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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