Up & Atom


In a 2-1 vote, NRC Commissioners have approved a new approach for evaluating where reactors can be sited in the United States, opening the door to siting advanced reactors in more densely populated areas than has been allowed for large, light-water reactors.

On July 13, the Commission approved an option recommended by the agency’s staff to revise the guidance in Regulatory Guide 4.7, “General Site Suitability Criteria for Nuclear Power Stations” (Guidance) to allow for a more flexible approach when implementing the requirements in 10 CFR Part 100. The current Guidance is written for the existing light water reactor fleet and provides that population density may not exceed 500 persons per square mile within 20 miles of a reactor site. The revised Guidance will provide for a “technology-inclusive, risk-informed, and performance-based criteria to assess population-related issues in siting advanced reactors.” Commissioners Wright and Hanson voted in favor of the recommendation, while Commissioner Baran dissented.

More than two years ago, in March 2020, the NRC staff proposed four options in SECY-20-0045 for changing the existing guidance and applicable regulations in 10 CFR Part 100, and recommended that the Commissioners approve Option 3, which would only revise the existing Guidance. Commissioner Wright voted to approve Option 3 in September 2020. The other two Commissioners did not submit their votes until last month, and their voting record was released on July 13, 2022.

The new approach acknowledges the need to reevaluate the siting criteria for advanced reactor designs that employ enhanced safety attributes. Many advanced reactor designs incorporate design-specific safety features that do not exist in the traditional light water reactor fleet, lending themselves to a risk-informed approach.

The new Guidance will allow the site licensing analysis to consider design-specific source terms and off-site consequences from licensing basis events. While the current deterministic Guidance focuses on population density within 20 miles, the new Guidance will allow for dose-based performance criteria for determining the area within which population density is assessed. The Commission directed the staff to provide appropriate guidance on assessing defense-in-depth adequacy and establishing hypothetical major accidents to evaluate. In addition, Commissioner Wright directed the staff to integrate Probabilistic Risk Assessment (PRA) and mechanistic source term methods into its approach to identify likely events, outcomes, and consequences.

Commissioner Baran dissented on the basis that, unlike existing light-water reactors, advanced reactors do not have decades of operating experience upon which to rely. In his view, it is premature for the NRC to reduce siting protections for advanced reactor technologies and using the existing Guidance for advanced reactors is consistent with a defense-in-depth strategy.

Morgan Lewis will continue to track regulatory developments in the advanced reactor developer space. If you have questions, please contact us.