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Submission of NEI White Paper: Modernizing Population-Relaed Siting Requirements for Advanced Reactors - Request for Regulatory Action
	ML25171A127
Person / Time
Site:	Nuclear Energy Institute, 99902028
Issue date:	06/20/2025
From:	Nichol M; Nuclear Energy Institute
To:	Gregory Bowman; Office of Nuclear Reactor Regulation, Document Control Desk
References
	Download: ML25171A127 (1)
	v • d • e

Marc Nichol Executive Director Phone: 202.713.8131 Email: mrn@nei.org June 20, 2025 Greg Bowman Deputy Director for New Reactors Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Submission of NEI White Paper: Modernizing Population-Related Siting Requirements for Advanced Reactors - Request for Regulatory Action Project Number: 689

Dear Mr. Bowman:

On behalf of the Nuclear Energy Institute (NEI)1 and its members, we are pleased to submit the enclosed white paper, Modernizing Population-Related Siting Requirements for Advanced Reactors, for the U.S. Nuclear Regulatory Commissions (NRC) immediate consideration.

The white paper proposes a risk-informed, performance-based approach to revising the NRCs current population-related siting requirements in 10 CFR Part 100, proposed 10 CFR Part 53, and related NRC regulatory guidance. Recognizing that the current Part 100 population-related siting requirements were developed more than 60 years ago for early large light-water reactors (LWRs), the paper highlights the evolving safety profiles of advanced reactors, including small modular reactors (SMRs), non-LWR designs, and microreactors. It also emphasizes the need for flexible, consequence-oriented siting criteria that reflect modern understanding of reactor safety and the rapidly evolving and diverse use cases for advanced reactors that could require locating such reactors closer to large population centers.

Building on the NRCs 2023 final rule establishing a scalable, performance-based framework for determining emergency planning zones (EPZs) for advanced reactors, NEI recommends that applicants who can demonstrate that no plume exposure pathway (PEP) emergency planning zone (EPZ) is required, or that the PEP EPZ does not extend beyond the site boundary, should be permitted to align the low-population zone (LPZ) and population center distance with the site boundary. We believe additional distance-based siting restrictions would provide no meaningful safety benefit and impose unnecessary barriers to advanced reactor deployment. We further recommend that the NRC allow reactor siting near or within densely populated centers when supported by design-specific safety analyses that leverage NRC-endorsed risk-informed methodologies like the Licensing Modernization Project (LMP) framework.

1 The Nuclear Energy Institute (NEI) is responsible for establishing unified policy on behalf of its members relating to matters affecting the nuclear energy industry, including the regulatory aspects of generic operational and technical issues. NEIs members include entities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect and engineering firms, fuel cycle facilities, nuclear materials licensees, and other organizations involved in the nuclear energy industry.

Mr. Greg Bowman June 20, 2025 Page 2 To reduce unnecessary burden, we propose specific revisions to 10 CFR § 100.1, § 100.21 and proposed § 53.530 that would enable the siting of new reactors in or near large population centers, without increasing risk to the public or reducing defense-in-depth. The paper discusses use of best-estimate assumptions and modern atmospheric dispersion modeling as a means of implementing consistent, technology-inclusive siting policies that enable the efficient deployment of advanced reactors for various commercial applications.

To achieve these important objectives, NEI respectfully requests that the NRC:

Initiate a public dialogue, including a public meeting, as soon as practicable to discuss the recommendations contained in NEIs white paper.

Formally evaluate potential revisions to 10 CFR Part 100 and proposed Part 53 and establish an aggressive timeline for proposing rule amendments addressing these issues to support near-term licensing actions.

Engage with industry stakeholders to develop appropriate risk-informed and performance-based guidance for applying population density siting criteria to advanced reactor applications.

Coordinate an evaluation of lessons learned from recent licensing activities, such as those for the Clinch River (GEH BWRX-300), Kemmerer (Natrium), and Long Mott (Xe-100) projects, to inform the NRCs reassessment and modification of its population-related siting regulations and guidance.

We believe these actions would help enable the deployment of advanced nuclear technologies and support the nations clean energy, energy security, and infrastructure modernization goals. In offering these proposed changes, NEI recognizes that siting a plant in or near a densely populated center could affect how an applicant demonstrates compliance with other siting criteria in Part 100, and that additional regulatory changes may be identified during interactions with the NRC on this paper.

NEI and its members look forward to working with the NRC to further modernize the regulatory framework to reflect the unique capabilities and safety characteristics of advanced reactors.

Please contact me, Marty ONeill (mjo@nei.org), or Julie McCallum (jgm@nei.org) if you have any questions or require additional information.

Sincerely, Marcus Nichol Executive Director, New Nuclear

Enclosure:

NEI White Paper: Modernizing Population-Related Siting Requirements for Advanced Reactors (May 2025) cc:

Jeremy Bowen, NRR/DANU Michael Wentzel, NRR/DANU/UARP William Reckley, NRR/DANU/UARP NRC Document Control Desk

nei.org WHITE PAPER NEI White Paper: Modernizing Population-Related Siting Requirements for Advanced Reactors Prepared by the Nuclear Energy Institute June 2025

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nei.org Acknowledgements This document was developed by the Nuclear Energy Institute (NEI). NEI acknowledges and appreciates the contributions of our members and other organizations in providing input, including through the NEI Siting Task Force.

NEI Project Leads: Kati Austgen and Martin ONeill Lead Authors:

Martin ONeill, NEI and Anne Leidich, Pillsbury Winthrop NEI Review Team: Kati Austgen, Jon Facemire, Julianne McCallum, Marc Nichol, Jennifer Uhle, David Young Notice Neither NEI, nor any of its employees, members, supporting organizations, contractors, or consultants make any warranty, expressed or implied, or assume any legal responsibility for the accuracy or completeness of, or assume any liability for damages resulting from any use of, any information apparatus, methods, or process disclosed in this report or that such may not infringe privately owned rights.

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nei.org Executive Summary The U.S. Nuclear Regulatory Commissions (NRCs) population-related siting requirements, codified in 10 CFR Part 100 and reflected in guidance documents such as Regulatory Guide (RG) 4.7, were developed over 60 years ago based on the technical and regulatory frameworks applicable to early large light-water reactors (LWRs). These requirements, which were established using deterministic methods and highly conservative assumptions, do not reflect the current understanding of nuclear accident risks or the evolving safety characteristics and risk profiles of advanced nuclear reactors, including small modular reactors (SMRs), non-LWRs, and micro-reactors.

The U.S. energy landscape is evolving rapidly due in large part to unprecedented load growth driven by data centers, manufacturing and industrial facilities, and end-use electrification. Rapid deployment of advanced reactors in a broader range of geographic and industrial settings is essential to meeting energy security, infrastructure modernization, and carbon reduction goals. The rigid application of current NRC population center distance requirements and population density criteria could severely constrain this deployment, even where advanced reactors pose minimal risk to the public. Thus, updating the NRCs population-related siting requirements to be risk-informed, performance-based, and technology-inclusive is imperative. It is also consistent with congressional directives in the Nuclear Energy Innovation and Modernization Act (NEIMA) and the Accelerating Deployment of Versatile, Advanced Nuclear for Clean Energy (ADVANCE) Act.

As discussed in this paper, NEI believes there is a clear and viable path to meeting this objective. In 2023, the NRC amended its emergency preparedness (EP) regulations in 10 CFR Part 50 to include a scalable, risk-informed, performance-based framework for determining the plume exposure pathway (PEP) emergency planning zone (EPZ) for SMRs and other new technologies (ONT). Under the new EP framework, an applicant may be able to demonstrate that no PEP EPZ is required, or that the PEP EPZ will not extend beyond the site boundary, using design-specific accident analyses. NEI recommends that the NRC amend its Part 100 regulations and proposed Part 53 regulations to allow the low-population zone (LPZ) and population center distance to coincide with the site boundary in such cases. We believe that additional distance-based siting restrictions would provide no meaningful safety benefit and impose unnecessary barriers to advanced reactor deployment.

NEI further recommends that the NRC revise its current Part 100 regulations, proposed Part 53 regulations, and regulatory guidance to allow siting of advanced reactors near or within high-density population centers when justified by design-specific safety analyses. While NRC guidance in Appendix A to Regulatory Guide 4.7, Revision 4 now permits alternative population density evaluations for advanced reactors, its application lacks clarity and full alignment with the analytical methods used in EPZ sizing.

Bridging this methodological gap - particularly in how best-estimate assumptions and modern atmospheric dispersion modeling are applied - will be crucial to implementing consistent, technology-inclusive siting policies that enable the efficient deployment of advanced reactors for various commercial applications.

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nei.org Table of Contents Introduction........................................................................................................................................ 1 Background......................................................................................................................................... 3 2.1 The Demand for Nuclear Energy and Its Diverse Use Cases..................................................... 3 2.2 NRC Risk-Informed and Performance-Based Activities for Advanced Reactors....................... 4 Overview of NRCs Population-Related Siting Criteria and Guidance................................................. 6 3.1 NRCs Current Population Siting Requirements and Guidance................................................. 6 3.2 Historical Origins and Evolution of NRCs Population Siting Requirements............................ 10 3.2.1 Early Attempts to Address Population Considerations in Reactor Siting...................... 10 3.2.2 Development of the 1962 Final Reactor Site Criteria Rule............................................ 12 3.2.3 Development of the 1996 Final Reactor Site Criteria Rule............................................ 17 Specific Bases for NEIs Position........................................................................................................ 19 4.1 The NRC Has Long Recognized the Need for Population-Related Siting Requirements That Are Risk-Informed and Performance-Based............................................................................ 19 4.2 The 2023 EP Rule Provides Appropriate Technical and Regulatory Bases for Achieving a Risk-Informed, Performance-Based Approach to Siting Advanced Reactors................................. 22 4.2.1 NRCs EPZ Requirements for the Current Fleet of Large LWRs..................................... 22 4.2.2 NRCs Alternative EPZ Sizing Requirements for Advanced Reactors and ONTs............ 24 4.3 The PEP EPZ Is Unnecessary for Power Reactors That Can Justify No EPZ or an EPZ Within the Site Boundary.......................................................................................................................... 25 4.4 The Site Boundary EPZ Approach Satisfies the Intended Functions of the LPZ and Population Center Distance....................................................................................................................... 28 4.4.1 Ability to Take Prompt Protective Measures................................................................ 28 4.4.2 Management of Societal Risk........................................................................................ 28 4.5 Appropriate Analysis Methods Can Be Used to Justify a Small Population Center Distance.. 31 4.5.1 Current NRC Regulations and Guidance Do Not Categorically Preclude the Siting of Advanced Reactors Near or Within High-Density Population Centers......................... 31 4.5.2 Applicants That Can Justify No EPZ or a Site Boundary EPZ Should Be Able to Justify a Very Small Population Density Distance Through Appropriate Analysis Methods....... 32 Summary and Recommendations..................................................................................................... 35 5.1 Potential Revisions to 10 CFR 100.1 and 100.21..................................................................... 36 5.2 Potential Revisions to Proposed 10 CFR 53.530, Population-related considerations......... 37

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nei.org Table of Figures Figure 1: Thermal and Electric Outputs from Nuclear Power Plants............................................................ 4 Figure 2: Traditional Approach for 10 CFR Part 100, Reactor Site Criteria................................................ 9 Figure 3: NEI 18-04 Framework for Establishing Defense-in-Depth Adequacy.......................................... 30 Table of Tables Table 1: NRC Definitions of Key Terms Relevant to Population-Related Siting Requirements.................... 7 Table 2: Potential PEP EPZ Determination Process Outcomes................................................................... 25

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nei.org 1 INTRODUCTION This paper discusses the need for technology-inclusive, risk-informed, and performance-based criteria for assessing certain population-related issues relevant to the siting of advanced nuclear reactors. Given the expected need to deploy advanced reactors at sites that are located within or near large population centers, a more flexible, risk-informed approach to siting based on the specific characteristics of individual reactor designs is warranted. The NRCs current population siting requirements in 10 CFR Part 100 were established more than 60 years ago during the commercial nuclear power industrys nascent stages, and about 20 years before the NRC issued its post-Three Mile Island Unit 2 (TMI-2) accident emergency preparedness (EP) regulations in 1980. As a result, those requirements were focused on early large light-water reactor (LWRs) technologies and developed using deterministic methods.

The NRC has recognized the need to update its population siting criteria to address new advanced reactors and their evolving use cases. In February 2024, the NRC revised its guidance on site suitability criteria for nuclear power stations to include alternative approaches to the populationdensity criterion and expand the regulatory guidance developed for large LWR technology with appropriate modifications for advanced reactor designs.1 However, the NRC did not revise its reactor siting regulations in 10 CFR Part 100, including the definition of population center distance in 10 CFR 100.3 - i.e., the distance from the reactor to the nearest boundary of a densely populated center containing more than about 25,000 residents. Nor did it modify the related requirement in 10 CFR 100.21(b) that [t]he population center distance, as defined in 10 CFR 100.3, must be at least one and one-third times the distance from the reactor to the outer boundary of the LPZ. In its October 2024 Proposed Part 53 Rule, the NRC opted to maintain the NRCs long-standing preference for siting reactors in areas of low population density using the current language from part 100 in proposed § 53.530(c).2 The proposed rule provides no technical or regulatory basis for that decision.

This issue is of major concern to the industry given the expected need to deploy advanced reactors at sites that are near or within large population centers to support various industrial and commercial applications beyond wholesale electricity. These use cases include, for example, providing electricity for data centers, clean tech factories, and hydrogen production facilities; supplying industrial process heat and steam; and replacing fossil fuels or retired coal-fired generation facilities. Because the prescriptive, deterministic requirements in Part 100 and Proposed Part 53 Rule do not account for the enhanced safety characteristics of advanced reactor designs, they could impose unnecessary restrictions on site locations for such reactors. Indeed, in SECY-24-0008, the NRC staff noted that some micro-reactor license applicants, for example, may seek to site reactors in densely populated areas to support the types of applications mentioned above.3 However, the staff also stated that current Commission policy and regulations would preclude siting a 1 Specifically, Appendix A (Alternative Approaches to Address Population-Related Siting Considerations) to Regulatory Guide (RG) 4.7, Revision 4, General Site Suitability Criteria for Nuclear Power Stations (Feb. 2024) (ML23348A082) provides guidance on alternatives to the established populationdensity criterion to support licensing for non-LWRs and light-water SMRs with attributes that could support siting a commercial nuclear power station closer to population centers than is typical for large LWRs. Appendix A includes alternative population density criteria based on estimates of radiological consequences from design-specific events and provides additional ways that applicants can meet the requirements of 10 CFR 100.21(h).

2 Risk-Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors; Proposed Rule, 89 Fed. Reg. 86,918, 86,931 (Oct. 31, 2024) (Part 53 Proposed Rule).

3 SECY-24-0008, Micro-Reactor Licensing and Deployment Considerations: Fuel Loading and Operational Testing at a Factory (Jan. 24, 2024),

Enclosure (Technical, Licensing, and Policy Considerations for Factory-Fabricated Micro-Reactors) at 27 (ML23207A252).

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nei.org 2 commercial power reactor, no matter the size or type of reactor, within a densely populated center.4 That outcome would contravene recent congressional directives in the Nuclear Energy Innovation and Modernization Act of 2019 (NEIMA) and the Accelerating Deployment of Versatile, Advanced Nuclear for Clean Energy Act of 2024 (ADVANCE Act), as well as other parallel NRC efforts to establish technology-inclusive, risk-informed, and performance-based licensing approaches for advanced reactors. Those efforts include, for example, the NRCs 2023 EP Rule, 2024 proposed Part 73 physical security rule, and endorsement of the Licensing Modernization Project (LMP) methodology. These recent legislative and regulatory actions are discussed further below.

The NRCs approach to population siting should not be an outlier. Rather, the NRC should provide advanced nuclear plant applicants with the flexibility to justify siting their plants near or within large population centers based on their specific reactors designs and safety attributes, which are expected to result in risk profiles that are significantly lower than the Commissions Safety Goals. Both the NRC staff and Commission have recognized as much. In SECY-20-0045, the staff noted that its efforts to address population-related siting considerations are an important part of the integrated approach to help inform the design and siting processes for advanced reactors.5 It also recognized that NEIMA requires the NRC to develop and implement risk-informed, performance-based methods to resolve policy issues such as siting considerations that may unnecessarily restrict the development of commercial advanced nuclear reactors.6 In voting on SECY-20-0045, Commissioner Wright emphasized that [t]his technology-inclusive, risk-informed approach moves away from deterministic siting criteria, consistent with the NRCs approach to establish emergency preparedness requirements for small modular reactors.7 In SECY-24-0008, the staff noted that it will inform the Commission if it becomes aware of any license applicants who intend to seek exemptions from Part 100 and will raise associated policy issues to the Commission accordingly.8 As set forth below, NEI contends that the NRCs 2023 EP Rule establishing alternative emergency planning zone (EPZ) sizing requirements for advanced reactors and other new technologies provides the necessary technical and regulatory bases for enabling the siting of new reactors in or near large population centers, without increasing risk to the public or reducing defense-in-depth.9 Therefore, we recommend that the NRC consider revising the relevant language in both Part 100 and proposed Part 53 to allow the low-population zone (LPZ) and population center distances to coincide with the site boundary for those sites at which an applicant can demonstrate that no plume exposure pathway EPZ is required, or that the EPZ does not extend beyond the site boundary, in accordance with NRC regulations discussed below.10 This change would simplify licensing of SMRs and other advanced reactors in urban areas where the population density may be large, but the reactors small size and/or the design already substantially reduces risk to the public, as demonstrated by the facilitys site boundary EPZ. We also 4 Id. at 26 (emphasis added).

5 SECY-20-0045, Population Related Siting Considerations for Advanced Reactors (May 8, 2020) (ML19262H055), at 7 (emphasis added).

6 Id.

7 Commissioner Wrights Comments on SECY-20-0045: Population Related Siting Criteria for Advanced Reactors at 1 (Sept. 10, 2020)

(ML22194A868).

8 SECY-24-0008, Enclosure at 27.

9 As discussed below, under the NRCs 2023 EP Rule, applicants need to establish their EPZ as the area within which public dose, as defined in 10 CFR20.1003, is projected to exceed 1 rem total effective dose equivalent (TEDE) over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months from the release of radioactive materials from the facility considering accident likelihood and source term, timing of the accident sequence, and meteorology. This calculated dose is much lower than the current regulatory requirement that the dose not exceed 25 rem TEDE at the exclusion area and low population zone boundaries as set forth in 10 CFR 50.34(a)(1).

10 As defined in 10 CFR 20.1003, the site boundary is that line beyond which the land or property is not owned, leased, or otherwise controlled by the licensee.

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nei.org 3 discuss the need for greater clarity and flexibility in applying the alternative population density criteria set forth in Appendix A to RG 4.7 to allow siting of advanced reactors within densely populated centers when sufficient technical justification exists.

The remainder of this paper includes four sections.Section II briefly discusses key commercial and regulatory considerations underlying the need for a more flexible, risk-informed approach to siting based on the specific characteristics of advanced reactor designs.Section III provides important regulatory background, including an overview of the NRCs population center distance requirement in Part 100 and proposed Part 53, and a detailed discussion of the origins and evolution of that requirement. The latter is necessary to fully understand the NRCs historical rationale for the population center distance requirement, which is based on very conservative assumptions and deterministic methods that are specific to large LWRs.Section IV provides the specific bases for NEIs position that a risk-informed and performance-based approach is needed to allow applicants to justify sites closer to population centers compared to historical siting of large LWRs, consistent with the NRCs EPZ sizing requirements for SMRs and other new technologies.Section V provides our specific recommendations, including proposed regulatory text changes for the NRCs consideration.11 BACKGROUND 2.1 The Demand for Nuclear Energy and Its Diverse Use Cases As a clean and highly reliable power source, nuclear energy is needed to meet rapidly growing electricity demand while simultaneously avoiding further carbon-intensive emissions. As noted in DOEs Advanced Nuclear Liftoff Report,12 the need for nuclear generation continues to increase with the rapid buildout of datacenters, hydrogen production facilities, and other electricity-intensive industrial facilities that require many gigawatts of power.13 Such facilities may require continuous electricity and, thus, potentially behind-the-fence generation of reliable power. Some of these facilities also need uninterrupted, high-pressure steam. The difficulty of transporting heat efficiently requires assets to be co-located close to facilities with relatively small physical footprints. Nuclear energys high power density, reliability, and ability to produce high temperatures make it conducive to meeting these needs.

Advanced nuclear reactors are especially well suited to replace current combined heat and power systems because they can produce on-site, grid-independent, highly consistent electricity and thermal energy with a temperature range of 200-850oC. Figure 1 provides an overview of thermal and electric outputs from nuclear. Using advanced reactors for these applications could in some cases require that they be located near or within large population centers.

11 NEIs proposed regulatory text changes are comprehensive with regard to those NRC regulations in Part 100 and proposed Part 53 specifically concerning population-related siting considerations. NEI recognizes that siting a plant in or near a densely populated center could affect how an applicant demonstrates compliance with other siting criteria in Part 100, and that additional regulatory changes may be identified during interactions with the NRC on this paper.

12 DOE, Pathways to Commercial Liftoff: Advanced Nuclear at 11 (Sept. 2024), https://liftoff.energy.gov/advanced-nuclear-2/.

13 For more detailed discussion of alternative use cases for advanced reactors, see National Association of Regulatory Utility Commissioners (NARUC) & National Association of State Energy Officials (NASEO), Energy and Industrial Use Cases for Advanced Nuclear Reactors (Oct.

2024), https://pubs.naruc.org/pub/09F52BB1-D92E-9CB4-C9E8-172331A1A9A5) (2024 NARUC/NASEO Use Case Report).

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nei.org 4 Figure 1: Thermal and Electric Outputs from Nuclear Power Plants (Source: NARUC/NASEO 2024 Use Case Report at 6 (Fig. 2), https://pubs.naruc.org/pub/09F52BB1-D92E-9CB4-C9E8-172331A1A9A5).

Additionally, nearly 200 gigawatts electric (GWe) of coal generation assets are expected to retire by 2050. Nuclear power is also well positioned to replace those assets given its high power density, high capacity factor, and low transmission requirements relative to other generation sources. Notably, a 2022 Idaho National Laboratory (INL) study analyzed almost 400 coal power plant sites and found that approximately 80 percent of those sites are conducive to hosting nuclear reactors.14 Nuclear power plants generally are less subject to geographic constraints than other clean energy technologies.

However, the siting of nuclear power reactors is subject to numerous NRC safety requirements, including the prescriptive population center distance requirement in Part 100 and the Proposed Part 53 Rule. Importantly, many additional coal plant communities that might host new nuclear power plants have populations exceeding 25,000 people.15 2.2 NRC Risk-Informed and Performance-Based Activities for Advanced Reactors Given their unique safety and environmental attributes, the NRC has been developing strategies to streamline the licensing of advanced reactors, including SMRs, non-LWRs, and micro-reactors. These strategies include increased use of risk-informed and performance-based approaches in NRC rules and guidance. For example, in August 2023, the NRC published its final rule amending Part 50 to include new alternative emergency preparedness (EP) requirements for SMRs and other new technologies (ONTs),

14 INL, Investigating Benefits and Challenges of Converting Retiring Coal Plants into Nuclear Plants (INL/RPT-22-67964 Revision 2) (Sept. 2022),

https://doi.org/10.2172/1886660.

15 INL, Stakeholder Guidebook for Coal-to-Nuclear Conversions at 4, Table 2-1 (Coal power plant community tier characteristics) (Apr. 2024),

https://fuelcycleoptions.inl.gov/SiteAssets/SitePages/Home/C2N_Guidebook_2024.pdf.

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nei.org 5 including non-LWRs, research and test reactors (RTRs), and medical radioisotope facilities.16 The new alternative requirements and related guidance in RG 1.242 adopt a performance-based, technology-inclusive, risk-informed, and consequence-oriented approach to EP, including a scalable approach for determining the size of the plume exposure pathway EPZ and licensee-defined performance objectives and metrics. Based on the expected safety enhancements in advanced reactor designs, the final rule allows applicants to develop EPZ sizes commensurate with their accident source terms, fission product releases, and accident dose characteristics considering site-specific meteorology.17 In doing so, the rule provides additional predictability and flexibility for advanced reactor developers that use simplified or other innovative means to accomplish their safety functions and provide enhanced margins of safety.18 We discuss the EPZ sizing requirements further in Section 4.2.2.

The NRC also has issued a proposed rule that would amend the NRCs Part 73 regulations to provide alternative risk-informed and performance-based physical security requirements for advanced reactors.

Like the aforementioned EP rule, the proposed rule recognizes that both SMR and non-LWR designs include potentially smaller reactor core sizes, lower power densities, lower probability of severe accidents, slower accident progression, different source term characteristics, and smaller offsite consequences of accidents.19 It further notes that advanced reactor vendors and applicants may design their facilities and site protective strategies to account for reliance on passive features, active engineered systems, and automation to achieve security functions with less reliance on human actions.

In June 2020, the NRC issued RG 1.233, Revision 0, which endorses the guidance contained in NEI 18-04, Revision 1, Risk-Informed Performance-Based Guidance for Non-Light Water Reactor Licensing Basis Development (Aug. 2019) (ML19241A472). NEI 18-04 describes an expanded role for probabilistic risk assessment (PRA) for non-LWRs beyond current 10 CFR Part 52 requirements or Commission policy for potential applications under 10 CFR Part 50. NEI 18-04 describes a systematic process for identifying and categorizing event sequences as anticipated operational occurrences (AOOs), design-basis events (DBEs), or beyond-design-basis events (BDBEs) for non-LWRs. The primary determinant for categorizing events is the estimated frequency of the event sequence. Design-basis accidents (DBAs) are derived from DBEs by assuming that only safety-related (SR) SSCs are available to mitigate the events. The methodology includes plotting event sequence families on the Frequency-Consequence (F-C) Target and assessing margins based on event frequency and estimated 30-day dose at the exclusion area boundary.

The Part 53 rulemaking is another example of the NRCs efforts to increase flexibility in the advanced reactor licensing process. In response to Section 103(a)(4) of NEIMA, the NRC is seeking to establish an technology-inclusive regulatory framework for optional use by applicants for new commercial advanced nuclear reactors.20 Part 53 will use methods of evaluation, including risk-informed and performance-based methods, which are flexible and suitable for application to advanced reactor technologies. The framework builds on the NRC-endorsed LMP methodology, a technology-inclusive approach to licensing that leverages PRA-based insights to provide applicants with design and operation flexibilities. The NRC also is evaluating how Part 53 could be used to implement certain provisions of the ADVANCE Act 16 NRC, Emergency Preparedness for Small Modular Reactors and Other New Technologies; Final Rule, 88 Fed. Reg. 80,050 (Nov. 16, 2023)

(2023 EP Rule). The NRC also issued RG 1.242, Revision 0, Performance-Based Emergency Preparedness for Small Modular Reactors, Non-Light-Water Reactors, and Non-Power Production or Utilization Facilities (Nov. 2023) (ML23226A036).

17 2023 EP Rule, 88 Fed. Reg. at 80,058.

18 Id. at 80,056.

19 NRC, Alternative Physical Security Requirements for Advanced Reactors; Proposed Rule and Guidance, 89 Fed. Reg. at 65,226, 65,230 (Aug. 9, 2024).

20 See note 2.

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nei.org 6 related to use and colocation of advanced nuclear reactors for nonelectric applications and the licensing and regulation of micro-reactors.

To date, the NRC has not fully pursued a similar approach to its population-related siting regulations in Part 100 and the Proposed Part 53 Rule. Establishing a more flexible, risk-informed and performance-based approach to siting advanced reactors could facilitate their deployment in areas where population density and/or the proximity to large population centers might previously have been a barrier.

OVERVIEW OF NRCS POPULATION-RELATED SITING CRITERIA AND GUIDANCE 3.1 NRCs Current Population Siting Requirements and Guidance 10 CFR 100.21 (Non-Seismic Siting Criteria) requires that a commercial reactor site have an exclusion area surrounding the reactor in which there are no permanent residents, and for which the reactor licensee has the authority to determine all activities, including exclusion or removal of personnel and property from that area, i.e., the exclusion area boundary (EAB). Section 100.21 also requires a low population zone (LPZ) around the exclusion area. The number and density of residents within the LPZ must be such that there is a reasonable probability that protective measures could be taken in the event of a serious accident.21 Specific distances to the EAB and the outer boundary of the LPZ are not prescribed by regulation.

Instead, the boundaries of the exclusion area and LPZ are set by dose limits of 25 rem total effective dose equivalent (TEDE) over the most limiting 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months for the exclusion area, and over the entire passage of the radioactive cloud for the LPZ, respectively.22 The distances to the EAB and LPZ thus may vary by reactor site. These distances also may vary in relation to the site boundary, which 10 CFR 20.1003 defines as that line beyond which the land or property is not owned, leased, or otherwise controlled by the licensee. While the EAB may be the same as the site boundary, in practice, the site boundary typically extends beyond the EAB, although the opposite also may occur (i.e., the EAB may extend beyond the site boundary, but the reactor licensee still must have the authority to determine all activities, including exclusion or removal of personnel and property from the area). The full definitions of the EAB, LPZ, site boundary, and population center distance (a concept discussed further below) are provided in Table 1. For purposes of this white paper, the focus is on the site boundary because, as discussed below, this is consistent with 10 CFR 50.33(g) and 50.160 and NRC regulatory guidance in Regulatory 1.242 for performance-based emergency preparedness for SMRs, non-LWRs, and non-power production or utilization facilities. Those regulations and guidance define the plume exposure pathway EPZ in relation to the site boundary, as defined in 10 CFR 20.1003.

21 10 CFR 50.2.

22 10 CFR 100.3, 100.11(a)(2). Under NRC regulations, this calculation is based upon a major accident, hypothesized for purposes of site analysis or postulated from considerations of possible accidental events, such as substantial meltdown of the core with subsequent release into the containment of appreciable quantities of fission products, considering the expected demonstrable containment leak rate and any fission product cleanup systems intended to mitigate the consequences of the accidents, together with applicable site characteristics, including site meteorology. 10 CFR 50.34, 52.79.

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nei.org 7 Table 1: NRC Definitions of Key Terms Relevant to Population-Related Siting Requirements Section 100.21(c)(2) requires an applicant to evaluate site atmospheric dispersion characteristics and establish dispersion parameters such that radiological dose consequences of postulated accidents meet the criteria set forth in 10 CFR 50.34(a)(1) for the type of facility proposed for the site. Section 50.34(a)(1)(ii)(D) requires an assessment that assumes a fission product release from the core into the containment while the facility is operating at the ultimate power level contemplated. Traditionally, this includes analysis of the postulated fission product release, using the expected demonstrable containment leak rate and any fission product cleanup systems intended to mitigate accident consequences, together with applicable site characteristics, including site meteorology, to evaluate the offsite radiological consequences. Safety analysis requirements in 10 CFR 52.17(a)(1)(ix), 52.47(a)(2),

and 52.79(a)(1)(iv) for early site permit (ESP), standard design certification, and combined operating license applications, respectively, describe the same type of analysis and use the same evaluation criteria of 25 rem TEDE at the EAB and LPZ as set forth in 10 CFR 50.34(a)(1). As noted in the NRCs Interim Staff Guidance (ISG) DANU-ISG-2022-01, Review of Risk-Informed, Technology-Inclusive Advanced Reactor ApplicationsRoadmap (Mar. 2024), which provides guidance on preparing non-LWR license applications, 10 CFR 50.34(a)(1)(ii)(D) is LWR-centric and does not consider non-LWR-specific concepts of core damage or functional containment for fission product retention. The LMP methodology found in NEI 18-04 and endorsed in RG 1.233 provides one approved methodology for identifying an adequate scope of beyond design-basis events for consideration of severe accident Exclusion area means that area surrounding the reactor, in which the reactor licensee has the authority to determine all activities including exclusion or removal of personnel and property from the area. This area may be traversed by a highway, railroad, or waterway, provided these are not so close to the facility as to interfere with normal operations of the facility and provided appropriate and effective arrangements are made to control traffic on the highway, railroad, or waterway, in case of emergency, to protect the public health and safety. Residence within the exclusion area shall normally be prohibited. In any event, residents shall be subject to ready removal in case of necessity. Activities unrelated to operation of the reactor may be permitted in an exclusion area under appropriate limitations, provided that no significant hazards to the public health and safety will result. [10 CFR 50.2; 10 CFR 100.23]

Low population zone means the area immediately surrounding the exclusion area which contains residents, the total number and density of which are such that there is a reasonable probability that appropriate protective measures could be taken in their behalf in the event of a serious accident.

These guides do not specify a permissible population density or total population within this zone because the situation may vary from case to case. Whether a specific number of people can, for example, be evacuated from a specific area, or instructed to take shelter, on a timely basis will depend on many factors such as location, number and size of highways, scope and extent of advance planning, and actual distribution of residents within the area. [10 CFR 50.2; 10 CFR 100.23]

Population center distance means the distance from the reactor to the nearest boundary of a densely populated center containing more than about 25,000 residents. [10 CFR 100.23]

Site boundary means that line beyond which the land or property is not owned, leased, or otherwise controlled by the licensee. [10 CFR 20.1003]

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nei.org 8 considerations. This is one accepted methodology providing an alternative to assessing a more deterministic postulated fission product release.

As a siting criterion, current section 100.21(b) requires that the distance to the nearest population center of more than about 25,000 people - the population center distance - is at least one and one-third (1.33) times the distance to the outer boundary of the LPZ. For operating reactors, the EAB and LPZ boundary distances may vary from site to site and reactor to reactor, because the distance determination depends partly on the need to meet the siting dose acceptance criteria at the chosen distance. Generally, large LWR EABs are about 0.5 miles, and LPZs are about 3 to 5 miles. The section 100.21(b) population center distance requirement results in the closest population center to the reactors lying outside of the LPZ. However, the population center could be inside the 10-mile plume exposure EPZ used for large LWRs.

Reflecting longstanding NRC policy for large LWRs, 10 CFR 100.21(h) provides that:

Reactor sites should be located away from very densely populated centers. Areas of low population density are, generally, preferred. However, in determining the acceptability of a particular site located away from a very densely populated center but not in an area of low density, consideration will be given to safety, environmental, economic, or other factors, which may result in the site being found acceptable.

RG 4.7 provides guidance for assessing the population around potential reactor sites in accordance with 10 CFR 100.21(h) and adds a population density criterion to the foregoing regulatory requirements. As noted in the current version (Rev. 4) of RG 4.7, for large LWRs:

Preferably, a reactor should be located so that, at the time of initial site approval and for about 5 years thereafter, the population density, including weighted transient population, averaged over any radial distance out to 20 miles (cumulative population at a distance divided by the area at that distance), is at most 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.23 RG 4.7 explains that this criterion is part of the NRCs defense in depth philosophy and facilitates emergency planning and preparedness, as well as reducing potential doses and property damage in the event of a severe accident.24 It further notes that [t]he numerical values in this guide are generally consistent with past NRC practice for large LWRs and reflect consideration of severe accidents, as well as the demographic and geographic conditions of the United States.25 Figure 2 illustrates the population-related distances and density criteria applicable to large LWRs.

23 RG 4.7, Rev. 4 at 19.

24 Id.

25 Id.

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nei.org 9 Figure 2: Traditional Approach for 10 CFR Part 100, Reactor Site Criteria (Source: William Reckley, NRC, NRCs Population-Related Siting Requirements for Advanced Reactors (Jan. 16, 2025) (ML25032A022))

As noted above, RG 4.7, Rev. 4 includes alternative approaches to the population-density criterion and expands the regulatory guidance developed for large LWR technology with appropriate modifications for advanced reactor designs. Specifically, Appendix A to RG 4.7 provides guidance on alternatives to the guidance in Section C.1.4 (Population Considerations) that establishes a fixed distance of 20 miles out to which population density is assessed for any new application. As currently written, an applicant can demonstrate compliance with 10 CFR 100.21(h) by siting a nuclear reactor where the population density does not exceed 500 persons per square mile out to a distance equal to twice the distance at which a hypothetical individual could receive a calculated TEDE of 1 rem over a period of 30 days from the release of radionuclides following postulated accidents.26 Appendix A acknowledges that if this criterion is met, the siting of a reactor might not be determined by population density considerations but would instead be governed by the regulatory requirement in 10 CFR 100.21(b) for reactors to be located distant from densely populated centers with more than about 25,000 residents.27 26 RG 4.7, Rev. 4 at 20 & App. A at A-2.

27 RG 4.7, Rev. 4, App. A at A-5, A-6.

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nei.org 10 3.2 Historical Origins and Evolution of NRCs Population Siting Requirements Although the NRCs population-related siting regulations have not changed appreciably since their initial issuance in 1962, they have a long and complex history that substantially pre-dates the 1962 rule.28 This history provides some important insights into why and how the requirements were developed, and why and how they may now be modified to address considerations unique to advanced reactors, especially given the myriad technical and regulatory developments of the last 60 years. Those developments include, but are not limited to, significant improvements in the industrys and NRCs understanding of severe accident phenomena, advances in reactor technology, and the expansion of the NRCs regulatory framework to include EP regulations, among other new requirements.

3.2.1 Early Attempts to Address Population Considerations in Reactor Siting The genesis of the NRCs population siting requirements can be traced back to the late 1940s. The Advisory Committee on Reactor Safeguard (ACRS), which was established in 1947 to advise the Atomic Energy Commission (AEC), developed the first rule-of-thumb estimate of an exclusion area around a nuclear power plant. It also introduced the concept of a hazard area just outside of the exclusion area in which people could live based on the lower hazard (i.e., risk) to the public. The ACRS noted that any large or industrially important centers of population would still need to be excluded from this lower hazard area. However, it did not identify or estimate a generically-appliable size for this area due to effects of design and site-specific features on the level of risk posed by a given reactor.29 The 1948 ACRS rule of thumb, albeit crude, was the first approach to quantify the risk as a function of distance from the reactor. At that time, the exclusion area, in miles from the reactor, was set at 0.01 times the square root of the thermal power of the reactor in kilowatts. Although this was reasonable for small reactors, it proved impractical as reactor thermal output increased. For example, a 1,000 megawatt electrical (MWe) power plant would require an exclusion area radius of 17 miles. This estimate was based on an extremely conservative estimate that 50 percent of all fission products would be released as a cloud that spread out from the reactor. The exclusion area distance determined how far a person must be from a nuclear power plant to limit his or her whole-body dose to less than 300 rem.30 No new technical approaches or metrics for siting were developed until the late 1950s. As a result, from 1948 through 1962, the AEC licensed plants on a case-by-case basis and did not use formal criteria or metrics for siting. The AEC instead focused on the role of the reactor containment structure and whether there would be a reasonable distance between the reactor and major population centers.

However, the license applications for the Plum Brook 60 MWt National Aeronautics and Space Administration (NASA) test reactor near Sandusky, OH, a BWR near Elk River, MN, a BWR in Dresden, IL, 28 The historical and regulatory background provided in this section is drawn from multiple sources, including proposed and final rules, Commission policy statements, and various reports cited herein. Key reports include the following: NUREG-0478, Metropolitan Siting - A Historical Perspective (Oct. 1978) (ML12187A192); Okrent, D., On the History of the Evolution of Light Water Reactor Safety in the United States (1978) (ML090630275) (Okrent Report); NUREG-0625, Report of the Siting Policy Task Force (Aug. 1979); WASH-1308, Population Distribution around Nuclear Power Plant Sites (1973) (ML12187A284); NUREG/CR-6295, Reassessment of Selected Factors Affecting Siting of Nuclear Power Plants (Feb. 1997) (https://www.osti.gov/servlets/purl/453736); Oak Ridge National Laboratory, ORNL/TM-2019/1197, Advanced Reactor Siting Policy Considerations (June 2019) (2019 ORNL Report) (ML19192A102).

29 2019 ORNL Report, App. B at B-1 to B-2; Okrent Report at 2-1, 2-8 to 2-9.

30 2019 ORNL Report, App. B at B-2; Okrent Report at 2-8; NUREG-0478 at 1.

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nei.org 11 Power Reactor Development Companys (PRDCs) Fermi 1 plant, and the Indian Point reactor about 24 miles from New York City, challenged the AECs concept of a reasonable distance.31 By 1956, population density issues were garnering increased attention. Senator Bourke Hickenlooper of the Joint Committee on Atomic Energy contacted the ACRS to inquire about the siting of nuclear reactors in populated areas, with a particular focus on the reactor then under construction in Shippingport, PA. The Acting Chairman of the AEC, W.F. Libby, recognized that newer reactors were expected to rely more upon the philosophy of containment than isolation as a means of protecting the public against the consequence of an improbable accident, but noted that in each case there will be a reasonable distance between the reactor and major centers of population.32 These interactions led to the first articulated test for siting a nuclear reactor: (1) recognizing all possible accidents which could release unsafe amounts of radioactive materials; (2) designing and operating the reactor in such a manner that the probability of such accidents is reduced to an acceptable minimum; and (3) by an appropriate combination of containment and isolation, protecting the public from the consequences of an accident, should it occur.33 The Price-Anderson Act of 1957 required, among other things, that the ACRS review commercial power reactor construction permit and operating license applications. During the hearings and public meetings for the aforementioned reactors, the ACRS expressed concerns regarding siting and other technical issues, including the probability of maximum credible accidents and their health and safety implications for surrounding populations. The AEC licensed the plants primarily based on the conclusion that engineered safety features would provide adequate protection. It did not establish any generic siting rules or criteria at the time.34 In 1959, however, as concerns about siting reactors near population centers mounted, the AEC denied a license application for a small pressurized water reactor (PWR) to be sited in Jamestown, NY. The lack of a consistent method for establishing exclusion area sizes and acceptable population densities, general opposition to prescriptive distances, and political pressure from the Joint Committee on Atomic Energy prompted the ACRS and AEC to consider methods based on a standardized accident and exposure analysis. These circumstances also led to the creation of an AEC special working group on siting criteria led by Dr. Clifford Beck, Chief of the AECs Hazards Evaluation Branch.35 In January 1959, Dr. Beck recommended to the ACRS that siting criteria should include the following:

anticipated exclusion area distance, population density outside the exclusion area, site meteorology, seismology, hydrology, and geology. He further recommended that proper emphasis be given to reactor design characteristics and safeguards given their effect on exclusion area distance. In parallel with the AEC special working groups activities, the ACRS Environmental subcommittee was developing siting criteria based on quantitative dose estimates. Dr. Beck disagreed with this approach due to the many variables involved in accurately estimating expected releases. He instead recommended that for small reactors (less than 100 MWt), an exclusion area distance of one-quarter mile be used, and for large 31 2019 ORNL Report, App. B at B-2; Okrent Report at 2-16; NUREG-0478 at 1-3, 7.

32 Letter from W.F. Libby, Acting Chairman, AEC, to Senator Bourke Hickenlooper (Mar. 14, 1956) (Okrent Report at 2-15 to 2-16).

33 2019 ORNL Report at 14; Okrent Report at 2-15 to 2-16; NUREG-0478 at 3 & App. A. The 1956 correspondences between Senator Bourke and W.F. Libby are included in the Okrent Report and Appendix A to NUREG-0478.

34 2019 ORNL Report, App. B at B-2 to B-3; Okrent Report at 2-29 to 2-30.

35 2019 ORNL Report, App. B at B-2; Okrent Report at 2-23, 2-36 to 2-37.

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nei.org 12 reactors, an exclusion area distance of one-half to three-quarters of a mile be used. These discussions formed the basis of the AECs first attempt at drafting a siting rule for nuclear reactors.36 3.2.2 Development of the 1962 Final Reactor Site Criteria Rule In May 1959, the AEC issued a proposed rulemaking with various factors to be considered in siting a nuclear reactor. The AEC noted that these would not be definitive criteria for general application due to the complex nature of the environment, the wide variation in environmental conditions from one location to another and the variations in reactor characteristics and associated protection which can be engineered into a reactor facility.37 Nonetheless, after noting that construction would be approved based on reasonable assurance that the potential radioactive effluents [from] normal operation or the occurrence of any credible accident, will not create undue hazard to the health and safety of the public, the AEC proposed the additional population-related guides in the evaluation of site for power and test reactors, beyond the proposed hazard analysis.38 The AECs additional guides stated that: (1) the exclusion area should be dependent on various factors, including reactor power level, design features and containment, and site characteristics; (2) there should be a minimum exclusion area of one-quarter mile for all reactors and one-half to three-quarters of a mile for large power reactors; (3) research reactors may require larger exclusion areas than power reactors of the same size; (4) population density should be small, reactors should be several miles distance from the nearest town or city, and large reactors should be 10 to 20 miles from large cities; and (5) reactor sites should also avoid the area several miles upwind from centers of population and nearness to air fields, arterial highways and factories.39 The AEC also noted that these factors (among others) would dictate in varying degrees the engineered protective devices for the particular nuclear facility under consideration, and the dependence which can be placed on such devices.40 While the proposed rulemaking was relatively vague, leaving large reactor undefined, public commenters generally opposed the use of minimum exclusion area and city distances. One representative comment suggest[ed] that all minimum distances and maximum population densities be eliminated from the proposed regulation and that such factors be given consideration only in relation to the proposed type, design and safeguards of the particular reactor.41 In April 1960, Mr. Price, the AECs Director of the Division of Licensing and Regulations, characterized the proposed rulemaking as a general indication that there ought to be some thought given to the size of the exclusion area with some examples for a particular size reactor, as to how far it ought to be from populated places, in ranges of numbers.42 The AEC then provided additional guidance when rejecting two proposed reactor sites (in La Crosse, WI and Jamestown, NY), suggesting that the applicants seek exclusion areas of 1,500 to 2,000 feet [approximately one-third of a mile] and distances from populated places of around 3 to 5 miles, characterizing this shift as more specific advice on what kind of distances to look for than the general guidance from the proposed rulemaking.43 36 2019 ORNL Report, App. B at B-2 to B-3; Okrent Report at 2-23, 2-29 to 2-30.

37 AEC, Site Criteria and Evaluation of Power and Test Reactors; Proposed Rule, 24 Fed. Reg. 4184 (May 23, 1959).

38 Id.

39 Id. at 4184-85.

40 Id.

41 Okrent Report at 2-27.

42 April 27, 1960 Hearing, Special Subcommittee on Radiation, Joint Committee on Atomic Energy at 196.

43 Id. at 197.

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nei.org 13 The lack of a consistent method for assessing exclusion area sizes and population density, as well as general opposition to prescriptive distances, prompted the ACRS and AEC to consider approaches based on a standardized accident and exposure analysis. In October 1960, the ACRS, with input from Dr. Beck and the special working group, proposed source term analysis in which [a]n arbitrary accident is assumed to occur which results in the release of fission products into the outermost building or containment shell, which then leaks out of the outermost barrier at a rate defined by the designed and confirmed leak rate.44 It also proposed a maximum once-in-a-lifetime emergency dose for the upper limit of exposure to a member of the public in a generalized accident.45 The ACRS arbitrarily selected an emergency dose of 25 rem whole body or equivalent integrated dose, consistent with Handbook 59 of the National Bureau of Standards, and a thyroid dose limitation of 200 to 300 rads.

While the ACRS suggested these dose limits, it asked the AEC to confirm through its staff or its advisors in this field that this suggested value of 25 rem whole body or equivalent is without significant biological effect.46 Based on these various suggestions, the ACRSs overall recommendation was that:

[T]here should be an exclusion radius in which no one resides. Surrounding this, there should be a region of low population density, so low that individuals can be evacuated if the need arises in a time which will prevent their receiving more than a dose of 25 r. Beyond this evacuation area, there should be no cities (above 10,000 to 20,000 population) sufficiently close so that the individuals in these cities might receive more than the lower of the following: (1) 4 x 106 man-rems in the generalized accident, and (2) 200 rems under the extremely improbable accident in which the outermost barrier fails completely to restrain all of the radioactivity of the generalized accident.47 The ACRS also recommended that the AEC should not include these criteria as prescriptive requirements in regulations or policy documents.48 In December 1960, the ACRS again presented a similar set of criteria in response to a request from AEC Commissioner Olson, noting that:

Under the extreme conditions of a serious reactor accident, it should be reasonably possible for persons off-site to take protective steps, such as evacuation and retirement to shelters, within a period of two hours so that within the two hours they will not receive more than a 25 rem whole body gamma dose or the inhalation of radioactive material which will give a dose of 300 rem to the thyroid, or 25 rem to the bones or lung.

The integrated man-rem dose for all people off-site receiving a radiation dose above 1 rem whole body, or equivalent thyroid, bone or lung dose, shall not exceed 4 x 106 man-rems.

The reactor should be located sufficiently distance [sic] from cities (metropolitan areas) of above 10,000 to 25,000 population so that no inhabitant receives more than 300 rems in the extremely 44 Letter from Leslie Silverman, Chairman, ACRS, to John A. McCone, Chairman, AEC,

Subject:

Reactor Site Criteria at 4 (Oct. 22, 1960) (included in the Okrent Report at 2-42 to 2-47).

45 Oct. 22, 1960 ACRS Letter at 4 (Okrent Report at 2-45).

46 Id. at 5 (Okrent Report at 2-46).

47 Id.

48 Id. (The Committee wishes to emphasize again that the numbers which have been used in discussion of the generalized accident should not be formalized into regulations or Commission policy.).

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nei.org 14 improbably [sic] accident defined by a complete failure of all confinement barriers and a source strength equal to most of the fission product inventory.49 The ACRS cautioned, however, that these numbers were given as examples to aid in understanding the problem and that their validity is open to question without further study.50 The AEC took these ACRS recommendations and on February 11, 1961, issued a proposed rule with similar criteria.51 The proposed rule was issued with the express recognition that it is not possible at the present time to define site criteria with sufficient definiteness to eliminate the exercise of agency judgment.52 Thus, it was designed primarily to identify a number of factors considered by the Commission as guides in evaluating proposed sites, particularly for reactors of a general type and design on which experience has been developed.53 The proposed rule set forth the following basic overall objectives:

1. Serious injury to individuals offsite should be avoided if an unlikely, but still credible, accident should occur.

2. Even if a more serious accident (not normally considered credible) should occur, the number of people killed should not be catastrophic.

3. The exposure of large numbers of people in terms of total population dose should be low in order to give recognition to this concept the population center distances to very large cities may have to be greater than those suggested by these guides.54 To meet these objectives, the proposed rule provided that the licensee would assume a fission product release and use the containment leak rate and meteorological data from the site to determine the EAB and LPZ based on dose to an individual within those bounds. The EAB would be such that an individual for two hours immediately following onset of the postulated fission product release would not receive a total radiation dose to the whole body in excess of 25 rem or a total radiation dose in excess of 300 rem to the thyroid from iodine exposure. The LPZ would be such that an individual on the outer boundary exposed to the radioactive cloud resulting from the postulated fission product release would not receive a total radiation dose to the whole body in excess of 25 rem or a total radiation dose in excess of 300 rem to the thyroid from iodine exposure. The proposed rule, however, did not specify a permissible population density or total population within this zone because the situation may vary from case to case as, for example, the number of people that could be evacuated from a specific area, or instructed to take shelter, on a timely basis will depend on many factors such as location, number and size of highways, scope and extent of advance planning, and actual distribution of residents within the area.55 Once the exclusion area and LPZ were calculated, the population center distance (i.e. the distance to the nearest population center containing more than 25,000 people) would be set to 1 times the distance 49 Letter from Leslie Silverman, Chairman, ACRS, to John A. McCone, Chairman, AEC,

Subject:

Reactor Site Criteria at 3 (Oct. 22, 1960) (Dec. 13, 1960 ACRS Letter) (included in the Okrent Report at 2-51 to 2-55).

50 Id. (Okrent Report at 2-54).

51 AEC, Reactor Site Criteria; Notice of Proposed Guides, 26 Fed. Reg. 1224 (Feb. 11, 1961).

52 Id.

53 Id. at 1224-1225.

54 Id.

55 Id. at 1225.

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nei.org 15 from the reactor to the outer boundary of the low population zone, although the proposed rule cautioned that for very large cities a greater distance may be necessary because of total integrated population dose considerations.56 The 1961 proposed rule reflected the ACRSs proposals, using a source term analysis roughly in line with that suggested by the ACRS. Much like the ACRSs October 1960 letter, the AEC relied on the National Bureau of Standards Handbook 59 Addendum to choose 25 rem as an exposure limit corresponding to the once in a lifetime accidental or emergency dose for radiation workers that may be disregarded in the determination of their radiation exposure status.57 As there is no such source for the 300 rem limit for the thyroid, it appears that this limit was based on the ACRS recommendations.

The one significant difference between the two proposals was in the treatment of large populations.

While the ACRS suggested a 4x106 man-rems limit to evaluate dose to a large group of people, along with a limit of 200 rem in the case of a containment failure, the proposed rule disregarded both of these suggestions in favor of simply setting large populations at a distance of one and one-third times the low population zone. The AEC Acting Director, Division of Licensing and Regulation, Robert Lowenstein, later explained this population center distance calculation as follows:

If one could be absolutely certain that no accident greater than the maximum credible accident would occur, then the exclusion area and low population zone would provide reasonable protection to the public under all circumstances. There does exist, however, a theoretical possibility that substantially larger accidents could occur. It is believed prudent at present, when the practice of nuclear technology does not rest on a solid foundation of extended experience, to provide protection against the most serious consequences of such theoretically possible accidents. Consideration of a population center distance is therefore prescribed: this is a distance by which the reactor would be sufficiently removed from the nearest major concentration of people that lethal exposures would not occur in the population center even from an accident in which the containment is breached.58 In short, the population center distance was intended to account for the theoretical possibility of an accident beyond the maximum credible accident specified in the rule.

It bears emphasis that when Part 100 was first developed, the maximum credible accident was assumed to be a loss-of-coolant accident (LOCA) that would result in a substantial core meltdown with subsequent release of appreciable quantities of fission products into containment. Given the relatively small size of reactors at the time, it was believed that this postulated core meltdown could be accommodated without a loss of containment integrity, thus providing an effective upper bound on offsite radiological consequences. As power reactors increased in size by roughly an order of magnitude, they were required to have emergency core cooling systems (ECCS) in accordance with Appendix K to 10 CFR Part 50. While effective ECCS operation reduced the potential for a substantial meltdown, concerns about containment failure due to steam or hydrogen explosions and containment overpressure failures remained. As increasing credit was given to engineered safety features, plants began to be located 56 Id.

57 Id. National Bureau of Standards Handbook 59 Addendum, available at https://orau.org/health-physics-museum/files/library/nbs/nbs addendum.pdf. The Handbook 59 Addendum relied on Andrew H. Dowdys Tabulation of Available Data Relative to Radiation Biology from 1949 to assert that exposures of 25 r and below would have no detectable clinical effects on the average normal individual.

58 Okrent Report at 2-55 (quoting Radiation Safety and Regulation, Hearings Before the Joint Committee on Atomic Energy, Congress of the United States, 87th Congress, First Session, June 12, 13, 14, and 15, 1961 at 222) (emphasis added).

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nei.org 16 closer to population centers. This trend prompted the concern that [a]n unbounded reduction of the distance factor as a tradeoff for added safety features can lead to an erosion of the protection provided by distance that was originally contemplated in Part 100.59 The ACRS, for its part, viewed Part 100 as a flexible rule that would be open to some interpretation. At the time, the ACRS Chairman, Theos J. Thompson, testified before the Joint Committee on Atomic Energy that the ACRS wanted the proposed rule to be a very flexible document where deviations should be allowed in cases where an applicant can show that his design or his siting of the reactor leads to a safe situation.60 In fact, he stated that the ACRS would like to encourage applicants to come in with deviations in those cases in which they believe that a valid reason for deviation exists.61 The ACRS viewed the proposed rule as a guide and not, in a true sense, as a regulation, and would have removed portions of the rule, including by eliminat[ing] the 2-hour provision on the 25 roentgen dose limit and substitut[ing] instead a limit recommended by the applicant on the basis of time to clear the area involved.62 The ACRS Chairman further endorsed the one and one-third population center distance criteria only for lack of a better alternative. According to the Chairman, the committee accepted [the city distance]

criteria as defined in the guides as a reasonable, though unprovable, statement of its judgment regarding the effects of genetic and somatic dose.63 While the ACRS would have preferred a man-rem dose analysis, they initially agreed quite well with the city distance concept as stated in the guide given the very infrequency of an accident with a containment failure.64 In April 1962, the AEC promulgated the final siting rule with only limited changes from the 1961 proposed rule.65 Those changes primarily involved moving the guidance for the method of determining the exclusion area and the LPZ out of the rule and into a separate guidance document. Although the final rule did not explicitly refer to the maximum credible accident, it retained the concept in 10 CFR 100.11 in a footnote to that regulation. The final rule also referenced Technical Information Document (TID)-14844, Calculation of Distance Factors for Power and Test Reactor Sites (Mar. 1962)

(ML021720780). Using a water-moderated (cooled) reactor as an example reactor type, TID-14844 presented a set of radii for the exclusion area and low population zone distances that was derived from an example analytical method for postulating a major reactor accident (defined as the maximum credible accident). For siting, TID-14844 considered the maximum credible accident to be a major accident involving significant core damage that is typically postulated to occur in conjunction with a large LOCA. Although TID-14844 is still referenced in Part 100, significant advances have occurred in understanding the timing, magnitude, and chemical form of fission product releases from nuclear power plant severe accidents.66 59 NUREG-0625 at 11.

60 Radiation Safety and Regulation, Hearings before the Joint Committee on Atomic Energy, Congress of the United States, 87th Congress, First Session, June 12, 13, 14, and 15, 1961 at 225 (emphasis added).

61 Id.

62 Id.

63 Id.

64 Id.

65 Reactor Site Criteria; Final Rule, 27 Fed. Reg. 3509 (Apr. 12, 1962).

66 See NRC, Nuclear Power Reactor Source Term, https://www.nrc.gov/reactors/new-reactors/advanced/references/nuclear-power-reactor-source-term.html.

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nei.org 17 3.2.3 Development of the 1996 Final Reactor Site Criteria Rule The NRC did not pursue any substantive changes to the Part 100 siting requirements until 1992, when it published a proposed rule including population density criteria for future nuclear power reactor sites.67 The proposed rule sought to basically decouple siting from accident source term and dose calculations.68 It noted that while accident source term and dose considerations are proposed to be applied to plant design aspects and moved to Part 50, reactor site criteria are expected to be independent of plant design and, as such, are independent of the plant type to be built at the site.69 The proposed rule would have required a minimum exclusion area distance of 0.4 miles (640 meters) for power reactors, although the NRC was considering whether or not this size unduly penalizes potential reactors that have significantly lower power levels.70 Notably, the NRC observed that the existing LPZ criteria had [s]everal practical problems and led to a population center distance with little practical effect.71 It further noted that the functions intended for the LPZ, namely, a low density of residents and the feasibility of taking protective actions, have been accomplished by other regulations or can be accomplished by other means.72 Instead of a low-population zone and population center distance, the NRC suggested adopting a limit of no more than 500 people per square mile averaged over any radial distance out to 30 miles.73 Moreover, the projected population density 40 years after initial site approval should not exceed 1000 people per square mile.74 This limit, however, would not be absolute:

Because analyses have shown that current plan [sic] designs can meet the Commissions Safety Goals and that other risks can be kept at a very low level at sites that have significantly higher population densities than those being proposed, the Commission wishes to emphasize that these population density levels do not indicate the upper limits of acceptability. These levels represent preferred values, that, if exceeded, require that an applicant provide justification for not locating a reactor at an alternative site having a lower population density.75 The NRC never adopted the 1992 proposed rule. Instead, on October 14, 1994, it published another draft siting rule, reversing its proposal in the 1992 rule to include population density limits in Part 100.76 The 1994 proposed rule was substantially similar to current 10 CFR 100.11. In that proposed rule, the NRC noted that siting factors were meant to assur[e] that radiological doses from normal operation and postulated accidents will be acceptably low and that site characteristics are amenable to the development of adequate emergency plans to protect the public.77 Thus, the NRC again decided to place dose limits and accident analyses at the center of the rule, without specifying the additional 67 NRC, Reactor Site Criteria Including Seismic and Earthquake Engineering Criteria for Nuclear Power Plants and Proposed Denial of Petition for Rulemaking From Free Environment, Inc. et al.; 57 Fed. Reg. 47,802 (Oct. 20, 1992).

68 Id. at 47,803.

69 Id. at 47803-04.

70 Id. at 47804.

71 Id.

72 Id.

73 Id. at 47805.

74 Id.

75 Id. (emphasis added).

76 NRC, Reactor Site Criteria Including Seismic and Earthquake Engineering Criteria for Nuclear Power Plants and Proposed Denial of Petition From Free Environment, Inc. et al.; Proposed Rulemaking, 59 Fed. Reg. 52,255 (Oct. 17, 1994).

77 Id. at 52,257.

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nei.org 18 population limits contained in RG 4.7.78 It proposed to keep the dose criteria in the 10 CFR 100.11.

However, for new reactors, the proposed rule would have resulted in a partial decoupling of siting from accident source term and dose calculations through the use of standardized designs.79 Essentially, design features would be discouraged in a standardized design to compensate for otherwise poor site conditions, but for custom plants that do not involve a standardized design, the source term and dose criteria [would] continue to provide assurance that the site is acceptable for the proposed design.80 This 1994 proposed rule was finalized in 1996.81 The final rule contained only minimal modifications to section 100.11, including: (1) replacing the 25 rem whole body dose and 300 rem thyroid dose standards with a 25 rem TEDE standard, and (2) specifying that the 2 hour2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months dose measure could occur in any two-hour period during an incident (versus the two hours immediately following a fission product release).

The NRC otherwise declined to modify the existing population density requirements. It found that the siting functions intended for the LPZ, namely, a low density of residents and the feasibility of taking protective actions, have been accomplished by other regulations or can be accomplished by other guidance.82 It further noted that [w]hereas the exclusion area size is based upon limitation of individual risk, population density requirements serve to set societal risk limitations and reflect consideration of accidents beyond the design basis, or severe accidents.83 These broader population density requirements serve to facilitate[] emergency preparedness and planning and reduce[]

potential doses to large numbers of people and property damage in the event of severe accidents.84 The final rule also noted that these requirements are particularly useful considering the risk of a core-melt together with early bypass of or containment failure likely lead[ing] to a large release.85 If a reactor was located nearer to a large city than current NRC practice permitted, the likelihood of exposing a large number of people to significant releases of radioactive material would be about the same as the probability of a core-melt and early containment failure: less than 10-6 per reactor year for future reactor designs or incredible.86 Thus, based solely upon accident likelihood, it might be argued that siting a reactor nearer to a large city than current NRC practice would pose no undue risk.87 However, the NRC still saw value in distance to population centers due to the reduced likelihood that radioactive material would be carried towards a city and reduced radiological dose consequences resulting from plume dilution and depletion with distance. The NRC thus opted to keep a two-tier approach, requiring that reactor sites be located away from very densely populated centers and reiterating that areas of low population density are generally preferred. Notably, while the NRC concluded that defense-in-depth considerations and the additional enhancement in safety to be gained 78 Id. at 52,260.

79 Id. at 52,257.

80 Id.

81 NRC, Reactor Site Criteria Including Seismic and Earthquake Engineering Criteria for Nuclear Power Plants; Final Rule, 61 Fed. Reg. 65,157 (Dec. 11, 1996).

82 Id. at 65,161.

83 Id. at 65,162.

84 Id.

85 Id.

86 Id.

87 Id.

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nei.org 19 by siting reactors away from densely populated centers should be maintained, it distinguished between current large LWRs and advanced or next-generation reactors with regard to siting distances:

In summary, next-generation reactors are expected to have risk characteristics sufficiently low that the safety of the public is reasonably assured by the reactor and plant design and operation itself, resulting in a very low likelihood of occurrence of a severe accident. Such a plant can satisfy the QHOs [quantitative health objectives] of the Safety Goal with a very small exclusion area distance (as low as 0.1 miles). The consequences of design basis accidents, analyzed using revised source terms and with a realistic evaluation of engineered safety features, are likely to be found acceptable at distances of 0.25 miles or less. With regard to population density beyond the exclusion area, siting a reactor closer to a densely populated city than is current NRC practice would pose a very low risk to the populace.88 SPECIFIC BASES FOR NEIS POSITION 4.1 The NRC Has Long Recognized the Need for Population-Related Siting Requirements That Are Risk-Informed and Performance-Based As explained above, the NRCs current population center distance requirement was developed and codified more than 60 years ago in very different technical, regulatory, and political environments relative to today. In short, the Part 100 regulations were developed as general criteria to assist applicants in evaluating their proposed sites at a time when reactor technology and plant sizes were rapidly evolving, the Commission had minimal experience in siting new plants, and its technical understanding of reactor accident risk (including how to reduce that risk) was much more limited than its current understanding. This led to policies and requirements that sought to limit societal risk by promoting remote siting of nuclear plants (via distance and population density criteria) based on deterministic methods and highly conservative assumptions. The population center distance requirement in 10 CFR 100.11 is one such requirement.

For the reasons discussed herein, the NRC should reconsider the population center distance requirement in Part 100, with the objective of ensuring that the requirement is modified and/or applied in a risk-informed and performance-based manner. First, due to extensive technical research, reactor operating experience, and the application of risk assessment techniques, the industrys and NRCs understanding of reactor accident risk has substantially improved over the past sixty years. As explained in a 2019 ORNL Report:

LWR operational data have accumulated over time, allowing for safety component and safety system reliability to be predicted more accurately with less uncertainty. In addition, better understanding of LWR fuel failure, coolant chemistry, aerosol behavior, accident progression, and failure timing have enabled better predictions of the timing and magnitude of fission product release from LWRs following severe accidents. The knowledge gained in modeling LWR fission product releases should provide a better basis for predicting fission product release associated with advanced reactors, although sufficient understanding of non-LWR fission product release and uncertainty must be demonstrated. Such improved understanding of fission product releases following an accident, coupled with appropriate emergency planning, 88 Id. (emphasis added).

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nei.org 20 could lead siting planners to support locating advanced reactors such as SMRs, non-LWRs, and micro-reactors closer to population centers without creating any increased risk to the public.

However, as the tsunami-induced accident at the Fukushima NPP has shown, one must also consider the possibility that land use may be denied following an accident. As a result, consideration should be given to the attributes of advanced reactors that fundamentally change the fission product release behavior following a reactor accident. This could include smaller source terms to minimize contamination potential, design attributes that eliminate or mitigate certain types of accidents, passive safety systems that initiate and operate without the need of operator action or other support systems, and reactor design characteristics such as low operating pressures that minimize the driving force to spread fission products beyond engineered barriers following an accident. In this case, enhanced tools to predict fission product release following an accident, coupled with improved accident mitigation attributes, should provide the opportunity to site advanced reactors closer to population centers while maintaining or improving current levels of [defense-in-depth]. To avoid the limitations of arbitrary population density guidance, a performance-based approach based solely on radiological dose analyses to the nearby population such as that found in NUREG-1537 could be employed for advanced reactor siting guidance.89 With regard to the last point, NUREG-1537 directs non-power reactor license applicants to evaluate the population within a distance of five miles (versus 20 miles) from the reactor, presumably based on the smaller core and source term associated with a non-power reactor.90 Also, no specific population density threshold is specified in NUREG-1537. As a result, some non-power reactors are located within large population centers. For example, the NIST Center for Neutron Research (NCNR), the nations largest RTR with a licensed maximum power level of 20 MWt, is located in Gaithersburg, MD, which has a reported population of 69,615 people and a population density of 6,745 ppsm.91 The Massachusetts Institute of Technology (MIT) Reactor has a licensed maximum power level of 6 MWt and is located in Cambridge, MA, which has a reported population of 118,211 people and a population density of 18,479 ppsm.92 The 2019 ORNL Report also discusses defense-in-depth considerations. Citing NUREG/KM-009, Historical Review and Observations of Defense-In-Depth (Apr. 2016) (ML16104A071), the report notes:

[B]ecause advanced reactor designs tend to preclude or severely mitigate accident categories by design, and because passive safety systems tend to increase the reliability of an appropriate and successful accident response, there is margin to consider changes in siting distances without compromising the overall [defense-in-depth] balance for public safety.93 Importantly, the foregoing statements are consistent with those made by the Commission and staff over the last three decades. In its 1996 final rule on power reactor siting criteria, for example, the 89 2019 ORNL Report at 13-14 (emphasis added).

90 For further discussion of the NRCs regulatory framework for RTRs, see Attachment A (NRC Regulation of Non-Power Reactors) to NEIs Regulation of Rapid High-Volume Deployable Reactors in Remote Applications (RHDRA) and Other Advanced Reactors (July 31, 2024)

(ML24213A337). Attachment A discusses the regulatory frameworks for nonpower reactors and power reactors, including their similarities and differences, and the potential applicability of non-power regulatory approaches for RHDRA and other similar advanced reactors.

91 See https://www.nist.gov/ncnr; https://worldpopulationreview.com/us-cities/maryland/gaithersburg.

92 See https://nrl.mit.edu/reactor/safety/; https://worldpopulationreview.com/us-cities/massachusetts/cambridge.

93 2019 ORNL Report at 7 (emphasis added).

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nei.org 21 Commission noted that next-generation reactors are expected to have risk characteristics sufficiently low that the safety of the public is reasonably assured by the reactor and plant design and operation itself, resulting in a very low likelihood of occurrence of a severe accident.94 In its 2008 Policy Statement on the Regulation of Advanced Reactors, the Commission stated:

Regarding advanced reactors, the Commission expects, as a minimum, at least the same degree of protection of the environment and public health and safety and the common defense and security that is required for current generation light-water reactors (LWRs). Furthermore, the Commission expects that advanced reactors will provide enhanced margins of safety and/or use simplified, inherent, passive, or other innovative means to accomplish their safety and security functions.95 The policy statement also identifies specific attributes that should be considered in advanced designs, including designs that incorporate the defense-in-depth philosophy by maintaining multiple barriers against radiation release, and by reducing the potential for, and consequences of, severe accidents. It further notes that the Commission expects that the safety features of these advanced reactor designs will be complemented by the operational program for Emergency Planning (EP), which, in turn, must be demonstrated by inspections, tests, analyses, and acceptance criteria to ensure effective implementation of established measures.96 The policy statement does not require advanced reactors to meet higher safety standards. Further, the NRC has been implementing the policy statement in ways that align requirements with advanced reactor safety profiles, as evidenced by the EP, physical security, and Part 53 rulemakings discussed in Section 2.2. Given these expectations and the complementary functions of the NRCs various siting criteria, the current population center distance requirement is inconsistent with industry and NRC efforts to implement risk-informed, performance-based, and consequence-oriented approaches for advanced reactors. Indeed, in SECY-20-0045, the NRC staff noted that its efforts to address population-related siting considerations are an important part of the integrated approach to help inform the design and siting processes and the related content of applications for licenses, certifications, and approvals for advanced reactors.97 It also acknowledged that NEIMA requires the NRC to develop and implement strategies for the increased use of risk-informed, performance-based techniques to resolve policy issues such as siting considerations that may unnecessarily restrict the development of commercial advanced nuclear reactors.98 In voting on SECY-20-0045, Commissioner Wright emphasized that the development of population-related siting criteria for advanced reactors is critical to establishing a timely, efficient, and predictable regulatory framework for such technologies. He further underscored the flexibilities inherent in the staffs recommended Option 3 to provide technology-inclusive, risk-informed, and performance-based criteria to assess certain population-related issues in siting advanced reactors:

94 61 Fed. Reg. at 65,162.

95 Policy Statement on the Regulation of Advanced Reactors; 73 Fed. Reg. 60,612, 60,615 (Oct. 14, 2008). The Commissions 2008 policy statement reinforced and updated the policy statements on advanced reactors published in 1986 and 1994.

96 Id.

97 SECY-20-0045 at 7 (emphasis added).

98 Id.

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nei.org 22 This approach is consistent with the Commissions 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 NRCs approach to establish emergency preparedness requirements for small modular reactors. This approach would also leverage existing requirements, operating experience, analyses, and research and allow for flexibilities based on design-specific characteristics of advanced reactor technology, including inherent safety features and lower power levels that may limit the release of radionuclides. The staffs recommended approach should effectively meet the NRCs important safety and security mission in a manner that does not inhibit the development and licensing of new technologies.99 Chairman Hanson similarly noted that for advanced reactors demonstrating enhanced safety attributes, it is reasonable 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.100 He also cited the use of modern methods to estimate design-specific source terms and off-site consequences from licensing basis events for new and novel technologies, which include, for example, non-LWR technologies that may be licensed using the LMP methodology described in RG 1.233 and DANU-ISG-2022-01.101 The ADVANCE Act, which seeks to advance the benefits of nuclear energy by enabling efficient licensing, regulation, and deployment of nuclear energy technologies, further reinforces this need. Section 203 directs the NRC to identify options for addressing any unique licensing issues or requirements relating to the licensing of nuclear reactors for nonelectric applications. Section 206 directs the NRC to identify and report on modifications to regulations, guidance, or policy needed to license and oversee nuclear facilities at brownfield sites. Section 208 directs the NRC to develop performance-based and risk-informed guidance and strategies for licensing and regulating micro-reactors based on their unique size, source terms, and simplified design characteristics. As part of that effort, the NRC must address siting, including in relation to the population density criterion limit described in SECY-20-0045.102 4.2 The 2023 EP Rule Provides Appropriate Technical and Regulatory Bases for Achieving a Risk-Informed, Performance-Based Approach to Siting Advanced Reactors 4.2.1 NRCs EPZ Requirements for the Current Fleet of Large LWRs As noted above, the NRCs Part 100 population distance requirements were established in 1962, nearly two decades before the NRC issued its revised EP regulations in 1980 following the TMI-2 accident. The NRCs nuclear power plant EP regulatory requirements are intended to provide reasonable assurance that adequate protective measures can and will be taken in the event of a radiological emergency. For the current LWR fleet, these requirements are codified at 10 CFR 50.47 (Emergency Plans), 10 CFR 50.54(q) and (t), and 10 CFR Part 50, Appendix E (Emergency Planning and Preparedness for Production and Utilization Facilities).

99 Commissioner Wrights Comments on SECY-20-0045: Population Related Siting Criteria for Advanced Reactors at 1 (Sept. 10, 2020)

(ML22194A868) (emphasis added).

100 Chairman Hansons Comments on SECY-20-0045: Population Related Siting Criteria for Advanced Reactors at 1 (June 24, 2022)

(ML22194A867).

101 Id.

102 NEI understands that the NRC staff is considering preparing a white paper on population density related siting criteria specifically for microreactors with a target date of Summer 2025. See NRCs Microreactor Activities Integration Tables (Table 8: Siting) (ML25036A199).

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nei.org 23 The NRC uses emergency planning zones, or EPZs, to enable the development of planned protective action strategies and measures, and necessary implementing procedures, which, in turn, expedite protective action recommendations and decisions during an emergency. Plans for addressing radiological incidents are applied by the response organizations in these zones, as applicable. Generally, the size of the EPZs for large LWRs is defined by (1) a plume exposure pathway (PEP) EPZ area of about 10 miles in radius and (2) an ingestion pathway EPZ (IPZ) area of about 50 miles in radius. The size of EPZs surrounding a particular nuclear power plant may be affected by such conditions as demographics, topography, land characteristics, access routes, and jurisdictional boundaries. Under Appendix E to Part 50, the size of EPZs may be determined on a case-by-case basis for gas-cooled nuclear reactors and for reactors with a power level of 250 megawatts thermal (MWt) or less.

The technical bases for the 10-mile EPZ and 50-mile IPZ for large LWRs are contained in NUREG-0396 (EPA 520/1-78-016), Planning Basis for the Development of State and Local Government Radiological Emergency Response Plans in Support of Light Water Nuclear Power Plants (1978) (ML051390356).103 NUREG-0396 introduced the concept of generic EPZs as the basis for preplanned response actions that would result in dose savings in a nuclear facilitys environs in the event of a reactor accident. The NRC/EPA Task Force on Emergency Planning that developed NUREG-0396 considered several rationales for establishing EPZ sizes, including risk, cost effectiveness, and the accident consequence spectrum.

After reviewing these alternatives, the Task Force concluded that the objective of emergency response plans should be to provide dose savings for a spectrum of accidents that could produce offsite doses in excess of the EPA Protective Action Guidelines (PAGs) contained in the EPAs Manual of Protective Action Guides and Protective Actions for Nuclear Incidents (EPA-400) (EPA PAG Manual).104 NUREG-0396 and EPA-400 identified the PAG dose guidelines (1-5 rem) as doses at which public protective actions should be considered and undertaken. The EPA PAG Manual provides recommended PAGs to guide the choice of protective action. The PAGs for evacuation and sheltering in place (during the early phase) and relocation (during the intermediate phase) are based on the projected dose to an individual.

The EPZ requirements in 10 CFR 50.47 applicable to current LWRs were based on the analysis and findings of the NRC/EPA Task Force documented in NUREG-0396, which defined the plume and ingestion exposure pathways and associated EPZs. In determining the plume exposure EPZ, the Task Force assessed projected doses from the traditional design-basis accidents (DBAs) and core melt sequences (including those resulting in immediate life-threatening doses of 200 rem or more) at various distances and constructed dose-distance curves.105 The spectrum of accidents considered principally included 103 The NRCs policy statement of October 23, 1979 (44 Fed. Reg. 61,123) incorporated NUREG-0396 guidance into EP regulations and guidance documents. Among other documents, NUREG-0396 is referenced in NUREG-0654/FEMA-REP-1, Revision 2, Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants: Final Report (Dec. 2019).

104 A PAG is the projected dose to an individual from a release of radioactive material at which a specific protective action to reduce or avoid that dose is recommended. The developers of the EPA PAGs considered three major principles in establishing exposure levels for the PAGs:

(1) prevent acute effects; (2) reduce risk of chronic effects; and (3) balance protection with other important factors and ensure that actions result in more benefit than harm. Importantly, PAGs were developed as guides to help public officials select protective actions under emergency conditions and are not meant to be applied as strict numeric criteria, but rather as guidelines to be considered in the context of incident-specific factors. As such, PAGs do not establish an acceptable level of risk for normal, non-emergency conditions, nor do they represent the boundary between safe and unsafe conditions.

105 NUREG-0396 refers to accidents in which there is core melting and/or containment failure as Class 9 accidents. It defines a Class 9 accident as follows: An accident considered to be so low in probability as not to require specific additional provisions in the design of a reactor facility. Such accidents would involve sequences of successive failures more severe than those postulated for the purpose of establishing the design basis for protective systems and engineered safety features. (Class 9 event sequences include those leading to total core melt and consequent degradation of the containment boundary and those leading to gross fuel clad failure or partial melt with independent failures of the containment boundary).

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nei.org 24 accidents postulated for purposes of evaluating plant designs (e.g., DBAs) and the spectrum of accidents assessed by the WASH-1400 Reactor Safety Study (RSS).106 For DBAs and more-frequent core melt sequences, NUREG-0396 concluded that a 10-mile PEP EPZ is of sufficient size to provide dose savings to the population in areas where the projected dose from design basis accidents could be expected to exceed the applicable PAGs under unfavorable atmospheric conditions. As discussed in Appendix I (Rationale for the Planning Basis) to NUREG-0396, the Task Force concluded that the PAG plume exposure of 5 rem (whole body) would not be exceeded beyond 10 miles for any site analyzed, and that even under the most restrictive PAG, a plume exposure value of 1 rem (whole body) would not require any consideration of emergency responses beyond 10 miles. It further concluded that it would be unlikely that any protective actions for the PEP would be required beyond the EPZ, and that the EPZ is of sufficient size for actions within this zone to provide substantial reduction in severe, early-stage health effects (such as those that could occur with doses greater than 200 rem) in the event of a complete core melt. Nevertheless, the NRC has noted that the current EPZs provide for a comprehensive emergency planning framework that would allow expansion of the response efforts beyond the designated distances should events warrant such an expansion.107 4.2.2 NRCs Alternative EPZ Sizing Requirements for Advanced Reactors and ONTs As noted, the NRC amended its Part 50 and 52 regulations in 2023 to include new alternative EP requirements for SMRs and other new reactor technologies, recognizing the passive safety features, relatively small cores, and other design features anticipated to result in smaller postulated releases and associated radiological doses as compared to large LWRs.108 The rule adopted a performance-based, technology-inclusive, risk-informed, and consequence-oriented approach.109 As outlined in revised section 50.33(g), the rule includes a scalable method for determining the PEP EPZ based on factors such as accident source term, fission product release, and associated dose characteristics, and a less prescriptive approach to emergency plan development and evaluation in 10 CFR 50.160.

New section 50.33(g)(2) contains requirements for determining a PEP EPZ. Specifically, section 50.33(g)(2)(i) contains two criteria for identifying the area to be encompassed by a PEP EPZ. First, it is the area where doses exceeding one rem TEDE are expected over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months following a radiological release when accounting for accident likelihood, source term, timing, and meteorology. Second, it is the area for which predetermined, prompt protective measures are necessary. Reflecting the and at the end of section 50.33(g)(2)(i)(A), areas to be included in a PEP EPZ must meet both criteria. As shown in Table 2, based on the event evaluation, dose assessment, and protective measures evaluation, there are three possible outcomes from the PEP EPZ assessment and how it relates to the site boundary: (1) no PEP EPZ, (2) PEP EPZ at the site boundary, and (3) PEP EPZ beyond the site boundary. Further, the rule does not require the designation of an ingestion planning zone. Instead, section 50.160 contains a requirement to describe or reference ingestion pathway response capabilities in the emergency plan.

106 WASH-1400 (NUREG-75/014), Reactor Safety Study: An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants (Oct. 1975)

(ML16225A002). For DBAs, there was a focus on the DBA loss-of-coolant-accident (LOCA) analysis since it resulted in the largest offsite dose of the considered DBAs. Analysis of the DBA LOCAs demonstrated that 2-hour doses greater than 25 rem (thyroid) and 5 rem (whole body) would not be exceeded beyond 10 miles for any site analyzed.

107 Emergency Planning Zones, Petition for Rulemaking; Denial; 79 Fed. Reg. 19,501, 19,502 (Apr. 9, 2014).

108 Applicants and licensees for SMRs, non-LWRs, and NPUFs may choose to adopt either the requirements of 10 CFR 50.160, or those in Appendix E to 10 CFR Part 50 and, for nuclear power reactor licensees, the planning standards in 10 CFR 50.47(b).

109 2023 EP Rule, 88 Fed. Reg. at 80,050, 80,057.

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nei.org 25 Table 2: Potential PEP EPZ Determination Process Outcomes (Source: NEI 24-05, Rev. 0 (ML24184C122))

Section 50.160 contains the emergency plan requirements for applicants using the alternative EP framework. Section 50.160(a) provides definitions, including a site boundary definition that is specified in 10 CFR 20.1003. Section 50.160(b)(1)(iii)-(iv)(A) provide performance-based requirements similar in a general nature to the 16 planning standards contained in 10 CFR 50.47, addressing topics such as emergency classification, staffing, radiological assessment, etc. However, the applicant has the flexibility to determine the performance objectives for the site emergency plan. In addition, requirements relating to offsite coordination and planning are separated and contained in section 50.160(b)(1)(iv)(B). This separation is necessary given the three potential PEP EPZ assessment outcomes identified above.110 Section 50.160(b)(2)-(4) contain additional emergency plan requirements for assessing hazards posed by contiguous or nearby facilities and their impact on emergency plans, a description of the PEP EPZ (if necessary), and a description of ingestion response planning. The ingestion response planning requirement replaces the ingestion planning zone requirement found in 10 CFR 50.47 and Appendix E.111 NEI 24-05, Rev. 0, An Approach for Risk-Informed Performance-Based Emergency Planning (June 2024)

(ML24184C122) provides more details on the implementation of the NRCs alternative EP framework, including its integration within the LMP framework.

4.3 The PEP EPZ Is Unnecessary for Power Reactors That Can Justify No EPZ or an EPZ Within the Site Boundary As discussed above, under the new EP framework for advanced reactors, an applicant may be able to demonstrate that no PEP EPZ is required, or that the PEP EPZ will not extend beyond the site boundary.

In either case, use of an LPZ and population center distance separate from the site boundary becomes unnecessary. First, for a reactor that can meet the dose requirements necessary to have an EPZ at the site boundary, the LPZ and population center distance should coincide with the site boundary. The LPZ and population center distance are generally less protective from a dose perspective (and thus closer to 110 If there is no PEP EPZ or a PEP EPZ at the site boundary, then only the requirements section 50.160(b)(1)(i)-(iv)(A) are applicable. If the PEP EPZ extends outside the site boundary, then the requirements of section 50.160(b)(1)(iv)(B) also apply.

111 The NRC also made conforming changes to 10 CFR 52.1, 52.17, 52.18, and 52.79 to allow the use of section 50.160.

Outcome Applicable Conditions No PEP EPZ This outcome is realized if doses greater than the established criteria are not projected to occur outside facility structures.

PEP EPZ at the Site Boundary This outcome is realized if doses greater than the established criteria are projected to occur at a maximum distance that does not exceed the site boundary. This outcome also applies to instances where doses greater than the established criteria are projected to occur at a maximum distance beyond the site boundary; however, a determination was made that no predetermined, prompt protective measures are necessary. In both cases, the licensee is responsible for the implementation of onsite protective measures under the requirements in 10 CFR 50.160(b)(1)(iii)(B).

PEP EPZ Beyond the Site Boundary This outcome is realized if doses greater than the established criteria are projected to occur at a maximum distance beyond the site boundary, and a determination was made that predetermined, prompt protective measures are necessary. In this case, the PEP EPZ is set at the derived distance, the licensee is responsible for the implementation of onsite protective measures under the requirements in 10 CFR 50.160(b)(1)(iii)(B), and the site would have offsite radiological emergency plans under the requirements in 10 CFR 50.160(b)(1)(iv)(B).

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nei.org 26 the reactor). There would be no additional benefit to establishing a specific LPZ or population center distance within the site boundary because the licensee controls the site and must control and limit the population within that area. The NRC staff recognized this fact in SECY-16-0012:

For example, future SMR [or other advanced reactor] applicants may be able to show that an individual at the EAB would not receive a dose that exceeds 1 rem TEDE within any 2-hour period of a release. This calculated dose is much lower than the current regulatory requirement that the dose not exceed 25 rem TEDE.

This results in the potential for the EAB and LPZ to be at the same distance around a very small site, potentially at a few hundred meters from the center of the reactor location or facility. The dose criteria which would allow for a smaller LPZ would also potentially allow the reactor to be considered for a location at a distance that is relatively close to a population center with at least 25,000 people.112 SECY-16-0012 further states:

The DBA dose analyses performed by an applicant to show compliance with the siting safety analysis regulations and their related radiological releases to the environment are expected to be included in the spectrum of analyses that form the technical basis for the EPZ distance.

Satisfying a 1 rem TEDE dose criterion for an EPZ of the same size as the EAB and LPZ would likely also demonstrate compliance by a large margin if compared with the 25 rem TEDE siting requirement in 10 CFR 50.34(a)(1)(ii)(D).113 Even before it issued its final 2023 EP Rule, the NRC had approved, on a case-specific basis, the identification of much smaller EPZs for proposed advanced reactors.114 In 2019, the NRC issued to the Tennessee Valley Authority (TVA) an ESP for the Clinch River Site in Tennessee. The ESP approved site suitability for the construction of two or more SMRs, with a maximum combined electrical output of 800 MW. In determining the PEP EPZ distance, TVA relied on the 10 CFR 50.47 pathway but requested exemptions for certain EP requirements using a methodology for determining the PEP EPZ that was based on the NRCs then-pending EP rulemaking and the three NUREG-0396 criteria listed above.115 TVA proposed either a two-mile or site boundary EPZ using a dose-based, consequence-oriented EPZ-sizing methodology based in part on the EPA PAGs. Therefore, TVA submitted two distinct major features emergency plans as part of its application - one that assumes a two-mile EPZ and another that assumes a site boundary EPZ. In alignment with the NUREG-0396 criteria, the approach contained two analyses, one for DBAs and less severe core melt accidents, which are compared to the EPA PAG of 1 rem, and 112 SECY-16-0012, Accident Source Terms and Siting for Small Modular Reactors and Non-Light Water Reactors at 4 (Feb. 2016)

(ML15309A319) (emphasis added).

113 Id. at 11 (emphasis added).

114 Although this discussion focuses on the Clinch River ESP and NuScale topical report examples, the NRCs 2023 EP Rule notes that [t]he principle of using dose versus distance to determine EPZ size has been used in the past when the NRC licensed several small reactors with a reduced EPZ size of 5 miles (8 km), including the Fort St. Vrain high-temperature gas-cooled reactor (HTGR) (842 MWt), the Big Rock Point boiling water reactor (BWR) (240 MWt), and the La Crosse BWR (165 MWt). 2023 EP Rule, 88 Fed. Reg. at 80,058.

115 In SRM-SECY-15-0077, Options for Emergency Preparedness for Small Modular Reactors and Other New Technologies (Aug. 4, 2015)

(ML15216A492), the Commission stated that for any SMR reviews conducted prior to the establishment of a rule, the staff should be prepared to adapt an approach to EPZs for SMRs under existing exemption processes.

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nei.org 27 an analysis for more severe core melt accidents, which are assessed in terms of the reduction of early health effects (200 rem).116 The NRC staff concluded that TVAs methodology for establishing a two-mile and site boundary EPZ is consistent with the methodology used to establish the ten-mile EPZs reflected in current regulations and recommended that the exemptions be granted.117 It found that the basis for establishing a site boundary and 2-mile EPZ in the ESP application maintains the same level of protection (i.e., dose savings) in the Clinch River site environs as that which exists at the 10-mile PEP EPZ for large LWRs. The staff noted that the methodology for determining the acceptability of all three distances (i.e., site boundary, 2-mile, and 10-mile PEP EPZs) uses the same radiation exposure bounding criteria/limits, which ensure that any radiation exposures beyond the PEP EPZ would be highly unlikely to exceed the EPA early phase PAGs.

The ACRS agreed with the staffs conclusions and recommended that the exemptions be granted.118 In 2015, NuScale submitted a licensing topical report (LTR) to the NRC on the methodology for establishing the technical basis for a site boundary PEP EPZ. After significant interactions with the NRC, revision 3 of the LTR was submitted in 2022119 and approved by the NRC that year.120 The NuScale approach to sizing the PEP EPZ is similar to the TVA approach described above. NuScale used a risk-informed approach to screen appropriate release sequences to be evaluated for determining the PEP EPZ size. The screening included quantitative PRA insights, including consideration of uncertainty, as well as application of engineering insights emphasizing safety margin and defense-in-depth. The process included consideration of internal events, external hazards, and all modes of operation, as well as other PRA risks. Based on the accident sequence screening, the risk results (including source terms and off-site dose versus distance) served as the basis for NuScales determination that the PEP EPZ could be limited to the site boundary.121 The ACRS concurred with the NRC staffs approval of NuScales EPZ methodology, noting that it is generally consistent with the technical basis of the current 10-mile EPZ prescribed in 10 CFR 50.47 (i.e.,

NUREG-0396), and there is reasonable assurance the methodology is adequate for sizing of the EPZ.122 It also found that the methodology is risk-informed, provides a technically consistent approach (with NUREG-0396) for EPZ sizing, and adequately considers seismic and multi-module impacts. The ACRS described the staffs evaluation as an example of how to use risk information, consequence analyses, 116 The less severe accident category includes core-melt accidents with intact containment, beyond-design basis scenarios, and accident scenarios with mean CDFs greater than 1 x 10-6/reactor-yr. The more severe accident category included core-melt accidents with postulated containment bypass or failure with potential for higher consequences with mean CDFs greater than 1 x 10-7/reactor-yr. TVAs methodology included four steps: (1) selecting and categorizing accident scenarios; (2) developing the fission product release to the environment as a function of time (radiological release source term); (3) calculating the projected dose consequences at a distance and comparing them to dose criteria for DBAs and less severe accidents; and (4) calculating the probability of dose exceedance at a distance, and evaluating the substantial reduction in early health effects criterion for more severe accidents.

117 Final Safety Evaluation Report for the Early Site Permit Application for the Clinch River Nuclear Site at 13-1 to 13-4, 13-24 to 13-41 (June 2019) (ML19162A157).

118 Letter from Michael L. Corradini, Chairman, ACRS, to Kristine L. Svinicki, NRC, Chair,

Subject:

Early Site Permit - Clinch River Nuclear Site, at 4-5 (Jan. 19, 2019) (ML19009A286).

119 See Letter from Carrie Fosaaen, NuScale, to NRC,

Subject:

NuScale Power, LLC Submittal of the Approved Version of NuScale Topical Report, Methodology for Establishing the Technical Basis for Plume Exposure Emergency Planning Zones at NuScale Small Modular Reactor Plant Sites, TR-0915-17772-P, Revision 3 (Oct. 26, 2022) (ML22161B010).

120 NRC Final Safety Evaluation for NuScale Licensing Topical Report TR-091517772, Revision 3 (Oct. 20, 2022) (ML22299A046).

121 Under NuScales methodology, the final EPZ size is the smallest distance at which the dose criteria, chosen to provide a level of protection that meets or exceeds the basis in NUREG-0396, are satisfied. These criteria are (1) a TEDE from the design basis source term is less than or equal to 1 rem; (2) the TEDE from less severe accidents (containment intact) is less than or equal to 1 rem; or (3) a substantial reduction in early health effects from more severe accidents (containment failure or bypass), i.e., an acute whole body dose less than 200 rem.

122 Letter from Joy L. Rempe, Chairman, ACRS, to Daniel H. Dorman, Executive Director of Operations, NRC at 3. (Oct. 19, 2022) (ML22287A155).

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nei.org 28 and considerations of uncertainty and defense in depth in justifying the adequacy of their safety finding.123 4.4 The Site Boundary EPZ Approach Satisfies the Intended Functions of the LPZ and Population Center Distance 4.4.1 Ability to Take Prompt Protective Measures An applicant that demonstrates compliance with the NRCs 2023 EP Rule will also satisfy the purposes of the LPZ and population center distance. The LPZ is intended to ensure that there is a reasonable probability that appropriate protective measures could be taken on behalf of residents within the LPZ during a serious accident. Nearly three decades ago, the Commission recognized that the siting functions intended for the LPZ, namely, a low density of residents and the feasibility of taking protective actions, have been accomplished by other regulations - including the NRCs EP regulations.124 As the 2023 EP Rule explains, the EPZ is a planning tool to ensure predetermined, prompt protective measures can and will be taken if accident conditions warrant. If both section 50.33(g)(2)(i) criteria are met, then an EPZ is required. However, if there is no need for predetermined, prompt protective measures, then the 2023 EP Rule still requires licensees to develop and maintain capabilities to assess, classify, notify, and recommend protective measures as conditions warrant.

Additionally, the 2023 EP Rule requires applicants and licensees complying with 10 CFR 50.160 to describe in their emergency plans the capabilities to prevent contaminated food and water from entering the ingestion pathway. The capabilities described in the emergency plan need to address major exposure pathways associated with the ingestion of contaminated food and water. As the NRC has noted, [e]ven in cases where the facilitys plume exposure pathway EPZ is bounded by the site boundary, the applicant or licensee must reference capabilities of Federal, State, and local authorities.125 These requirements provide the same capabilities available to identify and interdict contaminated food and water in the event of a radiological emergency as required under the EP regulations in Appendix E to 10 CFR Part 50 for currently operating nuclear power reactor licensees.

4.4.2 Management of Societal Risk By justifying no PEP EPZ or an EPZ at the site boundary, a licensee also will manage societal risk in a manner that is consistent with the population center distances intended purpose. The population center distance is the distance by which the reactor would be sufficiently removed from the nearest major concentration of people that lethal exposures would not occur in the population center even from an accident in which the containment is breached.126 It is intended to ensure that the cumulative exposure dose to the population as a whole is kept within bounds in the event of a postulated major accident.127 As discussed above, the AEC set the population center distance to 1.33 times the LPZ distance in 1961 to provide protection against the most serious consequences of theoretically possible accidents.128 Early 123 Id. at 4.

124 61 Fed. Reg. 65,161.

125 2023 EP Rule, 88 Fed. Reg. at 80,066.

126 Okrent Report at 2-55.

127 New England Coalition v. NRC, 582 F.2d 87, 91 (1978).

128 Okrent Report at 2-55.

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nei.org 29 recommendations for the population center distance were consistent with the eventual basis for the 10-mile PEP EPZ identified in NUREG-0396, which states that the EPZ should:

encompass those areas in which projected dose from DBAs could exceed the PAGs under unfavorable atmospheric conditions; encompass those areas in which consequences of less severe core melt accidents (referred to as Class 9 accidents in NUREG-0396) could exceed the PAGs; and be of sufficient size to provide for substantial reduction in early severe health effects (injuries or deaths) in the event of more severe core melt accidents.129 Although the population center distance in Part 100 is a multiplier applied to the LPZ, it originally used the same technical basis - a dose limit of 200 rem in the event of containment failure. The EPZ analysis serves the same purpose as the population center distance because it requires a substantial reduction in early health effects from more severe accidents with containment bypass,130 and thus ensures that lethal exposures would not occur in the population center even from an accident in which the containment is breached.131 Thus, because both boundaries serve the same purpose and are based on similar criteria, they should be set to the same distance when a licensee has justified using the site boundary as the EPZ.

Additionally, as discussed in the 2019 ORNL Report and recognized by the NRC, many advanced reactors are expected to have enhanced accident prevention and mitigation features or attributes.132 Such features may include passive safety systems that rely on natural phenomena such as gravity, natural circulation, and inherent material properties rather than active systems or operator intervention.

Advanced designs also may incorporate inherent reactivity control mechanisms to prevent criticality accidents. Lower operating pressures also help prevent damage to the reactor core or containment and limit the dispersal of radioactive materials. In addition, advanced reactors may have robust containment structures, potentially including below-grade or in-ground construction, which can withstand extreme external events (e.g., earthquakes, floods), and/or use advanced fuels (e.g., TRISO) that can withstand extreme temperatures without degradation and contain fission products within the fuel itself. These features provide multiple layers of defense to contain radioactive materials and prevent, or effectively limit, the physical release of radionuclides to the environment, even under severe accident conditions.

As a result, advanced reactors are expected to have extremely low risk safety profiles.133 129 NUREG-0936 at 16-17.

130 Id. at 17.

131 Okrent Report at 2-55.

132 ORNL Report at 7-10; NRC Response to Public Comments - Emergency Preparedness for Small Modular Reactors and Other New Technologies (NRC-2015-0225; 3150-AJ68) at 117 (Nov. 2023) (ML23229A227) (2023 EP Rule Comment Responses).

133 See, e.g., TerraPower, LCC, Kemmerer Power Station Unit 1 Preliminary Safety Analysis Report, Rev. 0, Chapter 4 (Integrated Evaluations) at 4.1-1 to 4.1-2 (Mar. 2024) (ML24088A065) (evaluating the overall integrated risk performance of the proposed Natrium plant as captured within the scope of the PRA for the PSAR against the three cumulative plant risk performance metrics contained in NEI 18-04, and concluding that the Site Boundary Risk, EAB Early Fatality Risk, and Latent Cancer Risk metrics are all satisfied with margin); TerraPower, LCC, Kemmerer Power Station Unit 1 Environmental Report at 5.11-3 to 5.11-4, 5.11-40 (Mar. 2024) (ML24088A072). (The early fatality risk within 1 mile of the EAB is zero, compared to the goal of 5 x 10-7 per plant-year. The latent cancer fatality risk within 10 miles of the EAB is 5.1 x 10-12 per reactor-year, compared to the goal of 2 x 10-6 per plant-year. The accident frequency 1.4 x 10-8 per reactor-yr. The population dose risk (PDR) is 1.5 x 10-4 person-rem per reactor-year, which is only 0.12 percent of the estimated dose of 0.127 person-rem per year from routine releases and roughly two to three orders of magnitude lower than the calculated PDRs for Generation III/III+ large LWRs).

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nei.org 30 In responding to public comments on the 2023 EP Rule, the NRC noted that 10 CFR 50.43(e) requires demonstration of the performance of safety features of new reactor designs prior to their approval, and that the rule maintains NRCs defense-in-depth philosophy. For non-LWR applicants using the LMP approach, for example, defense-in-depth adequacy is evaluated by using a series of risk-informed, performance-based decisions regarding design, plant risk assessment, selection and evaluation of LBEs, safety classification of SSCs, specification of performance requirements for SSCs, and programs to ensure these performance requirements are maintained throughout the life of the plant. Figure 3 illustrates the process for establishing defense-in-depth adequacy, as set forth in NEI-18-04.

Figure 3: NEI 18-04 Framework for Establishing Defense-in-Depth Adequacy (Source: NEI 18-04, Rev.1)

Thus, analyses of advanced reactor designs and attributes, including defense-in-depth adequacy, are expected to show that postulated reactor accidents will (1) result in a significantly reduced source terms and/or (2) limit any radioactive material fallout to within the site boundary or be limited to within a short distance of the EAB. This, in turn, would minimize the likelihood and extent of any radiological contamination of land that could require the condemnation of the land and permanent relocation of residents, thereby allowing advanced reactors to be sited very close to population centers with no undue risk to society and no sacrifice of current [defense-in-depth] principles in play with current siting guidance.134 As noted in Section 3.1 of the 2019 ORNL Report:

Significant siting flexibility is provided for advanced reactors with a reduced source term. For example, an advanced reactor with a tenth the source term of a large LWR could theoretically be located within 10 miles of a population center of 1 million people without an increase in the current accepted societal risk.135 134 2019 ORNL Report at 24.

135 Id. at 20.

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nei.org 31 Therefore, based on small LPZ distances commensurate with the dose reduction factors afforded by advanced reactors, low-population industrialized areas within a surrounding high-density population center could conceivably support advanced reactor siting within the requirements of 10 CFR 100.136 4.5 Appropriate Analysis Methods Can Be Used to Justify a Small Population Center Distance 4.5.1 Current NRC Regulations and Guidance Do Not Categorically Preclude the Siting of Advanced Reactors Near or Within High-Density Population Centers As discussed in Section 3.1, NRC guidance in RG 4.7 on siting commercial nuclear power plants uses a combination of distance and population density limits. The latter is intended to assist in implementing 10 CFR 100.21(h), which states:

Reactor sites should be located away from very densely populated centers. Areas of low population density are, generally, preferred. However, in determining the acceptability of a particular site located away from a very densely populated center but not in an area of low density, consideration will be given to safety, environmental, economic, or other factors, which may result in the site being found acceptable.137 For large LWRs, RG 4.7 provides that [p]referably, a reactor should be located so that the population density is at most 500 persons per square mile, and that [a] reactor should not be located at a site where the population density is well in excess of this value.138 As noted above, Revision 4 to RG 4.7, issued in February 2024, includes a new Appendix A that provides alternatives to the established populationdensity criterion that could support siting non-LWRs and light-water SMRs closer to population centers than is typical for large LWRs.139 These alternative population density criteria are based on estimates of radiological consequences from design-specific events. Namely, an applicant can demonstrate compliance with 10 CFR 100.21(h) by siting a nuclear reactor in a location where the population density preferably does not exceed 500 ppsm out to a distance equal to twice the distance at which a hypothetical individual could receive a calculated TEDE of 1 rem over a period of 30 days from the release of radionuclides following postulated accidents.140 Thus, while the NRC should consider revising 10 CFR 100.21(h) and RG 4.7 population density criteria to provide greater clarity and flexibility, the plain language of the current regulation and guidance gives the agency discretion in determining how close a reactor can be located to densely populated areas. That is, the current regulation and guidance do not preclude siting reactors near or within densely-populated areas. Rather, they reflect a general preference for siting reactors in areas of low population density and away from very densely populated centers. Implicit in both 10 CFR 100.21(h) and RG 4.7, however, is the Commissions longstanding recognition that these population density levels do not indicate the upper 136 Id. at 21-22 (emphasis added).

137 10 CFR 100.21(h) (emphasis added).

138 RG 4.7, Rev. 4 at 19.

139 Id. at 19-20.

140 Id., App. A at A-2.

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nei.org 32 limits of acceptability,141 and that next-generation advanced reactors could be sited closer to a densely populated city than is current NRC practice while pos[ing] a very low risk to the populace.142 Notably, in licensing large LWRs, the NRC has allowed some sites to be located in areas in which the population density exceeds 500 ppsm. In 2018, the NRC approved such a site at Turkey Point when considering the licenses for proposed Units 6 and 7. At that site, [t]he projected maximum density value determined within 20 miles... is about 200 people per square mile in excess of the 500 people per square mile which, for this site, is a reasonable proportion of the criterion.143 The NRC determined that this population density for the Turkey Point site was not well in excess of the criterion set forth in the guidance, and the applicant affirmed that population density would not pose a significant impediment to the development of emergency plans.144 As a result, the staff evaluated the physical characteristics of the site, with a focus on the security and emergency plans and measures that ensure the public health and safety, and found the Turkey Point site to be acceptable because the application demonstrated that the public health and safety would be assured.145 It also noted that the highest population density at any radial distance out to 20 miles for the Turkey Point site is comparable to that of previously licensed sites, such as the Limerick site density of 789 persons per square mile at 5 miles; the Zion site density of 668 persons per square mile at 10 miles; and the Connecticut Yankee site density of 716 persons per square mile at 20 miles.146 For the reasons discussed in this paper, the NRC should apply the population density criterion for SMRs and non-LWRs in a similarly flexible manner when public health and safety would be assured.

4.5.2 Applicants That Can Justify No EPZ or a Site Boundary EPZ Should Be Able to Justify a Very Small Population Density Distance Through Appropriate Analysis Methods If an applicant can justify no EPZ or an EPZ within the site boundary, then it should be able to establish a small population density distance that allows siting an advanced reactor within or near a large population center. As discussed above, the 2023 EP Rule requires applicants to determine the size of the plume exposure pathway EPZ for an SMR or ONT facility, and to submit the analysis for NRC approval.

The analysis must evaluate the expected public dose projected from the release of radioactive materials from the facility considering accident likelihood and other essential criteria, such as source term, timing of the accident sequence, and meteorology, against the criterion of 1 rem TEDE over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months . That criterion is based on lower end of the EPAs early phase PAG of 1 to 5 rem projected over four days (96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months ). As described in the EPA PAG Manual, the early phase is the beginning of a radiological incident for which immediate decisions for effective use of protective actions are required. Sheltering-in-place and evacuation are the principal protective actions and are intended to avoid inhalation of gases or particulates in an atmospheric plume and to minimize external radiation exposures.147 141 57 Fed. Reg. at 47,805.

142 61 Fed. Reg. at 65,162.

143 Fla. Power & Light Co. (Turkey Point Nuclear Generating Units 6 and 7), CLI-18-1, 87 NRC 39, 62 (2018).

144 Id. at 62, 63, n.139.

145 Id. at 62-63.

146 Id. at 63, n.140.

147 During the early phase of an incident, there are three main exposure pathways from airborne releases: (1) direct exposure to radioactive materials in an atmospheric plume; (2) inhalation of radionuclides from immersion in a radioactive atmospheric plume and inhalation of ground-deposited radionuclides that are resuspended into a breathing zone; and (3) deposition of radioiodine and particulates from a radioactive plume that can emit groundshine after the plume has passed. EPA chose the four-day (96-hour) period as the duration of exposure during the early phase because it is a reasonable estimate of the time necessary to make measurements, reach decisions, and prepare to implement further protective actions (such as relocation) if necessary.

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nei.org 33 The NRC has described the population density distance criterion of twice the distance to 1 rem in 30 days as being consistent with EPAs intermediate phase relocation PAGs, which are based on doses projected in the first several years following a postulated accident.148 The PAG for relocation of the public is 2 rem in the first year and 0.5 rem in any subsequent year.149 In the NRC staffs view, considering the possible estimated doses accumulated over a longer time period such as 30 days can serve to limit societal risks from postulated accidents beyond assessing the appropriate planning for immediate protective actions by limit[ing] the population potentially affected by longer-term protective actions such as being relocated.150 In addition, the staff chose to use the estimated doses accumulated over 30 days as part of the performance criteria specifically because that would conform with the models and calculations expected to be part of the [LMP-based] licensing process described in DG-1353, which was issued in final form as RG 1.233.151 In SECY-20-0045, the staff noted this criterion will generally result in the radius of the area in which population density is assessed being greater than twice the radius of the consequence-based plume-exposure emergency planning zone.152 In our comments on DG-4034 (draft RG 4.7, Rev. 4) and a supporting white paper, NEI asserted that 500 ppsm dose criterion of 2 times the distance to 1 rem in 30 days for advanced reactors is very conservative compared to the current level of protection accepted for large LWR siting.153 The NRC staff disagreed with that position and declined to accept NEIs proposed use of an alternative population density distance criterion of 5 rem in 30 days using best estimate dose calculations. In doing so, the staff noted it was not clear how the suggested criterion of 5 rem over the month following an accident relates to the consideration of relocating populations following an accident at a nuclear plant.154 Despite these differing views, there appears to be a viable path forward, although fully defining that path and its desired outcome likely will require further in interactions between the industry and staff and augmentation of current guidance, including identification of lessons learned from the application of the current guidance in Appendix A to RG 4.7. In one of its comment responses, the NRC staff stated:

The staff expects there to be some correlation between those plant designs that can take advantage of the performance-based emergency planning provisions of 10 CFR 50.160 and those proposing to justify the alternative approach in Appendix A for considering population density. Some aspects of modelling important design features and estimating offsite consequences will be similar for justifying alternatives for emergency planning, determinations of EABs and LPZs, and determining the distances out to which population density is assessed.

148 NRC Response to Public Comments on Draft Regulatory Guide (DG)-4034 at 14-15 (Response to NEI Comment #37).

149 EPA PAG Manual at 6, 9, 40-42. When projected doses are less than the relocation PAG of 2 rem in the first year, focused environmental decontamination and cleanup (e.g., scrubbing and flushing of surfaces with uncontaminated water, removing and disposing of soil and contaminated debris) may be able to reduce doses to populations that are not relocated. Keeping projected doses below the 0.5 rem PAG in the second and subsequent years may be achieved through the decay of shorter half-life radioisotopes, environmental decontamination and cleanup efforts, or other means of controlling public exposures, such as limiting access to certain areas. Id. at 9.

150 SECY-20-0045, Enclosure at 9-10.

151 Id. at 9. The methodology described in RG 1.233 includes using estimates of hypothetical doses over 30 days at the EAB for evaluating licensing basis events; classification of structures, systems, and components; and assessing defense in depth.

152 Id. at 9 (footnote 4).

153 Letter from Kati Austgen, NEI, to NRC,

Subject:

Comments on Draft Regulatory Guide (DG), DG-4034, General Site Suitability Criteria for Nuclear Power Stations (Docket ID: NRC-2023-0153) (Federal Register Notice 88 FR 71777) (Nov. 17, 2023) (ML23326A031) (includes as an attachment NEIs November 2023 White Paper titled Advanced Reactor Population-Related Siting Considerations).

154 NRC Response to Public Comments on Draft Regulatory Guide (DG)-4034 at 15 (Response to NEI Comment #37).

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nei.org 34 However, there are also differences between the various analyses in terms of assumptions and consideration of results (e.g., different exposure times).155 To date, the differences to which the staff alludes have not been fully delineated. Appendix A to RG 4.7 identifies a number of key actions for siting analyses that should be considered regardless of the approach taken.156 It also provides guidance for estimating offsite consequences for the three types of advanced reactor applications anticipated by the NRC.157 That guidance, however, focuses on methods for developing the source term to be used in the siting analysis and on the modeling of containment performance. It does not address the assumptions to be used in atmospheric dispersion modeling (e.g.,

using the MACCS code) needed to estimate offsite doses. Instead, it states that [t]he calculation of offsite doses should be in accordance with NRC-accepted methodologies, including associated computer models for the atmospheric dispersion of any released radioactive materials to areas surrounding the plant.158 In our comments on DG-4034, NEI suggested that Appendix A should specify that best estimate assumptions for weather, wind direction and shielding (e.g., average weather conditions, varied wind direction, credit for normal shielding) may be used in offsite consequence analyses. Although the staff did not include such language in the final Appendix A, it noted in its comment response that [a]n applicant could justify use of either conservative assumptions or mean values in the atmospheric dispersion analysis depending on their overall approach to demonstrating that adequate defense in depth is provided for a particular reactor design and site.159 It also stated that future revisions of guidance documents like RG 1.233 and RG 1.247 may address lessons learned from the first uses of the LMP and potential siting of new reactors based on the analyses under the LMP methodology.160 With both TerraPower and X-energy having submitted EPZ-related topical reports (TR) and construction permit (CP) applications to the NRC, such LMP-based lessons learned should come relatively soon. On March 20, 2023, TerraPower submitted TR number NAT-3056 on the PEP EPZ sizing for the Natrium design (ML23080A045). The most recent revision (Rev. 3) of that TR was submitted on October 30, 2024 (ML24304B034). The methodology aligns with the pathway provided by the 2023 EP Rule and RG 1.242.

The Preliminary Safety Analysis Report (PSAR) for Kemmerer Unit 1 (ML24088A065) states: Based on the preliminary PEP EPZ sizing analysis, Preliminary Emergency Planning Zone Determination Analysis

[March 2024 Technical Report TP-LIC-RPT-0012, Rev. 0 (ML24088A087)], which is incorporated by reference into the SAR, a PEP EPZ within the EAB is supported based on meeting the criteria in 10 CFR 50.33(g)(2)(i).161 The Kemmerer Unit 1 PSAR (see page 2.2-1) sets the EPZ, EAB, and LPZ at the same boundary (0.25 mile or 400m from the Kemmerer Unit 1 Reactor Building center point). Notably, TP-LIC-155 Id. at 27-28 (Response to NuScale Comment #4).

156 RG 4.7, Rev. 4, App. A at A-3. The specific key actions listed in RG 4.7 include: (1) performing a comprehensive event assessment to identify all credible events; (2) selecting an event or events that bound the credible events in terms of parameters (e.g., temperatures, stresses) to determine conservative estimates of the radionuclide release(s) from the first barrier (and potentially intermediate barriers) that should be used for the siting evaluation; (3) considering uncertainties related to the performance of the barriers commensurate with the scope of the analysis performed; and (4) demonstrating adequate defense in depth for confining and retaining radionuclides considering the uncertainties related to barrier performance.

157 As discussed in RG 4.7, Appendix A, NRC anticipates three types of advanced reactor applications: (1) non-LWR technologies using the LMP methodology (RG 1.233); (2) LWR technologies using a traditional major accident approach or a deterministic approach to assess the potential consequences from reactor accidents (RG 1.183); and (3) non-LWR technologies not using the LMP methodology and choosing to use a traditional or deterministic approach to establish requirements for a containment-type barrier for limiting the release of radionuclides.

158 RG 4.7, Rev. 4, App. A at A-4.

159 NRC Response to Public Comments on Draft Regulatory Guide (DG)-4034 at 21 (Response to NEI Comment #44).

160 Id. at 20.

161 Kemmerer Unit 1 PSAR at 11.3-3 (emphasis added).

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nei.org 35 RPT-0012 indicates that the source terms for the events needed for the EPZ sizing assessment were evaluated using MACCS, and that the events were first assessed at the 30-day boundary doses. It further notes that for events that do not exceed the criterion levels of 1 rem for the mean TEDE and 5 rem for the 95th percentile TEDE, a 4-day dose would also not exceed these levels. This bounding evaluation was performed for all events to assess the exact source terms requiring evaluation for the 4-day dose.

On March 28, 2025, the NRC staff issued its final Safety Evaluation (SE) (ML25076A653) for TR number NAT-3056, Rev. 3, finding the TR to be acceptable for referencing in licensing actions to the extent specified and under the limitations and conditions delineated in the TR and SE. In February 2025, the NRC staff notified TerraPower that it had completed its draft SE with open items for the Kemmerer Power Station Unit 1 CP application, and was targeting June 2026 for the final SE (ML25055A019).

In November 2024, X-energy submitted to the NRC a topical report (TR 010229, Rev. 1) (ML24331A305) that describes the methodology to be used to establish the site-specific PEP EPZ size for Xe-100 advanced reactor plants. Similar to TerraPowers methodology, X-energys approach is designed to align with the NRCs 2023 EP Rule (revised section 50.33 and new section 50.160) and RG 1.242, Appendix A.

It also builds on the approach described in NEI 24-05, which incorporates concepts from NUREG-0396.

The NRC is reviewing TR 010229, and had scheduled a regulatory audit of the TR for the first week of April. On March 31, 2025, Long Mott Energy, LLC, a wholly owned subsidiary of The Dow Chemical Company, submitted a CP application (ML25090A057) to the NRC to construct an 800 megawatts-thermal nuclear power plant comprising four X-energy Xe-100 small modular high-temperature gas-cooled reactors and associated common facilities, designated the Long Mott Generating Station (LMGS),

in Calhoun County, TX. The PSAR states that the EAB and LPZ are entirely contained within the LMGS site boundary in an area controlled by the site owner. It further states that the preliminary PEP EPZ sizing analysis results justify the PEP EPZ boundary corresponding to the site boundary (as defined in 10 CFR 20.1003 and contemplated in 10 CFR 50.33(g)(2)(ii)).162 The NRCs review of the TerraPower and X-energy/Dow TRs and CP applications should help further elucidate the correlation between those plant designs that can take advantage of the performance-based emergency planning provisions of 10 CFR 50.160 and those proposing to justify the alternative approach in Appendix A for considering population density.

SUMMARY

AND RECOMMENDATIONS NEI recommends that the NRC modernize its populated-related siting regulations and guidance. In doing so, the NRC should embrace a risk-informed, performance-based, and consequence-oriented approach to siting - one that reflects current knowledge, leverages advanced reactor design attributes, and facilitates the siting of next-generation nuclear technologies near or within large population centers without compromising public health and safety. Advanced reactors will have features (e.g., passive systems, smaller cores, low operating pressures, and robust containment and fuel designs) that limit accident risks and support the application of risk-informed and performance-based siting criteria. Such reactors should be capable of meeting applicable radiological dose limits with substantial margin.

162 Long Mott Generating Station, Construction Permit Application, Part II: Preliminary Safety Analysis Report at 2.1-8 to 2.1-10 (including Fig.

2.1.2-1), 2.1-13, 11.4-1 (Mar. 31, 2025) (ML25090A061).

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nei.org 36 The NRCs 2023 EP Rule provides the necessary regulatory framework to scale PEP EPZs for advanced reactors based on plant-specific design and consequence analyses. Given this framework, NEI contends that the LPZ and population center distance should be permitted to coincide with the site boundary when an applicant demonstrates a sufficiently low offsite dose. Such applicants also should be able to establish a small population density distance that allows siting an advanced reactor within or near a large population center. Recent NRC regulatory precedents and ongoing activities support this view. The NRC has approved reduced EPZs for both the Clinch River SMR project and NuScale LTR, concluding that the applicants methodologies maintained a level of protection equivalent to current large LWR standards. More recently, the NRC approved TerraPowers TR for its PEP EPZ methodology for the Natrium reactor technology. These actions are consistent with recent statutory directives - like those in NEIMA and the ADVANCE Act - that call for risk-informed, performance-based, and technology-inclusive NRC regulations. Indeed, the NRC has developed such regulations and guidance in other contexts (e.g.,

in the proposed Part 53 and Part 73 rules and in its LMP-related guidance). The NRCs Part 100 and proposed Part 53 regulations should not be an exception to this trend.

Accordingly, the NRC should revise certain population-related siting provisions in its current Part 100 regulations and proposed Part 53 regulations (as issued on October 31, 2024), as recommended below.163 In offering these proposed changes, NEI recognizes that siting a plant in or near a densely populated center could affect how an applicant demonstrates compliance with other siting criteria in Part 100, and that additional regulatory changes may be identified during interactions with the NRC on this paper.

5.1 Potential Revisions to 10 CFR 100.1 and 100.21 10 CFR 100.21 should be amended to eliminate the LPZ and population center distance for facilities where no plume exposure pathway EPZ is required or the EPZ does not extend beyond the site boundary. Proposed deletions to the current regulatory text are shown in strikethrough. Proposed textual additions are shown in underlined red font.

Revise § 100.1(d) as follows: This approach incorporates the appropriate standards and criteria for approval of stationary power and testing reactor sites. The Commission intends to carry out a traditional defense-in-depth approach with regard to reactor siting to ensure public safety.

Siting away from densely populated centers has been and will continue to be an important factor in evaluating applications for site approval. However, the Commissions use and application of risk-informed, performance-based, and consequence-oriented methods may permit reactor siting near or within densely populated centers.

Revise § 100.21(a) as follows: Every site must have an exclusion area and a low population zone, as defined in § 100.3. For a site where an applicant can justify that no plume exposure pathway emergency planning zone (EPZ) is required or that the plume exposure pathway EPZ does not extend beyond the site boundary, the low population zone will coincide with the site boundary; Revise § 100.21(b) as follows: The population center distance, as defined in § 100.3, must be at least one and one-third times the distance from the reactor to the outer boundary of the low population zone. In applying this guide, the boundary of the population center shall be 163 In the interim, the information and positions set forth in this paper potentially could be used to support case-by-case exemption requests.

June 2025

nei.org 37 determined upon consideration of population distribution. Political boundaries are not controlling in the application of this guide. For a site where an applicant can justify that no plume exposure pathway EPZ is required or that the plume exposure pathway EPZ does not extend beyond the site boundary, the population center distance will coincide with the site boundary; Delete § 100.21(h) in its entirety. Develop risk-informed, performance-based guidance on the population density criterion to potentially allow siting of low-consequence reactors close to or within densely populated centers containing more than about 25,000 residents.

Alternatively, if § 100.21(h) is retained, then revise it as follows: Reactor sites should be located away from very densely populated centers. Areas of low population density are, generally, preferred. However, in determining the acceptability of a particular site located away from a very densely populated center but not in an area of low density, consideration will be given to safety, environmental, economic, or other factors, which may result in the site being found acceptable even if it is not located in an area of low-population density, including a site for a reactor that is located close to or within a densely populated center containing more than about 25,000 residents.

5.2 Potential Revisions to Proposed 10 CFR 53.530, Population-related considerations Revise the introductory paragraph to proposed § 53.530(c) as follows: Every site must have an exclusion area, a low-population zone, and a population center distance as de"ned in § 53.020. For sites that establish that no plume exposure pathway emergency planning zone (EPZ) is required or that the plume exposure pathway EPZ does not extend beyond the site boundary in accordance with the requirements of § 53.1109(g)(2) of this chapter, the low-population zone and population center distance would coincide with the site boundary.

Delete proposed § 53.530(c) in its entirety. Develop risk-informed, performance-based guidance on the population density criterion to potentially allow siting of low-consequence reactors close to or within densely populated centers containing more than about 25,000 residents.

Alternatively, if § 53.530(c) is retained, then revise it as follows: (c) Reactor sites should be located away from very densely populated centers. Areas of low-population density are, generally, preferred. However, in determining the acceptability of a particular site located away from a very densely populated center but not in an area of low-population density, consideration will be given to safety, environmental, economic, or other factors, which may result in the site being found acceptable even if it is not located in an area of low-population density, including a site that is located close to or within a densely populated center containing more than about 25,000 residents.

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