2. SMRs are generally not safer than large light-water reactors.
We now come to the other three critical issues developed by Lyman.
3. SMRs will not reduce the problem of radioactive waste.
“The industry very misleadingly claims that some SMRs will reduce the intractable problem of managing long-lived radioactive waste by generating less waste or even ‘recycling’ their own waste or that produced by other reactors”, Lyman says bluntly.
Why very misleading, according to the American expert?
Because, first of all, in terms of the quantity of highly radioactive isotopes formed when atomic nuclei are split and release energy, “small reactors produce just as many as large reactors per unit of heat generated”.
“Moreover, for reactors with denser fuels, the volume and mass of the spent fuel generated may be lower, but the concentration of fission products in the spent fuel and the heat generated by decay products – factors that really matter for safety – will be proportionately higher”.
So the lower waste output is ultimately only apparent, because they produce the same quantity of highly radioactive isotopes per unit of energy generated.
And so everyone, public or private, who operates SMRs “will have to safely manage the storage of significant quantities of spent nuclear fuel on site for a long time, just as all other nuclear power plants do”.
It is therefore untrue, as some suppliers claim (Lyman names an energy giant at the forefront of SMR construction), that the reactors will be taken away once the fuel can no longer be used. “They are not credible, since there are no realistic prospects for licensing centralised sites where used reactors could be taken in the near future”.
The result: “Any community with an SMR will have to plan on effectively being a long-term nuclear waste disposal site”.
4. SMRs cannot be relied on to provide reliable, resilient off-grid power to facilities such as data centres, bitcoin mining, hydrogen production or petrochemicals.
Despite developers’ claims, no SMR design “is capable of operating safely without reliable access to grid electricity to power cooling pumps and other vital safety systems”.
This is because SMRs, just like today’s nuclear plants, will be vulnerable to extreme weather events or other disasters that could cause a loss of off-site power and force them to shut down.
Should such an event occur – and it is likely to – “a user such as a data centre operator would have to provide backup power, probably from diesel generators, for both the data centre and the reactor”.
This means that the level of reliability characteristic of operating light-water reactors is still far from being reached by SMRs. “Most likely”, Lyman writes, “it will take decades of operating experience. A premature introduction based on unrealistic performance expectations could prove extremely costly for any company wishing to experiment with SMRs”.
5. SMRs do not use fuel more efficiently than large reactors.
The claim that SMRs are more efficient than large reactors because they use less fuel is, according to Lyman, misleading. Let’s see why.
“In terms of the quantity of heat generated, the amount of uranium fuel that must undergo nuclear fission is the same whether the reactor is large or small”.
Furthermore, it is true that reactors using coolants other than water, typically operating at higher temperatures, can see their efficiency in converting heat into electricity increase. But “this is not an effect large enough to offset other factors that reduce fuel-use efficiency”.
Lyman explains: “Some SMR designs require a type of uranium fuel called ‘high-assay low-enriched uranium (HALEU)’, which contains higher concentrations of the isotope uranium-235 than conventional light-water reactor fuel. Although this reduces the total mass of fuel the reactor needs, it does not mean that less uranium is used or that less waste is produced by the ‘front-end’ mining and milling activities (in the nuclear fuel cycle, the fuel preparation stage): if anything, the opposite is more likely to be true.
“One reason is that producing HALEU requires a relatively large amount of natural uranium to feed into the enrichment process that increases the concentration of uranium-235”.
“For example, the TerraPower Natrium reactor, which would use HALEU enriched to about 19% uranium-235, will require 2.5 to 3 times more natural uranium to produce a kilowatt-hour of electricity than a light-water reactor. Smaller reactors, such as the 15-megawatt Oklo Aurora, are even more inefficient”.
There is therefore an efficiency problem. “Improving the efficiency of these reactors can only come with significant advances in fuel performance, which could take decades to develop”.
Moreover, this inefficiency potentially has significant environmental repercussions. “Reactors that use uranium inefficiently have a disproportionate impact on the environment because of the polluting activities of uranium mining and processing”. They are also “less effective at mitigating carbon emissions, because uranium mining and milling are carbon-intensive compared with other parts of the uranium fuel cycle”.
The conclusion of Lyman’s piece has the same virtue of clarity as the rest of his article. It is worth quoting in full:
“SMRs may have a role in our energy future, but only if they are sufficiently safe and secure. To that end, a realistic understanding of their costs and risks is essential. By painting an overly rosy picture of these technologies with often misleading information, nuclear bros are distracting attention from the need to address the many challenges that must be resolved to make SMRs a reality and, ultimately, are doing their cause a disservice”.
