A Stanford University and University of British Columbia study into the waste streams from three proposed small modular reactor (SMR) designs predicts complex technical problems and high costs that will occur in the management of spent nuclear fuel and other radioactive waste from both light water and advanced SMR designs
The Stanford-led research, published this week by the National Academy of Sciences (NAS), finds “small modular reactors will exacerbate challenges of highly radioactive nuclear waste.”
“The takeaway message for the industry and investors is that the back end of the fuel cycle may include hidden costs that must be addressed,” says study co-author and UBC professor Allison Macfarlane, who is also a former NRC Commissioner (2012-2014).
There are significant issues regarding the findings of the report. This blog post briefly describes the main findings of the NAS published report and then poses some questions about the caveats and limitations of the study that will add some much needed perspective to the press statement and the report.
According to a press statement from Stanford University, released ahead of the NAS report, the study has following conclusion.
“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 study lead author Lindsay Krall, a former MacArthur Postdoctoral Fellow at Stanford University’s Center for International Security and Cooperation (CISAC). “These findings stand in sharp contrast to the cost and waste reduction benefits that advocates have claimed for advanced nuclear technologies.”
Krall and her team say that for this study, they analyzed the nuclear waste streams from three types of small modular reactors being developed by Toshiba, NuScale, and Terrestrial Energy. Each company uses a different design. Results from case studies were corroborated by theoretical calculations and a broader design survey. This three-pronged approach enabled the authors to draw disturbing conclusions but these findings come along with a very big caveat.
“The analysis was difficult, because none of these reactors are in operation yet,” said study co-author Rodney Ewing, the Frank Stanton Professor in Nuclear Security at Stanford and co-director of CISAC. “Also, the designs of some of the reactors are proprietary, adding additional hurdles to the research.”
The Stanford study focuses on neutron bombardment of structural materials that make up the reactor including its steel and concrete.
Energy is produced in a nuclear reactor when a neutron splits a uranium atom in the reactor core, generating additional neutrons that go on to split other uranium atoms, creating a chain reaction. Some neutrons escape from the core. This is a problem called neutron leakage, These materials become radioactive when “activated” by neutrons lost from the core.
Too Many Neutrons
The new study found that, because of their smaller size, small modular reactors will experience more neutron leakage than conventional reactors. This increased leakage affects the amount and composition of their waste streams.
“The more neutrons that are leaked, the greater the amount of radioactivity created by the activation process of neutrons,” Ewing said. “We found that small modular reactors will generate at least nine times more neutron-activated steel than conventional power plants. These radioactive materials have to be carefully managed prior to disposal, which will be expensive.”
The study also asserted that the spent nuclear fuel from small modular reactors will be discharged in greater volumes per unit energy extracted and can be far more complex than the spent fuel discharged from existing power plants.
“Some small modular reactor designs call for chemically exotic fuels and coolants that can produce difficult-to-manage wastes for disposal,” said co-author Allison Macfarlane, professor and director of the School of Public Policy and Global Affairs at the University of British Columbia. “Those exotic fuels and coolants may require costly chemical treatment prior to disposal.”
“The takeaway message for the industry and investors is that the back end of the fuel cycle may include hidden costs that must be addressed,” Macfarlane said. “It’s in the best interest of the reactor designer and the regulator to understand the waste implications of these reactors.”
The study also concludes that SMRs “are inferior to conventional reactors with respect to radioactive waste generation, management requirements, and disposal options.”
The research team estimated that after 10,000 years, the radiotoxicity of plutonium in spent fuels discharged from the three study modules would be at least 50 percent higher than the plutonium in conventional spent fuel per unit energy extracted.
Because of this high level of radiotoxicity, geologic repositories for small modular reactor wastes should be carefully chosen through a thorough siting process, the authors said.
“We shouldn’t be the ones doing this kind of study,” said Ewing. “The vendors, those who are proposing and receiving federal support to develop advanced reactors, should be concerned about the waste and conducting research that can be reviewed in the open literature.”
What’s Wrong with this Study?
To begin with the text of the Stanford press statement has a caveat the size of the Brooklyn Bridge.
“The analysis was difficult, because none of these reactors are in operation yet,” said study co-author Rodney Ewing, the Frank Stanton Professor in Nuclear Security at Stanford and co-director of CISAC. “Also, the designs of some of the reactors are proprietary, adding additional hurdles to the research.”
This is a significant shortcoming of the report. The absence of quality assured test data is a compelling reason to question the report as a whole as well as its particular findings. Had the authors called for such testing, rather than leaping to conclusion in its absence, the report might have built a stronger case for its conclusion.
In short, without this kind of information, the report’s conclusions will be seen as resting on conjecture, and theory, and not engineering test results. It is plausible to predict the report will be strongly criticized on this point. In point of fact, the report’s press statement notes, “results from case studies were corroborated by theoretical calculations.” Simulation and modeling will only take you so far.
Also, the authors don’t include references to any findings about the spent fuel from SMRs that have emerged from the NRC’s licensing review of NuScale’s SMR nor any of the pre-licensing topical reports from other vendor applicants that can be released without compromising proprietary information. There are multiple light water and advanced reactors in pre-licensing talks with the agency so there is no shortage of data in the NRC’s ADAMS online library to review.
The research team had an obligation to discuss the report with the NRC prior to publication, especially due to the fact that Allison MacFarlane, a former NRC Commissioner, is one of the co-authors. Her expertise alone is insufficient for this purpose.
There is no reference to findings about spent fuel for SMRs undertaken by the Canadian Nuclear Safety Commission’s (CNSC) vendor design review (VDR) which included the NuScale SMR as well as 12 other SMR designs of which 9 are advanced designs that use HALEU fuels with enrichment levels of between 5-19% U235.
Also, since the report carries the imprint of the National Academy of Sciences, one would assume that peer review would have included experts on spent nuclear fuel at the NRC and outside the government who would have questioned some of the report’s findings. More than a decade ago the US government published a “Blue Ribbon Report” on spent nuclear fuel. At a minimum its findings should have been part of the baseline literature review of your study. A review of the cited references in the report indicates it was not accessed by the research team.
The Stanford study focuses on neutron bombardment of structural materials that make up the reactor including its steel and concrete. Typically, materials testing takes place in test reactors to address in exact engineering terms how much impact the neutrons in the reactor will have on materials. The study’s principals could have picked up the phone and called the scientists at the Idaho National Laboratory familiar with the work that has been done over decades at the Advanced Test Reactor to get some answers to their questions. Apparently, the research team did not do this as there is no citation for it in the full text of the report.
IAEA Addressed the Issue of Spent Fuel for SMRs in 2019
The research team also had an obligation to address the global aspects of SMRs as there are dozens of designs in development worldwide. The IAEA would have been a good place to start.
The IAEA said in 2019 that spent fuel from SMRs could be handled according to methods used for existing reactors. Here’s a section of their article along with the URL for the complete post
“Countries with established nuclear power programs have been managing their spent fuel for decades. They have gained extensive experience and have proper infrastructure in place. For these countries, management of spent fuel arising from SMRs shouldn’t pose a challenge if they opt to deploy SMRs based on current technologies, said Christophe Xerri, Director of the Division of Nuclear Fuel Cycle and Waste Technology at the IAEA.”
“Since this type of small modular reactor will be using the same fuel as conventional, large nuclear power plants, it’s spent fuel can be managed in the same way as that of large reactors,” Xerri said.”
Even for SMRs based on new technologies, such as high temperature gas cooled reactors, which will use fuel packed in graphite prismatic blocks or graphite pebbles, countries that have nuclear power plants will already have solutions in place for storing and managing spent fuel. “They can either use existing infrastructure or adjust it for the new radioactive waste streams,” Xerri said.”
The report sails past obvious solutions which include reprocessing spent nuclear fuel or using salt formations like the one at the Waste Isolation Pilot Plant for a geologic repository.Jim Conca, a Ph.D. nuclear scientist, wrote to me in an email about the Stanford study saying, “The salt in New Mexico that hosts WIPP could take all of this no problem, as the salt’s performance is independent of the waste form or level of activity, although bureaucratically we can only put TRU there even though WIPP was designed and built for everything.”
Readers should also know that when WIPP was first being designed in the late 1970s, it was intended to take not only spent nuclear fuel, but also high level military nuclear waste such as spent fuel from navy ships and submarines. Instead, the navy reprocessed its spent fuel at the Naval Reactors site in Idaho until the early 1990s.
Swift Response from SMR Developers
Although the Stanford report was released over the long US Memorial Day weekend, responses to it from the SMR developer community were swift and to the point.
“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. 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,” said Simon Irish, CEO of Terrestrial Energy.
Note: Terrestrial Energy hosted the 32nd GIF Molten Salt Reactor steering committee meeting at its Oakville, Canada office on May 3-5, 2022. This bi-annual gathering of world nuclear experts is part of the Generation IV International Forum (GIF).
NuScale Power lodged this objection. “We don’t agree with the conclusion that the NuScale design creates more used spent fuel per unit of energy compared to currently operating light water reactors,” says NuScale spokesperson Diane Hughes.
“The paper uses outdated design information for the energy capacity of the NuScale fuel design and wrong assumptions for the material used in the reactor reflector, and on burnup of the fuel. With the correct inputs, NuScale’s design compares favorably with current large pressurized water reactors on spent fuel waste created per unit of energy. These inputs are publicly available to the paper’s authors and their omission undermines the credibility of the paper and its conclusions.”
A spokesman for the Third Way, a DC think tank that studies energy issues, said this about the report, “It fails to recognize that because some advanced SMRs are more efficient than existing reactors they are expected to produce less waste overall not more. The study mixes different reactor designs and uses what appears to be old information. Any long-term waste solution, whether a centralized repository or recycling, can easily accommodate the waste, because nuclear plants, whether large or small, produce a small amount of high-level waste.”
It is entirely predictable that there will be more and considerable criticism of the report from developers of SMRs and the nuclear energy industry in general.
Krall is now a scientist at the Swedish Nuclear Fuel and Waste Management Company. Co-authors of the study are Rodney Ewing, the Frank Stanton Professor in Nuclear Security at Stanford and co-director of CISAC, and Allison Macfarlane, professor and director of the School of Public Policy and Global Affairs at the University of British Columbia and former chairman of the U.S. Nuclear Regulatory Commission, where she took a particular interest in waste management.
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