An arguably definitive study of new advanced non-water cooled nuclear options, including molten salt reactors and liquid sodium cooled fast reactors, from the US Union of Concerned Scientists, concludes that none can be ready for at least a decade, more like two, and there are none that meet safety, security, sustainability criteria, apart possibly from once-through breed and burn reactors. If we want nuclear it says it would more sensible just to upgrade the standard, more familiar, water cooled reactors.
It sets the scene by noting that, in the United States, so-called Light Water Reactors (PWRs and BWRs) have dominated, these using ordinary water to cool their hot, highly radioactive cores, as opposed to reactors like the Canadian CANDU that use ‘heavy water’, with a double neutron hydrogen isotope, as a moderator. Support for LWRs has continued, despite some economic problems, which have bedevilled expansion in the US and elsewhere: ‘new nuclear plants have proven prohibitively expensive and slow to build, discouraging private investment and contributing to public skepticism’.
The UCS report notes that, ‘in the 2000s, amid industry hopes of a nuclear renaissance, the Nuclear Regulatory Commission (NRC) received applications to build more than two dozen new reactors. All were evolutionary versions of the light-water reactor (LWR)…. Companies such as Westinghouse, which developed the AP1000, promised these LWR variants could be built more quickly and cheaply while enhancing safety.’ However, ‘prospective purchasers cancelled nearly all of those proposals even before ground was broken, and the utilities that started building two AP1000 reactors at the V.C. Summer plant in South Carolina abandoned the project after it experienced significant cost overruns and delays. Only one project remains- two AP1000 units at the Alvin W. Vogtle plant in Georgia - but its cost has doubled, and construction is taking more than twice as long as originally estimated’.
Given the problems with LWRs, the idea of looking at other reactors concepts has gathered pace. That is the focus of the UCS report. It notes that these ‘non-LWRs’ are sometimes referred to as ‘advanced reactors’, but says that is a misnomer for most of the designs being pursued today, which mostly descend from those proposed many decades ago, adding that ‘at least one NLWR concept, the liquid metal–cooled fast reactor, even predates the LWR’. Some were tested, but most of the early non-LWR reactor ideas were subsequently abandoned, with, famously, one early fast reactor, sited near Detroit, suffering a partial melt down in 1966.
Nevertheless, the UCS notes, NLWR designers now claim that the latest variants have ‘innovative features that could disrupt the nuclear power industry and solve its problems. They state variously that their designs could lower costs, be built quickly, reduce the accumulation of nuclear waste, use uranium more efficiently, improve safety, and reduce the risk of nuclear proliferation. More specifically, they cite the advantages of features such as passive shutdown and cooling, the ability to consume or recycle nuclear waste, and the provision of high-temperature process heat for industrial applications such as hydrogen production. And some NLWR vendors claim that they can demonstrate, license, & deploy their designs within a decade or two’. The report goes on to demolish just about all these claims.
It concludes that ‘while some NLWR designs offer some safety advantages, all have novel characteristics that could render them less safe’. It warns that ‘the claim that any nuclear reactor system can “burn” or “consume” nuclear waste is a misleading oversimplification. Reactors can actually use only a fraction of spent nuclear fuel as new fuel, and separating that fraction increases the risks of nuclear proliferation and terrorism.’ Although some NLWR systems could use uranium more efficiently and generate smaller quantities of long-lived transuranic isotopes in nuclear waste, ‘for most designs these benefits could only be achieved by repeatedly reprocessing spent fuel to separate out these isotopes and recycle them in new fuel—and that presents unacceptable proliferation and security risks’.
However, the UCS does accept that ‘once-through, breed-and-burn reactors have the potential to use uranium more efficiently without reprocessing’, although, ‘many technical challenges remain’. A case in point is Terrapower’s experience with their ‘Traveling Wave Reactor’. It’s an old idea: a ‘nuclear candle’, with a wave of uranium and resultant plutonium fission running slowly from one end to another. The company spent years exploring this co-joined ‘breed and burn’ system, with backing from Bill Gates, but then abandoned it as un-workable, even with a major design revision. They’ve moved on to Natrium, a liquid sodium cooled fast reactor. UCS says that it’s ‘less uranium-efficient than an LWR’.
The nuclear industry is clearly desperate for a way ahead, but the UCS doesn’t see it happening, at least not much and not soon. It notes that some developers of NLWRs say that they will be able to deploy their reactors commercially as soon as the late 2020s. However, the UCS says ‘such aggressive timelines are inconsistent with the recent experience of new reactors such as the Westinghouse AP1000, an evolutionary LWR. Although the AP1000 has some novel features, its designers leveraged many decades of LWR operating data. Even so, it took more than 30 years of research, development, and construction before the first AP1000—the Sanmen Unit 1 reactor in China—began to produce power in 2018’.
The UCS report is also pretty sniffy about the novel application idea of developing high-coolant-temperature reactors for non-nuclear industrial process heat supply. It says ‘there is little evidence that the industries that would utilize such heat are themselves interested in using nuclear power. And it is unclear why these other industries would want to incur the additional risks of operating nuclear reactors in proximity to chemical plants’.
The UCS review does not look specifically at the comparative economics of the various NLWR systems. That would be very hard at this stage, when we are mostly talking about unbuilt concepts, some of which would involve the establishment of major new expensive fuel reprocessing facilities. It also doesn’t look at fusion, which some see as a longer term option. But it does cover most of the other issues and options – and quite comprehensively, at least in terms of US NLWR developments. And it seems that there, apart from a few exceptions, all we are left with, by way of near-future nuclear options, are revamped LWRs.
That classification does of course include mini-PWR designs, like NuScale’s Small Modular Reactor. But the UCS is none too keen on SMRs, as witness its earlier report on them –it says ‘small isn’t always beautiful’. A more recent review of SMRs by Prof. M.V. Ravana, from the University of British Columbia, looking more at the economics, came to similar conclusions: ‘Pursuing SMRs will only worsen the problem of poor economics that has plagued nuclear power and make it harder for nuclear power to compete with renewable sources of electricity.’ For example, he says ‘operating nuclear reactors in a load-following mode would reduce the capacity factor, which would increase the cost of electricity generated’ and he claims that ‘nuclear advocates seem to be clutching at straws by emphasizing these options’.
There may be a role for some SMRs in remote locations and even for a few larger LWRs for specialist purposes, but in the main, Ravana says, ‘because there is no evidence of adequate demand, it is financially not viable to set up the manufacturing facilities needed to mass produce SMRs and advanced reactors. [..] SMR plans run into a chicken and egg problem: without the factory, they cannot ever hope to achieve the theoretical cost reductions that are at heart of the strategy to compensate for the lack of economies of scale.’
So it does seem from these reports that new nuclear is stymied on most fronts, a view mostly shared by a new very clear analysis of the UK situation from the University of Sussex Energy Group and also in the useful SMR overview in NuClear News 131.