Small modular reactors: our nuclear future?

Hailed as one of the solutions to the current energy crisis, Small Modular Reactors - or SMRs - are intended to fill the renewables “gap” when supplies from alternative sources cannot be relied upon: like the loss of solar power at night, for instance. The intention is that they should step into the breach to replace the UK’s ageing and retiring nuclear fleet as the last few existing nuclear stations go offline. So, has new research suggesting that SMRs will produce 30 times more nuclear waste than existing larger station designs effectively put the concept on hold? Chris Smith spoke with Sheffield University’s Claire Corkhill, who works on how we handle nuclear waste, to hear her take on the matter…

Claire - The paper that was published this week by Lindsay Krall and her colleagues at Stanford took a look at how much radioactive waste is gonna be generated from small modular reactors compared with the larger types of pressurised water reactor that are being built around the world, including in the UK at Hinkley Point C. And what they did was an assessment of exactly what kinds of wastes are gonna be generated in terms of the nuclear fuel, but also reactor components. And what they found was that a small modular reactor will generate about 30 times more radioactive waste than a pressurized water reactor, depending on the reactor design.

Chris - And when you say a pressurized water reactor, we're talking about the sorts of things. We are currently deploying more mainstream, large nuclear reactor that we currently use to generate electricity.

Claire - Yeah, that's right. So we currently have one of these at Sizewell B and we're building another at Hinkley Point C, they generate about three gigawatts of electricity. So that's like boiling a hundred thousand kettles all at once^*. Whereas the small modular reactors, which are really relatively new on the scene, these are much, much smaller and they're a hundred megawatts of electricity. So that's more like boiling three hundred kettles at once.

Chris - But the government have very much got behind this concept. Haven't they? The regulator received an approach from Rolls Royce to table some ideas or some plans for how to do this. A number of other companies have now entered the market with designs to do this. People think that they're an excellent idea. Why is there this disparity?

Claire - Well, one of the major reasons, and for the popularity of SMRs is really their size. They're much smaller than these very large PWR reactors, which are extremely expensive to build. We've seen the cost of that Hinkley Point C reactor just increase and increase by millions and tens of millions of pounds, year on year throughout the construction process. So by building smaller reactors, the advantages that we can manufacture all of the components within the UK, we can use the supply chain that's already established here to build more economic reactors.

Chris - Well, if there are economies of scale that you can get with the SMRs, why does that not also transfer to the waste?

Claire - That's really interesting question. That's precisely what Lindsay Crawl and her co authors have discovered in this paper. One of the major issues is actually to do with the size. So if we think about how a nuclear reactor works, we have uranium atoms that are splitting and they create neutrons subatomic particles. And these neutrons, we use them to power the chain reaction. They go on to split more atoms of uranium. Now to make that as efficient as possible, we need to keep the neutrons inside the reactor. But the problem with small modular reactors is it's difficult to do and what we get is something called neutron leakage. What that means is that these neutrons then start to interact with the structural components inside the nuclear reactor, and it turns them radioactive. So the stainless steel, for example, that the reactor's built out of then becomes radioactive. And that is then when it comes to decommissioning those reactors intermediate level waste that we have to manage and dispose of.

Chris - Where does the difference between relative and absolute come into this? Because relatively, yes, it's producing about 30 times more waste than a massive great power station. But given that these are much smaller, does it still not translate into a very small amount of waste? And given the other benefits that would come with embracing this technology, it still adds up to a good thing, or is the case overnight becoming a lot less compelling thanks to this research?

Claire - We really do need a short term fix to the energy crisis. And there's good potential for small modular reactors to come to the rescue here. That being said, you know, in comparison to other technologies like wind and solar and so on, they don't create the same kinds of wastes as we've been discussing here. So I think it's a balance. We need to think about what we need in terms of generating our electricity now and what we are happy with being the consequences moving forward in the future.

[*We think Claire meant a million or so kettles here, rather than 100,000: assuming a very energy-hungry kettle draws 15A at 240 volts, 100,000 such kettles would use only 15*240*100,000 = 375,000,000, or 0.375GW, rather than 3GW.]