Atomic Show #300 – Dr. Lindsay Krall, “Nuclear Waste from Small Modular Reactors”
Dr. Lindsay Krall is a geochemist currently working on projects characterizing the behavior of radioactive isotopes that will eventually be stored in a deep geologic repository being designed in Sweden for construction within the next decade. During a three year post doctoral period she worked under a MacArthur Foundation grant program to study the projected production of waste from small modular reactors. She received mentoring and guidance from Dr. Allison Macfarlane and Dr. Rodney Ewing, but performed most of the work as an individual researcher. As we discussed during this episode of the Atomic Show, the study topic was only marginally related to her academic and professional field.
During her post doc period, she presented various stages of her work at conferences and in journal articles. She told me that those progress reports generated few questions and apparently little interest.
But the final paper documenting her study results produced a minor eruption inside the world of people that are interested in the development and deployment of small modular reactors and advanced nuclear energy production systems. The paper, titled “Nuclear Waste from Small Modular Reactors” was published in the Proceedings of the National Academies of Science. It included the discussion-provoking conclusion that “SMRs will produce more voluminous and chemically/physically reactive waste than LWRs.”
Aside: I question the author’s choice to use the word “will” instead of “might”. There are far too many uncertainties and technology-specific conditions for such certainty. End Aside.
Unlike most of the thousands of study papers published in scientific journals each year, this one stimulated immediate attention with articles in mainstream outlets like Bloomberg, Reuters, The Globe and Mail, and the Register, presumably written by journalists that had access to a pre-print version of the paper. That active promotional effort was a bit of a surprise to the study’s primary author, though she had been advised by her coauthors to be ready for media inquiries.
Dan Yurman at Neutron Bytes published a detailed review of the paper.
The study focused on three SMR designs out of the dozens that are currently under development. The three selected systems included the 160 MWth version of the NuScale Power Module, a version of the Terrestrial Energy Integrated Molten Salt Reactor (IMSR) and the Toshiba 4S. Developers of the NuScale Power Module and the IMSR published prompt responses to the PNAS paper, the Toshiba 4S has not been under active development for at least half a decade.
Both of the responses challenged the study’s decision to use obsolete versions of designs that are still evolving and have not yet been built. They challenged some of the paper’s assumptions about neutron leakage and stated that it cannot be computed with simple volume-related equations. One statement from the paper received particular attention from Terrestrial Energy.
“Molten salt- and sodium-cooled SMRs will use highly corrosive and pyrophoric fuels and coolants that, following irradiation, will become highly radioactive.”Correction of Factual Errors in PNAS Article “Nuclear waste from small modular reactors”
No reactor design proposes to use pyrophoric fuels and sodium coolant activity levels are generally low enough to allow it to be handled as low level waste.
One of the key study decisions received little attention in the widespread coverage about the study’s critical conclusions. For reasons of simplification, resources and study duration, the authors chose to ignore recycling, reuse, dilution and reprocessing, even though all of those waste reduction techniques are being actively researched as part of the DOE’s advanced reactor development program.
This study also neglects to consider reprocessing, recycling, and dilution because these treatments will not eliminate the need for the storage, transportation, treatment, and disposal of radioactive materials.Krall et al “Nuclear waste from small modular reactors”, Proceedings of the National Academies of Science, May 31, 2022
While it’s true that waste reduction techniques do not completely eliminate waste, that statement is incongruous in a paper that quantifies waste production and numerically compares it to existing systems.
Dr. Krall and I had an enlightening discussion about her work and some of the responses it has generated. She hopes that the paper will help to stimulate more work on the back end of new reactor development projects. She recognizes the value of nuclear energy and appreciates the fact that she is currently living in Scandinavia, where there are a relatively large number of operating nuclear reactors and not very much natural gas supplying electricity.
Note: This episode was planned to be produced in a more timely fashion after the paper was released, but production delays changed the schedule. After a couple of attempts that included a gross operator error (failing to push the record button) I met with Dr. Krall on October 26th to discuss her paper, its widespread distribution and the impacts of the paper’s results.
I hope you enjoy the episode and choose to participate in the discussion here.
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I listened to the podcast interview with Dr. Lindsay Kroll and I thought
it was a bit surreal and somewhat entertaining from a black humor
perspective. It reminded me of an interrogation scene from “Law
FWIW, it should be noted that the paper was discussed on this site
back in August as part of the blog entry titled “Why are smaller reactors
attracting so much interest?” (04 Aug 2022)
Macfarlane’s “Burning waste or playing with fire?” article published in the Bulletin of Atomic Scientists, 09/2018 was the most levelheaded Gen3/4 reality check I had read until this PNAS article superseded it with more detail. The authors place high importance on high-level waste stability in [hypothetical] geologic repositories. Whether or not we eventually build such a repository, it is hard to fault the authors for highlighting the hand-waviness of the “back-end” of the fuel cycles pitched for MSRs, SFRs, PBMRs, etc. All of these alternative reactors are DOA without a CRADLE TO GRAVE PLAN for their waste streams that is NO LESS STABLE, TIMELESS, or MORE EXPENSIVE than putting H/LWR fuel in air-cooled shielded trashcans on a concrete pad.
ASIDE: Despite the 60-year licensed lifespan, the casks obviously have an INDEFINITE lifespan – the rain wets them and the sun dries them. Steel components can be designed for infinite fatigue life if the stress field/cycle is well-understood (examples in your car).
The discharge burnup [easily] calculated from chapter 4 of the NuScale Design Certification (i.e. ~35 GWD/TU) is about 70% of what we achieve in the existing LWRs; the enrichment required to achieve this lesser burnup is incrementally ~0.7% higher. In various forums, I’ve used these simple ratios to demonstrate that NuScale will generate 40% more spent fuel/MWe than fleet LWRs, and will have similarly elevated fuel costs. The authors of the PNAS article calculate NuScale will produce 70% more waste. FWIW, CANDU generates 600% more waste by the same calculation with a slight, yet calculable improvement in fuel utilization. It is easy to show the HALEU PBMR types will generate 20X the waste volume of LWRs and the fuel will prove difficult to reprocess (if ever desired).
The authors clearly value nuclear power, argue for incremental improvements to LWR technology and highlight flaws and gaps in proposed [meme] reactors that are obvious, even to a lowly utility employee like myself.
Let this sink in: “reprocessing, recycling, and dilution will not eliminate the need for storage, transportation, treatment and disposal of radioactive materials.”
A patriotic quote from the 09/2018 article showing the intent of what is mistaken by startups as criticism: “We urge policymakers to critically assess non-traditional fuel cycles, including the feasibility of managing their unusual waste streams, any loopholes that could commit the American public to financing quasi-reprocessing operations, and the motivation to rapidly deploy these technologies.”
Michael Scarangella writes:
> Let this sink in: “reprocessing, recycling, and dilution will not eliminate
> the need for storage, transportation, treatment and disposal of radioactive
That may be true, but at risk of supporting the current thing since 1970,
I will note that switching fuel cycles from U238-P239 to Th232-U233 would,
if successful, reduce the radiotoxic lifetime of used fuel from 100Ks of
years to less than 500 years.
This fact argues in favor of Deep Isolation’s design concept of vendor-specific
borehole technology, vs. the one-size-fits-all Yucca Mountain mega-disposal site.
Reprocessing/recycling at an SMR plant could accomplish the same thing
as using Thorium fuel but without having to switch fuel cycles.
Both of these approaches may be expensive in their current form, but my
understanding of DOE’s funding boost is that its purpose is to enable
developers to do R&D to investigate ways of reducing cost while improving
safety, security, and other things.
“This study also neglects to consider reprocessing, recycling, and dilution …”
In so saying, this study wants us to neglect the needs of future generations of fast-neutron reactors. This study also neglects to place the oncoming wave of small nuclear reactors in the context of the imperative to replace all fossil fuels by 2050. This study also neglects to compare their (imagined) problems with “nuclear waste” with the overwhelmingly greater problems with waste CO2 in the atmosphere, that nuclear electricity stands to replace if it were not delayed by these imaginary difficulties.
Understandably, this study neglects to state that the MacArthur Foundation is committed to “a peaceful world”. Greenpeace is similarly committed to “world peace”. The code attracts funding. If both organisations were to change their commitment to “a fossil-free world” they could do far more service to the world’s humanity, environment and prosperity.
Roger Clifton writes:
> If both organisations were to change their commitment to “a fossil-free world”
> they could do far more service to the world’s humanity, environment and prosperity.
I agree. It would be beneficial to think of nuclear and “renewable” energies
as partners in a zero-carbon collaboration rather than as rivals in a zero-sum
Although I agree that political organizations like Greenpeace should adopt a
clearly defined fact-based endorsement of a “fossil-free” world and should
consider what it would most likely mean to make such an endorsement, I would
not expect that such organizations would (or should) be likely to make such
an endorsement into their primary goal at the expense of their ideological
commitment to “world peace”, whatever they mean by that.
I do think that making an empirically based endorsement of a “fossil-free”
world requires an empirically based understanding of the difference between
the explosive energy of nuclear detonations and the controlled energy of
nuclear reactors, fast and slow as well as new and old. The difference
is one of timescales, between the subatomic timescales of neutrons and
protons and the molecular timescales of thermal and chemical instruments
and mechanical feedbacks. My understanding of what enables nuclear
reactors to work across timescale gaps is based on “delayed neutrons”
which Wikipedia defines as follows
In nuclear engineering, a delayed neutron is a neutron emitted after
a nuclear fission event, by one of the fission products (or actually,
a fission product daughter after beta decay), any time from a few
milliseconds to a few minutes after the fission event. Neutrons born
within 10E-14 seconds of the fission are termed “prompt neutrons”.
My understanding of what STEM education needs in order to work
across information gaps created by political fear of all things nuclear
is to impart a clear understanding of what enables nuclear reactors to
work across timescale gaps. To me, that is basic science, same as
interstellar distance gaps and what it would take for humans to travel
between planetary systems. It would take far longer than the entire
existence of human societies to date.
Because of this, there is no planet B. We have to deal with the
realities of the planet we live on now. Starting today.
MacFarlane and Krall are calling attention to Figures of Merit (FOM) that are useful for qualifying proposed reactors regardless of their proponents’ aggressive marketing claims: 1) will they be easier to operate? 2) will they more economical to operate? 3) will they make more mess while operating? 4) will they improve fuel utilization? 5) will they be safer? 6) will their decommissioning and spent fuel storage be cheaper/easier?
Nuclear startups are trying to ride the coattails of an emotion-based, anti-technological environmental movement that hates nuclear power. Emotion is irrelevant in engineering – hand wringing about the fissile needs of “future generations” is irrelevant. Level heads can evaluate if proposed power plant designs improve on [at least most of] the basic FOM with emphasis on ECONOMICS. With startups, NuScale included, there is an apparent inversion in roles regarding proof of concept, improvement, economics. The onus should be on the originating organization to prove that a reactor concept improves the basic FOM prior to receiving gobs of tax money to build their science projects, but instead gobs of money are thrown at Kairos Power, General Fusion, Terra Power’s Nutria™, etc. No practiced engineer would imagine the basic economics and reliability of a SFR would be improved by adding a nitrate salt heat sink, or that a PBMR would become disruptive upon convolution with the MSR. This is wasteful government spending on bad ideas – cronyism – lack of creativity and evidence of systemic corruption. It’s not MacFarlane and Krall’s job to enter the vacuum of reason and highlight obvious gaps. The onus is NOT on them. Their challenges should be welcomed, considered, and addressed. The demise of any particular nuclear startup is even more certain without FOCUSING on MacFarlane and Krall’s challenges.
Thanks for supplying a good concise list of criteria for evaluating prospective
entrants into the SMR market. I would add: 7) will they lower the collective
carbon footprint and increase the reliability of electrical grids that would
otherwise need to depend on increased use of fossil fuels to recharge
I won’t speculate further on this set of criteria. The marketplace will
more likely decide once there are real products out there to compete
with upkeep of the existing nuclear fleet.
The author’s represent the government establishment. This establishment is communicating it’s concerns with plain language, citing difficulties in handling, transporting, storing, radioactive materials that are demonstrably less chemically stable than clad oxide, which is used in the BN800 SFR for these very reasons. The author’s note that recycling is currently not economical, and does not negate the need for storing transporting and handling unconventional fuels. With all of the unconventional startups, there is a mountain of engineering to be done, presumably at great cost, to actually implement, let alone close, their fuel cycles. There is a handful of MSR ‘startups’ – they don’t want to work together to achieve a common goal – instead they want the glory of having their own flavor become standard. There is hubris in their presumption of novelty in their designs – anybody educated in fission understands that a bucket is the simplest reactor concept (outwardly). That does not make it the simplest reactor to operate. Perhaps it is time that the ThorCons take a deep dive into the banalities of licensing transport, storage and handling mechanisms to flesh out their schemes. If the opponent (establishment) tells you why they oppose your proposal, there is work to be done – the criticism is a favor.
Without arguing your points, I’ll ask a question. If the establishment is so right, why aren’t they building more capacity to meet serious market demand?
On the contrary, we must actively contradict McFarlane and Krall. Any use of the terms, easier to operate, more economical, more messy, improve fuel efficiency, safer, spent fuel, cheaper, etc are emotive slurs that would mislead the naïve to believe that reactors are faulty in those regards. Any competent engineer requires only that a reactor design should be sufficiently easy, sufficiently economical, sufficiently clean, sufficiently fuel-efficient, sufficiently safe, and sufficiently cheap. Further, used fuel should be reused over and over again until only fission products are left, to be easily buried as deeply as the fearful require.
Fear mongering is the weapon of nuclear energy’s competitors. We should not be party to it.
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