THE horizontal boring machine at the nuclear Advanced Manufacturing Research Centre (AMRC) in Sheffield cuts large steel components with microscopic precision. Judging by the build-up of swarf around it, the machine is much in demand; some of the world’s biggest engineering firms are using it to help design what some say is the next big thing in civil nuclear power—Small Modular Reactors, or SMRs.

Such reactors are often billed as one solution for a nuclear industry bedevilled by massive cost overruns and technical snafus. The spiralling cost of the proposed Hinkley Point C power station in Somerset is a case in point; Électricité de France (EDF), the main contractor, has been hesitating over whether to press on with the controversial £18 billion ($25.9 billion) project. SMRs are mini-reactors that can produce anything from about 50 to 400 megawatts of electricity, much less than the gigawatt or so that most existing big reactors can put out, or the two 1,600MW reactors planned for Hinkley Point. Their backers argue that SMRs make more sense.

First, small reactors can be built by the dozen in a factory, proponents argue, and then transported to sites and plugged in. This means economies of volume rather than of scale. SMRs should also produce revenues more quickly than big reactors. Around eight SMRs in the same place would be needed to produce the equivalent power of, for example, Hinkley. But whereas the first SMR on site could be lighting up the country within three to five years of being ordered, thus beginning to pay for itself and the SMRs to come, conventional big reactors can take ten years or more to plug in and start making money.

SMRs have other advantages too, their fans allege. Rolls-Royce is designing a 220MW SMR that, at 16 metres in height and four metres in diameter, could be transported by truck, train or barge. They are supposed to use much less water for cooling than conventional reactors, so they need not be located by the sea or large rivers. Easier to power up, they could respond more flexibly to peaks in demand than many of their larger counterparts.

Britain’s government is in theory enthusiastic: it needs a nuclear option to meet stringent emissions targets and replace ageing plants. The National Nuclear Laboratory estimates that SMRs could provide 7GW of power, equivalent to a bit over two Hinkleys. In 2015 the government promised £250m for nuclear research, part of it to finance a competition for the best SMR design. Rolls-Royce, which makes nuclear reactors for submarines, is submitting what is likely to be the only domestic proposal. Foreign companies such as NuScale and Westinghouse of America may also bid.

This official commitment sounds encouraging, but for many in the industry it is too little and perhaps also too late. To develop and test a prototype SMR, according to Mike Tynan, the head of the nuclear AMRC, could cost up to £2 billion. The licensing process alone, to ensure that this new technology is safe, would cost millions and take five years or so. Its probable share of the British market is too small to cover such sums and sustain a profitable domestic manufacturing operation, argues David Orr, head of developing SMRs at Rolls-Royce. Britain may be too far behind the field to pick up much foreign business.

While Britain has dithered, the American government has spent hundreds of millions of dollars encouraging and commissioning prototype designs. NuScale’s design, backed by $217m from the American Department of Energy, could begin its licensing process this year. NuScale also has a prospective customer for an SMR, a municipal utility in Idaho. China, South Korea and other countries have a lead on Britain too. Mr Tynan argues that if the British government decided quickly to bear more of the risks in developing SMRs, the country could still exploit its nuclear know-how to compete in a global market that may be worth up to £400 billion.

Not everyone believes that SMRs are the nuclear industry’s silver bullet, however. Some of the challenges that face big reactors—in particular, safety—confront smaller ones too. There is a reason why, historically, reactors have grown bigger and bigger: similar solutions to similar problems can be exploited more efficiently. SMRs have the edge when they can be placed in locations where big reactors cannot. But Britons are not famous for welcoming unwanted developments into their green and pleasant neighbourhoods.

The government may have been slow to see the potential of SMRs. More importantly, successive generations in government have been slow to pick a design for big reactors and stick to it. If there is to be a nuclear future for British industry, this is the nettle that politicians must grasp.