Agency favors revising population-related siting rules for advanced reactors

July 28, 2022, 9:30AMNuclear News

The Nuclear Regulatory Commission recently approved, in a 2–1 vote, a recommendation from its staff that could potentially lead to the siting of advanced reactors in more densely populated areas than is permitted for traditional light water units.

NRC chairman Christopher Hanson and David Wright voted in favor of the recommendation, with Jeffery Baran casting the lone “nay” vote. (There are currently two open seats on the five-member commission.)

In a May 2020 paper, agency staff proposed to the commissioners four options on the subject of population-related siting considerations for advanced reactors, with the term “advanced reactors” defined as light water small modular reactors, non–light water reactors, and microreactors. According to the paper, “attributes of advanced reactors are expected to provide a reduced likelihood of accidents and to result in a smaller and slower release of radioactive material in the unlikely event of an accident.”

The recommendation: The staff paper recommended revising Regulatory Guide 4.7, General Site Suitability Criteria for Nuclear Power Stations. Currently, RG 4.7 states, “A reactor should be located so that, at the time of initial plant approval within about five years thereafter, the population density, including weighted transient population, averaged over any radial distance out to 20 miles . . . does not exceed 500 persons per square mile. A reactor should not be located at a site where the population density is well in excess of this value.”

The guide, staff suggested, should be revised “to provide technology-inclusive, risk-informed, and performance-based criteria to assess population-related issues in siting advanced reactors.”

From aye to nay: In his endorsement of the recommendation, Hanson noted that the existing guidance on population-related siting pertains only to standard large light water reactors. “It does not account for potential, smaller reactor designs that employ enhanced safety attributes such as those specified in the commission policy on advanced reactors,” he wrote. “For reactors demonstrating these attributes, it is reasonable in my view to have a regulatory pathway that gives applicants the flexibility to justify sites closer to population centers compared to historical siting of large light water reactors.”

Wright added, “This approach is consistent with the commission’s long-standing recognition that improvements in reactor design may potentially affect siting decisions. This technology-inclusive, risk-informed approach moves away from deterministic siting criteria, consistent with the NRC’s approach to establish emergency preparedness requirements for small modular reactors.”

In his dissent, Baran pointed out that unlike the current fleet of reactors, advanced reactor designs do not have decades of operating experience and that in many cases the new designs have yet to be built or operated. “In my view, we should not reduce siting protections for advanced reactor technologies at this time,” Baran said. “Instead, [the] NRC should initially retain the existing siting guidance. Based on six decades of experience, this long-standing approach will provide the necessary defense-in-depth for new technologies while they gain operating experience. . . . As advanced reactors are deployed and operating experience is gained with these designs, it may make sense for NRC to revisit the siting restrictions. But for now, it would be prudent to retain this effective tool for protecting the public.”

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