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Small nuclear reactors produce '35x more waste' than big plants

At least one manufacturer would like to disagree with study's conclusions

Updated Mini nuclear reactors that are supposed to usher in an era of cheaper and safer nuclear power may generate up to 35 times more waste to produce the same amount of power as a regular plant, according to a study.

A team of researchers at Stanford University and the University of British Columbia came to this conclusion after studying a design from each of three small modular reactor (SMR) manufacturers: NuScale Power, Toshiba, and Terrestrial Energy.

The study, published this week, found that not only did those particular SMR approaches generate five times the spent nuclear fuel (SNF), 30 times the long-lived equivalent waste, and 35 times the low and intermediate-level waste (LILW), their waste is also more reactive, therefore more dangerous and consequently harder to dispose of.

Fission-powered SMRs have been around for a long time – think nuclear submarines – but they've emerged as the next generation of nuclear power because they're supposed to be smaller, even more safe to operate, and cheaper. Reactors considered SMRs generate 300MWe or less, while traditional light-water reactors (LWR) can reach a thousand or more MWe.

In the UK, aerospace company Rolls-Royce is slated to build a £210 million ($261 million) SMR manufacturing plant, while the US Department of Energy has partnered with NuScale on its work. Still, the paper's authors said, "few studies have assessed the implications of SMRs for the back end of the nuclear fuel cycle."

Less efficient by design?

Watt for watt, the paper claims, SMRs with water, molten salt, and sodium-cooled reactors "increase the volume of nuclear waste in need of management and disposal by factors of 2 to 30," with the wide range attributed to different designs and materials. 

Much of the waste can be attributed to chemically reactive fuels and coolants used in SMRs to catch stray neutrons, the researchers wrote. Neutrons that are lost in the fission process interact with the material surrounding the fuel assemblies, which generates radioactive waste. In essence, the smaller size of SMRs leads to them generating more waste.

More waste, and more hazardous too, it seems. The higher potency of the spent fuel and waste material means that it can't be stored in the same manner as nuclear waste from traditional LWR plants, we're told. New storage methods would need to be developed, the researchers said, which "will introduce costs and radiation exposure risks to the nuclear fuel cycle."

Hang on a minute

Diane Hughes, VP of marketing and communication at NuScale, disagreed with the paper's conclusions. She described NuScale's SMRs as producing waste consistent with well-established storage guidelines the US has been using for more than 60 years. 

"The study uses outdated design information for the energy capacity of the NuScale fuel design, wrong assumptions for the material used in the reactor reflector, and incorrect assumptions on burn-up of the fuel.  With the correct inputs, NuScale's design compares favorably with current large PWRs on spent fuel waste created per unit energy," Hughes said.

She added that NuScale's take on the paper is supported by information it presented to the National academy of Sciences, Engineering and Medicine, and said that the study applies conclusions that don't apply to NuScale's technology.

As to the claims that their SMRs generate more waste, Hughes said the study is wrong on that count, too: NuScale's latest SMR, a 250MW thermal core, outperforms the 160MW model the paper studied. "The NuScale 250 MWt design does not produce more SNF than the small quantities typically observed in the existing LWR fleet," Hughes said. NuScale didn't mention whether it reactor generates more LILW or longer-lived material that needs to be disposed.

Spokespeople for Toshiba and Terrestrial Energy were not available for comment. ®

Updated to add

Terrestrial Energy is unsatisfied with the SMR study, and disagreed with its conclusions.

"Terrestrial Energy's IMSR Generation IV fission plant generates electric power at nearly 50 percent higher thermal efficiency than a conventional reactor, so clearly it produces less radioactive waste or activity per unit power," said Simon Irish, CEO of Terrestrial Energy.

"Terrestrial Energy is developing a conversion process using ANSTO Synroc technology for a waste form that is far more geologically stable than that of current reactors. The Generation IV International Forum in part defines a successful Generation IV technology as one that creates less waste – our IMSR technology embodies that objective, which was set by international experts."

A spokesperson for Toshiba Energy Systems & Solutions told us: "Toshiba did not participate in this study. The methodology and/or condition of this study are not clear so Toshiba will not make a comment on the conclusion of this study."

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