While the NRC does not decide where an applicant should build a reactor, when an applicant proposes to build a new reactor project, the NRC evaluates whether and to what extent the site and reactor design provides reasonable assurance of adequate protection of public health and safety using the siting criteria set forth in 10 CFR Part 100 of the NRC regulations. In a 2-1 vote—with Chairman Hanson and Commissioner Wright voting to approve, and Commission Baron voting to disapprove—the Commission has accepted a new approach for evaluating where reactors can be sited, opening the door to positioning advanced reactors in more densely populated areas than has been allowed for large, light-water reactors.
Background on the new approach
This revised siting method comes from SECY-20-0045, “Population-Related Siting Considerations for Advanced Reactors”, in which the NRC staff proposed four siting-related options to the Commission in March 2020. The options assessed possible changes to the existing guidance and applicable regulations in 10 CFR Part 100 to address population-related siting considerations for advanced reactors. Ultimately, the staff’s recommendation was to revise the population-related siting guidance in Regulatory Guide 4.7, “General Site Suitability Criteria for Nuclear Power Stations,” related to 10 CFR Part 100.21(h), “Reactor Site Criteria,” to provide technology-inclusive, risk-informed, and performance-based criteria to assess certain population-related issues in siting advanced reactors.
Key changes in the new approach
The new approach recognizes the need to reevaluate siting criteria for advanced reactor designs that employ enhanced safety features because many advanced reactor designs incorporate design-specific safety features that do not exist in the typical light water reactor fleet. Therefore, while the current NRC guidance on this topic deterministically limits population density to not exceed 500 persons per square mile within 20 miles of a reactor site, the new Commission-approved approach would allow the use of modern methods to estimate design-specific source terms and off-site consequences from licensing basis events. Instead of a “one-size-fits-all” standard of 20 miles, the recommendation also specifies a dose-based performance criterion for determining the area within which population density is assessed.
In his vote sheet, Commissioner Hanson noted the importance of the risk-informed methodology described in Regulatory Guide 1.233, which provides guidance on assessing uncertainties and adequacy of defense-in-depth – an aspect “particularly important for evaluating new and novel technologies,” according to Chairman Hanson. The Chairman therefore asked the staff to provide appropriate guidance on assessing defense-in-depth adequacy and establishing hypothetical major accidents to evaluate, a directive included in SRM-SECY-20-0045. In addition, Commissioner Wright directed the staff to integrate Probabilistic Risk Assessment and mechanistic source term methods into its approach to identify likely events, outcomes, and consequences.
Commissioner Wright voted to approve in September 2020, whereas the other two Commissioners did not submit votes until June 2022, and their voting record was released on July 13, 2022. Commissioner Baran disapproved the recommended approach stating that “unlike existing light-water reactors, advanced reactors do not have decades of operating experience” upon which to rely.
