Stanford’s Questionable Study on Spent Nuclear Fuel for SMRs

questionA 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.

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

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

(05/31/22) “Our 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.

06/03/22: Terrestrial Energy responded further to the Proceedings of the National Academy of Sciences (PNAS) article on used fuel from SMRs.  (Full Text of letter PDF file with extensive comments)

“Terrestrial Energy is deeply disappointed in the poor quality of this article and its numerous and significant factual errors. The article in several instances implies that any single shortfall of any small modular (SMR) system is universal to other SMR designs. As such, the article fails to comply with the Academy’s high standards. The article’s conclusion is the most egregious case in point:”

“Molten salt- and sodium-cooled SMRs will use highly corrosive and pyrophoric fuels and coolants that, following irradiation, will become highly radioactive.”  (italics added)

“Such a statement ignores well-established fact in the field: No reactor uses or proposes using pyrophoric fuels. While sodium reactors indeed have a pyrophoric coolant, the coolant does not become highly radioactive. However, the sentence clearly implies both molten salt and sodium cooled reactors have pyrophoric fuels and coolants, which is simply false.”


(05/30/22) The firm 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.”

(06/01/22: NuScale has written a letter to NAS about the paper. 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.

Third Way

(05/31/2) A spokesman for the DC think tank which 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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Dan Yurman ~ The Twitter feed is a hiatus due to the turmoil on that platform. The news feed of nuclear energy headlines can be found on Mastodon at: ~ About this blog and disclaimers for NeutronBytes ~ ~ Contact Me ~ neutronbytes [at] gmail [dot] com ~ Text via Signal 216-218-3823 ~ I am NOT active on Facebook, Reddit or Instagram. Attempt no landings there. ** Header Image Credit: ~ ** Emails sent by readers about blog posts are considered to be comments for publication unless otherwise noted. ** The content of this blog is protected by copyright laws of the U.S. "Fair use" provisions apply. The RSS feed is for personal use only unless otherwise explicitly granted.
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16 Responses to Stanford’s Questionable Study on Spent Nuclear Fuel for SMRs

  1. brianrlcatt says:

    THis really confuses types of waste at the most basic levels of subject knowledge. These people are experts? Really? The reactor materials are not classified as high level waste and can be disposed of quite differently from yer actual fuel rods. They will be relatively low level radioisotopes of their existing elements, not fission products or heavy actinides.. And a bit more activated material is still a LOT less activity than spent fuel over a lifetime of operation – in terms of absolute total activity and activity per unit mass.

    Disposal of reactor materials is simple and relatively inexpensive. It’s a bit hard for them to be toxic hazards, They’re only metal, after all. The whole premise of this paper seems to be to make SMRs a bad idea, based on a straw man proposition about activated plant material. Not a real problem.

    A whole subject introductory PPT here. Slides 16, 17 and 18 refer. Not really designed for viewing in non presentation mode, but these slides are OK. UK regulations apply. E&OE


  2. Edward T. says:

    It is good to know that we can still find America’s “best and brightest” to rehash the spent fuel issues over and over….. Over forty years of papers, research, failed pilots, scuttled projects. The only thing that gets done is we schedule another symposium where the computer analysts and policy wonks produce seances, not solutions. Congratulations to them all. They should all be forced to watch in continuous cycles the VICE documentaries titled” While the Rest of Us Die”

    Liked by 1 person

  3. JGrams says:

    The report conveniently omits reference to actinide-burner SMR designs such as the GT-MHR, EM2, and SSR-W, the first two of which have been in development for well over 30 years.

    Liked by 3 people

  4. xovermaniac says:

    I know this may sound conspiratorial but has anyone looked into the past associations of these researchers as well as the regulators in the NRC to see if any of them were members of the Sierra Club or Greenpeace?


  5. “but these findings come along with a very big caveat… The analysis was difficult, because none of these reactors are in operation yet”

    I agree that this is a large caveat.

    But why is it we are supposed to accept the rosy predictions for cost and performance but not the not-so-rosy predictions for waste streams when they both suffer the same very big caveat?

    That sounds like special pleading.


  6. Mike Keller says:

    I think more properly, the waste generated should be evaluated on the basis of net electrical output, as opposed to the reactor’s thermal output.
    Net electrical accurately portrays useful energy, whereas reactor thermal output does not. Why is this important? Because the thermal efficiency of the cycle can make a large impact on the amount of radioactive waste produced, relative to the net megawatt-hours produced. More efficient cycles inherently produce less waste than less efficient cycles. By this measure, on a normalized basis, the NUSCALE design does produce somewhat more waste than a large conventional nuclear, although the difference is not particularly significant.
    Gas reactors, with their higher thermal efficiencies, produce less fuel waste than conventional water reactors. Hybrid cycles that concurrently use nuclear and other fuels (e.g. natural gas and/or hydrogen) inherently have significant reductions in nuclear waste, relative to conventional water reactor cycles.
    Speaking for Hybrid Power Technologies LLC (I am the president of the firm) I characterize the Stanford study as somewhat useful, but only in a very broad-brush context.


  7. Charles McCombie says:

    The key point made by Mike Keller about the higher themal efficiencies of some of the SMRs is one of the overarching points that the authors omit. For an electricity producing reactor, the right metric is waste per GWh. Even more importantly, reduction of wastes need not be put forward as a driver for SMRs. Even if they do not reduce wastes, they may be attractive because of increased safety, decreased need for capital investment, versatility (including remote siting, process heat, etc.), lower costs in series production (not yet proven). Finally, even if somewhat more wastes did result, the challenge of safe waste management and disposal is not strongly related to the waste volumes which are always small realtive to other options.


    • Mike Keller says:

      Some of the SMR’s have higher efficiencies than conventional large water reactors, some do not, for instance NUSCALE. However, the additional waste ( on a normalized basis) is not that significant in the case of NUSCALE. There are other factors that come into play, including, fuel burn up and reprocessing of fuel, which creates radioactive waste due to the chemical processes involved. If the spent fuel has to be processed into a special form for long term burial, that also creates additional radioactive waste.
      In my view, the best approach would be high efficiency, high burnup and not having to process the spent fuel for long term burial. The approach advocated by Deep Isolation Inc. (deep horizontal drilling) looks pretty good for permanent disposal.
      From my standpoint, reasonably competitive economics is the key for nuclear power. Unclear if the advanced reactors, including SMR’s, can make the cut. Some might, others probably not. As always, the impact of political interference is a wild card.


  8. enzo says:

    we can use submarine and carrier reactor as baseline for this evaluation?


  9. Kit P says:

    What’s the problem again?

    I an an old retitred engineer. Along the way, I worked on Yucca Mountain. The conclustion I come to is that high level radioactive waste is a problem that must be solved before glaciers cover Norht America again.

    The problem nuclear power has is cheap fossil fuels which also produce hazardous waste waste.

    SMR are a solution looking for a probem.


    • Mike Keller says:

      Gee, I thought global warming was going to solve the ice age problem.
      On a more serious note, the folks at Deep Isolation Inc. have come up with a solution building on horizontal drilling used in the oil & gas industry. The Northern Europeans have built a deep structure in basalt rock. Both solutions are quite viable. The Yucca mountain fiasco in Nevada is not a particularly sound solution due to ground water issues. The salt formation project in New Mexico is also viable. The US problem is the primarily incompetence of government bureaucrats who have zero incentive to actually solve problems.


      • > building on horizontal drilling used in the oil & gas industry

        There are a number of advantages to this concept:

        1) the technical side is well developed
        2) because it’s small, it opens a much greater number of sites for use. For instance, one might imaging boring at the site of the plant
        3) security seems much simpler, even in the distributed case

        There are problems:

        a) if a canister breaks there may be no way to retrieve it (remember Windscale?)
        b) … at which point everything on the other side is inaccessible
        c) … so if it happens on the way down, the site is rendered unusable
        d) and if we do ever want to reprocess, access is both serial and may lead to (a)

        Mixed blessings, as always.


        • Mike Keller says:

          Not so sure trying to recover the spent fuel in deep isolation for reprocessing of plutonium is a good idea. Strikes me deep isolation should be a one-way ticket.


      • Kit P says:

        What ground water issue?

        I would not have signed off on my part of the Yucca Mountain TSPA if it was.

        Fifty years of high level waste history in the US, the short course. WWII ended with the start of the atomic age. The evil emipre got the bomb and we were in a race to make bombs. We also learned to make electricty using fission.

        About the time I enetered the nuclear industry and we also got hiuppies who said fission products were dangerous ingnoring the 30 years of safely handing spent fuel. About 40 years ago I learned at a confernece how to safely store fissikon products in my childrens drinking water resouvoir. DOE was looking at places to store the waste for 10,000 years.

        There was a place in Neveda where we tested nuke weapons undertground. One name is the Neveda Test Site, aka Yucca Mountain. If we drill a tunnel a 1000 feet below the and a 1000 feet above the ground water, we could put spent fuel there.

        The hippies went to court and said 10,000 years is ‘arbitrary’. So we used a super computer to model surface water dripping on spent fuel, migrating to the ground water, then getting to the nearest well in the Great Basin.

        When I reviewed the computer output, I suggested that we label the horizontal axis in glacial maximums. It will take 3 or 4 for water to get there.

        All the fission products will be gone.

        Our planet has been in an ice age for a few million years. The amount of water in ice grows and then some of it melts for realtively short period of time.

        On a serious note, spent fuel should be moved south before being buried in ice.


        • Mike Keller says:

          I think you will find that the waste canisters have to be made of special materials due to potential corrosion. The tunnels also have to have special provisions. As I recall from reports, more of a long-term hydraulic issue associated with the formation’s naturally occurring brine water.


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