to spark up the world's mini-reactors.

The prospects for mini-reactors, like those for large reactors, depend on a combination of technical, commercial and regulatory factors. The stars do not seem to be aligning for large reactors. But they are no longer the only game in town.