The 2021 ANS Winter Meeting included an executive session on advanced reactor licensing, featuring the leaders of four of the top advanced reactor companies: Mike Laufer, chief executive officer of Kairos Power; Jake DeWitte, CEO of Oklo; Simon Irish, CEO of Terrestrial Energy; and Harlan Bowers, president of X-energy.
Kairos Power is developing the KP-FHR, a fluoride salt–cooled high-temperature reactor; Oklo, the Aurora microreactor; Terrestrial Energy, the Integrated Molten Salt Reactor, or IMSR; and X-energy, the Xe-100 reactor and a smaller unit designed for remote locations, the Xe-Mobile.
Session moderator Judi Greenwald, executive director of the Nuclear Innovation Alliance, noted in her introductory remarks that existing licensing policies and practices were developed for conventional large light water reactors, adding that a core focus of her organization is to analyze current approaches to nuclear regulation and recommend reforms to enable advanced reactor innovation. “Our view is that both the Nuclear Regulatory Commission and advanced reactor developers have important roles to play in making the process work,” she said. “The effective, efficient, and timely licensing of advanced reactors is not only a safety and commercialization imperative, it is also a climate imperative.”
The deployment of new clean energy sources and infrastructure, Greenwald declared, must begin immediately and continue for the foreseeable future to meet global carbon-reduction objectives and expand worldwide access to reliable and affordable energy. “We all know that the future role of advanced nuclear energy depends on companies providing solutions that are timely and economically competitive,” she said. “Advanced reactor developers are using innovative approaches to meet social, regulatory, and business needs. We know these include new technologies, analysis methods, and business models. Companies also need innovative licensing strategies.”
Following brief general comments from each of the panelists, Greenwald posed the question, “How does your approach to licensing and regulation leverage the unique design attributes and advantages of your company’s technology, specifically with respect to safety and risk?” The panelists provided the following responses.
Bowers (Xe-100): “For this particular type of advanced reactor, the advantage from a licensing perspective comes from the technology’s fuel design,” Bowers said. “By using the tristructural isotropic [TRISO] ceramic-coated fuel configuration packaged in a graphite matrix, we engage a concept called functional containment. Radionuclides contained within those tristructural isotropic coatings, specifically the silicon carbide coating, enables us to do a couple of things. One is to get rid of the larger containment structures. Secondly, it allows us to shrink the emergency planning zone because the mechanistic source term is greatly reduced. And it improves the safety case, because the fuel is able to go to much higher temperatures and continue to retain those radionuclides. So we've got multiple benefits that come starting at the kernel and the particle level of the fuel design.”
Laufer (KP-FHR): “Essentially, our reactor combines the fundamental safety case of both the gas reactors and the fluid fuel concepts,” Laufer said. “I say repeatedly that the economic potential of our reactor technology is intimately linked with the safety case, and it is. One of our fundamental goals is to dramatically reduce the physical footprint of components and systems in the reactor and, in particular, structures that are important to safety. That allows us to focus our unique development needs on those aspects. But it also allows us to iterate much more quickly with more freedom in everything that’s outside of that envelope. So for us, the inherent safety of the technology is really central.”
Laufer also noted that Kairos has been in pre-application review with the NRC for almost three years. “The obvious reason to do that is, if we're trying to sell commercial reactors, we need to demonstrate to utilities that we have a path forward through the licensing process,” he said. “And I’m sure the experience with all the developers is that until you can clear that hurdle and actually get through the licensing process, it’s very hard to get to the next round of conversations, because you’re not treated as being a real entity.”
Irish (IMSR): “There’s a technology aspect and a design aspect,” Irish said. “First, the technology aspect. As you know, we're using a molten salt, and molten salts have very high thermal stability and neutronic stability. They're excellent heat transfer fluids. So you have a medium for fission that has, I would say, a different profile, a different set of safety features that we believe are advantageous when doing two things. First, making the safety case to regulators. Second, achieving a commercial objective.”
The design aspect, Irish continued, involves the “IMSR Core-unit,” a patented innovation that integrates the primary reactor components, including the graphite moderator, into a sealed, replaceable reactor core. “We think that’s a design feature that permits us to have an efficient regulatory process,” he said. “And through the use of low-enriched uranium, we’re seeking to leverage the existing regulatory architecture of fuel supply—and it is a substantial architecture as well. So we’re not seeking a new architecture with a new, different fuel form, but to use the architecture that exists around current nuclear fuel supply today.”
DeWitte (Aurora): “We have a mix of favorable attributes from the integrated system approach,” DeWitte said. “We have a fuel form whose improvement has been well demonstrated with years of operation across a number of different fast reactors that have operated before, highlighted, of course, by EBR II’s phenomenal safety case that couples fuel performance and the thermal expansion capabilities and feedback effects associated with metallic fuel in a fast reactor system, as well as the phenomenal heat transfer capabilities of liquid metals to allow you to have a system that's well harmonized, well coupled, if you will. It gives you strong negative reactivity, feedback coefficients, as well as really powerful cooling capabilities that can rely just on natural forces to ultimately reject heat.
“And I think you see that reflected across a number of different designs on the fast reactor side,” DeWitte continued. “And so for us, being really small further simplifies that. We have less heat to move. We have less overall inventory. And those afford us some benefits. So when you talk about a microreactor being really small, you change the story on inventory. You change the story on power density. You just have less overall in terms of what you need to manage. So you can rely on fairly simple designs of passive airflow over systems to make sure you reject all your decay heat cooling that way.”
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