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# Advanced Reactors Sub-Arena

Advanced reactors comprise one of four sub-arenas that the staff of the U.S. Nuclear Regulatory Commission (NRC) identified in considering which areas of the reactor safety arena to target for greater use of risk information. This page summarizes the following aspects of this sub-arena with *expanding menus*:

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**Objective**

**Objective**
Develop a coherent risk-informed and performance-based regulatory structure for design certification, licensing, and oversight of advanced reactors.

A coherent risk-informed and performance-based regulatory structure would offer significant improvements in effectiveness and efficiency (compared to the structure that has evolved for current-generation LWRs). For example, such coherence would ensure that the safety reviews conducted by the NRC consider design and operational aspects in an integrated manner. The bases for developing such a regulatory structure for licensing and oversight of advanced reactors are articulated in numerous Commission documents and policy statements. However, this guidance occurs largely in the context of existing and new LWRs and, consequently, needs to be adapted for advanced reactors.

**Basis**

**Basis**
The bases for a coherent risk-informed and performance-based regulatory structure arise from the potential to realize benefits that are captured in the screening criteria that the NRC staff considers in undertaking regulatory improvement initiatives:
              - Effectiveness : One hallmark of effectiveness is the ability to model the tradeoffs that are involved in a complex safety review. Sometimes, such tradeoffs are represented as the ability to achieve desired outcomes in the licensing process. A risk-informed and performance-based regulatory structure is inherently better able to do this, especially if it is applied in the early phases of developing a new regulatory structure for advanced reactors.
              - Effective Communication : The explicit modeling of decision-making promotes transparency. Sometimes, the traditional prescriptive regulatory structure lacks transparency because it tends to emphasize compliance with a prescribed quantity, rather than focusing on the safety function.
              - Research : The NRC staff has conducted significant research into the models and methodologies for the risk-informed and performance-based regulatory structure and the products and expertise from this work are available for implementation. Particularly notable examples include NUREG-1860, NUREG/BR-0303, and SECY-05-0138. Specific details will need to be determined and guidance developed based on the particular technology and design aspects of the application.
              - Costs : The implementation of a coherent risk-informed and performance-based regulatory structure for advanced reactors will entail a combination of short- and long-term costs. The new regulatory approaches are likely to result in short-term costs. However, when considered in the context of implementing the Commission's strategic objectives, there are sound reasons to expect a significant reduction in the total cost to society.
              - Obstacles : There are no apparent factors (e.g., state-of-the-art, adverse stakeholder perception) that would preclude implementing a risk-informed and performance-based approach to the design certification, licensing, and oversight of advanced reactors once sufficient operating experience is available to provide input to the activities.

The NRC developed its strategic planning process as a result of considerable effort (beginning in the late-1990s) to improve the agency's regulatory structure in a forward-looking way, while preserving the gains that the agency had achieved in operating reactor safety. Using the most recent version of the Strategic Plan, development of a coherent risk-informed and performance-based regulatory structure for advanced reactors will involve implementing the strategies that the Commission articulated in the goal of "Safety". Under "Safety" strategies, the Commission directed the staff to "Use sound science and state-of-the-art methods to establish, where appropriate, risk-informed and performance-based regulations." This element continues to be part of the Strategic Plan for the Fiscal Year (FY) 2008–2013.

The basic infrastructure for the implementation of a risk-informed and performance-based approach exists at a high-level in Commission documents, such as the "White Paper on Risk-Informed and Performance-Based Regulation." The staff has also developed some specific guidance, including the risk-informed process for implementing the single-failure criterion (SECY-05-0138), but more may need to be developed. In many instances, the high-level documents superficially apply only to existing LWRs; however, more thorough study reveals considerable applicability to all reactor technologies. For example, the Reactor Oversight Process (SECY-99-007 and SECY-99-007A, as well as related staff requirements memorandum) provides a risk-informed and performance-based structure, although it is overlaid on top of existing LWR requirements.

**Goals**

**Goals**
The staff's risk-informed and performance-based goals for advanced reactors relate to the following activities:
              - Ensure advanced reactor applicants use risk-informed safety insights to select among alternative features, operational strategies, and design options to reduce or eliminate the significant risk contributors of existing operating plants.
              - Ensure that the risk associated with advanced reactor designs compare favorably with the Commission's goals of less than 1E-04/year for core damage frequency and less than 1E-06/year for large release frequency

## List of Risk-Informed and Performance-Based Activities

This list shows the ongoing licensing initiatives, projects, and activities that the staff of the U.S. Nuclear Regulatory Commission (NRC) has targeted for greater use of risk information in the Advanced Reactors Sub-Arena within the Reactor Safety Arena:
            - Advanced Reactor Content of Application Project
            - Technical Assistance for Research on Innovative Methods and Technologies to Enhance Seismic Safety for Design and Construction of Commercial Reactors
            - Risk-Informed Review of Small Modular Reactor (SMR) Designs
            - Non-Light Water Reactor Licensing Modernization
            - Risk-informed Emergency Planning Zone Size Evaluation
            - Advanced Reactor Regulatory Framework
            - Physical Security for Advanced Reactors
            - Regulatory Guidance on Advanced Non-LWR PRA Acceptability
            - Risk-informed Tools for Advanced Non-LWR Component Performance

## Advanced Reactor Content of Application Project

**Summary Description**

**Summary Description**
The purpose of the Advanced Reactor Content of Application Project (ARCAP) is to develop technology-inclusive, risk-informed and performance-based application guidance. The ARCAP guidance is intended to be used for an advanced reactor application for a combined license, construction permit, operating license, design certification, standard design approval, or manufacturing license. The industry-led TI-CAP's purpose is to develop the content for specific portions of the safety analysis report (SAR) that would be used to support an advanced reactor application. ARCAP is a long-term project that will support the near-term advanced reactor applicants under 10 CFR Part 50 and Part 52, and also support the 10 CFR Part 53 rulemaking effort.

See the Advanced Reactor Content of Application Project public webpage for an updated listing of public meeting and publicly available documents.

**FY 2023**
In FY 2023, the NRC staff published the following documents for public comment:
              - DG-1404 Revision 1 Guidance on TICAP for Non-Light Water Reactors
              - DANU-ISG-2022-01 ARCAP Roadmap Interim Staff Guidance.
              - DANU-ISG-2022-02 ARCAP Chapter 2 Site Information.
              - DANU-ISG-2022-03 ARCAP Chapter 9 Normal Effluents.
              - DANU-ISG-2022-04 ARCAP Chapter 10 Occupational Dose.
              - DANU-ISG-2022-05 ARCAP Chapter 11 Organization and Human-System Consideration.
              - DANU-ISG-2022-06 ARCAP Chapter 12 Post-construction Inspection, Testing, and Analysis Program.
              - DANU-ISG-2022-07 ARCAP Risk-informed Inservice Inspection and Inservice Testing.
              - DANU-ISG-2022-08 ARCAP Risk-informed Technical Specifications.
              - DANU-ISG-2022-09 ARCAP Fire Protection for Operations.

See the Advanced Reactor Content of Application Project public webpage for an updated listing of public meeting and publicly available documents.

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## Technical Assistance for Research on Innovative Methods and Technologies to Enhance Seismic Safety for Design and Construction of Commercial Reactors

**Summary Description**

**Summary Description**
The objective of this research is to develop a technology-inclusive (TI), risk-informed and performance-based (RIPB) pathway for ANLWRs to address seismic safety within the LMP framework.  Part of the contract will aim at (i) evaluating feasibility and adequacy of potential technical criteria through demonstration studies, (ii) performing communication and outreach activities to help reach consensus with pertinent stakeholders on a viable and practical TI-RIPB approach forward for ANLWR seismic safety (iii) developing associated implementation guidance, and (iv) identifying potential regulatory improvements for future rulemaking activities.  The other part of the contract is to identify and evaluate technical criteria for regulatory guidance for the design and review of TI technologies included in licensing application for commercial NPPs.  The contract was awarded in June 2020.

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2020**

We'll not be receiving any deliverables until 2021.

**FY 2021**

Two new regulatory guides (RGs) are currently under development as part of this research. The first one RG for RIPB Seismic Safety, provides an alternative seismic safety approach that incorporates RIPB principles in graded seismic design using a combination of seismic design category (SDC) and design limit state (LS). The document will provide regulatory positions and process for how to determine alternate SDCs and LSs for SSCs considering LMP or other framework in combination the performance standards such as ASCE 1,4, and 43. This RG will provide considerations for applications referencing the RIPB approach under several regularity environments (e.g., Part 50/52 or Part 53). The preliminary draft guide will be completed by February 2022 and the final draft by June 2022.

The other RG under development provides guidance for incorporating seismic isolation technologies in future reactor applications. This guideline will provide criteria and implementation process that leverage ASCE 4 and 43 relevant provisions to extent practicable and the safety aspects with RIPB and LMP under several regularity environments (e.g., Part 50/52 or Part 53). The preliminary draft guide will be completed by February 2022 and the final draft by June 2022.

**FY 2022**

No Update

**FY 2023**
The staff reviewed and evaluated the Nuclear Energy Institute (NEI) 18 04, Revision 1, "Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development," issued August 2019, and RG 1.233, "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." After reviewing and evaluating the American Society of Civil Engineer (ASCE) standards ASCE 1-22 (Draft), "Standard for Geotechnical Analysis, Design, Construction, Inspection and Monitoring of Nuclear Safety-Related Structures,” ASCE 4-16, “Seismic Analysis of Safety-Related Nuclear Structures," and 43-18 (Draft), "Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities," the NUREG/CR 7253, "Technical Considerations for Seismic Isolation of Nuclear Facilities," NUREG/CR 7254, "Seismic Isolation of Nuclear Power Plants using Sliding Bearings," and NUREG/CR 7255, "Seismic Isolation of Nuclear Power Plants using Elastomeric Bearings," the staff drafted two pre-decisional regulatory guides: "Technology-Inclusive, Risk-Informed, and Performance-Based Methodology for Seismic Design of Commercial Nuclear Plants" and "Seismically Isolated Nuclear Power Plants." These two draft regulatory guides are associated with the development of 10 CFR Part 53 rulemaking that has not been finalized. These pre-decisional, draft regulatory guides are publicly available now (ML22276A149 and ML22276A154) and will be finalized based on public feedback and the Part 53 rulemaking.

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## Risk-Informed Review of Small Modular Reactor (SMR) Designs

**Summary Description**

**Summary Description**
In the Staff Requirements Memorandum (SRM) COMGBJ-10-0004/COMGEA-10-0001, "Use of Risk Insights to Enhance the Safety Focus of Small Modular Reactor Reviews," dated August 31, 2010, the Commission provided direction to the NRC staff on the preparation for, and review of, small modular reactor (SMR) applications, with a near-term focus on integral pressurized-water reactor designs. The Commission directed the NRC staff to more fully integrate the use of risk insights into pre-application activities and the review of applications and, consistent with regulatory requirements and Commission policy statements, to align the review focus and resources to risk-significant structures, systems, and components (SSCs) and other aspects of the design that contribute most to safety in order to enhance the effectiveness and efficiency of the review process. The Commission directed the NRC staff to develop a design-specific, risk-informed review plan for each SMR design to address pre-application and application review activities. In response, staff developed the review philosophy and framework described in Introduction - Part 2: Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: Small Modular Reactor Edition. It included a graded review approach to categorize SSCs using both safety classification and risk significance and the creation of Design Specific Review Standards (DSRSs) specific to each SMR design.

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2015 Status**

The DSRS for the NuScale design has been drafted to provide guidance to the NRC technical staff for review of the NuScale Design Certification Application (DCA). In the Federal Register Notice of June 30, 2015, the NRC solicited public comment on the DSRS and Safety Review Matrix for the NuScale design. The comment period ended on August 31, 2015 and the staff continued to evaluate the comments received.

**FY 2016**

The final version of the NuScale DSRS was published on August 5, 2016. Additionally, staff developed a set of tools and strategies, including a SSC review tool, to assist technical reviewers and their management implement a risk-informed review. The staff briefed the ACRS on their plans on August 16, 2016.

**FY 2017**

The staff applied the SSC review tool and other strategies to develop a graded review approaches for various technical areas. Senior managers presented examples of review approaches to their peers for feedback and to achieve a common management understanding of the proposed scope and depth of review in the various technical disciplines. The staff also briefed the ACRS on the staff's review approaches on May 3, 2017. The staff issued the NuScale DSRS Scope and Safety Review matrix in April 2017 to link NuScale design-related DC, COL, or ESP sections to an existing SRP or DSRS section.

**FY 2018**

The staff continued to use risk insights to prioritize resources on the more safety significant aspects of the ongoing NuScale DCA review. This activity uses risk insights to prioritize staff review efforts on the more safety significant aspects of the NuScale design for a more effective and efficient review.

**FY 2019**

The staff continued to develop risk-informed approaches to ensure an effective and efficient review of the NuScale DCA. Examples are described in the SECY papers identified below.

SECY 18-0099, "NuScale Power Exemption Request from 10 CFR Part 50, Appendix A, General Design Criterion 27 ('Combined Reactivity Control Systems Capability')," explains how the staff used risk insights as part of the justification for granting the partial exemption to GDC 27.

SECY 19-0047, "Containment Performance Goals for the NuScale Small Modular Reactor Design," explains how the staff applied an alternative approach to the containment performance goals by verifying that the NuScale design prevents a large radiological release to the environment. Through this approach, the staff ensures that the NuScale design achieves the goals of containment performance by an alternate means and that this approach provides reasonable assurance of adequate protection of public health and safety.

Additionally, in the SRM to SECY 19-0036 "Application of the Single Failure Criterion to NuScale Power LLC's Inadvertent Actuation Block Valves," the Commission stated that the staff should apply risk-informed principles when strict, deterministic criteria is unnecessary to provide for the reasonable assurance of adequate protection of public health and safety.

**FY 2020**

The staff completed the NuScale Design Certification Application (DCA) Safety Evaluation Report (SER) in August 2020, completing the technical review within the forty two-month published schedule.  This review included granting several exemption requests to 10 CFR Parts 50 and 52, based in part on risk informed reviews.  For example, the exemption request to not meet 10 CFR Part 50, Appendix J, Integrated Leakage Rate Testing, was granted by relying on alternate means (a combination of analysis and pre-operational testing) thereby eliminating any periodic containment vessel pressure testing. The DCA technical review also addressed licensing and design changes late in the review. Staff review and approval of the Topical Report for Alternate Source Term Methodology (ADAMS Accession No. ML20176A494) was based in part on risk informing accident source terms.  The potential for boron recriticality led to design changes. Staff review of this issue led to the identification of a successful recovery strategy to prevent potential reactivity insertion accidents associated with boron dilution sequences.

Also in 2020, GEH submitted three topical reports (LTRs) describing the safety features of the BWRX-300 SMR design in advance of submitting its application.  Staff has prepared a SER for the RPV isolation and overpressure protection LTR, and is currently reviewing the LTRs for containment performance and reactivity control.  GEH is basing their approach on meeting risk goals or providing risk arguments for not meeting certain regulations.

**FY 2021**

No Update

**FY 2022**

No Update

**FY 2023**
In preparation for the submittal of the NuScale standard design approval application (SDAA), the NRC staff collected preliminary risk insights in support of a graded review of the SDAA. These risk insights were leveraged by the NRC staff in its early review of the standard design approval application by: (1) identifying focus areas for the review; (2) grading the review scope and schedule; and (3) supporting decision-making during the acceptance review of the application. The SDAA was accepted and docketed for review in July 2023. As part of its safety review, the NRC staff is continuing to leverage risk insights. In addition to facilitating an effective review, these insights, in conjunction with the use of an integrated team of reviewers from different subject areas, are being actively used to support the resolution of challenging technical issues. This use of risk insights in all aspects of the NuScale SDAA review is aligned with the implementation of the lessons learned from the NuScale design certification application review and is an example of being a more modern risk-informed regulator.

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## Non-Light Water Reactor Licensing Modernization

**Summary Description**

**Summary Description**
The NRC is supporting risk-informed activities related to the Licensing Modernization Project (LMP) being led by Southern Company, coordinated by NEI, and cost-shared by DOE. The LMP's objective is to develop technology-inclusive, risk-informed, and performance based regulatory guidance for licensing non-LWRs. See more information at the NRC's webpage on the Licensing Modernization Project.

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2022**

Staff provided feedback on the Westinghouse eVinci microreactor white paper EVR-SAR-GL-002-NP, Revision 0 “Licensing Basis Event Identification, SSC Classification and Defense-in-Depth Adequacy”. The white paper presents the intended processes for developing the selection of Licensing Basis Events, the safety classification of structures, systems, and components, and an evaluation of defense-in-depth (DID) Adequacy.

**FY 2023**
No Update

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## Risk-informed Emergency Planning Zone Size Evaluation

**Summary Description**

**Summary Description**
In SECY-18-0103, the staff proposed to amend regulations to specify new alternative emergency preparedness framework for small modular reactors, and other new technologies, that would allow these facilities to develop a performance-based emergency preparedness program rather than using the existing deterministic emergency preparedness requirements in 10 CRF 50.33(g).  The Commission published proposed rule (NRC-2015-0225) "Emergency Preparedness Requirements for Small Modular Reactors and Other New Technologies," which, if approved as a final rule, would provide new alternative emergency preparedness requirements that would adopt a performance-based, technology-inclusive, risk-informed, and consequence-oriented approach. The new alternative emergency preparedness requirements and guidance would adopt a scalable plume exposure pathway emergency planning zone approach and address ingestion response planning.  The final draft rule is scheduled to be provided to the Commission by December 30, 2021 for review and approval.  Additional information is available at the Small Modular Reactor and Non-Light Water Reactor Technical and Policy Issues webpage.

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2017 Status**

The staff initiated the review of this LTR in December 2016.

**FY 2018**

The staff continued to review the LTR to determine the acceptability of applying risk-informed methodology to establish the EPZ sizing for the NuScale plant.

This activity will determine the acceptability of the risk-informed methodology to establish the EPZ sizing for the NuScale plant.

**FY 2019**

In support of the potential emergency preparedness rulemaking, the staff is developing guidance that adopts a consequence-oriented, risk-informed, performance-based and technology-inclusive approach for establishing an appropriate emergency planning zone based on analyzing a spectrum of credible accidents for a specific reactor design and site (ML18082A044).

The staff continued to review NuScale's topical report, "Methodology for Establishing the Technical Basis for Plume Exposure Emergency Planning Zones at NuScale Small Modular Reactor Plant Sites" , which proposes a risk-informed approach to establish the plume exposure emergency planning zone size.

The Clinch River Nuclear Early Site Permit Application included a risk informed methodology to calculate the plume exposure pathway emergency planning zone. The staff found this was a reasonable approach in their Advanced Safety Evaluation Report with No Open Items. The permit application is awaiting a decision from the Commission (also see Early Site Permit Application - Clinch River Nuclear Site - Applicant Documents).

**FY 2020**

On December 12th, 2019, the Commission approved publication of the proposed rule (SRM-SECY-18-013). In May 2020, staff published a propose rule (10 CFR 50.160, FR 28436, Vol. 85, No. 92) to amend its regulations to include new alternative emergency preparedness (EP) requirements for small modular reactors (SMRs) and other new technologies (ONTs), such as non-light-water reactors (non-LWRs) and certain non-power production or utilization facilities (NPUFs).  The new EP requirements would acknowledge technological advancements and other differences from large LWRs that are inherent in SMRs and ONTs.  Concurrently, the NRC is issuing for public comment draft Regulatory Guide (DG), DG-1350, "Performance-Based Emergency Preparedness for Small Modular Reactors, Non-Light-Water Reactors, and Non-power Production or Utilization Facilities (ADAMS Accession No. ML18082A044)."

Information related to the consequence-oriented, risk-informed, performance-based and technology-inclusive approach for establishing an appropriate emergency planning zone can be found at Small Modular Reactor and Non-Light Water Reactor Technical and Policy Issues, Item II. Information on the planned rulemaking activities can be found at Planned Rulemaking for Emergency Preparedness Requirements for Small Modular Reactors and Other New Technologies.

**FY 2021**

No Update

**FY 2022**

The final rule package (SECY-22-0001) was provided to the Commission January 18, 2022.

**FY 2023**

No Update

**FY 2024**
The final rule package was published in the Federal Register on November 16, 2023 and became effective December 18, 2023.

 |  

## Advanced Reactor Regulatory Framework

**Summary Description**

**Summary Description**
The staff has developed a vision and strategy to assure that the NRC is ready to review potential applications for non-light water reactor (non-LWR) technologies effectively and efficiently. The staff described the vision and strategy in "NRC Vision and Strategy: Safely Achieving Effective and Efficient Non-Light Water Reactor Mission Readiness," which was published in the Federal Register on July 21, 2016, for stakeholder input. The NRC updated its Vision and Strategy Document to reflect stakeholder feedback in December 2016.

To achieve the goals and objectives stated in the NRC's vision and strategy, the NRC has developed implementation action plans (IAPs). The IAPs identify the specific activities the NRC will conduct in the near-term (within 5 years), mid-term (5-10 years), and long-term (beyond 10 years) timeframes. The NRC released its draft IAPs to obtain stakeholder feedback during a series of public meetings held between October 2016 and March 2017. The staff considered the ACRS comments and stakeholder feedback in the final Near-Term, Mid-Term and Long-Term IAPs which were issued on July 12, 2017.  Key activities related to the development of an advanced reactor regulatory framework include the following:
                - Part 53 – Risk Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors
                - Flexible Licensing Processes for Advanced Reactors
                - Industry-Led Licensing Modernization Project
                - Advanced Reactor Content of Application Project
                - Advanced Nuclear Reactor Generic Environmental Impact Statement (GEIS)
                - Fusion Energy Reactors

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2021**

See Summary Description

**FY 2022**

On September 30, 2022, the NRC staff released the draft proposed rulemaking package, including the draft proposed rule language for both Framework A and B, the preamble (e.g., statements of consideration), and five draft guidance documents supporting the draft proposed rule language. In May/June 2022, NRC staff released its second iteration of preliminary proposed rule language for Framework A (Probabilistic Risk Assessment (PRA)-led approach) and the first iteration of the preliminary proposed rule language for Framework B (Traditional Use of Risks Impacts, Principal Design Criteria, and the Alternative Evaluation of Risk Insights (AERI) approach). In November 2022, staff will present to the Commission a paper outlining options for a risk-informed regulatory framework for commercial fusion energy systems.

**FY 2023**
On March 1, 2023, the NRC staff submitted SECY-23-0021, "Proposed Rule: Risk-Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors (RIN 3150-AK31; NRC-2019-0062)," to the Commission for consideration. The NRC staff released several iterations of preliminary proposed rule language to support numerous opportunities for public engagement (see the Part 53 public website for a complete list of public meetings). Additional details related to the Part 53 rulemaking schedule and major milestones can be found on the NRC's rulemaking website.

 |  

## Physical Security for Advanced Reactors

The U.S. Nuclear Regulatory Commission (NRC) is developing specific physical security requirements for advanced reactors, which refers to light-water small modular reactors and non-light-water reactors. The NRC is proposing a limited-scope rulemaking that would provide a clear set of alternative, performance-based requirements and guidance for advanced reactor physical security that would reduce the need for exemptions to current physical security requirements when applicants request permits and licenses. This rulemaking would provide additional benefits for advanced reactor applicants by establishing greater regulatory stability, predictability, and clarity in the licensing process.

Additional information is available at the Advanced Reactors web page.

 |  

## Regulatory Guidance on Advanced Non-LWR PRA Acceptability

**Summary Description**

**Summary Description**
Regulatory guidance is needed that provides the staff position on what constitutes an acceptable PRA for an ANLWR and how the ANLWR PRA standard and peer review guidance are used to demonstrate conformance with the staff position. This regulatory guidance is expected to provide a definition for what constitutes a PRA and a staff position on PRA acceptability for ANLWRs addressing the (1) scope of a PRA, (2) technical elements of a PRA, (3) level of detail of a PRA, and (4) plant representation in the PRA model. This regulatory guidance will also provide a staff position on the consensus ANLWR PRA standard and industry peer review PRA programs, demonstration of the acceptability of an ANLWR PRA, and documentation to support a regulatory submittal. Finally, this regulatory guidance will also provide the NRC endorsement of the published ASME/ANS ANLWR PRA standard and related industry guidance documents on PRA peer review.

**Previous Fiscal Years**

**Previous Fiscal Years**
**FY 2020**

The staff are in the process of developing the staff position on ANLWR PRA acceptability and are preparing for the review and endorsement of the published ANSI consensus standard for ANLWR PRA and related peer review guidance.

**FY 2021**

The staff reviewed the published ASME/ANS NLWR PRA consensus standard, ASME/ANS RA-S-1.4-2021, “Probabilistic Risk Assessment Standard for Advanced Non- Light Water Reactor Nuclear Power Plants.” The staff made publicly available a pre-decisional draft version of the trial use RG 1.247 to facilitate discussions of stakeholder views and perspectives. Publication of RG 1.247 for trial use is anticipated by mid-FY2022.

**FY 2022**

In March 2022, staff issued for trial use and comment RG 1.247. Comment responses are available at 87 FR 62894.  Also see Endorsement of ASME/ANS RA-S-1.4 Probabilistic Risk Assessment Standard for Advanced Non-Light Water Reactor Nuclear Power Plants website.

**FY 2023**
Regulatory Guide 1.247 "Acceptability of Probabilistic Risk Assessment Results for Non-LWR Risk Informed Activities" was issued for trial use in March 2022. The staff will continue gaining experience with the implementation of the RG and new risk-informed application reviews. The length of the trial period is yet to be determined. The trial period will depend on a number of ongoing activities such as accruing lessons learned from the implementation of the RG and continued development of PRA standards. Also see Endorsement of ASME/ANS RA-S-1.4 Probabilistic Risk Assessment Standard for Advanced Non-Light Water Reactor Nuclear Power Plants website.

## Risk-informed Tools for Advanced Non-LWR Component Performance

**Summary Description**

**Summary Description**
The development of risk-informed tools is valuable to NRC staff when performing safety assessments of Advanced Non-light Water Reactor (ANLWR) components. There is significant experience within the NRC and abroad with evaluating light water reactor (LWR) components, but ANLWRs do not have the same depth of background, and thus development of risk-informed tools is of particular interest at the design stages for ANLWRs. In Regulatory Guide 1.87 Revision 2, the NRC endorsed Section III Division 5 (III-5) of the 2017 edition of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) which provides guidance on high temperature nuclear construction. Subsection HH Subpart A and B in III-5 provide probabilistic failure methodologies for non-metallic components. These failure methodologies are quite complex, and development of computational tools is necessary for implementing these methods. A computational tool has been developed by the NRC to model graphite behavior and make use of the non-metallic guidance in the III-5.

**FY 2023**
A graphite modeling tool was developed within Idaho National Laboratory’s (INL) finite element framework MOOSE. Within MOOSE, the graphite tool was made available within Grizzly which focusses on thermo-mechanical behavior modeling. The graphite tool itself has three main pieces. The first piece focusses on thermo-mechanical modeling of graphite, which includes the effects of irradiation. The second piece models the effects of degradation of the graphite from oxidation, and the final piece implements the probabilistic structural failure criteria provided in III-5 of the ASME BPVC. A technical letter report, TLR-RES/DE/REB-2022-11, was published which provides an overview of the graphite tool. The graphite tool is under constant development and currently looks to develop functionality to model degradation effects prevalent in a molten salt environment.

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Page Last Reviewed/Updated Wednesday, February 21, 2024

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