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NEI - an Approach for Risk-Informed Performance-Based Emergency Planning
	ML24184C122
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Site:	Nuclear Energy Institute
Issue date:	06/30/2024
From:	; Nuclear Energy Institute
To:	; Office of Nuclear Reactor Regulation
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ML24184C120	List: ML24184C121; ML24184C122;
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	NEI 24-05, Rev 0
	Download: ML24184C122 (1)
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nei.org NEI 24-05, Rev 0 An Approach for Risk-Informed Performance-Based Emergency Planning Prepared by the Nuclear Energy Institute June 2024

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nei.org Revision Table Revision Description of Changes Date Modified Responsible Person 0

Initial Issue

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nei.org Acknowledgements This document was jointly developed by Argonne National Laboratory (ANL) and the Nuclear Energy Institute.

ANL Project Lead: David Grabaskas NEI Project Lead: David Young Amir Afzali, Aalo Atomics Parthasarathy Chandran, GE-Vernova Ben Chen, ANL Brandon Chisholm, Southern Company Karl Fleming, KNF Consulting Services LLC Dennis Henneke, GE-Vernova Robert E. Kahler, Consultant ANL and NEI acknowledge and appreciate the diligent efforts of NEI members and other organizations that contributed to this document. In particular, the project team would like to thank Mark Cunningham and Keith Woodard for their contributions and review.

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 Table of Contents Introduction..................................................................................................................................... 1 1.1 Project Objectives............................................................................................................... 1 1.2 Document Structure........................................................................................................... 2 1.3 Acronyms............................................................................................................................ 3 Regulation........................................................................................................................................ 5 2.1 EPZ Determination.............................................................................................................. 6 2.2 Emergency Plan Requirements........................................................................................... 7 Project Goals and scope................................................................................................................. 11 3.1 Goals................................................................................................................................. 11 3.1.1 Align with §50.160 Requirements....................................................................... 11 3.1.2 Ensure Consistent Determination of Reasonable Assurance.............................. 12 3.1.3 Allocate Resources in an Efficient and Effective Manner.................................... 12 3.1.4 Maintain Consistency with LMP Scope and Applicability.................................... 12 3.1.5 Leverage Insights from LBEs................................................................................ 12 3.1.6 Detail PEP EPZ Determination Process................................................................ 12 3.1.7 Maintain Consistency with the LMP/TICAP Framework...................................... 13 3.2 Scope................................................................................................................................. 15 3.3 Integration within LMP..................................................................................................... 17 PEP EPZ Determination.................................................................................................................. 18 4.1 Method Overview............................................................................................................. 18 4.2 Spectrum of Events........................................................................................................... 19 4.2.1 Identify LBEs with Radionuclide Release............................................................. 19 4.2.2 Hazard Events...................................................................................................... 21 4.2.3 Security Events..................................................................................................... 22 4.3 Event and Evaluation and Dose Assessment.................................................................... 23 4.3.1 Perform Probabilistic Dose Aggregation.............................................................. 24 4.3.2 LBE Dose Criteria Comparison............................................................................. 26 4.3.3 LBE Uncertainty and Cliff-Edge Analyses............................................................. 28 4.3.4 Assessments of Events from Alternative Hazards Methods................................ 29 4.3.5 Event Evaluation and Dose Assessment Results.................................................. 30 4.4 Protective Measure Evaluation......................................................................................... 31 4.4.1 Derived Distance Beyond the Site Boundary....................................................... 31

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nei.org 4.4.2 Derived Distance at or within the Site Boundary................................................ 34 4.5 PEP EPZ Determination..................................................................................................... 34 4.6 Implementation Considerations....................................................................................... 36 4.6.1 Pre-Selected PEP EPZ Distance Evaluation.......................................................... 36 4.6.2 Non-Uniform PEP EPZs......................................................................................... 37 4.7 Example Analysis............................................................................................................... 37 4.7.1 Spectrum of Events.............................................................................................. 37 4.7.2 Event Evaluation and Dose Assessment.............................................................. 39 4.7.3 Protective Measures Evaluation.......................................................................... 42 4.7.4 Results.................................................................................................................. 44 Emergency Plan Development....................................................................................................... 45 5.1 Maintenance of Performance - §50.160(b)(1)(i).............................................................. 46 5.2 Performance Objectives - 50.160(b)(1)(ii)....................................................................... 47 5.3 Emergency Response - 50.160(b)(1)(ii)............................................................................ 47 5.3.1 Event Classification.............................................................................................. 47 5.3.2 Protective Actions................................................................................................ 50 5.3.3 Communications.................................................................................................. 51 5.3.4 Command and Control......................................................................................... 51 5.3.5 Staffing and Operations....................................................................................... 52 5.3.6 Radiological Assessment...................................................................................... 52 5.3.7 Reentry................................................................................................................. 53 5.3.8 Critique and Corrective Actions........................................................................... 53 5.4 Planning Activities - §50.160(b)(1)(iv).............................................................................. 53 5.4.1 Onsite Planning Activities.................................................................................... 53 5.4.2 Offsite Planning Activities.................................................................................... 54 5.5 Hazard Analysis - §50.160(b)(2)....................................................................................... 54 5.6 EPZ - §50.160(b)(3)........................................................................................................... 55 5.7 Ingestion Pathway - §50.160(b)(4)................................................................................... 56 References..................................................................................................................................... 57 Appendix A. Utilization of LBEs to Inform PEP EPZ Determination............................................................ 60 Appendix B. Consequence Analysis Methodology...................................................................................... 62 Appendix C. Derivation of Probabilistic Dose Aggregation Criteria............................................................ 64 Appendix D. PEP EPZ Evaluation at Predetermined Distance..................................................................... 67

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nei.org Table of Figures Figure 1.1: Document Outline....................................................................................................................... 2 Figure 2.1: EP Rulemaking Framework [5].................................................................................................... 5 Figure 3.1: Goals of the Developed Approach for EP.................................................................................. 11 Figure 3.2: LMP Layers of Defense Framework [1]..................................................................................... 14 Figure 3.3: Relationship of TICAP to an Advanced Reactor Application[8]................................................ 15 Figure 4.1: Overview of PEP EPZ Determination Process........................................................................... 18 Figure 4.2: Spectrum of Events for PEP EPZ Determination....................................................................... 19 Figure 4.3: PEP EPZ Event Evaluation and Dose Assessment Process........................................................ 24 Figure 4.4: Example LBE-specific Dose-versus-Distance Curves................................................................. 25 Figure 4.5: Example Cumulative Dose-versus-Distance Curve................................................................... 26 Figure 4.6: Example of Potential Cliff-Edge Effect...................................................................................... 29 Figure 4.7: Example Dose-versus-Distance Curve for Potential Additional Events.................................... 30 Figure 4.8: Results of PEP EPZ Event Evaluation and Dose Assessment..................................................... 31 Figure 4.9: Example Spatial Dose Assessment [20].................................................................................... 33 Figure 4.10: PEP EPZ Determination Process Outcome Flowchart............................................................. 35 Figure 4.11: Example Analysis - LBEs on Frequency versus Consequence Plot......................................... 38 Figure 4.12: Example Analysis - LBE 1 Rem Dose-versus-Distance Curves................................................ 39 Figure 4.13: Example Analysis - LBE 200 Rem Dose-versus-Distance Curves........................................... 40 Figure 4.14: Example Analysis - Cumulative Dose-versus-Distance Curves............................................... 41 Figure 4.15: Example Analysis - Cumulative 95th Percentile Dose-versus-Distance Curves....................... 42 Figure 4.16: Example Analysis - LBE Breakdown........................................................................................ 43 Figure 5.1: RSF Decomposition for IC Identification................................................................................... 50 Figure C.1: Conditional Probability of Exceeding Whole Body Dose-versus-Distance [36]........................ 65 Table of Tables Table 2.1: 10 CFR 50.33 (g)(2)....................................................................................................................... 6 Table 2.2: 10 CFR 50.160(b)(1) Text.............................................................................................................. 7 Table 2.3: 10 CFR 50.160(b)(2)-(4) Text...................................................................................................... 10 Table 3.1: 10 CFR 50.160 Sections and Areas of Additional Guidance....................................................... 16 Table 4.1: PEP EPZ Determination Cumulative Dose-versus-Distance Criteria.......................................... 27 Table 4.2: Potential PEP EPZ Determination Process Outcomes and Requirements................................. 36 Table 4.3: Potential Reasons for Non-Uniform PEP EPZs........................................................................... 37 Table 4.4: Example Analysis - LBEs.............................................................................................................. 38 Table 4.5: Example Analysis - Protective Measures Evaluation - Beyond the SB...................................... 43 Table 4.6: Example Analysis - Protective Measure Evaluations - Within the SB....................................... 44 Table 4.7: Example Analysis - PEP EPZ Determination Results.................................................................. 45 Table 5.1: Technology-Inclusive Emergency Classification Levels.............................................................. 48 Table D.1: Example Analysis Mean Dose Estimates.................................................................................... 67 Table D.2: Example Analysis 95th Percentile Dose Estimates...................................................................... 68

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nei.org 1 INTRODUCTION At a fundamental level, nuclear facility safety is built upon the concept of defense-in-depth (DID), which entails multiple, independent layers of protection for public health and safety. Within the DID structure, emergency preparedness (EP) is the last layer of defense and provides reasonable assurance that adequate protective measures can and will be taken in the event of a radiological emergency. Over several decades, the EP regulatory framework has evolved in response to lessons learned from actual events, experience with maintaining and testing EP capabilities, and advances in a wide range of technologies. Furthering this evolution, recent developments in risk-informed performance-based (RIPB) design and licensing approaches provide an opportunity to leverage insights regarding the attributes of a specific facility and site to inform EP.

1.1 Project Objectives This project is part of an effort under the U.S. Department of Energy (DOE), Nuclear Energy (NE),

Advanced Reactor Regulatory Development (ARRD), Regulatory Framework Modernization area to develop guidance regarding the use of RIPB insights as part of EP, including the analyses and outcomes of the U.S. Nuclear Regulatory Commission (NRC)-endorsed Licensing Modernization Project (LMP)1 [1].

The high-level goal of the project is summarized below:

Goal: Establish an approach that leverages the insights from technology-inclusive RIPB design and licensing methods to develop an EP strategy that provides reasonable assurance of adequate protection of the public health and safety while allocating resources for dose savings in an efficient and effective manner.

The developed approach should provide a systematic, holistic, predictable, and transparent pathway for determining appropriate site-specific EP capabilities based on the attributes of a facility and its safety case. Such an approach will enable vendors to enhance the economic viability of their designs while ensuring adequate protection of public health and safety, and thus promote the deployment of innovative technologies. This outcome is consistent with the NRC's Principles of Good Regulation and stated Commission policies.

Given that the LMP framework is an industry-developed and NRC-endorsed approach to RIPB safety case development and licensing [2], the central objective of this project is to develop and achieve NRC endorsement of a methodology for determining site-specific EP requirements as part of an integral RIPB safety case. This includes leveraging the insights gained from the LMP process, such as the utilization of Licensing Basis Events (LBEs) and associated attributes (e.g., frequency, timing, consequence, etc.) to inform:

1) The determination of the plume exposure pathway (PEP) emergency planning zone (EPZ).

2) The development of appropriate emergency plans (actions, resources, coordination, etc.),

including consideration of the ingestion pathway.

1 As noted in Figure 5.3 of ref [1], emergency planning is a key element of the layers of defense in the evaluation of DID adequacy in establishing an LMP-based safety case.

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nei.org 2 1.2 Document Structure Figure 1.1 shows an overview of the document structure, beginning with Section 2, which provides a review of applicable regulation. Section 3 describes the goals and scope of the project, including which areas and topics are covered by the developed guidance. Sections 4 and 5 detail the developed methodology, with the PEP EPZ determination process described first, followed by considerations for the development of an emergency plan.

Figure 1.1: Document Outline

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nei.org 3 1.3 Acronyms Acronym Definition ARRD Advanced Reactor Regulatory Development AOO Anticipated Operational Occurrence*

BDBE Beyond-Design-Basis Events*

CDC Complementary Design Criteria*

DID Defense-in-depth DOE Department of Energy DBA Design-Basis Accident*

DBE Design-Basis Event*

DBHL Design Basis Hazard Level*

EAL Emergency Action Level ECL Emergency Classification Level EPZ Emergency Planning Zone EP Emergency Preparedness EAB Exclusion Area Boundary FRMAC Federal Radiological Monitoring and Assessment Center IC Initiating Condition LERF Large Early Release Frequency LBE Licensing Basis Event*

LMP Licensing Modernization Project LWR Light Water Reactor LOCA Loss-of-Coolant-Accident MHTGR Modular High-Temperature Gas-Cooled Reactor NPUF Non-Power Utilization Facilities

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nei.org 4 Acronym Definition NE Nuclear Energy NEI Nuclear Energy Institute NRC Nuclear Regulatory Commission ORO Offsite Response Organization ONT Other New Technology PEP Plume Exposure Pathway PRA Probabilistic Risk Assessment RIE Reduction in Effectiveness RG Regulatory Guide RFDC Required Functional Design Criteria*

RSF Required Safety Function*

RIPB Risk-Informed Performance-Based SAR Safety Analysis Report SRDC Safety-Related Design Criteria*

SB Site Boundary SMR Small Modular Reactor SSC Structures, Systems, and Components TICAP Technology-Inclusive Content of Applications Project TIRICE Technology-Inclusive Risk-Informed Change Evaluation TEDE Total Effective Dose Equivalent

- These are terms used in the LMP methodology and defined in NEI 18-04. The terms are used in this document consistent with their definitions in NEI 18-04.

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nei.org 5 REGULATION In recognition of evolving and new nuclear technologies, limitations of existing regulation and guidance, and improvements in methods and data, the NRC staff sought the Commissions approval to initiate a rulemaking to revise EP regulation and guidance for small modular reactors (SMRs) and other new technologies (ONTs) in SECY-15-0077 [3]. Within this context, ONTs refer to a wide range of technologies, including non-light water reactors (NLWRs) and certain non-power utilization facilities (NPUFs), such as medical isotope facilities licensed under 10 CFR part 50. With the approval of SRM-SECY-15-0077, a rulemaking effort was initiated in 2016,2 and in January 2022, the NRC staff submitted the final rule to the Commission for approval as SECY-22-0001 [4]. The final rule was approved by the Commission in August 2023 and published in the Federal Register in November 2023.3 The most significant components of the final rule are the addition of §50.33(g)(2), which contains criteria for determining the area of a PEP EPZ, and 10 CFR 50.160, Emergency preparedness for small modular reactors, non-light-water reactors, and non-power production or utilization facilities. Both sections apply only to SMRs and ONTs and are outlined in Figure 2.1. This new EP framework is RIPB to allow greater flexibility and innovation by industry. In particular, the rule revised §50.47 to exempt a licensees emergency plan from meeting the 16 planning standards contained therein if §50.160 is used or if the PEP EPZ does not extend beyond the site boundary4 (SB). It is also important to note that Appendix E to 10 CFR 50 does not apply to applicants using §50.160. These changes obviate the need for an applicant to obtain approved exemptions from requirements that would not be appropriate for NLWR designs.

Figure 2.1: EP Rulemaking Framework [5]

2 Refer to regulations.gov docket: NRC-2015-0225.

3 88 FR 80050.

4 As defined by §20.1003, that line beyond which the land or property is not owned, leased, or otherwise controlled by the licensee.

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nei.org 6 2.1 EPZ Determination The new §50.33(g)(2) contains requirements for determining a PEP EPZ; these requirements are presented in Table 2.1. Specifically, §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 total effective dose equivalent (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

§50.33(g)(2)(i)(A), areas to be included in a PEP EPZ must meet both criteria. Under the new EP framework, it is possible to determine that no PEP EPZ is necessary. Further, the rule does not require the designation of an ingestion planning zone; instead, §50.160 contains a requirement to describe or reference ingestion pathway response capabilities in the emergency plan.

Table 2.1: 10 CFR 50.33 (g)(2)

Section Text

§50.33(g)(2) Small modular reactor, non-lightwater reactor, or non-power production or utilization facility applicants complying with § 50.160 who apply for a construction permit or an operating license under this part, or small modular reactor or non-light water reactor applicants complying with § 50.160 who apply for a combined license or an early site permit under part 52 of this chapter, must submit as part of the application the analysis used to determine whether the criteria in § 50.33(g)(2)(i)(A) and (B) are met and, if they are met, the size of the plume exposure pathway EPZ.

(i) The plume exposure pathway EPZ is the area within which:

(A) Public dose, as defined in § 20.1003 of this chapter, is projected to exceed 10 mSv (1 rem) total effective dose equivalent 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; and (B) Pre-determined, prompt protective measures are necessary.

(ii) If the application is for an operating license or combined license or if the application is for an early site permit and contains plans for coping with emergencies under § 52.17(b)(2)(ii) of this chapter, and if the plume exposure pathway EPZ extends beyond the site boundary:

(A) The applicant shall submit radiological emergency response plans of State, local, and participating Tribal governmental entities in the United States that are wholly or partially within the plume exposure pathway EPZ.

(B) The exact configuration of the plume exposure pathway EPZ surrounding the facility shall be determined in relation to the local emergency response needs and capabilities as they are affected by such conditions as demography, topography, land characteristics, access routes, and jurisdictional boundaries.

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nei.org 7 (iii) If the application is for an early site permit that, under § 52.17(b)(2)(i) of this chapter, proposes major features of the emergency plans and describes the EPZ, and if the EPZ extends beyond the site boundary, then the exact configuration of the plume exposure pathway EPZ surrounding the facility shall be determined in relation to the local emergency response needs and capabilities as they are affected by such conditions as demography, topography, land characteristics, access routes, and jurisdictional boundaries.

2.2 Emergency Plan Requirements

§50.160 contains the emergency plan requirements for applicants utilizing the alternative EP framework, as shown in Table 2.2. §50.160(a) starts with definitions, including a SB definition which is specified in §20.1003. §50.160(b)(1)(iii)-(iv)(A) provide performance-based requirements similar in a general nature to the 16 planning standards contained in §50.47. This includes 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, the requirements pertaining to offsite coordination and planning are separated and contained in §50.160(b)(1)(iv)(B). This separation is necessary as it is possible to have no PEP EPZ or a PEP EPZ at the SB, where only the requirements §50.160(b)(1)(i)-(iv)(A) are applicable. If the PEP EPZ extends outside the SB, then the requirements of §50.160(b)(1)(iv)(B) also apply.

§50.160(b)(2) - (4) contain additional emergency plan requirements for the assessment of 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; these are shown in Table 2.3. The ingestion response planning requirement takes the place of the ingestion planning zone requirement found in 10 CFR 50.47 and Appendix E. Lastly, conforming changes were also made to §52.1, §52.17,

§52.18, and §52.79 to allow the use of §50.160.

Table 2.2: 10 CFR 50.160(b)(1) Text Section Text

§50.160(b)(1)

Requirements. The emergency plan shall contain information needed to demonstrate compliance with the elements set forth in this paragraph. The applicable requirements of § 50.47(a)(1) apply to applications submitted under this section.

(1) Performance-based framework. Demonstrate effective response in drills and exercises for emergency and accident conditions.

§50.160(b)(1)(i)

Maintenance of performance. Maintain in effect preparedness to respond to emergency and accident conditions and describe in an emergency plan the provisions to be employed to maintain preparedness.

§50.160(b)(1)(ii)

Performance objectives.

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nei.org 8 Section Text (A) By the beginning of each calendar quarter, develop and maintain a complete list of performance objectives for that calendar quarter; and (B) Maintain records showing the implemented performance objectives and associated metrics during each calendar quarter for the previous eight calendar quarters.

§50.160(b)(1)(iii) Emergency response performance. The emergency response team must have sufficient capability to demonstrate the following emergency response functions using drills or exercises:

(A) Event classification and mitigation. Assess, classify, monitor, and repair facility malfunctions in accordance with the emergency plan to return the facility to safe conditions.

(B) Protective actions. Implement and maintain protective actions for onsite personnel for emergency conditions and recommend protective actions to offsite authorities as conditions warrant.

(C) Communications. Establish and maintain effective communications with the emergency response organization and make notifications to response personnel and organizations who may have responsibilities for responding during emergencies.

(D) Command and control. Establish and maintain effective command and control for emergencies by using a supporting organizational structure with defined roles, responsibilities, and authorities for directing and performing emergency response functions as described in paragraph (b) of this section.

(E) Staffing and operations. Establish staffing for the facility necessary to implement the roles and responsibilities in paragraph (b)(1)(iii) of this section.

(F) Radiological assessment. Assess radiological conditions in and around the facility during emergencies, including:

(1) Radiological conditions. Assess, monitor, and report radiological conditions to the applicable response personnel using installed or portable equipment.

(2) Protective equipment. Issue and use protective equipment necessary to continue and expand mitigation and protective action strategies.

(3) Core or vessel damage. Assess, monitor, and report to the applicable response personnel the extent and magnitude of damage to the core or other vessel containing irradiated special nuclear material, such as fuel or targets, as applicable.

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nei.org 9 Section Text (4) Releases. Assess, monitor, and report to the applicable response personnel the extent and magnitude of all radiological releases, including releases of hazardous chemicals produced from licensed material.

(G) Reentry. Develop and implement reentry plans for accessing the facility after emergencies.

(H) Critique and corrective actions. Critique emergency response functions and implement corrective actions after drills and exercises, and after emergencies, if they occur.

§50.160(b)(1)(iv) Planning activities.

(A) Maintain the capability to:

(1) Prepare and issue public information during emergencies.

(2) Implement the NRC-approved emergency response plan in conjunction with the licensees Safeguards Contingency Plan.

(3) Establish voice and data communications with the NRC for emergencies.

(4) Establish an emergency facility or facilities from which effective direction can be given and effective control can be exercised during an emergency, with capabilities to support the emergency response functions as described in paragraph (b)(1)(iii) of this section.

(5) Provide site familiarization training for any offsite organization that may respond to the site in the event of an emergency.

(6) Establish methods for maintaining the emergency plan, contacts and arrangements, procedures, and evacuation time estimate up to date, including periodic reviews by the onsite and offsite organizations.

(B) For a plume exposure pathway EPZ that extends beyond the site boundary, the emergency plan must describe:

(1) The contacts and arrangements made and documented with Federal, State, local, and Tribal governmental agencies, as applicable, with responsibilities for coping with emergencies, including the identification of the principal coordinating agencies, and the coordinated reviews of changes in offsite and onsite planning and preparation; (2) Offsite organizations responsible for coping with emergencies and the means of notifying, in the event of an emergency, persons assigned to the emergency organizations, including the means of validating notifications, the time period by

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nei.org 10 Section Text which notifications must be completed, and primary and secondary methods to complete notification; (3) The protective measures to be taken within the EPZ to protect the health and safety of the public in the event of an emergency, including the procedures by which the protective measures are implemented, maintained, and discontinued; (4) An evacuation time estimate of the areas within the EPZ; (5) The offsite facility and any backup facilities to coordinate the onsite response with the offsite response; (6) The means of making offsite dose projections and the means of communicating the offsite dose projections to the offsite response coordinating agencies; (7) The means by which public information is provided to the members of the public concerning emergency planning information, public alert notification system, and any prompt actions that need to be taken by the public; (8) The general plans and methods to allow reentry into the EPZ during and after an emergency; and (9) The drill and exercise program that tests and implements major portions of planning, preparations, and the coordinated response by the onsite response organization with the offsite response organizations within the EPZ without mandatory public participation.

¢ - Only applicable if the PEP EPZ is outside the site boundary.

Table 2.3: 10 CFR 50.160(b)(2)-(4) Text Section Text

§50.160(b)(2) Hazard analysis. Conduct a hazard analysis of any contiguous or nearby facility, such as industrial, military, and transportation facilities, and include any credible hazard into the licensees emergency preparedness program that would adversely impact the implementation of emergency plans.

§50.160(b)(3) Emergency planning zone. For an applicant, whose analysis required by § 50.33(g)(2) meets the criteria in § 50.33(g)(2)(i), determine and describe the boundary and physical characteristics of the EPZ in the emergency plan.

§50.160(b)(4) Ingestion response planning. Describe or reference in the emergency plan the capabilities that provide actions to prevent contaminated food and water from entering into the ingestion pathway.

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nei.org 11 PROJECT GOALS AND SCOPE 3.1 Goals The primary objective of this project is to provide guidance for the development of a RIPB PEP EPZ and emergency plan that complements the RIPB safety case development described in NEI 18-04 and NEI 21-

07. Based on the evaluation performed in ref [6], a series of goals were established to guide the development of an approach that utilizes RIPB insights to inform the establishment of a site-specific EP program. The goals are presented in Figure 3.1 and discussed in the subsections below.

Figure 3.1: Goals of the Developed Approach for EP 3.1.1 Align with §50.160 Requirements With the recent issuance of the SMR & ONT EP final rule, a RIPB framework for EP is now available for SMRs, NLWRs, and NPUFs [7]. §50.160 provides an alternative performance-based EP framework, including an approach for determining the size of the PEP EPZ, thus avoiding exemptions that may have been necessary when using §50.47 and Appendix E. Therefore, the developed approach should align with the requirements contained in the rule, including the revised §50.33 and new §50.160.

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nei.org 12 3.1.2 Ensure Consistent Determination of Reasonable Assurance While the developed approach should align with the new EP framework under §50.160, historical considerations regarding the implementation of the requirements in §50.47 and Appendix E are informative for establishing reasonable assurance for the protection of public health and safety. This is not to imply that the requirements should be identical, but that similar considerations can guide the determination of the appropriate level of protection for emergency workers and the public, when considering the safety case of the facility and the totality of the available DID layers. Therefore, past regulatory positions regarding reasonable assurance for the protection of public health and safety can provide valuable insights for the developed approach. This includes the use of risk-informed, evidence-based information to develop appropriate EP strategies.

3.1.3 Allocate Resources in an Efficient and Effective Manner EP is fundamentally about planning to ensure that the appropriate resources are available to adequately respond during a radiological emergency. These resources include personnel, facilities and equipment, plus the communication pathways and organizational structure necessary to utilize them. Since the resources needed to support an EP program and an actual emergency response are finite, it is necessary to allocate these in the most efficient and effective manner while maintaining reasonable assurance of adequate protection. The developed approach should support this objective, a goal that aligns with the NRC Principles of Good Regulation. As highlighted in ref [6], compliance with NRC regulation provides reasonable, but not absolute, assurance that adequate protective measures can be taken in a radiological emergency.

3.1.4 Maintain Consistency with LMP Scope and Applicability The LMP developed a technology-inclusive approach for the selection of LBEs; classification and special treatments of structures, systems, and components (SSCs); and assessment of DID. The assessments included within the LMP approach address internal events along with internal and external hazards. The developed approach for EP should be consistent with the LMPs focus on plant-wide performance rather than on individual reactors or modules, and include pathways for the consideration of internal and external hazards and their impact on EP.

3.1.5 Leverage Insights from LBEs As detailed in the SMR & ONT EP rule, certain EP elements are informed by radiological consequence (dose) assessments, including accident likelihood and source term, timing of the accident sequence, and meteorology. Under the LMP approach, LBEs are identified using a RIPB process, which characterizes those attributes stated in the SMR & ONT EP rule. The LBEs represent a comprehensive spectrum of events for the facility, including internal events and internal and external hazards, and should be leveraged, to the extent practical, to inform EP elements, including the PEP EPZ, emergency action levels (EALs), monitoring resources, etc.

3.1.6 Detail PEP EPZ Determination Process The SMR & ONT EP rule provides criteria for determining a PEP EPZ in §50.33(g)(2)(i). The guidance for performing this determination is found in RG 1.242. While the regulatory criteria and RG provide high-level requirements and implementing guidance, stakeholders have identified the need for detailed instructions on the use of LMP-related information, such as the spectrum of LBEs, to support a PEP EPZ

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nei.org 13 determination. The developed approach should specify the recommended methods for utilizing LMP information to perform the analysis required by§50.33(g)(2) and the incorporation of the assessment and findings within the greater LMP RIPB safety case, discussed further in Section 3.1.7.

In addition, under §50.33(g)(2)(i) and §50.160, there are three possible outcomes from the PEP EPZ assessment and how it relates to the SB: no PEP EPZ, PEP EPZ at the SB, and PEP EPZ beyond the SB. The developed PEP EPZ determination process should be consistent with these possible outcomes.

3.1.7 Maintain Consistency with the LMP/TICAP Framework The LMP approach provides a comprehensive examination of plant safety, including consideration of all radionuclide sources found within a plant. For each source, Required Safety Functions (RSFs) are identified that are necessary to maintain the consequences of LBEs within acceptable limits. As outlined in Figure 3.2, the LMP approach uses a layers of defense framework that precludes or limits a potential radionuclide release for all modelled event sequences. It is important to note that the LMP layers of defense framework is organized in the framework of an LBE. The plant design and operational features that control plant disturbances in the prevention of an initiating event serve as Layer 1 of DID.

Layer 2 of DID is responsible for controlling the response to an initiating event and ensuring that the resulting event sequence family terminates as an Anticipated Operational Occurrence (AOO), which prevents its progression into a Design-Basis Event (DBE). Event sequence families more severe than AOOs are controlled by Layer 3 of DID to maintain plant conditions within the design basis. Event sequences more severe than DBEs are controlled by Layer 4 of DID through maintenance of RSFs and terminate as Beyond-Design-Basis Events (BDBEs). Significant radionuclide releases are only possible in situations where the RSFs are not preserved. The last DID layer, Layer 5, provides for mitigation of radiological consequences to the public by implementing emergency plan protective actions and limiting adverse public health and safety impacts.

The Technology-Inclusive Content of Applications Project (TICAP) provides detailed guidance on the structure of a safety analysis report (SAR) that uses the LMP approach [8]. Specifically, the TICAP structure describes the identified RSFs and associated Required Functional Design Criteria (RFDC),

Safety-Related Design Criteria (SRDC), and Complementary Design Criteria (CDC) to be assigned to a plants SSCs. The latter criteria are used to address the capability and reliability of each SSC classified as Non-Safety Related with Special Treatment (NSRST). These SSCs are classified as such when they meet SSC risk-significant criteria or determined to provide functions necessary for adequate defense-in-depth.

The SAR also outlines the layers of defense that achieve DID for the plant. The result is a holistic plant license application based on the LMP RIPB safety case, as shown in Figure 3.3.

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nei.org 14 Figure 3.2: LMP Layers of Defense Framework [1]

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nei.org 15 Figure 3.3: Relationship of TICAP to an Advanced Reactor Application[8]

EP is an integral part of the LMP layers of defense framework, with the identified set of LBEs and RSFs, RFDCs, SRDCs, and CDCs providing vital insights for developing central elements of an emergency plan.

The developed approach for EP should not only be consistent with the LMP layers of defense framework and DID evaluations but also integrate into the overall RIPB safety case developed by LMP and described by TICAP.

3.2 Scope As highlighted in Section 1.1, the project seeks to incorporate EP as an integral part of the RIPB safety case created through the LMP and TICAP approach. The following guidance describes how RIPB information can be used to inform the development of the PEP EPZ and emergency plan. Consistent with the LMP approach, the developed method is applied on a plant-wide basis,5 rather than for individual reactors, and assesses emergency planning and response needs for both core and non-core sources of radioactivity. As with LMP, the method includes consideration of events caused by internal events and internal and external hazards. Although not addressed within LMP, the method also examines the impact of security events to ensure a comprehensive EP strategy. Lastly, in alignment with LMP, the current guidance focuses on NLWRs; however, applicants using other technologies addressed by the SMR and ONT EP rule may find that they can adapt aspects of the developed approach for their licensing purposes.

To supplement the material found in RG 1.242, Sections 4 and 5 provide guidance for determining the PEP EPZ and the development of the emergency plan. Given the importance of the PEP EPZ determination process in establishing the bounds of emergency planning, the method for establishing 5 Consistent with LMP [1], the plant is defined as the collection of site, buildings, radionuclide sources, and SSCs seeking a single design certification or one or more operating licenses under the LMP framework. The plant may include a single reactor unit or multiple reactor modules as well as non-reactor radionuclide sources.

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nei.org 16 the PEP EPZ is reviewed first in Section 4. This is followed by Section 5, which contains guidance for developing the emergency plan, including the use of insights gained from the performance of the steps in Section 4. The subsections of Section 5 follow the format of the required emergency plan content listed in §50.160.

Concerning emergency plan development, Table 3.1 provides a cross-reference between the requirements contained in §50.160 and the additional guidance that is provided as part of this project.

The guidance in RG 1.242 is not repeated; instead, the sections below provide supplemental guidance on aspects of the emergency plan that can be informed by LMP-related information. Similarly, areas of regulation that are covered in other industry guidance documents, such as the Nuclear Energy Institute (NEI) framework for performance-based EP program metrics [9], are also not repeated here.

Table 3.1: 10 CFR 50.160 Sections and Areas of Additional Guidance

§50.160 Description Document Section Comment (a)

Definitions No Additional Guidance Provided:

Section covers definitions.

(b)(1)(i)

Maintenance of Performance Section 5.1 Supplemental Guidance Provided:

Additional guidance provided regarding changes to the emergency plan due to updates to the PRA, LBEs, or other aspects of the LMP analysis.

(b)(1)(ii)

Performance Objectives No Additional Guidance Provided:

Section focuses on the development of performance objectives for monitoring emergency plan effectiveness. NEI has developed supplemental guidance associated with this topic [9].

(b)(1)(iii) Emergency

Response

Section 5.3 Supplemental Guidance Provided:

Additional guidance provided regarding the derivation of initiating conditions and emergency action levels, along with the determination of necessary protective actions and radiological assessment capabilities.

(b)(1)(iv) Planning Activities Section 5.4 Supplemental Guidance Provided:

Additional guidance provided regarding part (B),

which details offsite emergency planning aspects, if the PEP EPZ extends beyond the SB.

(b)(2)

Hazard Analysis Section 5.5 Supplemental Guidance Provided:

Additional guidance provided regarding the assessment of nearby or co-located facility hazards and the potential impact on the implementation of emergency plans.

(b)(3)

PEP EPZ Section 4 and Section 5.6 Supplemental Guidance Provided:

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nei.org 17 Additional guidance provided regarding the PEP EPZ determination approach and associated information in the emergency plan.

(b)(4)

Ingestion Pathway Section 5.7 Supplemental Guidance Provided:

Additional guidance provided regarding ingestion pathway considerations for the identified spectrum of LBEs.

(c)

Implementation No Additional Guidance Provided:

Regulatory implementation details.

3.3 Integration within LMP As highlighted in Section 3.1.7, EP is part of the LMP layers of defense framework and the integrated RIPB safety case. Therefore, the interface between the plant design process and the EP evaluation differs from typical past practice. Historically, the plant design has been established (or the plant has already been built), and then the design is subsequently evaluated to determine the necessary elements of EP, such as protective measures. Within the LMP framework, there is the potential for iteration between the plant design and EP evaluation as part of an integrated assessment. For example, the findings of a preliminary EP evaluation for a conceptual plant design could be used to inform changes to the plant design that would prevent or mitigate accident scenarios determined to require protective measures.

The integrated nature of the LMP process and the potential for iteration between plant design and EP evaluation require certain considerations to ensure that feedback is captured appropriately, such as the following:

How the EP evaluation and determination of protective measures (if necessary) impact the consequence associated with LBEs and subsequent decision-making that is based on the LBEs How the EP evaluation and determination of protective measures (if necessary) impact the integral risk measures The first point highlights the connection between EP evaluations and the consequences of LBEs identified through the LMP process. For initial LBE consequence assessments as part of LMP, a vendor may conservatively assume that no protective measures were implemented. Other LMP assessments, such as the classification of SSCs, may utilize these results for preliminary decision-making. However, after the EP evaluation is performed, the consequences associated with LBEs may require updating to account for protective measures, if determined to be necessary. Therefore, decision-making based on the LBE results may also require revision.

The second point is also related to the consequence associated with LBEs but in relation to the plants integral risk metrics under the LMP approach, such as the quantitative health objectives (QHOs) [10].

Changes to the LBE consequences based on the implementation of protective measures (if determined to be necessary) will subsequently impact the integral risk metric results.6 This process also provides 6 EP focuses on dose savings, which as part of the risk triplet (what are the consequences?) subsequently reduces plant risk.

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nei.org 18 information regarding the risk impact of protective measures, which can be insightful for the evaluation of protective measures. This topic is further discussed in Section 4.4, including how the EP evaluation and determination process integrates with the LMP evaluation of DID adequacy performed as part of the integrated decision-making process (IDP) conducted by the interdisciplinary IDP panel.

PEP EPZ DETERMINATION Central to the development of an emergency plan is the determination of a PEP EPZ, as it establishes the bounds for required planning and informs other aspects of the emergency plan. This section details the developed method for determining the need for a PEP EPZ and its size, utilizing the criteria contained in

§50.33(g)(2)(i).

4.1 Method Overview Based on an analysis of applicable regulation and guidance, and previous EPZ sizing methodologies detailed in ref [6], a PEP EPZ determination process was developed that utilizes RIPB insights from the LMP approach, along with other considerations. An overview of the process is provided in Figure 4.1, with the noted subsections providing instructions for each step. The process begins with the identification of a spectrum of events for consideration, including LBEs from the LMP approach and potentially other events as well. Next, the events utilized for the PEP EPZ determination are evaluated and a series of dose assessments are performed. Based on the findings of this step, a protective measures evaluation is conducted, which informs the final PEP EPZ determination.

Figure 4.1: Overview of PEP EPZ Determination Process

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nei.org 19 4.2 Spectrum of Events As depicted in Figure 4.2, a spectrum of events is considered in the PEP EPZ determination process. The spectrum is primarily composed of those LBEs with a radionuclide release, as identified through the LMP approach; however, the process also includes an option for the use of alternative approaches for the selection of events related to hazards, along with the consideration of security-related events. Each of these elements is discussed in the following subsections.

Figure 4.2: Spectrum of Events for PEP EPZ Determination7 4.2.1 Identify LBEs with Radionuclide Release The PEP EPZ determination process utilizes site-specific RIPB information created as part of the LMP approach: therefore, the spectrum of events for consideration consists primarily of a previously identified set of LBEs. Specifically, the PEP EPZ determination assessment utilizes the LBEs from the AOO, DBE, and BDBE categories, which have been defined in terms of event sequence families from the PRA. In keeping with the implementation of the LMP approach, all event sequence families from the PRA with a frequency of 5E-7 per plant year or greater, when assessed at the 95th percentile, are included in the PEP EPZ determination process. Further discussion on the utilization of LBEs for establishing a spectrum of accidents to inform EP, including the PEP EPZ, is provided in Appendix A. Because the PEP EPZ assessment is focused on the protection of public health and safety during a radiological emergency, only those LBEs with a radionuclide release are included in the evaluation.

PRA Technical Adequacy and Acceptability It is important to note that the plant PRA must be technically adequate and acceptable for use in defining LBEs for the PEP EPZ determination assessment. As stated in RG 1.242 [11]:

the applicant should justify that the PRA is acceptable for this use, and that it considers internal and external hazards, all modes of operation, and all significant radionuclide sources. The PRA should also include event sequences involving single or 7 The dashed line indicates an optional pathway.

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nei.org 20 multiple modules/units, if applicable, to provide useful risk insights into the source-term selection process. The treatment of uncertainties in the PRA should quantify the impacts of uncertainties using quantitative uncertainty analyses supported by sensitivity analyses.

Since it is assumed that the applicant is utilizing the LMP approach, the acceptability of the PRA for risk-informed applications has likely already been demonstrated by satisfying the requirements of the ASME/ANS NLWR PRA standard [12], as endorsed by RG 1.247 [13]. This includes technical adequacy and PRA attributes such as the scope, level of detail, degree of realism, etc. However, it is understood that the PRA scope may differ depending on analysis selections made by the applicant, such as the treatment of hazards. Justification must be provided if the scope of the PRA utilized to select LBEs differs from that outlined above, and NRC acceptance may require additional review. Similarly, for aspects not contained within the scope of the PRA, supplemental analyses may be necessary to evaluate their impact on EP and the PEP EPZ.

Preliminary LBE Screening A preliminary LBE screening analysis may be performed to identify LBEs that do not need be considered further in the PEP EPZ determination. This screening can potentially reduce the number of LBEs requiring subsequent consequence/dose assessments and the associated effort and resources. It is important to note that screened-out LBEs are retained for consideration as part of emergency plan development, detailed in Section 5. A preliminary screening can be conducted based on several factors, including:

LBE Estimated Dose: Screening based on very low doses outside facility structures.

LBE Estimated Timing: Screening based on very long times to an appreciable radiological release and consideration of the time available for implementation of protective measures.

Use of Alternative Hazards Method: Screening of LBEs associated with a hazard that will be assessed utilizing an alternative method (described in Section 4.2.2).

Bounding or conservative dose estimates (e.g., from accident analyses performed for other parts of an application) can be used to screen out LBEs with radionuclide releases that are unlikely to influence a PEP EPZ determination.

An LBE may also be screened out based on the time available for the implementation of protective measures for the public. This screening considers both the timing of the accident sequence, as required by §50.33(g)(2)(i)(A), and the need for predetermined, prompt protective measures,8 as stated in §50.33(g)(2)(i)(B). If an offsite response organization (ORO)9 would have sufficient time to take actions to protect the public without the need for the actions to be predetermined (i.e., planned in advance so as to be taken promptly), then an LBE can be screened out from the remainder of the PEP EPZ determination process. These would typically be sequences that take many hours to progress to the 8 Predetermined prompt protective measures could include public alerting and notification, implementation of pre-planned sheltering or evacuation strategies, distribution of KI pills, etc.

9 As further discussed in Section 4.4.2, predetermined, prompt protective measures for public safety are taken by OROs. Within the SB, public safety is the responsibility of the licensee and is considered under §50.160(b)(1)(iii)(B).

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nei.org 21 point where a member of the public could be exposed to 1 rem TEDE over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months from the release of radioactive materials. Timing assessments should consider the following factors:

The time from the initiation of the event until emergency response personnel would recognize that a significant radiological release10 is likely to occur (based on the accident trajectory) or has occurred.

The elapsed time needed for emergency response personnel to notify an ORO of a potential or actual significant radiological release and the time required by the ORO to formulate protective measures for the public.

The elapsed time necessary for an ORO to implement protective measures for the public in the affected areas.

LBEs may be screened out if it can be demonstrated that there is sufficient time available, considering the above factors, for an ORO to implement ad hoc protective measures for the public in the areas projected to receive a dose exceeding 1 rem TEDE over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months from the release of radioactive materials. Information from the LBE event sequence progression and source term/consequence assessment can aid in informing this assessment. The protective actions taken by an ORO would typically be guided by a communitys comprehensive or all-hazards emergency plan, developed in accordance with State and/or FEMA guidance.

Different methods may be used to determine the elapsed time needed by an ORO to implement ad hoc protective measures for the public in an affected area. These may include reviews/studies of actual emergency responses and evacuations, use of analytical techniques such as evacuation time estimates, and interviews with ORO personnel. While the analysis discussed here focuses on a preliminary screening, a further detailed assessment of event timing will also be conducted as part of the protective measures evaluation discussed in Section 4.4.

At noted above, the event timeline(s) used to assess whether predetermined, prompt protective measures are needed should consider all key recognition and decision points stretching from accident initiation to implementation of protective actions for the public. For example, in the Low-Power EP Final Rule [13], the NRC stated that an ORO would have at least 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months from the initiating event to take adequate precautionary actions to protect the public near the site, thus obviating the need for predetermined, prompt protective measures [10]. The total amount of time sufficient for implementation of ad hoc protective measures is LBE-and site-specific, and includes considerations such as the location of the plant and the neighboring population. Key recognition and decision points include the time of accident initiation, the time needed to diagnose the event and attempt preventive or mitigative actions, and the time of recognition of the need for protective measures.

LBEs associated with hazards that will be assessed by an alternative method can also be screened out, as further detailed in Section 4.2.2.

4.2.2 Hazard Events Under the LMP approach, internal and external hazards are included within the PRA analysis and LBE identification. However, there may be situations where it is advantageous to utilize an alternative 10 A significant radiological release is one that results in a dose exceeding that defined in §50.33(g)(2)(i)(A).

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nei.org 22 approach for the selection of a hazard event to be evaluated as part of the PEP EPZ determination. Such approaches may be beneficial given the uncertainties associated with certain hazards or to align with the analysis methods selected by the vendor for hazard design considerations and the demonstration of satisfaction of other regulatory criteria. The use of alternative hazards approach may also allow an earlier evaluation of hazard impact on EP, before detailed probabilistic analyses have been performed.

Therefore, a pathway is provided in the developed method for the use of deterministic, margins-based, simplified risk assessment, or other approaches to select and assess one or more hazards. This is similar to the LMP approach where different methods for the derivation and assessment of design basis hazard levels (DBHLs) are available in the LMP approach [1, 2].

The utilization of an alternative approach for the assessment of an internal or external hazard event is dependent on NRC acceptance of the method. An example of an alternative approach is the NEI method for the selection of the seismic scenario to be considered in a PEP EPZ determination [14], which recommends using a response spectrum at twice the Ground Motion Response Spectra or spectra scaled to 1.0g peak ground acceleration, whichever is lower. Similar methodologies could be proposed for other external hazards or internal hazards. If an alternative approach is utilized for bounding a hazard, LBEs initiated by the hazard can be screened out from further consideration in the PEP EPZ process and replaced with the event determined by the alternative process.

If an alternative approach is utilized for the selection of hazard events, it is important to ensure that the scope of the evaluation is consistent with that of LMP and the assessment process described in this document. Specifically, the alternative hazard approach must be applied on a plant-wide basis, including consideration of non-core sources of radioactivity and potential effects in all operational modes.

4.2.3 Security Events

Background

As noted in 10 CFR 50.33 and 10 CFR 50, Appendix E, the basis for the 10-mile PEP EPZ applied to large LWRs licensed under Part 50 or Part 52 is NUREG-0396. The determination of the 10-mile distance was arrived at through the assessment of dose-distance curves derived from a spectrum of accidents; however, the spectrum of accidents reviewed in NUREG-0396 did not include security-initiated events.

Following the attacks of 9/11, the NRC undertook studies to determine if the consideration of hostile actions warranted any changes to the EPZ basis or size. These studies found that the consequences from a hostile action would be no more severe than those from the accidents considered in NUREG-0396 (e.g., see the discussion of this topic in NSIR/DPR-ISG-01, Interim Staff Guidance - Emergency Planning for Nuclear Power Plants). As a result, no regulatory changes affecting the 10-mile EPZ basis or size were made.

EP is comprehensive in that it addresses the potential consequences from a spectrum of accidents, including internal events, and internal and external hazards. Security-related events are not specifically cited as an EPZ sizing consideration within NUREG-0396 or the SMR & ONT EP rule; however, security events are considered in this guidance for completeness of the PEP EPZ. While the LMP approach does not evaluate security-related initiating events, the LBEs for a facility do provide a comprehensive assessment of potential accident sequences and associated consequences. For this reason, accidents resulting from security events may be eliminated from detailed consideration in a facilitys PEP EPZ technical basis.

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nei.org 23 Guidance An applicant should state that security events are removed from detailed consideration in the facilitys PEP EPZ technical basis. This decision should be supported by documenting:

the LBEs that were used to establish the basis for the EPZ size, and compliance with regulatory requirements to protect against applicable design-basis and beyond-design-basis threats.

A basis should also discuss the facilitys security-by-design features and available capabilities for mitigating beyond-design-basis events. The applicant should conclude that, based on the above information, the consequences from security-related events are adequately considered in the determination of the PEP EPZ.

Security considerations are further included in the development of the emergency plan, discussed in Section 5.

4.3 Event and Evaluation and Dose Assessment Once the spectrum of events is established utilizing the process in the preceding section, a radiological dose assessment is performed. The dose assessment process presented here is conducted for a range of distances, starting from the distance directly beyond the facility11 to areas beyond the SB. This is to allow analyses aligned with the three possible outcomes of the PEP EPZ determination process: no PEP EPZ, PEP EPZ at the SB, and PEP EPZ beyond the SB. However, the analysis can also be conducted at a predetermined distance, such as the SB, to align with an applicants licensing strategy. This approach is further discussed in Section 4.6.1 and Appendix D.

As outlined in Figure 4.3, the unscreened (screened-in) LBEs with radionuclide release undergo a probabilistic dose aggregation assessment to determine those LBEs that have sufficient potential dose and likelihood of occurrence to warrant consideration within the PEP EPZ determination process. As will be further detailed, this evaluation approach is based on NUREG-0396 and recent NRC studies regarding methodologies for EPZ sizing [16, 17]. A dose assessment is also performed for events selected using an alternative hazards approach. The following subsections provide further detail on these steps.

11 Utilizing a definition similar to that of the operations boundary in ANSI/ANS-15.16-2015 [15], which refers to the area within the SB such as the reactor building (or the nearest physical personnel barrier in cases where the reactor building is not a principal physical personnel barrier) where the reactor chief administrator has direct authority over all activities. The term reactor facility is not used, as the assessed radionuclide release may originate from a building not directly associated with the reactor, such as a fuel handling or rad waste building.

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nei.org 24 Figure 4.3: PEP EPZ Event Evaluation and Dose Assessment Process12 4.3.1 Perform Probabilistic Dose Aggregation A probabilistic dose aggregation is performed for those LBEs with radionuclide release that are retained as part of the preliminary screening analysis. The probabilistic dose aggregation supports compliance with both §50.33(g)(2)(i)(A) and (B), as it identifies distances at which the 1 rem TEDE dose will be exceeded and provides useful insights for determining whether predetermined, prompt protective measures are needed. The probabilistic dose aggregation assesses the potential consequences associated with the identified spectrum of LBEs and the likelihood of occurrence. In this process, the dose associated with each LBE that includes a radionuclide release13 is evaluated at different distances from the plant, resulting in dose-versus-distance curves. An example plot for three LBEs is presented in Figure 4.4. The dose-versus-distance curves are developed for specific dose values and represent the frequency of an individual receiving a given dose (or greater) at various distances for each LBE.

Depending on the goals of the PEP EPZ determination process and projected doses, distances may range from directly beyond the facility to distances beyond the SB.

12 The dashed lines indicate an optional pathway (alternative hazards assessment).

13 Not including LBEs that were removed as part of the preliminary screening process.

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nei.org 25 Figure 4.4: Example LBE-specific Dose-versus-Distance Curves Of specific importance for the PEP EPZ determination process are the dose-versus-distance curves for 1 rem and 200 rem. As will be further detailed in the following subsections, the 1 rem curve aligns with

§50.33(g)(2)(i)(A), which indicates exceedance of the EPA PAGs [18], while the 200 rem curve is an indicator of the potential for early health effects and aligns with the historic criteria from NUREG-0396.

The dose-versus-distance curves are created utilizing mean values of LBE frequency and consequence, with further consideration of uncertainty in later steps. In this context, the mean value refers to the uncertainty associated with LBE frequency and consequence, calculated for the maximum dose receptor. Additional detail regarding the consequence analysis method utilized to develop the curves is provided in Appendix B; however, the dose includes the 96-hour period after the release of radioactive material and does not credit protective measures.

Utilizing the individual LBE 1 rem and 200 rem dose-versus-distance curves, cumulative frequency curves for the plant are created by summing the frequencies of the individual LBE curves, as demonstrated by the example cumulative curves in Figure 4.5. Cumulative curves are useful in the developed PEP EPZ determination process as they provide a comprehensive assessment of the potential dose consequences for the spectrum of LBEs with an integrated perspective of the likelihood of occurrence. In essence, the cumulative curves provide a holistic view of the potential doses associated with the plant. The use of cumulative curves also largely alleviates any potential differences caused by the discretization of events within the plant PRA or LBE structure.

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nei.org 26 Figure 4.5: Example Cumulative Dose-versus-Distance Curve 4.3.2 LBE Dose Criteria Comparison For the LBE dose assessment, the cumulative 1 rem and 200 rem dose-versus-distance curves developed in the preceding step are compared to two frequency criteria outlined in Table 4.1 to aid in the determination of appropriate PEP EPZ.

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nei.org 27 Table 4.1: PEP EPZ Determination Cumulative Dose-versus-Distance Criteria Criteria Evaluation Reasoning A

Evaluation of the cumulative 1 rem curve at a frequency of 1E-5 per plant year

Compliance with the §50.33(g)(2)(i)(A) requirement to identify the area where public dose is projected to exceed 1 rem TEDE over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months from the release of radioactive material.

Compliance with §50.33(g)(2)(i)(B) that predetermined, prompt protective actions are not necessary beyond the PEP EPZ, as doses exceeding the EPA PAGs are not expected.

Maintain consistency with threshold for current large LWR EPZ basis (NUREG-0396).

B Evaluation of the cumulative 200 rem curve at a frequency of 1E-6 per plant year

Maintain consistency with early health effects threshold in the current large LWR EPZ basis (NUREG-0396).

Assurance that the need for predetermined protective measures will be assessed for rarer radiological release events with possible early health effects.

For criterion A, an assessment is performed of the 1 rem cumulative dose-versus-distance curve at a frequency of 1E-5 per plant year to derive an associated distance. The criterion aligns with

§50.33(g)(2)(i)(A), which specifies a TEDE value of 1 rem over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months . As the 1 rem criterion is derived from the EPA PAGs, this evaluation also demonstrates compliance with §50.33(g)(2)(i)(B) in that it signifies that protective measures are not expected to be needed beyond the derived distance. The selection of the frequency value for criterion A is described in Appendix C of this project and is partially based on the analysis performed for NUREG-0396. If the cumulative dose-versus-distance curve is below the frequency criteria, then no PEP EPZ distance is derived from the comparison.

Criterion B performs an evaluation of the 200-rem cumulative dose-versus-distance curve at a frequency of 1E-6 per plant year, or one in a million plant years. The criterion aligns with the approach utilized in NUREG-0396 and ensures an equivalent level of protection for radiological emergencies that may result in early health effects. Criterion B provides additional assurance regarding the need for protective actions when considering LBEs with lower frequencies but potentially larger consequences. As described in Appendix C, such analysis is consistent with the historical criteria regarding possible early health effects for severe low frequency events.

The frequency criteria are utilized as evaluation metrics to guide PEP EPZ determination rather than delineating specific quantitative thresholds of acceptability. The behavior of the cumulative dose-versus-distance curves near the frequency criteria can influence the determination of the derived distances. For example, an evaluation of the cumulative 1 rem dose-versus-distance curve in Figure 4.5 at a frequency of 1E-5 per plant year yields a derived distance between 500m and 750m. This topic is further discussed in the following subsection regarding uncertainty and cliff-edge analyses and in Section 4.6 regarding the application of the approach.

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nei.org 28 The frequency criteria comparison may result in two derived distances (one from the 1 rem curve and another from the 200-rem curve), a single distance (if one of the curves is below the frequency criteria),

or no derived distances (if both curves are below the frequency criteria). The following uncertainty and cliff-edge analysis also impacts whether and where a distance is derived. If multiple distances are derived, the limiting (i.e., largest) distance is utilized for subsequent assessments.

4.3.3 LBE Uncertainty and Cliff-Edge Analyses The evaluation of the frequency criteria in Table 4.1 includes an assessment of the impact of uncertainty and an evaluation of cliff-edge effects. As mentioned previously, the dose-versus-distance curves utilize mean values of frequency and consequence. The uncertainty assessment examines the impact of uncertainty in both frequency and consequence on the distances derived during the frequency criteria evaluation described in the preceding step. Specific quantitative criteria for the evaluation of uncertainties are not provided; instead, the general influence of uncertainties on the location and shape of the cumulative dose-versus-distance curves is assessed. Such a process could include an evaluation of the cumulative dose-versus-distance curves at the 95th percentile to gauge if there are significant changes to the derived distance or the evaluation of the location of a supplemental curve (such as 5 rem) in frequency space. The specific approach to the uncertainty evaluation is purposefully left to the applicant, as different uncertainties may be the dominant contributors and various methods may be used to evaluate their impact and justify the derived distance, such as the use of bounding values, sampling, etc. Insights can also be gained from the uncertainty evaluations previously completed by the applicant as part of LMP analyses. In general, the uncertainty evaluation should consider those factors discussed in NUREG-1855 [19], including parameter, modeling, and completeness uncertainty.

The cliff-edge evaluation is related to the uncertainty assessment but with a specific focus on significant changes to the derived distance due to small changes in the cumulative dose-versus-distance curve results. An example is provided in Figure 4.6, where the frequency criteria at 1E-5 per plant year would indicate a distance between 500m and 750m. However, a small increase in the frequency of the cumulative dose-versus-distance curve would result in a derived distance of over 2000m. The cliff-edge evaluation can likely be performed as part of the greater uncertainty assessment, but specific justification may be warranted for distances derived from cumulative dose-versus-distances curves that have flat regions near the frequency criteria.

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nei.org 29 Figure 4.6: Example of Potential Cliff-Edge Effect 4.3.4 Assessments of Events from Alternative Hazards Methods In addition to the LBE analysis, a dose-versus-distance assessment should be performed if an alternative method was utilized for the selection of a hazard event. For this assessment, only the 96-hour dose-versus-distance curve is determined for the event(s), as there is no associated frequency, by following the consequence method outlined in Appendix B. The curve is then compared to a value of 1 rem to determine an associated distance for potential protective measures, in accordance with

§50.33(g)(2)(i)(A). Figure 4.7 provides an example dose-versus-distance curve and comparison to 1 rem.

The analysis should include an evaluation of dose uncertainty, similar to that described in Section 4.3.3 for LBEs, but with a focus on the consequence analysis. Depending on the number of hazards addressed through alternative methods, there may be multiple distances derived from this analysis, given multiple dose-versus-distance curves. If the dose-versus-distance curve(s) does not exceed 1 rem at any distance, with the proper consideration of uncertainty, then no distance is derived from the analysis; however, the events selected utilizing an alternative hazards approach are retained for further consideration as part of the development of the emergency plan, discussed in Section 5.

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nei.org 30 Figure 4.7: Example Dose-versus-Distance Curve for Potential Additional Events 4.3.5 Event Evaluation and Dose Assessment Results There are several results from the event evaluation and dose assessment. First, the analysis of LBEs may return one or more distances depending on the results of the 1 rem and 200 rem cumulative dose-versus-distance curves. It is also possible that no distance was derived from these analyses if both curves were sufficiently below the frequency thresholds. This could be a result of small, estimated doses or the low frequency of LBEs. Second, for a hazard assessed using an alternative method, one or more additional distances may be derived based on the 1 rem location on the dose-versus-distance curve(s). It is also possible that no distance is derived from this analysis if the curve(s) is below 1 rem.

Figure 4.8 depicts the possible outcomes of the event evaluation and dose assessment and next steps. If a distance was derived from the LBE analysis, or an alternative hazard assessment, then a protective measures evaluation is performed, as discussed in the following subsection. If no distance was derived from any of the conducted analyses, then the conclusion is that no PEP EPZ is required because the criteria in §50.33(g)(2)(i)(A) was not met beyond the boundary of facility structures.

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nei.org 31 Figure 4.8: Results of PEP EPZ Event Evaluation and Dose Assessment14 4.4 Protective Measure Evaluation If a distance was derived from the preceding event evaluation and dose assessment, then a protective measures evaluation is performed. Since both criteria in §50.33(g)(2)(i) must be met for areas included within a PEP EPZ,15 the evaluation must also demonstrate a need for predetermined, prompt protective measures. The results of the protective measures evaluation are considered by the LMP IDP to establish if predetermined, prompt protective measures are warranted as part of the assessment of plant DID adequacy.

As noted in Section 4.2.1, within the context of EP activities, the term predetermined, prompt protective measures means actions taken by an ORO to protect the public in offsite locations.

Protective measures for onsite members of the public and plant workers are taken by the licensee using actions developed under the requirements of §50.160(b)(1)(iii)(B). Therefore, the protective measures evaluation differs depending on whether the derived distance is beyond the SB, as described in the following subsections.

4.4.1 Derived Distance Beyond the Site Boundary If the derived distance is beyond the SB, the protective measures evaluation of the PEP EPZ determination process further explores the need for predetermined, prompt protective measures based on the attributes of the site, such as population distribution, and the specific LBEs and potential 14 Figure assumes that the dose assessment included distances directly beyond the facility.

15 As denoted by an and at the end of §50.33(g)(2)(i)(A).

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nei.org 32 additional events16 under consideration. The protective measures evaluation examines those LBEs that were the dominant contributors to the dose versus distance curve. This may be a single LBE or a set of LBEs, and the example in Section 4.7 provides a demonstration of the process. The protective measures evaluation focuses on the effectiveness of protective actions and the potential dose savings, which can be influenced by characteristics of the LBEs and site.

LBE Characteristics The characteristics of the LBEs, including timing, initiating event, and radionuclide release can impact the need for protective measures. Although event timing was used as an initial screening criterion for LBEs in an earlier step, an additional and more detailed assessment of timing should be conducted to evaluate the need for predetermined, prompt protective measures. In general, this would entail choosing one or more of the methods discussed under the Preliminary LBE Screening step of Section 4.2.1 and performing a more detailed analysis. For example, an evacuation time estimate might be performed if one was not done to support the preliminary screening step. Detailed studies to evaluate the capabilities and readiness of OROs near the site to take ad hoc protective actions could be performed. Other assessment actions not contemplated at the initial screening step could also be pursued such as convening a panel of EP experts to obtain their assessment and recommendations.

The LBE initiating event can affect the protective measures that can be implemented. For example, if the event is caused by a severe external hazard, such as a large seismic event or severe hurricane, there may be limited options regarding protective measures. It is noted in the EPA PAGs that projected doses up to five times the EPA PAGs may be justified in place of evacuation under hazardous environmental conditions [18].

Following the convention and definition of PRA terms in the NLWR PRA standard, initiating events are defined at the point of plant disturbance and any initiating event can be caused by an internal event, or induced by an internal or external hazard. For example, a breach of the reactor cooling boundary may be defined as an initiating event in the internal events part of the PRA. If this event is caused by a seismic event, it is referred to as a seismically induced breach of the reactor coolant boundary. An internal or external hazard event may or may not cause an initiating event.

Lastly, the characteristics of the radionuclide release, such as isotopes, physical form, release energy, etc. should be used to evaluate potential protective measures and their effectiveness. This includes the dispersion characteristics, including spatial dependences, discussed further under site characteristics.

Site Characteristics Population distribution should be considered in the protective measures evaluation. There may be cases where an area outside the SB is projected to receive a dose greater than 1 rem but the area is not populated, which could be the case for remotely sited plants. A site could have offsite areas receiving greater than 1 rem but the affected population is under the control of the facility licensees organization (e.g., an SMR on a military base) and therefore subject to protective actions directed by the licensee.

The possibility of non-uniform PEP EPZ distances, which is further discussed in Section 4.6.2, may also influence this evaluation, 16 Where other events would be those selected by an alternative hazards approach.

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nei.org 33 The dose assessment may also be refined with additional site-specific information to provide further insight regarding the need for protective measures. For example, a directional dose assessment can provide spatially-dependent results based on the characteristics of the release and meteorology of the site, as shown by the example in Figure 4.9. Such analysis can enhance the information regarding predicted individual doses and the impact on population centers, although they are dependent on the pedigree of supporting data. The results can also support the development of non-uniform PEP EPZ distances, discussed in Section 4.6.2. If protective measures are deemed warranted, the analyses can aid in the optimization of the actions and inform procedures in the emergency plan. Similarly, detailed uncertainty or sensitivity analyses can also be performed to provide additional clarity regarding potential doses.

Figure 4.9: Example Spatial Dose Assessment [20]

Effectiveness of Protective Measures and Potential Dose Savings Central to the evaluation is the assessment of the effectiveness of potential predetermined protective measures for achieving dose savings. The consequences of the LBEs or other events can be evaluated with and without differing protective measure strategies to gauge the impact on dose results and provide insight regarding whether predetermined protective measures are warranted. Similarly, the effectiveness of ad hoc, rather than predetermined, protective measures can also be evaluated, as it may be determined that such actions provide sufficient dose savings. As noted in the EPA PAGs, the capability to conduct ad hoc protective measures may depend upon the ability of the facility to provide prompt dose projections [18].

Past EPZ analyses have utilized integral assessments of plant risk as a gauge of the effectiveness and benefit of predetermined protective measures. As highlighted in Section 3.3, through the reduction in consequence, protective measures also reduce plant risk. For example, studies conducted for the Seabrook Nuclear Power Plant evaluated the difference in plant risk (and comparison to the QHOs) to demonstrate that the minimal dose savings provided by predetermined protective measures did not offer significant risk reduction to the public and were of questionable benefit [21].

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nei.org 34 The factors discussed above are considered as part of the LMP IDP to determine if predetermined, prompt protective measures are warranted. This is a necessary evaluation as part of the determination of the adequacy of plant DID, within the layers of defense framework shown in Figure 3.2. The criteria within §50.33(g)(2)(i) and guidance provided here aid in the determination process. As noted in RG 1.242, the IDP should consider the DID philosophy, the maintenance of sufficient margins, and treatment of uncertainties [11].

4.4.2 Derived Distance at or within the Site Boundary For cases where the distance derived from the Section 4.3 analysis is at or within the SB, the protective measures evaluation should align with the protective action requirements under §50.160(b)(1)(iii)(B).17 Protection of members of the public within the SB, such as personnel of co-located industrial/commercial facilities and visitors, is the responsibility of the licensee. The licensees protective actions are described in the emergency plan and may include assembly and sheltering in an assembly area, evacuation from the site, and radiological monitoring and decontamination. As with the protective measures evaluation discussed in the preceding subsection, the characteristics of the LBEs that result in doses exceeding the EPA PAGs within the SB can inform the appropriate protective actions. Further discussion regarding protective actions under §50.160(b)(1)(iii)(B) is provided in Section 5.3.2.

4.5 PEP EPZ Determination Based on the event evaluation, dose assessment, and protective measures evaluation, there are three potential outcomes of the PEP EPZ determination process. These align with the requirements in

§50.33(g)(2)(i) and §50.160 and are shown in Figure 4.10.

17 §50.33(g)(2)(i)(B) relates to predetermined, prompt protective measures for the public, which are the responsibility of OROs and not necessary when estimated doses do not exceed the EPA PAGs beyond the SB. §50.160(b)(1)(iii)(B) applies to personnel within the SB, including workers and nonessential individuals and members of the public as stated in RG 1.242 [11]. Similarly, as noted in the statements of consideration for the SMR & ONT EP final rule, under §50.160(b)(2) a licensee must assess facility hazards and provide for protective actions for the other facilitys personnel or other on-site individuals, such as visitors.

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nei.org 35 Figure 4.10: PEP EPZ Determination Process Outcome Flowchart 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 SB: This outcome is realized if doses greater than the established criteria are projected to occur at a maximum distance that does not exceed the SB. This outcome also applies to instances where doses greater than the established criteria are projected to occur at a maximum distance beyond the SB; 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 §50.160(b)(1)(iii)(B).

PEP EPZ beyond SB: This outcome is realized if doses greater than the established criteria are projected to occur at a maximum distance beyond the SB, and a determination was made that predetermined, prompt protective measures are necessary. In this case, the PEP EPZ is set at the derived distance,18 the licensee is responsible for the implementation of onsite protective 18 As noted in §50.33(g)(2)(ii)(B), The exact configuration of the plume exposure pathway EPZ surrounding the facility shall be determined in relation to the local emergency response needs and capabilities as they are affected by such conditions as demography, topography, land characteristics, access routes, and jurisdictional boundaries.

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nei.org 36 measures under the requirements in §50.160(b)(1)(iii)(B), and the site would have offsite radiological emergency plans under the requirements in §50.160(b)(1)(iv)(B).

The results of the PEP EPZ determination process establish the applicable requirements under §50.160, as outlined in Table 4-2. First, if the PEP EPZ is beyond the SB, the applicant must provide additional information to satisfy §50.160(b)(1)(iv)(B) regarding offsite organizations and §50.160(b)(3) describing the PEP EPZ. If the PEP EPZ is at the SB, then only §50.160(b)(3) must be satisfied. If no PEP EPZ is established, then, the applicant must only satisfy the requirements of § 50.160(a), (b)(1)(i)-(iv)(A), (b)(2),

(b)(4) and (C).

Table 4.2: Potential PEP EPZ Determination Process Outcomes and Requirements Outcome Justification Additional Emergency Plan Requirements1 PEP EPZ > SB The event evaluation and dose assessment results in a derived distance outside the SB.

AND there is a need for predetermined, prompt protective measures outside the SB.

50.160(b)(1)(iv)(B)

50.160(b)(3)

PEP EPZ = SB The event evaluation and dose assessment results in a derived distance outside the SB.

AND there is no need for predetermined, prompt protective measures outside the SB.

50.160(b)(3)

The event evaluation and dose assessment results in a derived distance within the SB.

No PEP EPZ The event evaluation and dose assessment results derive no distance.

1 In addition to the emergency plan requirements provided in 50.160(a), (b)(1)(i) - (iv)(A), (b)(2), (b)(4), and (c).

4.6 Implementation Considerations 4.6.1 Pre-Selected PEP EPZ Distance Evaluation The practical application of the PEP EPZ determination process described in Section 4.1 may differ depending on the motivation of the applicant. If the applicant is seeking to establish the adequacy of the SB or other pre-selected distance as the PEP EPZ, the associated calculations may focus on demonstrating the satisfaction of the regulatory criteria only at that distance, rather than developing complete dose-versus-distance curves. This could simplify the analysis and reduce the amount of effort needed to perform the assessments. However, such an approach must still demonstrate that uncertainties or cliff-edge effects do not impact the conclusions of the analysis. For example, this may require analyses proving that there is not a significant increase in the likelihood of the assessed doses (1 and 200 rem) at distances just within the selected PEP EPZ or a demonstration of sufficient margin to the criteria. Similarly, if an applicant is seeking to have no PEP EPZ, then the analyses would focus on demonstrating that doses do not exceed the dose criteria outside of the facility structures. The example in Section 4.7 is repeated in Appendix D utilizing a pre-selected PEP EPZ distance to demonstrate such an approach.

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nei.org 37 4.6.2 Non-Uniform PEP EPZs As highlighted in Section 4.4, there may be cases where applicants pursue non-uniform PEP EPZs with varying distances in different directions from the plant, or the PEP EPZ determination process may dictate such results. There are multiple reasons why an applicant may pursue non-uniform PEP EPZ sizes, as detailed in Table 4.3. Based on these factors, the PEP EPZ consequence assessment described in Appendix B would require sufficient detail to discern directional dose impact. This information could be coupled with other site characteristics, such as population distribution, geography, and meteorology, to demonstrate the appropriate PEP EPZ.

Table 4.3: Potential Reasons for Non-Uniform PEP EPZs Reason Description SB layout Sites that utilize the SB as the PEP EPZ may have non-uniform sizes. This could be the result of the plant layout, constraints from neighboring facilities, or local geography.

Population Distribution Variations in the population distribution near the plant may result in non-uniform PEP EPZs, as predetermined actions may not be necessary in areas with no predicted population.1 Co-located Facilities The co-location of other industrial facilities may require specific consideration in the sizing of the PEP EPZ in certain directions.

Meteorological Phenomena Plants may seek to account for specific meteorological phenomena that reduce the dose from radioactive material in certain directions.2 1 Waterways and large bodies of water (lakes, seas, and oceans) are not intrinsically areas of no predicted population.

2 Sufficient data would be needed to account for such phenomena.

In addition, the EPA PAGs note that other factors may impact the precise shape of the EPZ, including political boundaries, facilities with different dose mitigation capabilities (hospitals, prisons, etc.), and features readily identifiable to people within the areas. The PEP EPZ may be further subdivided, using readily identifiable features, to aid in the implementation of protective measures for only certain areas of the EPZ [18].

4.7 Example Analysis An example analysis is provided to demonstrate the application of the PEP EPZ determination process.

The example does not represent a specific NLWR design but is based on public information regarding NLWR PRAs and the experience of the authors. For the assessment, the SB is assumed to be at a uniform distance of 500m from the facility, with a co-located industrial facility within the SB.

4.7.1 Spectrum of Events To prepare for the PEP EPZ determination process, a set of LBEs was identified using the LMP approach, which is listed in Table 4.4. Certain LBEs with a mean frequency below 5E-7 per plant year were

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nei.org 38 included, given that the 95th percentile of frequency would exceed 5E-7 per plant year. Figure 4.11 shows the LBEs plotted on the LMP frequency versus consequence curve.

Table 4.4: Example Analysis - LBEs LBE Mean Frequency

(/plant year)

Mean Dose1 (rem)

LBE Mean Frequency

(/plant year)

Mean Dose1 (rem)

LBE-1 8.10E+00 0

LBE-20 3.00E-04 5.51E-02 LBE-2 7.70E+00 0

LBE-21 2.00E-04 5.43E-05 LBE-3 2.00E+00 0

LBE-22 2.00E-04 2.18E-02 LBE-4 1.50E-01 2.35E-05 LBE-23 8.00E-05 5.68E-03 LBE-5 1.00E-01 0

LBE-24 5.00E-05 5.26E-02 LBE-6 8.00E-02 0

LBE-25 4.00E-05 5.43E-05 LBE-7 8.00E-02 0

LBE-26 3.00E-05 0

LBE-8 4.00E-02 2.35E-05 LBE-27 3.00E-05 0

LBE-9 3.00E-02 2.35E-05 LBE-28 3.00E-05 0

LBE-10 2.00E-02 2.67E-04 LBE-29 2.00E-05 7.81E-02 LBE-11 8.00E-03 2.35E-05 LBE-30 2.00E-05 2.67E-04 LBE-12 5.00E-03 1.05E-03 LBE-31 1.00E-05 2.58E-02 LBE-13 4.00E-03 2.67E-04 LBE-32 2.00E-05 2.50E+00 LBE-14 3.00E-03 5.43E-05 LBE-33 1.00E-06 0

LBE-15 1.00E-03 5.68E-03 LBE-34 1.00E-06 0

LBE-16 1.00E-03 1.05E-03 LBE-35 5.00E-07 2.50E+01 LBE-17 9.00E-04 0

LBE-36 3.00E-07 2.35E-05 LBE-18 8.00E-04 5.43E-05 LBE-37 3.00E-07 1.00E+00 LBE-19 4.00E-04 2.67E-04 LBE-38 2.00E-07 1.50E+02 1 30-day TEDE at EAB (assumed to be consistent with the SB for the example).

Figure 4.11: Example Analysis - LBEs on Frequency versus Consequence Plot19 19 Presented results utilizing mean frequency and consequence.

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nei.org 39 To start the PEP EPZ determination process, the LBEs without radionuclide release are screened. Of the set of 38 LBEs, 12 LBEs are screened as they are not associated with a radionuclide release, leaving 26 LBEs for further analysis. Given the simplified nature of the analysis, no additional screening was performed based on dose magnitude or timing using the approach discussed in Section 4.2.1. Similarly, an alternative method for assessing LBEs from hazard initiators was not utilized.

4.7.2 Event Evaluation and Dose Assessment Next, the probabilistic dose aggregation process was performed. For the example analysis, assumptions were made regarding the degree of uncertainty in both LBE frequency and consequence to develop associated dose-versus-distance curves for each LBE, which are provided in Figure 4.12 for 1 rem and Figure 4.13 for 200 rem. As noted in Section 4.3.1, this assessment utilizes the mean values for frequency and consequence when considering a 96-hour TEDE evaluation and the modeling assumptions in Appendix B. It is important to note that not all LBEs with radionuclide release have resulting 1 rem and 200 rem curves. This is due to the very low likelihood of certain LBEs resulting in a release of that magnitude. For example, LBE-14 has a mean frequency of 3E-3 per plant year and a mean consequence of 5.4E-5 rem at the SB (500m). The consequence of the LBE does not approach 1 rem at the minimum distance considered,20 even when accounting for uncertainty in the source term and offsite dispersion analyses. In total, seven LBEs have corresponding 1 rem curves, and two LBEs have 200 rem curves.

Figure 4.12: Example Analysis - LBE 1 Rem Dose-versus-Distance Curves 20 A minimum distance of 100m from the facility was utilized for the example analysis.

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nei.org 40 Figure 4.13: Example Analysis - LBE 200 Rem Dose-versus-Distance Curves In the following step, the individual LBE dose-versus-distance curves are aggregated to form cumulative curves, presented in Figure 4.14. The aggregation process sums the LBE frequencies to develop the cumulative curves. The 1 rem cumulative curve is then compared to the 1E-5 per plant frequency metric in criterion A. This assessment results in a distance between 750 to 1000m. Next, the 200 rem curve is compared to the 1E-6 per plant year frequency metric outlined in criterion B. For this assessment, the 200 rem curve is completely below 1E-6 per plant year, and therefore, a distance is not derived from the assessment.

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nei.org 41 Figure 4.14: Example Analysis - Cumulative Dose-versus-Distance Curves The analysis then moves to the uncertainty and cliff-edge effect assessments. A simplified uncertainty assessment was performed, given the nature of the example. 95th percentile dose-versus-distance curves were developed, as provided in Figure 4.15. For the 1 rem curve, uncertainty in the analysis indicates that such doses may be possible up to distances of approximately 1250m. The 200 rem curve remains below the 1E-6 per plant year frequency criteria even with the consideration of uncertainty.

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nei.org 42 Figure 4.15: Example Analysis - Cumulative 95th Percentile Dose-versus-Distance Curves For the cliff-edge assessment, only a qualitative evaluation of the shape of the cumulative dose-versus-distance curves was performed. Neither curve demonstrates behavior regarding a potential cliff-edge near the frequency evaluation criteria (i.e., a flat slope). Therefore, based on the findings of the uncertainty and cliff-edge assessments, the derived distance from the 1 rem curve is between 750 to 1250m.

4.7.3 Protective Measures Evaluation Given that the event evaluation and dose assessment found a distance exceeding the EPA PAGs beyond the SB, a protective measures evaluation is performed. The evaluation begins with an assessment of the need for predetermined, prompt protective measures beyond the SB. To inform the analysis, the LBEs that are the dominant contributor to the 1 rem curve are identified, as shown in Figure 4.16. In total, there are four LBEs that contribute to the cumulative 1 rem curve exceeding 1E-5 per plant year frequency; however, only a single LBE contributes to the 1 rem curve beyond the SB. A simplified protective measures evaluation was performed for LBE-32, as detailed in Table 4.5. LBE-32 represents a prolonged loss of heat removal scenario, which results in core damage after several days. Mitigating radionuclide retention barriers are successful, which results in doses slightly above the EPA PAGs beyond the SB. Given the time available for OROs to take ad hoc protective measures,21 it is determined that predetermined, prompt protective measures are not warranted.

21 An actual analysis would also evaluate the capabilities of OROs to implement protective actions. In addition, the evaluation would examine the characteristics of the site and location of the public to determine if predetermined protective measures are necessary. This evaluation would then be reviewed by the IDP as part of the assessment of plant DID adequacy.

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nei.org 43 Figure 4.16: Example Analysis - LBE Breakdown LBE Event Description Protective Measures Evaluation LBE-32 Core damage event due to extended (multi-day) loss of heat removal with successful radionuclide retention barriers mitigating total radionuclide release.

Significant time available for event recognition and protective measure execution by OROs before radionuclide release occurs.

Table 4.5: Example Analysis - Protective Measures Evaluation - Beyond the SB The protective measures evaluation then focuses on those LBEs that result in doses exceeding the EPA PAGs for onsite personnel, in alignment with §50.160(b)(1)(iii)(B). The protective measures evaluation centers on the dominant four LBEs, outlined in Table 4.6. This includes LBE-32, along with three LBEs with smaller predicted doses. As demonstrated in Figure 4.16, at close distances, the 1 rem curve is largely dominated by two LBEs, with minor contributions from two LBEs with lower frequency. As detailed in Table 4.6, LBE-20 is an extended release of radioactive gases from a breach in a purification system. Therefore, evacuation of onsite personnel from the site would be warranted for dose savings. In contrast, LBE-24 and LBE-29 are immediate but short-duration releases of radioactive gas, meaning evacuation would likely be ineffective. A shelter-in-place order for onsite personnel is likely the optimal action for dose savings. As previously described, LBE-32 relates to a core damage accident; however, the minor radionuclide release does not occur for several days, which provides adequate time for the development and implementation of protective measures by the onsite emergency response personnel.

Based on the evaluation, protective measures of evacuation and shelter-in-place for onsite personnel within the SB are determined to be warranted to address different accident conditions. The resultant protective actions are to be developed, described in the emergency plan, and evaluated (further discussion in Section 5).

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nei.org 44 Table 4.6: Example Analysis - Protective Measure Evaluations - Within the SB LBE Event Description Protective Measures Evaluation LBE-20 Extended release of radioactive gases due to breach in reactor coolant purification system.

Given extended nature of the release, evacuation of onsite personnel1 from the site is recommended for dose savings.

LBE-32 Release from the fuel due to extended (multi-day) loss of heat removal with successful radionuclide retention barriers mitigating total radionuclide release.

Significant time available for event recognition and protective measure execution by plant emergency response personnel before radionuclide release occurs.

LBE-24 Puff release of radioactive gases through stack due to failure of purification system scrubber.

As the radionuclide release is an immediate, single puff release, a shelter-in-place order for onsite personnel is recommended for dose savings.

LBE-29 Minor release of radioactive gases from breached spent fuel due to fuel handling accident.

Possible protective measures similar to LBE-

24.

1Onsite personnel includes nonessential workers and members of the public.

4.7.4 Results The results of the example PEP EPZ determination process are summarized in Table 4.7. First, a spectrum of events was established using the LBEs identified through the LMP approach. An alternative hazard event selection was not utilized. Next, the event evaluation and dose assessment were performed utilizing the set of LBEs. The comparison to criterion A (1 rem curve) found that doses exceeding 1 rem over 96 hours0.00111 days 0.0267 hours 1.587302e-4 weeks 3.6528e-5 months were possible at a distance of 750m to 1000m from the facility. No distance was derived from criterion B (200 rem curve), as releases of that magnitude were at a very low frequency of occurrence. The uncertainty and cliff-edge assessments determined that the 1 rem curve may extend slightly beyond 1000m based on the consideration of uncertainties. A protective measures evaluation was performed for the four LBEs that are the primary contributors to the 1 rem curve. The evaluation centered first on predetermined, prompt protective measures beyond the SB, which were found unnecessary. The evaluation found that protective measures were warranted within the SB.

Based on these findings, the PEP EPZ is established at the SB (500m).

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nei.org 45 Table 4.7: Example Analysis - PEP EPZ Determination Results Analysis Step Assessment Spectrum of Events LBEs identified through LMP approach, no alternative hazard event selection considerations.

Event Evaluation and Dose assessment The LBE assessment resulted in the following findings:

Criterion A: 1 rem curve - Distance of 750m to 1000m Criterion B: 200 rem curve - No distance derived Uncertainty/Cliff-Edge Assessment: 1 rem curve may extend to 1250m due to uncertainty Protective Measures Evaluation Beyond the SB:

One LBE contributed to doses exceeding the EPA PAGs beyond the SB; however, there is adequate time for OROs to implement protective measures.

Predetermined, prompt protective measures are not warranted.

Within the SB:

Four LBEs contribute to the 1 rem curve within the SB.

Protective measures were developed for onsite personnel, given the nature of the releases.

PEP EPZ Determination The analysis determined that doses exceeding the EPA PAGs were possible beyond the SB but predetermined, prompt protective measures are not warranted. Within the SB, protective measures are warranted. Therefore, the PEP EPZ is established at the SB (500m).

EMERGENCY PLAN DEVELOPMENT This section provides guidance regarding the development of an emergency plan, including the utilization of insights from the LMP approach, such as the identified layers of defense and the spectrum of LBEs. The subsections below follow the presentation order of the required emergency plan contents listed in §50.160 (see Table 2.2 and Table 2.3). The information in this section should be used in conjunction with the NRC guidance found in RG 1.242.

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nei.org 46 5.1 Maintenance of Performance - §50.160(b)(1)(i)

§50.160(b)(1)(i) centers on maintaining effective preparedness for emergencies. As described in RG 1.242, this includes two general aspects. Firstly, the emergency plan should include a general description of the facility; any site-specific definitions; and any relevant appendices, drawings, diagrams, and other information needed to demonstrate compliance with §50.160(b)(1)(i). This aspect is relatively self-explanatory, so further guidance is not provided here. Secondly, there must be a description of the process for maintaining and making changes to the emergency plan to account for facility changes, including the change process required by §50.54(q). Given potential changes in the risk profile of the plant, this aspect is relevant to the current effort.

The PEP EPZ determination process described in Section 4 and the guidance for the development of an emergency plan found in this section utilize information and insights from the set of LBEs derived from the LMP approach. Because of this, there is the potential that subsequent changes to the PRA (e.g., to event sequences or event sequence families) could impact the PEP EPZ determination results and/or emergency plan contents. Changes in the plant PRA may occur due to operating experience with plant systems and equipment, modifications to the facility design or operation, updated external hazard information, or revisions to modeling techniques. In general, the PEP EPZ and emergency plan elements should be derived such that they are robust against small changes in the PRA and LBEs.

Since there is the possibility of substantive changes to the PRA and LBEs over the lifetime of a facility, changes to the plant PRA must be tracked to evaluate their impact on the PEP EPZ determination and emergency plan. This requirement is not unique to EP, as changes to the PRA must also be tracked and assessed for impacts on other risk-informed applications. The Technology-Inclusive Risk-Informed Change Evaluation (TIRICE) project is currently developing guidance regarding how such changes could result in license modifications under §50.59 [22], with the upcoming Technology Inclusive Management of Safety Case (TIMaSC) project providing additional guidance on maintenance of the safety case during plant operation. Although changes to the emergency plan are outside the scope of TIRICE, a plant utilizing the LMP process must employ an approach for tracking changes to the plant risk profile and the possible impact on all risk-informed aspects of the plant license. The guidance developed under TIRICE, and future guidance under TIMaSC, could be utilized to inform an approach for assessing the potential impact of PRA changes on a site PEP EPZ and emergency plan.

§50.54(q)(3) and (4) provide requirements for the evaluation and approval of changes to emergency plans. Any change considered to be a reduction in effectiveness (RIE) of the emergency plan requires NRC approval prior to implementation. This includes plant configuration changes that would create a RIE without a commensurate change in the emergency plan.22 Guidance on the evaluation of changes to identify a RIE is provided in RG 1.219 [23]. This guidance does not allow the use of risk insights from the plant PRA for the determination of RIE; however, it can inform the evaluation of changes affecting a PEP EPZ or a site emergency plan developed using the RIPB approach in this document.

If a PRA change were to occur that resulted in LBE modifications that impacted the PEP EPZ determination, then the PEP EPZ assessment for the site would be revised and the appropriate change process followed to update PEP EPZ and emergency plan. However, the likelihood of an LBE requiring the implementation of the emergency plan has no relevance in determining whether a particular change reduces the effectiveness of the emergency plan, independent of changes to the PEP EPZ determination.

22NRC Information Notice IN 2005-19, Effect of Plant Configuration Changes on the Emergency Plan.

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nei.org 47 Stated another way, changes to the plant risk profile are accounted for through the LBE assessment and subsequent PEP EPZ determination process, which then informs the content of the emergency plan. This process is similar to the approach utilized for changes to site emergency plans during a shift to decommissioning operations, where changes to the plant risk profile result in a reduction in the EPZ and necessitate changes to the emergency plan.23 5.2 Performance Objectives - 50.160(b)(1)(ii)

Section §50.160(b)(1)(ii) provides requirements for establishing performance objectives to evaluate the emergency response functions described in §50.160(b)(1)(iii). NEI has developed supplemental guidance on this topic [9]; therefore, further guidance is not provided here. The NEI document provides generic EP program objectives and metrics, including evaluation frequency, evaluation criteria, and performance thresholds.

5.3 Emergency Response - 50.160(b)(1)(ii) 50.160(b)(1)(iii) focuses on emergency response performance, including the demonstration of the following functions, which are detailed in the following subsections.

Event Classification Protective Actions Communications Command and Control Staffing and Operations Radiological Assessment Reentry Critique and Corrective Actions 5.3.1 Event Classification The emergency plan must describe the capabilities and procedures used to assess, classify, monitor, and repair facility malfunctions. Emergency classification is an important function because the declared emergency classification level (ECL) will set in motion predetermined actions by each response organization. In general, an emergency classification scheme should include initiating conditions (ICs) for each applicable ECL and EALs for each IC. An IC is a description of an event or condition, the severity or consequences of which meets the definition of an ECL. An EAL is a predetermined, site-specific, observable threshold for an IC that, when met or exceeded, places the plant in a given ECL. The analyses performed as part of the LMP approach, and the resulting insights, can be utilized to inform the development of the ECLs, ICs, and EALs.

23See NRC rulemaking effort regarding regulatory improvements for the transition to decommissioning (Docket NRC-2015-0070).

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nei.org 48 The developed approach has established technology-inclusive ECLs based on the layers-of-defense concept used by LMP. To do this, the definitions for the four ECLs found in NEI 99-01 [24] and NEI 07-01

[25] were modified to remove references to reactor design-specific attributes (such as core damage and containment integrity). In addition, wording changes were made to include an explicit connection to the plant RSFs and those SSCs performing the RSFs. The resulting new definitions is presented in Table 5.1.

Table 5.1: Technology-Inclusive Emergency Classification Levels Level Technology-inclusive Description Notification of Unusual Event Events are in progress or have occurred which indicate a potential degradation to a capability to perform a RSF, or indicate a security threat to facility protection has been initiated. No releases of radioactive material requiring offsite response or monitoring are expected unless further degradation of capabilities providing RSFs occurs.

Alert Events are in progress or have occurred which involve an actual or potential substantial degradation in the capability to perform a RSF or a security event that involves probable life-threatening risk to site personnel or damage to safety significant SSCs because of hostile action. Any radionuclide releases are expected to be limited to small fractions of the EPA PAG exposure levels.

Site Area Emergency Events are in progress or have occurred which involve actual or likely failure of SSCs, or the capability, to perform a RSF or hostile action that results in intentional damage or malicious acts;

1) toward site personnel or equipment that could lead to the actual or likely failure or;

2) that prevent effective access to, equipment needed for the protection of the public.

Any releases are not expected to result in exposure levels which exceed EPA PAG exposure levels beyond the site boundary.

General Emergency Events are in progress or have occurred which result in the failure to perform a RSF and involve actual or imminent release of radioactive material that would be reasonably expected to exceed EPA PAG exposure levels offsite. This includes degradation resulting from hostile actions.

An applicant can use the above ECL definitions as a basis for the identification of site-specific ICs. Since a radionuclide release is possible only if the performance of a RSF is degraded or lost, the ICs should be qualitative statements regarding the capability of SSCs to perform the RSFs or events that could cause a degraded or lost RSF (e.g., an earthquake of certain severity). Utilizing terminology from NEI 99-01,

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nei.org 49 these represent symptom-based and event-based ICs.24 Symptom-based ICs could include direct monitoring, such as coolant pump status, or indirect monitoring that would indicate a potential failure of an SSC to perform an RSF, such as a radiation monitoring indicating the failure of a physical radionuclide barrier for a non-core source of radioactivity. Event-based ICs include thresholds for natural phenomena and man-made hazard events.

When identifying ICs and EALs, all LBEs and other events used to determine the PEP EPZ should be reviewed, including those that were not considered in the PEP EPZ determination process (because they were screened out or at sufficiently low frequency). Although predetermined, prompt, protective measures may not be needed for many LBEs, it is still necessary for the emergency classification scheme to recognize and account for them through an examination of the full range of conditions and events that may impact plant safety. This will ensure that all required emergency plan functions, including onsite protective actions, are initiated by the declaration of an appropriate ECL.

The central consideration for selecting ICs and EALs is the availability, performance, and safety classification of the SSCs that perform safety significant functions for preventing and mitigating LBEs.

Safety significant functions are those PRA Safety Functions performed by SR and NSRST SSCs that meet risk significance criteria or determined to be necessary for adequate DID. These SSCs include radionuclide transport barriers and inherent and intrinsic features of the reactor and plant. The associated PRA Safety Functions include those responsible for preventing and mitigating initiating events as well as halting the progression of an LBE into an adverse end state with a radionuclide release. Of particular importance are the safety significant SSCs responsible for performing the PRA Safety Functions and other functions necessary for adequate DID. When assessing LBEs to help develop ICs, the following questions should be asked:

What SSCs are available to support each safety significant function?

How well are the SSCs performing their safety significant functions; are there any indications of degradation or loss of SSC capability?

How many layers of defense have been penetrated as the LBE progresses?

What is the state of the radionuclide sources and the barriers to their release?

Another aid for determining ICs and EALs is the SAR structure defined in the TICAP approach. The SAR provides the RSFs for the plant, including discretization into RFDCs, then SRDCs that are assigned to specific safety-related SSCs. In addition, the requirements associated with non-safety related with special treatment (NSRST) SSCs are also derived through complementary design criteria (CDC), which either provide risk significant functions or other functions necessary for adequate DID. For each LBE, this information can be utilized to help develop the ICs for each RSF, as outlined in Figure 5.1. Symptom-based ICs can be identified to assess the performance of the SSCs, while event-based ICs can be established based on the estimated severity of events and degradation/loss of SSC performance.

24 NEI 99-01 also includes fission product barrier-based ICs. However, since radionuclide retention through physical barriers is a RSF for radionuclide sources, it is included within the symptom-based ICs in the approach here. In addition, the physical barriers utilized for radionuclide retention by NLWRs may differ.

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nei.org 50 Figure 5.1: RSF Decomposition for IC Identification25 It is important to note that depending on the potential dose consequence of the LBEs, there may not be ICs applicable to every ECL. For example, if all LBEs result in offsite doses below the EPA PAGs, then there may not be ICs for the General Emergency level. This outcome is similar to existing EP requirements for fuel cycle facilities, which include only two levels of emergency classification as the EPA PAGs are not expected to be exceeded beyond the SB. If an applicant has determined that there is no PEP EPZ or one at the SB, then there would not be a need to include the General Emergency ECL in the site emergency classification scheme. However, depending on the attributes of the plant and associated LBEs, the applicant may wish to retain the General Emergency ECL, and an associated discretionary IC and EAL, as a conservative measure for very low frequency, high consequence LBEs, which were of insufficient frequency to impact the PEP EPZ determination.

Once the set of ICs is developed and mapped to the ECLs based on their severity and consequences, the EALs for each IC should be identified. As noted above, EALs are predetermined, site-specific, observable thresholds for an IC that, when met or exceeded, place the plant in a given ECL. For each IC, the applicant should list the plant indications, from both operational and radiological monitoring systems, and the associated readings/values that operators can use to determine when an IC is met and an ECL declaration is required. It is necessary to demonstrate that there are sufficient monitoring capabilities to properly identify the ICs/EALs, including both symptom-based and event-based ICs/EALs. With respect to radiation monitoring, some IC/EAL considerations may overlap with the requirements for radiological assessment, discussed in Section 5.3.6. EALs may also be based on event reports from onsite or offsite sources.

5.3.2 Protective Actions

§50.160(b)(1)(iii)(B) centers on protective actions for personnel within the SB, including workers and the public, and the offsite public. The range of protective actions for both populations will be informed by the spectrum of LBEs and results of the PEP EPZ determination process, including the protective measures evaluation discussed in Section 4.4.2. It is important to note that the range of protective actions must address radiological releases, toxic chemicals, and other industrial hazards that could 25 Complementary design criteria are specified for risk significant functions or safety functions deemed necessary for DID that are assigned to NSRST SSCs. The structure shown in the figure could be utilized with the LBE information and layers of defense framework to determine ICs and EALs.

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nei.org 51 impact implementation of the site emergency plan. The consideration of worker occupational safety impacts, such as potential exposures to hazardous materials, are outside the scope of PRA and LMP analyses; however, hazards presented by contiguous or nearby industrial facilities must be considered to ensure that the emergency plan can be effectively implemented.

The emergency plan must detail the protective actions that would be taken for onsite workers and onsite members of the public during a radiological emergency. Actions taken to protect onsite members of the public are formulated and directed by the licensee and may include assembly and sheltering in an assembly area, evacuation from the site, and radiological monitoring and decontamination. Insights from LBE analyses should be utilized to inform the assessment of worker and visitor protective actions, such as the magnitude and characteristics of radionuclide and hazardous material releases. The LBE analyses can also inform the protective actions necessary for plant workers performing accident or event mitigation measures. For example, an evaluation of manual actions required by accident procedures would identify the locations that plant personnel may have to access and thus the needed protective actions.

If protective measures were deemed necessary beyond the SB based on the PEP EPZ determination process (discussed in Section 4.5), they would be detailed in fulfillment of that process and the requirement in §50.160(b)(1)(iv)(B). The identified measures should be used to develop predetermined protective action recommendations that the licensee could transmit to an ORO during the accident. A site without an offsite PEP EPZ must also have the capability to recommend protective actions to offsite authorities as conditions warrant (i.e., formulate and communicate ad hoc protective action recommendations as needed).

5.3.3 Communications

§50.160(b)(1)(iii)(C) requires establishing and maintaining effective communications with the emergency response organization and making notifications to response personnel and organizations who have responsibilities during emergencies. The specific communication requirements are partly derived from the PEP EPZ determination process, and the emergency classification and protective measures evaluations. However, additional information regarding worker communication methods, equipment, personnel, etc. is required. The assessment of emergency communication needs should include:

1) Links between licensee emergency response facilities and staff

2) Capabilities for communicating with onsite workers in the facility and in the field

3) Links to State and/or local OROs, including first responder organizations like police, fire, and EMTs.

5.3.4 Command and Control

§50.160(b)(1)(iii)(D) provides requirements associated with command and control during an emergency response. The needs of the command and control structure are largely dependent on the emergency response functions described in the emergency plan to meet other requirements in §50.160(b). The determination of necessary command and control capabilities should consider the personnel, facilities, equipment, and methods needed to perform all required functions. Facilities with very limited consequence potential may be able to employ a simple command and control structure with reduced

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nei.org 52 response personnel due to the limited need for protective and mitigation actions and coordination with other response organizations.

5.3.5 Staffing and Operations

§50.160(b)(1)(iii)(E) provides the requirements associated with staffing and operations for an emergency response. Like the preceding section on command and control, these needs, including location, organization, capabilities, etc., are largely determined by the contents in other parts of the emergency plan. Specific staffing and activation capabilities, and training needs, are also dependent on the characteristics of the facility. For this reason, insights from LBE and other event analyses, such as internal hazards, should be used to inform the development the staffing and operations requirements (e.g., unique radiological monitoring considerations or fire/hazardous material situations).

5.3.6 Radiological Assessment As presented in §50.160(b)(1)(iii)(F), there are four aspects to the radiological assessment capabilities described in the emergency plan:

(1) Radiological conditions. Assess, monitor, and report radiological conditions to the applicable response personnel using installed or portable equipment.

(2) Protective equipment. Issue and use protective equipment necessary to continue and expand mitigation and protective action strategies.

(3) Core or vessel damage. Assess, monitor, and report to the applicable response personnel the extent and magnitude of damage to the core or other vessel containing irradiated special nuclear material, such as fuel or targets,26 as applicable.

(4) Releases. Assess, monitor, and report to the applicable response personnel the extent and magnitude of all radiological releases, including releases of hazardous chemicals produced from licensed material.

All four aspects can be informed by information and insights from the dose assessments performed in support of the PEP EPZ determination, as well as other LBE analyses referenced in an application (e.g.,

the location and characteristics of radionuclide sources in the plant). The release scenarios for each source would be considered when determining the types and placement of radiation monitors, portable monitoring equipment, and protective equipment. The monitoring capabilities derived through this process would complement those necessary for normal operational monitoring and personnel protection. A core/fuel or vessel damage assessment process for use during an emergency is also necessary, or arrangements with the reactor supplier could be made to provide this service during an emergency.

Facilities with LBEs that could require offsite protective measures should have the capability to monitor for potential radionuclide releases and make real-time dose projections. Here, real-time means the ability of the plant staff to gather meteorological and radiation monitoring data and perform a dose assessment. Such information, when transmitted to offsite authorities, will optimize the selection and 26 From RG 1.242, For the purposes of this guidance, a target is special nuclear material irradiated or processed within a utilization facility or production facility, respectively, as defined in 10 CFR 50.2, for the purposes of producing or extracting fission products for research, development, or commercial sale.

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nei.org 53 implementation of protective measures, thereby utilizing available resources in the most efficient manner.

5.3.7 Reentry

§50.160(b)(1)(iii)(G) provides requirements for reentry into facilities following a radiological emergency.

Guidance on reentry is not provided here, although it is important to note that there are crosscutting considerations regarding the monitoring and assessment capabilities described in the preceding sections and those necessary to ensure safe reentry.

5.3.8 Critique and Corrective Actions

§50.160(b)(1)(iii)(H) addresses the critique of emergency response functions after drills and exercises, and subsequent implementation of corrective actions. This topic is closely related to the performance objectives discussed in Section 5.2 and the referenced NEI guidance document; therefore, no further guidance is provided here.

5.4 Planning Activities - §50.160(b)(1)(iv)

§50.160(b)(1)(iv) centers on onsite and offsite (if necessary) planning activities.

5.4.1 Onsite Planning Activities

§50.160(b)(1)(iv)(A) pertains to onsite planning and includes the six aspects below:

1) Public information

2) Coordination with safeguards contingency plan

3) Communication with NRC

4) Emergency facility or facilities

5) Site familiarization training

6) Emergency plan maintenance Topics 1, 2, 3, and 5 are largely outside the scope of this project.

With respect to topic 4, the number and type of emergency facilities, and their associated capabilities, are based on what is needed to implement the response functions and capabilities described in the site emergency plan (as discussed in Section 5.3). The requirements for emergency facilities should also be informed by the potential consequences of accidents, which are a function of the spectrum of LBEs (as discussed in Section 4.2). For example, if there are LBEs that would result in the inhabitability of the control room or an onsite emergency facility, then there may be a need for a backup location. The impact of non-radioactive hazards, such as corrosive smoke from a sodium fire at a sodium fast reactor facility, should also be considered.

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nei.org 54 Emergency plan maintenance is related to the approach to address emergency plan changes, as previously discussed in Section 5.1, but with greater focus on the change process and personnel responsible for changes.

5.4.2 Offsite Planning Activities

§50.160(b)(1)(iv)(B) pertains to offsite planning for sites with a PEP EPZ that extends beyond the SB.

There are nine aspects to the required offsite planning activities:

1) The contacts and arrangements made and documented with Federal, State, local, and Tribal governmental agencies

2) Notification of offsite organizations

3) Protective measures

4) Evacuation time estimate study

5) Emergency response facilities

6) Offsite dose projections

7) Dissemination of public information

8) Reentry

9) Drills and exercises The guidance in RG 1.242 should be followed to develop these sections of the emergency plan. The area encompassed by the PEP EPZ, as determined in Section 4, and related insights from its development will inform offsite planning activities. For example, PEP EPZ-related information will help identify the offsite organizations to be contacted, the preplanned protective measures, and areas where dissemination of public information would be necessary. The capabilities to provide offsite dose projections coincide with the radiological assessment requirements in §50.160(b)(1)(iii)(F).

5.5 Hazard Analysis - §50.160(b)(2)

§50.160(b)(2) requires a hazard analysis of any contiguous or nearby facilities, including any credible hazards that could adversely impact the implementation of the emergency plan. Specifically, this requirement is focused on examining how such hazards could affect the implementation of emergency response functions. There are three general types of scenarios that should be considered:

External hazard:

o An external hazard, such as natural phenomena, impacts the nuclear plant and the co-located/nearby facility simultaneously.

o Example: A seismic event that results in damage at the nuclear plant and the release of toxic material from a co-located/nearby chemical facility.

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nei.org 55 Nuclear plant event initiated by an event at the contiguous/nearby facility:

o An event at the co-located/nearby facility and the resulting hazard causes a condition at the nuclear plant that may jeopardize RSF performance (i.e., result in an EAL threshold exceedance).

o Example: The release of toxic gas for a co-located/nearby chemical facility impacts the operation of the nuclear plant.

Event at the contiguous/nearby facility initiated by a nuclear plant event:

o An event at the nuclear power plant impacts a co-located/nearby facility and results in an additional hazard.

o Example: A release of radioactive material from the nuclear plant results in operational disruptions at a co-located/nearby chemical facility and the release of toxic gases.

Development of an emergency plan should consider all three categories of events and the potential impacts to the performance of emergency response functions, including onsite and offsite protective measures. The hazard assessment should consider the progression of the hazard from the contiguous/nearby facility, the conditions requiring onsite protective actions, and the affected areas.

Once the hazard impacts are identified, they should be reviewed against the assumptions used in previously performed radiological dose/consequence assessments to determine if any changes are needed (e.g., the location of the offsite population, their ability to take protective actions, and dose receptor characteristics such as breathing rate).

The potential impact on nuclear plant operations from external hazards and hazards from co-located/nearby facilities (the first two categories) are assessed as part of a site-specific PRA developed and utilized in the LMP approach. Therefore, insights from the LMP analysis can inform the assessment conducted in fulfillment of this requirement. However, there may be aspects of the event that are not fully characterized in the PRA. For example, the PRA evaluation of a hazard may be focused on impacts to plant operations and not consider the potential repercussions on the effectiveness of onsite protective measures (if deemed necessary).

The third category of potential events (nuclear power plant events impacting co-located/nearby facilities) is typically not considered within plant PRAs and additional analyses may be required. The spectrum of LBEs can be used as the basis for an assessment to identify the impacts on co-located/nearby facilities from accidents at the nuclear plant. There may also be non-radiological consequences associated with nuclear plant events (e.g., chemical hazards) that are not captured by an LMP LBE/PRA assessment. Such considerations should be included in the evaluation of the impact on co-located/nearby facilities.

5.6 EPZ - §50.160(b)(3)

§50.160(b)(3) provides requirements associated with determining and describing the PEP EPZ. If a PEP EPZ was determined to be necessary based on the analysis discussed in Section 4, the boundary and physical characteristics are described. The applicant may also note the intersection between the PEP EPZ and emergency planning for onsite personnel, such as those inside the facility, described in

§§50.160(b)(1)(iii)(B) and 50.160(b)(1)(iv)(A).

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nei.org 56 5.7 Ingestion Pathway - §50.160(b)(4)

Under §50.160, a predetermined ingestion pathway EPZ is not required; however, it is necessary to describe the capabilities that provide actions to prevent contaminated food and water from entering the ingestion pathway. As detailed in RG 1.242, this includes Federal, State, and local resources that are available to protect the ingestion pathway in the case of a radiological emergency. For example, at the Federal level, there are the Federal Radiological Monitoring and Assessment Center (FRMAC) and the Advisory Team for Environment, Food and Health (Advisory Team). These capabilities are generally independent of the plant technology and are not discussed here.

As stated in RG 1.242, it is also necessary to describe the Federal, State, local, or licensee capabilities that support intermediate and long-term monitoring, analysis, and interdiction or embargo. Whether the licensee requires radiological monitoring capabilities to assist with such events largely depends on whether offsite authorities have the necessary resources to assess the expected radionuclide releases from the plant, as derived from the spectrum of LBEs. This assessment is similar to the radiological monitoring analysis discussed in Section 5.3.6. This could include consideration of potential radionuclide releases with unique ingestion pathway concerns.

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nei.org 57 REFERENCES

1. Nuclear Energy Institute, "Risk-Informed Performance-Based Guidance for Non-Light Water Reactor Licensing Basis Development," NEI 18-04 Rev 1, 2019.

2. U.S. Nuclear Regulatory Commission, "Guidance for a Technology-Inclusive, Risk-Informed, and Performance-Based Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light-Water Reactors," RG 1.233, 2020.

3. U.S. Nuclear Regulatory Commission, "Options for Emergency Preparedness for Small Modular Reactors and Other New Technologies," SECY-15-077, 2015.

4. U.S. Nuclear Regulatory Commission, "Final Rule: Emergency Preparedness for Small Modular Reactors and Other New Technologies," SECY-22-0001, 2022.

5. U.S. Nuclear Regulatory Commission, "Presentation to the Advisory Committee on Reactor Safeguards: 10 CFR Parts 50 and 52 Emergency Preparedness for Small Modular Reactors and Other New Technologies," 2021.

6. D. Grabaskas et al., "Towards Risk-Informed Performance-Based Emergency Planning: Review of Regulation, Guidance, and Methods," ANL/NSE-24/4, 2024.

7. U.S. Nuclear Regulatory Commission, "Final Rule: Emergency Preparedness for Small Modular Reactors and Other New Technologies," VR-SECY-22-0001, 2023.

8. Nuclear Energy Institute, "Technology Inclusive Guidance for Non-Light Water Reactors " NEI 21-07, Rev 1, 2022.

9. Nuclear Energy Institute, "Recommended Framework for Performance-Based Emergency Preparedness Program Metrics," 2023.

10. U.S. Nuclear Regulatory Commission, "Safety Goals for the Operation of Nuclear Power Plants,"

Federal Register, 51 FR 30028, 1986.

11. U.S. Nuclear Regulatory Commission, "Performance-Based Emergency Preparedness for Small Modular Reactors, Non-Light-Water Reactors, and Non-Power Production or Utilization Facilities," RG 1.242, Rev 0, 2023.

12. American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS),

"Probabilistic Risk Assessment for Advanced Non-Light Water Reactor Nuclear Power Plants,"

ANSI/ASME/ANS RA-S-1.4-2021, 2021.

13. U.S. Nuclear Regulatory Commission, "Acceptability of Probabilistic Risk Assessment Results for Non-Light-Water Reactor Risk-Informed Activities," Trial Use R.G. 1.247, 2022.

14. Nuclear Energy Institute, "Selection of a Seismic Scenario for an EPZ Boundary Determination,"

Rev 1, 2024.

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15. American National Standards Institute/American Nuclear Society, "Emergency Planning for Research Reactors," ANSI/ANS-15.16-2015, 2015.

16. U.S. Nuclear Regulatory Commission, "Generalized Dose Assessment Methodology for Informing Emergency Planning Zone Size Determinations," Task 1.1-1.3 Report for User Need NSIR-2017-002, 2018.

17. U.S. Nuclear Regulatory Commission, "Required Analyses for Informing Emergency Planning Zone Size Determinations," Task 1.4 Report for User Need NSIR-2017-002, 2018.

18. U.S. Environmental Protection Agency, "PAG Manual - Protective Action Guides and Planning Guidance for Radiological Incidents," 2013.

19. U.S. Nuclear Regulatory Commission, "Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decisionmaking," NUREG-1855 Revision 1, 2017.

20. U.S. Nuclear Regulatory Commission, "RASCAL 3.0.5 Workbook," NUREG-1889, 2007.

21. K. Fleming, A. Torri, K. Woodard, J. Lewis, and T. Mikschl, "Seabrook Station Emergency Planning Sensitivity Study," PLG-0465, 1986.

22. Nuclear Energy Institute, "Technology Inclusive Risk Informed Change Evaluation (TIRICE):

Guidance for the Evaluation of Changes to Facilities Utilizing NEI 18-04 and NEI 21-07," NEI 22-05, Rev 0, 2024.

23. U.S. nuclear Regulatory Commission, "Guidance on Making Changes to Emergency Plans for Nuclear Power Plants," RG 1.219, 2011.

24. Nuclear Energy Institute, "Development of Emergency Action Levels for Non-Passive Reactors,"

NEI 99-01, Rev 6, 2012.

25. Nuclear Energy Institute, "Development of Emergency Action Levels for Passive Reactors," NEI 07-01, Rev 1, 2013.

26. Electric Power Research Institute, "Technical Aspects of ALWR Emergency Planning," TR-113509, 1999.

27. NuScale Power LLC, "Methodology for Establishing the Technical Basis for Plume Exposure Emergency Planning Zones at NuScale Small Modular Reactor Plant Sites," TR-0915-17772-NP, Rev 3, 2022.

28. U.S. Nuclear Regulatory Commission, "Safety Evaluation for Nuscale Topical Report, TR-0915-17772, Revision 3, Methodology for Establishing the Technical Basis for Plume Exposure Emergency Planning Zones at Nuscale Small Modular Reactor Plant Sites " 2022.

29. U.S. Nuclear Regulatory Commission, "Severe Accident Risks: An Assessment for Five U.S.

Nuclear Power Plants," NUREG-1150, 1990.

June 2024

nei.org 59

30. U.S. Nuclear Regulatory Commission, "Special Committee Review of the Nuclear regulatory Commissions Severe accident Risks Report (NUREG 1150)," NUREG-1420, 1990.

31. U.S. Nuclear Regulatory Commission, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition," NUREG-0800, 2007.

32. U.S. Nuclear Regulatory Commission, "Preapplication Safety Evaluation Report for the Modular High-Temperature Gas-Cooled Reactor (MHTGR) - Draft Copy of the Final Report," NUREG-1338, 1995.

33. U.S. Nuclear Regulatory Commission, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant Specific Changes to the Licensing Basis," RG 1.174, Rev 0,1998.

34. D. Clayton and N. Bixler, "Assessment of the MACCS Code Applicability for Nearfield Consequence Analysis," SAND2020-2609, 2020.

35. D. Clayton, "Implementation of Additional Models into the MACCS Code for Nearfield Consequence Analysis," 2021.

36. U.S. Nuclear Regulatory Commission and Environmental Protection Agency, "Planning Basis for the Development of State and Local Government Radiological Emergency Response Plans in Support of Light Water Nuclear Power Plants," NUREG-0396, EPA 520/1-78-016, 1978.

37. U.S. Nuclear Regulatory Commission, "Reactor Safety Study, an Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, Executive Summary," WASH-1400 (NUREG 75/014),

1975.

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nei.org 60 APPENDIX A. UTILIZATION OF LBES TO INFORM PEP EPZ DETERMINATION As noted in Section 4.2, the PEP EPZ determination process includes the consideration of LBEs from the LMP approach to represent the spectrum of potential accidents that inform the analysis. The selection of LBEs identified by the LMP approach is considered sufficient to capture the spectrum of potential accidents for several reasons, further detailed here.

A.1.

LBE Determination As defined in NEI 18-04 [1] and RG 1.233 [2], the LBE categories include all event sequence families with frequencies above 5E-7 per plant year at the 95th percentile when considering uncertainties. Regarding event frequency, there is significant regulatory precedent regarding the utilization of 1E-7 per year mean frequency as the threshold for the evaluation of less probable, severe events, as outlined below

[26]. In addition, the NRC recently approved the utilization of a 1E-7 per year screening threshold for non-seismic events as part of the NuScale EPZ approach, as it was consistent with NUREG-0396 [27, 28].

The use of 5E-7 per year at the 95th percentile is in general alignment with this precedent.

NUREG-1150 [29] used a frequency cutoff of 1E-7 per year for PRA accident sequence progression; NUREG-1420 [30] discusses probability cutoff criteria for PRAs, and indicates that consequences with frequencies lower than about 1E-7 per year are not meaningful for decision making; Standard Review Plan [31] (Section 2.2.3) guidance specifies evaluation of potential accidents from hazards which exceed 1E-7 per year; NUREG-0396, Figure I-11, has a conditional probability range down to 1E-3 which corresponds to 1E-7 per year absolute probability.

NUREG-1338 [32] draft Pre-Application SER for MHTGR, states as part of justification for reduced EP that sequences appearing to have a frequency in the range of about 1E-7 per year will be examined for residual risk.

Regulatory Guide 1.174 [33] specifies that, when using PRA to support decisions to modify an individual plants licensing basis, an increase of less than 1E-7 per year in the Large Early Release Frequency (LERF) is recognized as very small and will not prevent NRC to consider the proposed modification.

A.2.

Consideration of DBAs Regarding the assessment of DBAs, the developed PEP EPZ determination process accounts for DBAs through the inclusion of analogous event sequences within the PRA. Therefore, the DBAs are assessed in accordance with their estimated frequency of occurrence. This approach differs from past methods, such as that used in NUREG-0396, which assessed the consequence associated with DBAs regardless of their estimated frequency of occurrence. There are multiple reasons why the approach was selected in the PEP EPZ determination process described here.

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nei.org 61 First, the nature of DBAs within the LMP approach is fundamentally different when compared to traditional LWR licensing. For the LWRs assessed as part of NUREG-0396, DBAs were deterministically selected and were the primary driver for plant design and associated safety analysis. Only later in the development of the operating LWR fleet was PRA and the use of risk insights introduced as supplementary information. Under the LMP, the approach is essentially reversed, with PRA insights leading the assessment of plant safety and DBAs acting as supplemental information. This approach is possible due to the comprehensive nature of the PRA and the maturation of PRA technology. With LMP, DBAs are derived from DBEs by only crediting SR SSCs. For the PEP EPZ determination process, event sequences that are analogous to the DBAs are included within the PRA and addressed at their appropriate frequency level during LBE categorization, ensuring that such events are not neglected.

In the LMP approach to defining DBAs, each DBA is not selected or directly associated with a frequency, but rather is defined by a set of deterministic rules linked to the user selection of which SSCs available on all the DBEs are selected as SR for the performance of the RSFs. The purpose of the DBAs in the LMP approach is to demonstrate that 10 CFR 50.34 and 10 CFR 100 dose criteria can be satisfied for the DBEs modified to only rely on SR SSCs in the performance of the RSFs. As these events are not selected on the basis of LBE frequency, they cannot be evaluated on the F-C target and they do not contribute to the cumulative risk targets.

Second, as the project goals in Section 3.1 state, one of the objectives of the approach is to allocate resources in an efficient and effective manner for dose savings to workers and the public. The utilization of best-estimate risk information and associated LBE attributes is the best available pathway to accomplish this objective. If DBAs are included within the PEP EPZ determination process as postulated scenarios without consideration of the frequency of occurrence, their inclusion could lead to a distortion of the analysis findings and a misallocation of resources. In addition, the consequence assessment of DBAs typically differs from that of LBEs in terms of codes, assumptions, etc. These inconsistencies introduce practical challenges to the inclusion of DBAs within the PEP EPZ determination process.

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nei.org 62 APPENDIX B. CONSEQUENCE ANALYSIS METHODOLOGY The development of the dose-versus-distance curves discussed in Section 4.3 requires a consequence assessment for each identified LBE or other event with radionuclide release, which estimates the dose to individuals at different locations. The consequence assessment consists of two major elements: the mechanistic source term analysis, which examines the release, transport, and retention of radionuclides from the source to the environment, and the radiological consequence analysis, which examines the dispersal of radionuclides in the environment and subsequent dose to individuals. The ASME/ANS NLWR PRA standard can be utilized to inform the execution of both assessments, as it contains mechanistic source term and radiological consequences elements and associated requirements [12]. In addition, Appendix A of RG 1.242 provides high-level guidance regarding consequence assessment [11].

Given that the PEP EPZ determination process discussed here utilizes the outputs of the LMP approach, a mechanistic source term and radiological consequence analysis have already been completed for each LBE. However, the previously completed assessments may not fully satisfy the needs of the PEP EPZ determination process, depending on the goals of the assessment and utilized approach (as discussed in Section 4.6.1). While the source term assessment performed as part of LMP assessments is likely applicable, there may be differences in the radiological consequence assessment. Under the LMP framework, the consequences of LBEs are evaluated for the 30-day TEDE at the EAB for comparison to the frequency versus consequence curve, and for offsite early fatality and latent cancer fatalities for comparison to the QHOs. These analyses include the consideration of uncertainty. Such results may be sufficient if the applicants goal is to demonstrate the acceptability of the SB as the PEP EPZ. However, if the applicant wishes to demonstrate that a PEP EPZ is not needed, additional consequence assessment may be needed detailing doses within the SB.

RG 1.242 notes that key considerations for the radiological consequence model include the meteorological input, the atmospheric transport model, the exposure parameters, and the dose estimation for pathway contributors. For the dose-versus-distance curves discussed in Section 4.3.1, the consequence assessment should use the following assumptions:

No credit for protective measures 96-hour exposure duration following plume arrival Cloudshine, groundshine, inhalation, and resuspension dose pathways Mean meteorology (or mean results of sampled meteorology)

Straight line trajectory, plume centerline These attributes are generally consistent with the approach utilized in NUREG-0396, although the exposure time differs and is more conservative, as discussed in Appendix C. The approach is generally straightforward in nature, reducing the potential effort for the initial steps of the process. If the developed dose-versus-distance curves exceed the criteria established in Table 4.1, further refined consequence analysis can be performed for the contributing LBEs as part of the protective measures evaluation. As mentioned in Section 4.4, a detailed consequence analysis may include further consideration of uncertainties, spatial dose evaluations, or refinement regarding timing.

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nei.org 63 While the selection of models and parameters for offsite radiological consequence are well established, the assessment of doses within the SB can be challenging. The assessment of atmospheric transport models for their applicability to near-field (<500m) dispersion is a matter of current research [34, 35]. An applicant may select different atmospheric transport models for analyses inside and outside the SB. In such cases, the applicant should provide justification for the selection and a consideration regarding how to utilize both models in a manner that achieves consistent dose estimates. The selection of appropriate atmospheric transport models may depend on the specific attributes of the radionuclide release and site characteristics. In addition, at close distances to the facility, direct radiation exposure may also be possible, such as due to the loss of shielding, even without a plume release to the environment.

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nei.org 64 APPENDIX C. DERIVATION OF PROBABILISTIC DOSE AGGREGATION CRITERIA NUREG-0396 documents the NRC/EPA Task Force on Emergency Planning derivation of the 10-mile PEP EPZ utilized by the existing LWR fleet [36]. Specifically, Appendix I notes the quantitative assessments and qualitative evaluations performed to support the 10-mile basis. Various rationales were explored for establishing the planning basis, including risk, probability, cost effectiveness, and consequence spectrum. The task force judged that the consequence of a spectrum of accidents should be the principal rationale for the planning basis, tempered by probability (frequency) considerations. As noted in NUREG-0396, the concept of accident probability was deemed important in terms of evaluating the range of consequences of accident sequences and setting reasonable bounds on the planning basis [36].

In the NUREG-0396 EPZ evaluation, consideration was given to the consequences from a spectrum of accidents postulated for various purposes, including those discussed in environmental reports, accidents postulated for purposes of evaluating plant designs (e.g., DBAs), and the spectrum of accidents assessed by the WASH-1400 Reactor Safety Study [37]. It was determined by the task force that the environmental reports were too limited in scope and detail to be useful. Therefore, the assessment focused on the DBA assessment and the WASH-1400 results.

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-LOCA 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 [36].

The WASH-1400 results were utilized to examine the likelihood of doses at different distances from the plant using a probabilistic dose aggregation process similar to that described in Section 4.3.1. The analysis generally focused on the WASH-1400 results for PWR-2 designs, with results presented in Figure C.1.

It is important to note that the WASH-1400 results used in the NUREG-0396 analysis only included at-power internal events for a single reactor, meaning external hazards, other operational modes, multi-unit plants, and non-core sources of radioactivity were not considered. In addition, doses were calculated for a 24-hour exposure period27 and with no consideration of uncertainty.

27 The assessment included a dose commitment of 1 year for inhaled material [16].

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nei.org 65 Figure C.1: Conditional Probability of Exceeding Whole Body Dose-versus-Distance [36]28 As the results in Figure C.1 demonstrate, the conditional probability of exceeding 1 rem at 10-miles from the site is approximately 0.3. Similarly, the conditional probability of exceeding 200 rem at 10-miles from the site is approximately 0.03. As these results are conditional on a core melt accident with a frequency of 5E-5 per year, that gives the following frequencies of exceedance at 10 miles:

1 rem:

5 x 105 1 yrx 0.3 = 1.5 x 105 1 yr 200 rem:

5 x 105 1 yrx 0.03 = 1.5 x 106 1 yr The frequency metrics for criteria A and B discussed in Section 4.3.2 were selected in part based on these results. The frequency values were conservatively rounded down to the nearest order of magnitude. The frequency metric for criterion A indicates that the likelihood of an event resulting in doses requiring protective measures outside the PEP EPZ is less than 1 in 100,000 years for the plant. As stated by NUREG-0396, if the U.S. operates 100 power reactors, there is a 0.1% chance of a reactor 28 Probabilities are conditional on a core melt accident (5E-5). Whole body dose calculated includes: external dose to the whole body due to the passing cloud, exposure to radionuclides on ground, and the dose to the whole body from inhaled radionuclides. Dose calculations assumed no protective actions taken, and straight-line plume trajectory.

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nei.org 66 accident requiring protective actions outside a PEP EPZ in a given year [36]. From a state resource perspective, the probability of occurrence is even lower. Similarly, criterion B implies that the likelihood of an event resulting in doses that may cause early health effects outside the PEP EPZ is less than 1 in 1,000,000 years for the plant. The criteria are also aligned with the NRC/EPA task forces belief that it is not appropriate to develop specific plans for the most severe and most improbable Class 9 events

[36].

The frequency metrics for criteria A and B provide useful guides for selecting the distance where predetermined measures are considered warranted for potential dose savings and are aligned with the regulatory precedent in NUREG-0396. As noted in RG 1.242 [11], the likelihood of exceeding a TEDE of 10 mSv (1 rem) at the proposed EPZ boundary should be consistent with the evaluation in Appendix I to NUREG-0396, which provides relative probabilities of exceeding certain critical doses as a function of distance from the facility for a spectrum of severe accidents. The developed criteria A and B also have additional conservatisms compared to NUREG-0396, given the scope of the LBE assessment (all hazards, sources, and operational modes), the 24-hour versus 96-hour exposure period, and consideration of uncertainty.

In keeping with the goals and objectives of the current EP effort, developing predetermined protective measures based on lower frequency levels would not be an efficient or effective utilization of plant resources and the resources of offsite organizations.

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nei.org 67 APPENDIX D. PEP EPZ EVALUATION AT PREDETERMINED DISTANCE The example analysis described in Section 4.7 is repeated here but utilizing a different application of the PEP EPZ determination process. In this analysis, the desire is to establish the PEP EPZ at the SB, with the evaluation seeking to confirm the adequacy of that distance. Such an approach could reduce the effort and resources necessary to complete the PEP EPZ determination process.

For the assessment, the same spectrum of events described in 4.7.1 is considered. The central difference is the event evaluation and dose assessment process. Instead of developing dose-versus-distance curves for the LBEs, the doses near the SB distance are found, as outlined in Table D.1.29 Those doses greater than 1 rem are highlighted in red. Only a single LBE exceeds 1 rem at the SB with frequency above 1E-5 per plant year (LBE-32), which aligns with criterion A in Table 4-1. There are other LBEs that exceed 1 rem at the SB but at very low frequency that would not contribute significantly to a cumulative 1 rem dose curve at the SB. Similarly, while LBE-38 has a dose at 500m approaching 200 rem, it is at a frequency well below the 1E-6 per plant year threshold of criterion B in Table 4.1.

Table D.1: Example Analysis Mean Dose Estimates LBE Mean Frequency

(/plant year)

Mean Dose (rem) at Distance from Facility 100m 300m 500m LBE-4 1.50E-01 7.58E-04 2.53E-04 2.35E-05 LBE-8 4.00E-02 7.58E-04 2.53E-04 2.35E-05 LBE-9 3.00E-02 7.58E-04 2.53E-04 2.35E-05 LBE-10 2.00E-02 8.61E-03 2.87E-03 2.67E-04 LBE-11 8.00E-03 7.58E-04 2.53E-04 2.35E-05 LBE-12 5.00E-03 3.39E-02 1.13E-02 1.05E-03 LBE-13 4.00E-03 8.61E-03 2.87E-03 2.67E-04 LBE-14 3.00E-03 1.75E-03 5.84E-04 5.43E-05 LBE-15 1.00E-03 1.83E-01 6.11E-02 5.68E-03 LBE-16 1.00E-03 3.39E-02 1.13E-02 1.05E-03 LBE-18 8.00E-04 1.75E-03 5.84E-04 5.43E-05 LBE-19 4.00E-04 8.61E-03 2.87E-03 2.67E-04 LBE-20 3.00E-04 1.78E+00 5.93E-01 5.51E-02 LBE-21 2.00E-04 1.75E-03 5.84E-04 5.43E-05 LBE-22 2.00E-04 7.03E-01 2.34E-01 2.18E-02 LBE-23 8.00E-05 1.83E-01 6.11E-02 5.68E-03 LBE-24 5.00E-05 1.70E+00 5.66E-01 5.26E-02 LBE-25 4.00E-05 1.75E-03 5.84E-04 5.43E-05 LBE-29 2.00E-05 2.52E+00 8.40E-01 7.81E-02 LBE-30 2.00E-05 8.61E-03 2.87E-03 2.67E-04 LBE-31 1.00E-05 8.32E-01 2.77E-01 2.58E-02 LBE-32 2.00E-05 8.06E+01 2.69E+01 2.50E+00 LBE-35 5.00E-07 8.06E+02 2.69E+02 2.50E+01 LBE-36 3.00E-07 7.58E-04 2.53E-04 2.35E-05 29 While the approach selected here presents the calculated dose at varying distance, an alternative method would be to present the frequency of a specific dose for each LBE at a set distance. For example, demonstrating that the frequency of 1 rem for an LBE is well below 1E-5 per plant year at 500m.

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nei.org 68 LBE-37 3.00E-07 3.23E+01 1.08E+01 1.00E+00 LBE-38 2.00E-07 4.84E+03 1.61E+03 1.50E+02 To examine uncertainties or possible cliff-edge effects, a simplistic analysis was performed regarding 95th percentile values for dose, as outlined in Table D.2. In a real analysis, uncertainty regarding LBE frequency can also be assessed. The dose uncertainty results identify one additional LBE with a dose above 1 rem at the SB of 500m (LBE-37), but this is an LBE with a mean frequency of 3E-7 per plant year, which is well below the frequency threshold for consideration.

Table D.2: Example Analysis 95th Percentile Dose Estimates LBE 95th Dose (rem) at Distance from Facility 100m 300m 500m LBE-4 1.90E-03 6.32E-04 5.88E-05 LBE-8 1.90E-03 6.32E-04 5.88E-05 LBE-9 1.90E-03 6.32E-04 5.88E-05 LBE-10 2.15E-02 7.18E-03 6.68E-04 LBE-11 1.90E-03 6.32E-04 5.88E-05 LBE-12 8.47E-02 2.82E-02 2.63E-03 LBE-13 2.15E-02 7.18E-03 6.68E-04 LBE-14 4.38E-03 1.46E-03 1.36E-04 LBE-15 4.58E-01 1.53E-01 1.42E-02 LBE-16 8.47E-02 2.82E-02 2.63E-03 LBE-18 4.38E-03 1.46E-03 1.36E-04 LBE-19 2.15E-02 7.18E-03 6.68E-04 LBE-20 4.44E+00 1.48E+00 1.38E-01 LBE-21 4.38E-03 1.46E-03 1.36E-04 LBE-22 1.76E+00 5.86E-01 5.45E-02 LBE-23 4.58E-01 1.53E-01 1.42E-02 LBE-24 4.24E+00 1.41E+00 1.32E-01 LBE-25 4.38E-03 1.46E-03 1.36E-04 LBE-29 6.30E+00 2.10E+00 1.95E-01 LBE-30 2.15E-02 7.18E-03 6.68E-04 LBE-31 2.08E+00 6.94E-01 6.45E-02 LBE-32 2.02E+02 6.72E+01 6.25E+00 LBE-35 2.02E+03 6.72E+02 6.25E+01 LBE-36 1.90E-03 6.32E-04 5.88E-05 LBE-37 8.06E+01 2.69E+01 2.50E+00 LBE-38 1.21E+04 4.03E+03 3.75E+02 Based on the event evaluation and dose assessment, a protective measures evaluation beyond the SB is necessary, with a focus on LBE-32, as was performed in Section 4.7.3. As it was demonstrated that predetermined, prompt protective measures were not warranted for LBE-32, the PEP EPZ can be established at the SB. To fully define and characterize the PEP EPZ, a protective measures evaluation within the SB is still necessary and would be similar to that conducted in Section 4.7.3.

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