Small modular reactor firms cast doubt on nuclear waste study

A recent paper claiming a new nuclear power technology may be up to 30 times more wasteful than conventional power plants was met with swift rebuttal by small modular reactor developers.

The findings, published in the Proceedings of the National Academy of Sciences, or PNAS, drew from three small modular reactor design proposals developed by the companies Toshiba Corp., Terrestrial Energy Inc. and NuScale Power Corp. "Simple metrics, such as estimates of the mass of spent fuel, offer little insight into the resources that will be required to store, package, and dispose of the spent fuel and other radioactive waste," lead author Lindsay Krall, a scientist at the Swedish Nuclear Fuel and Waste Management Co., said in a May 30 news release.

But on June 1, NuScale said through a spokesperson the paper was based on outdated design information and came to the "wrong assumptions" about other aspects of the company's proposed power plant.

"With the correct inputs, NuScale's design compares favorably with current large pressurized water reactors on spent fuel waste created per unit of energy," NuScale spokesperson Ryan Dean said in an email. "These inputs are publicly available to the paper's authors and their omission undermines the credibility of the paper and its conclusions."

NuScale's response included a copy of a letter sent by Chief Technology Officer and co-founder Jose Reyes, the same day the paper was published, to PNAS editor-in-chief May Berenbaum requesting a "prompt correction."

PNAS spokesperson Prashant Nair said the academic journal was aware of the letter and looking into it.

Flexible nuclear power

Small modular reactors, or SMRs, are to conventional nuclear reactors as prefabricated homes are to houses. Backers, including the U.S. Department of Energy, tout SMRs as a low-carbon electricity source with lower capital investment and greater siting flexibility than existing nuclear power plants. However, the technology has yet to go into operation in the U.S. To date, only one design — submitted by NuScale — has been approved by the U.S. Nuclear Regulatory Commission.

The conclusion of the May 31 study was that SMRs may come with hidden costs.

"Our results show that most small modular reactor designs will actually increase the volume of nuclear waste in need of management and disposal, by factors of 2 to 30 for the reactors in our case study," said Krall, a former MacArthur postdoctoral fellow at Stanford University's Center for International Security and Cooperation. The paper was co-authored by Rodney Ewing, co-director of the university center, and Allison Macfarlane, director of the School of Public Policy and Global Affairs at the University of British Columbia and a former NRC commissioner.

Waste is classified as spent nuclear fuel or low- and intermediate-level waste, or LILW, which may include radioactive paper, rags, tools, chemical sludge or metal nuclear fuel cladding. According to the report, SMRs would produce 5.5 times the spent nuclear fuel, 30 times the long-lived LILW and 35 times the short-lived LILW of a gigawatt-scale pressurized water reactor.

Reyes disagreed on the point of spent fuel consumption, writing that the authors are mistaken to assert that NuScale SMRs would produce "significantly more spent nuclear fuel than existing light water reactors," or LWRs, the standard technology for large-scale nuclear plants.

According to Reyes, the report authors draw their findings from a preliminary NuScale design with a 160-MW thermal core, not the latest design, which has a 250-MW thermal core. Characteristics of the 250-MW thermal core were presented in 2021 to an ad hoc committee of experts that included McFarlane, Reyes said, and NuScale's responses to that committee, including data on NuScale's fuel consumption rate, were made publicly available.

"These values are within the values typically observed in the existing fleet of LWRs," Reyes wrote to PNAS, referring to NuScale's average fuel burnup and design basis maximum exposure. "Therefore, the NuScale 250 MWt design does not produce more [spent fuel] than the small quantities typically observed in the existing LWR fleet."

Other objectors

NuScale was not the only developer to dispute that SMRs are more wasteful.

Terrestrial Energy CEO Simon Irish said in an emailed statement that the company's advanced nuclear plant "generates electric power at nearly 50% higher thermal efficiency than a conventional reactor, so clearly it produces less radioactive waste or activity per unit power."

Another developer not analyzed in the study, GE Hitachi Nuclear Energy Canada Inc., said the company's small modular reactor technology would operate with the same fuel as much of the existing boiling water reactor nuclear plants. "The characteristics of this fuel are well understood," GE Hitachi spokesperson Jon Allen said.

Toshiba declined to comment on the May 31 paper.

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