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Stanford’s Questionable Study on Spent Nuclear Fuel for SMRs

Dan Yurman's picture
Editor & Publisher, NeutronBytes, a blog about nuclear energy

Publisher of NeutronBytes, a blog about nuclear energy online since 2007.  Consultant and project manager for technology innovation processes and new product / program development for commercial...

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  • Jun 1, 2022
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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.

canadian-advanced-smrs-in-cnsc-vdr-v2

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

what are SMRs

“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.”

wippThe 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.

# # #

Discussions
Jim Stack's picture
Jim Stack on Jun 2, 2022

When you are dealing with deadly waste and trying to make power it is a loser no matter how you try to do it. QUOTE=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.

Dan Yurman's picture
Dan Yurman on Jun 2, 2022

The team of researchers used incorrect data and never fact checked their findings with NuScale before publishing the report.  NuScale CEO Jose Reyes, who is a member of NAS and serves on several NAS committees related to nuclear energy, send NAS a letter on 5/31/22 detailing the technical basis for the mistakes in the NAS report. 

It disputes on technical grounds the assertion by the authors of the NAS study that SMRs produce more nuclear waste than conventional large scale PWRs. Read the full text here as reported by the American Nuclear Society.   https://www.ans.org/news/article-4013/nuscale-responds-to-smr-critique/

In summary NuScale Power lodged this objection.

“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.”

Michael Keller's picture
Michael Keller on Jun 6, 2022

The NUSCALE reactor is less efficient than a large conventional reactor and has a lower fuel burn-up. Those factors mean the smaller reactor creates more nuclear waste in terms of relative energy production (per kWh net output).

Michael Keller's picture
Michael Keller on Jun 6, 2022

The additional waste from the NUSCALE reactor is around 25%. Also means more uranium is required, on a normalized kilowatt- hour basis.

More efficient and higher burn-up yields less waste. Reprocessing fuel also inherently creates more waste due to the nature of the chemical separation methods used. Turning the fuel into some form of glass for disposal also creates more waste. 

 

Roger Arnold's picture
Roger Arnold on Jun 9, 2022

Michael, what's your basis for asserting that the NuScale reactor is less efficient than a large conventional reactor and has a lower fuel burn-up? Something you read in the NAS study that Dan demolishes? Its authors are all geologists and policy wonks. Smart people, perhaps, but not a nuclear engineer or physicist among them.

I'm not a nuclear engineer either, but I started professional life as a physicist. I know enough about absorption cross sections and neutron economies in reactors that, were I asked to design one and high fuel burn-up were a design priority, size of the reactor wouldn't be an issue. My design might not be safe or economical; see "not a nuclear engineer". There are rafts of little details about which I'm blissfully ignorant. But I know enough to recognize that the scale issue on which the study authors rest their case is almost entirely bogus. 

Michael Keller's picture
Michael Keller on Jun 13, 2022

The Nuscale reactor relies on natural circulation versus forced circulation used with conventional reactors. Natural convection necessarily must reduce the coolant temperature in order to avoid fuel damage. The lower coolant temperature, in turn reduces the steam temperature in the boiler. That lower temperature directly leads to lower efficiency.

Forced circulation is much more effective for heat transfer than natural circulation. As such, conventional reactors can operate at higher temperatures than natural circulation reactors.

Michael Keller's picture
Michael Keller on Jun 13, 2022

Further, economies of scale traditionally leads to larger output and higher efficiency in order to become more competitive. That is the historical pattern seen with generating facilities (including renewable power). Small reactors are going in exactly the opposite direction. That does not bode well for the competitiveness of small reactors.

FYI I am a nuclear engineer.

Michael Keller's picture
Michael Keller on Jun 13, 2022

Further, the published average burn-up figures for Nuscale are less than conventional reactors - looks to be around 45 versus 55 mWd/metric ton of uranium. The difference appears largely related to natural convection versus forced circulation.

Dan Yurman's picture
Dan Yurman on Jun 13, 2022

Since your focus is on the NuScale SMR, the following information is relevant to the dialog.

The report by the National Academy of Sciences has been strongly criticized in the US on several grounds.  Most importantly, two developers of small nuclear reactors (SMRs) have documented numerous technical errors in the report. The American Nuclear Society (ANS) published a letter from NuScale Power which has the details about these errors.  (URL below)  

https://www.ans.org/news/article-4013/nuscale-responds-to-smr-critique/

The letter is too long to reproduce here. 

Readers can access the letter from Terrestrial Energy at the URL below. Note that the firm is developing an SMR that uses a molten salt design with a high RPV output temperature.      https://www.terrestrialenergy.com/media/  

Both SMR developers cited numerous technical errors in the NAS report. 

END

 

 

Michael Keller's picture
Michael Keller on Jun 13, 2022

The report in question does bring up some potentially vexing issues, but more in a broad sense. I would be  disinclined to become defensively overly fixated on details in the report, as some of the vendors have become. The big picture view is more important.

Roger Arnold's picture
Roger Arnold on Jun 9, 2022

Excellent article,  Dan. You've done a thorough job of demolishing the Stanford study from a technical standpoint. The comments from Dr. Xerri at the IAEA and from the SMR developers at NuScale Power and Terrestrial Energy are particularly telling.

Unfortunately, exposing the technical and methodological flaws of the study won't be enough. Technical arguments sail right past those who have already been persuaded that nuclear power is a Bad Thing. The nameless horrors of the Unsolved Problem of nuclear waste is their last retreat for justifying their opposition. The Stanford study is certain to be seized upon as "proof" that SMR technology has nothing to offer and is actually a dire threat to life on earth. They're stuck in an apocalyptic myth sold to the world by anti-nuclear soldiers of coal interests in the decades when nuclear power was threatening the supremacy of coal. Times have changed but myths, once sold, take on a tenacious life of their own.

I wish everyone in the anti-nuclear crowd would watch this TED video in which Michael Shellenberger explains why he changed his mind about nuclear power. One of the things that really comes across is how outrageously overblown the whole issue of nuclear wastes actually is. In that light, the technical merits of the Stanford study are a distraction. Even if their conclusions about a potential 30-fold increase in low and intermediate level wastes from SMR were actually correct, it wouldn't matter. They'd still be insignificant.

Dan Yurman's picture
Thank Dan for the Post!
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