Authors of SMR study reply to NuScale comments

June 13, 2022, 3:01PMNuclear News

On June 2, Nuclear Newswire published a letter from Jose Reyes, chief technology officer at small modular reactor developer NuScale Power, to May R. Berenbaum, editor-in-chief of Proceedings of the National Academy of Sciences, regarding a research article published by PNAS two days previous. The article, “Nuclear waste from small modular reactors,” has grabbed more than a few headlines for its claim that SMRs will actually generate more nuclear waste than a standard large pressurized water reactor.

Reyes had directed his comments to what he termed “a factual error” in the PNAS article. “The authors mistakenly assert that NuScale small modular reactors will produce significantly more spent nuclear fuel than existing light water reactors,” he wrote.

Those authors—Lindsay Krall, Allison Macfarlane, and Rodney Ewing—have since responded to Reyes, via their own letter, and have requested that Nuclear Newswire publish the rejoinder. The letter is reproduced below, in its entirety.

June 9, 2022
Dr. Jose N. Reyes
Chief Technology Officer & Co-Founder
NuScale Power

Response to Letter by Dr. Jose N. Reyes
published on June 2nd, Nuclear Newswire of ANS

Dear Dr. Reyes:

We are writing to respond to your letter published in the Nuclear Newswire concerning a “factual error” in our recent paper published in Proceedings of the National Academy of Sciences of the United States of America entitled “Nuclear waste from small modular reactors.” Your letter, addressed to Dr. May Berenbaum, editor of PNAS, was not copied to the authors of the paper, but we have noted your letter, as it was distributed widely to a number of news outlets and featured in toto in Nuclear Newswire of the American Nuclear Society.

First, we want to emphasize that our decision to analyze the NuScale 160-MW thermal core was deliberate and driven by the information available at the time of our study. One of the challenges of completing our analysis was the lack of access to relevant design specifications. For this reason, we focused on the NuScale 160-MWth reactor because the design specifications had been submitted to the Nuclear Regulatory Commission for certification and review. This provided a referenceable source for our analysis. In addition, we filed a request under the Freedom of Information Act to the NRC to obtain the burn-up figure for the NuScale 160-MWth reactor. However, the burn-up figure was redacted from the application; hence, the parameter was calculated as described on page 8 of the SI Appendix.

In general, we focused on the designs being presented to the NRC. Concerning the parameters for the 250-MWth design, the presentation and information provided to the Academy committee did not provide all the information necessary for a quantitative analysis. Our understanding is that NuScale will be submitting a new application for the 250-MWth design to the NRC this coming December.

We emphasize that our study focused on the NRC-certified, 160-MWth NuScale iPWR design because it had been reviewed during the certification process and an adequate amount of information was available on the core design. This is not a “factual error” in our study, but rather a choice we made that is clearly stated in the study. Once the necessary design parameters for the 250-MWth reactor are available, then an analysis can be completed of this larger NuScale reactor. Based on our present understanding, we anticipate that a future analysis will show that the 250-MWth reactor generates less waste per unit energy-equivalent than the 160-MWth reactor but more than a larger LWR. In other words, smaller reactors generate more waste—exactly the point of our paper in PNAS.

Finally, one error in Dr. Reyes’ letter is that Richard Meserve is not the chair of the Academy’s ad hoc committee on Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and Waste Aspects of Advanced Nuclear Reactors. Janice Dunn Lee is the chair of this committee.


Lindsay M. Krall
MacArthur Fellow (2019–2020)
Center for International Security and Cooperation
Stanford University

Allison M. Macfarlane
Professor and Director, School of Public Policy and Global Affairs
University of British Columbia

Rodney C. Ewing
Frank Stanton Professor in Nuclear Security and Co-Director
Center for International Security & Cooperation
Stanford University

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