ML23097A127

Enclosure - X Energy, LLC – NRC Feedback Regarding Xe-100 Licensing White Paper Probabilistic Risk Assessment Technical Adequacy Approach (EPID L-2022-LRO-0150/CAC 000431)

ML23097A127
Person / Time
Site:	99902071
Issue date:	05/31/2023
From:	Andrew Proffitt NRC/NRR/DANU/UAL1
To:	Chapman T X-Energy
Devlin-Gill S
Shared Package
ML23097A124	List: ML23097A123 ML23097A127
References
EPID L-2022-LRO-0150, CAC 000431
Download: ML23097A127 (1)

Text

Enclosure X Energy, LLC - NRC Feedback Regarding Xe-100 Licensing White Paper Probabilistic Risk Assessment Technical Adequacy Approach (EPID L-2022-LRO-0150 / CAC 000431)

SPONSOR AND SUBMITTAL INFORMATION Sponsor: X Energy, LLC (X-energy)

Project No.: 99902071 Submittal Date: November 10, 2022 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML22318A236 Brief Description of the White Paper:

The white paper (WP) submitted by letter dated November 10, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22318A236), describes the approach and methods X-energy is using to develop the Xe-100 technical adequacy requirements for construction permit (CP)/operating license (OL) applications and the standard design. The WP also proposes the Xe-100 approach to evaluating the environmental risks of severe accidents.

Action Requested: X-energy requested the U.S. Nuclear Regulatory Commission (NRC) staff, feedback on the approach and methods for licensing submittals. X-energy also seeks the NRC staff feedback on the proposed approach to support its development of Xe-100 Environmental Reports.

FEEDBACK AND OBSERVATIONS The NRC staff are making no regulatory findings on this WP, and nothing herein should be interpreted as official agency positions.

The NRC staff observations and feedback are provided below.

1.

(General) X-energy is implementing the risk-informed, performance-based (RIPB) approach under the Licensing Modernization Project (LMP) in accordance with Regulatory Guide (RG) 1.233, Revision 0, 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 (ML20091L698). Under the LMP process, probabilistic risk assessment (PRA) plays an enhanced role in the RIPB process to inform the licensing basis and the content of licensing applications. The LMP process has not yet been fully exercised in a licensing process; thus, the NRC staff encourages X-energy to engage with the NRC staff in follow-on discussions during PRA and LMP implementation.

2.

(General) The NRC staff notes that the following guidance documents are under development or consideration and encourages X-energys continued attention to their development:

Draft Regulatory Guide (DG)-1404, Guidance for a Technology Inclusive Content of Application Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light-Water Reactors (ML22076A003) is intended to endorse Nuclear Energy Institute (NEI) 21-07, Technology Inclusive Guidance for Non-Light Water Reactor Safety Analysis Report: For Applicants Utilizing NEI 18-04 Methodology, Revision 1 (ML22060A190), with clarifications and additions.

The NRC staff is considering the development of additional regulatory guidance focusing on CP stage PRA that follows the LMP process and plans to engage the stakeholders on the subject. This guidance, once developed, may supplement the guidance in DG-1404.

DG-1413, Technology-Inclusive Identification of Licensing Events for Commercial Nuclear Plants, provides the NRC staffs guidance on identifying licensing events used to inform the design basis, licensing basis, and content of applications for commercial nuclear plants. A pre-decisional version of this DG has been released to support public discussion and can be found at (ML22146A045).

3.

Overall, the WP discusses the approaches and methodologies established for CP, OL, and standard design applications to address the PRA technical adequacy. However, in several places, the term PRA or Xe-100 PRA was used without indicating the specific application stage, e.g., CP stage PRA, OL stage PRA, and so on. The above-mentioned terms could be found in the Abstract section and Sections 2.2.6, 2.3, 2.3.5, 3.1, 3.2, 3.3.1, 3.3.2, and etc. For clarity, it is helpful to specify the intended stage(s) when mentioning PRA in the WP.

X-energy should update the abbreviations/acronyms table (pages viii - ix) to capture and define each of the abbreviations/acronyms on its first use in the document. Examples include OLA, FSAR, DCD, DBE, BDBE, JCNRM, and NSRST.

4.

(Page 3) Specifically, NEI 18-04 establishes a risk informed methodology supporting compliance with.

10 CFR 50.34(a)(3) - Principal Design Criteria (PDC)

10 CFR 50.34(a)(4) - Analysis and Evaluation of [Structures, Systems, and Components]

10 CFR 50.34(a)(7) - Quality Assurance Program The NRC staff makes the following observations:

(1)

For the three regulatory requirements listed under Title 10 of the Code of Federal Regulations (10 CFR) 50.34(a), Preliminary safety analysis report, the use of the more precise titles or descriptions is better for clarity (e.g., emphasize the preliminary nature of the criteria, design, and analysis). For example,

10 CFR 50.34(a)(4) has the following: A preliminary analysis and evaluation of the design and performance of structures, systems, and components of the facility (2)

The three regulatory requirements listed should generally be viewed as examples since the methodology in NEI 18-04 can support compliance with other applicable requirements under 10 CFR 50.34(a). In addition to supporting compliance with regulatory requirements, the NEI 18-04 methodology may be used to justify the requests for exemptions from certain applicable regulations.

5.

(Page 4) Section 2.2.1 has the title 10 CFR 50.34(a)(1) - Contents of applications; technical information. This exact section/title combination is not included in 10 CFR 50.34. Clarify if this section is specific to 10 CFR 50.34(a)(1), which describes a portion of the content of a CP application (CPA), or 10 CFR 50.34, Contents of applications; technical information.

6.

(Pages 4-5) Section 2.2.1 discusses 10 CFR 50.34(a), but does not discuss 10 CFR 50.34(b), Final safety analysis report. In the abstract on page vii, the WP states that Furthermore, this document describes the approach X-energy plans to take in future submittals for a 10 CFR 50 Operating License Application (OLA). Therefore, 10 CFR 50.34(b) should have been discussed in this section for completeness.

7.

(Pages 5-6) Section 2.2.2, 10 CFR 50.34 (f)(1)(i) PRA to Improve Reliability of Core and Containment Heat Removal Systems, discusses 10 CFR 50.34(f)(1)(i), PRA to Improve Reliability of Core and Containment Heat Removal Systems. The final sentence of Section 2.2.2 states that Therefore, X-energy will meet the intent of this requirement despite no explicit requirement to follow the regulation for an advanced [non-light water reactor (Non-LWR)]. The NRC staff notes that if the ongoing 10 CFR Part 50 and 52 alignment rulemaking1 is completed, 10 CFR 50.34(f)(1)(i) may become an explicit requirement for applicants under 10 CFR Part 50.

8.

(Page 6) The last paragraph of Section 2.2.3, 10 CFR 50.71 (h) Maintenance of Records - PRA, states that X-energy will meet the intent of these requirements for an OLA by developing a PRA in accordance with the [American Society of Mechanical Engineers/American Nuclear Society (ASME/ANS) RA-S-1.4-2021, Probabilistic Risk Assessment Standard for Advanced Non-Light Water Reactor Nuclear Power Plants]

standard. X-energy expects to update the PRA on a periodicity no greater than four years. The NRC staff notes that if the ongoing 10 CFR Part 50 and 52 alignment rulemaking is completed, 10 CFR 50.71(h) may become an explicit requirement for OL holders under 10 CFR Part 50. The NRC staff notes that the proposed rule may increase the PRA update periodicity to five years.

1 SECY-22-0052, Proposed Rule: Alignment of Licensing Processes and Lessons Learned from New Reactor Licensing (RIN 3150 AI66) (ML21159A055), issued on June 6, 2022.

9.

(Page 11) Section 2.3, Regulation Implementation Guidelines, states that X-energys approach will consider, NRC input on NEI 20-092 and the ASME/ANS Non-LWR PRA standard to determine the requirements for establishing PRA technical adequacy for risk-informing the Xe-100 licensing basis. The NRC staff endorsement of both of these documents is captured in RG 1.247, Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities (ML21235A008), which the NRC staff published for trial use. X-energy listed RG 1.247 as the first item listed for consideration. Thus, it is not clear what is meant by NRC input regarding NEI 20-09 and the ASME/ANS non-LWR PRA standard.

Section 2.3 also states that X-energys approach will consider NRC input on NEI 18-04 to determine the requirements for establishing PRA technical adequacy for risk-informing the Xe-100 licensing basis. The NRC staff endorsement of NEI 18-04 is captured in RG 1.233, which is also listed for consideration. Thus, it is not clear what NRC input represents in this case.

10. (Page 12-13) Section 2.3.2, RG 1.233 TI-RIPB Methodology to Inform the Licensing Basis, states that The guidance allows assumptions around site characteristics and external hazards for approvals prior to site selection which aligns with the X-energy approach for CPA. It is unclear what X-energy means by approvals in that sentence.

Approvals could be referring to a future topical report before a site selection, or it could be referring to the approval of a CPA where a site must be selected, and site-specific characteristics and external hazards should be adequately addressed. Another interpretation of approvals could be in the context of Commission approval of the safety of design features or specification, such as in 10 CFR 50.35(a), Issuance of construction permits. The meaning of approvals in this sentence should be clarified.

In addition, the section also discusses the lack of site details at a CPA stage. Clarify what is meant by the lack of site details or site information at the CP stage. Such details and information should generally be available because a CP requires a site be selected.

11. (Page 14) Section 2.3.4, SECY-19-0084: New Reactor Licensing Rulemaking, states that SECY-19-0084 reinforced the NRC staff intent for rulemaking to include PRA requirements for new licenses under 10 CFR 50. The NRC staff indicated that the time frame for developing a PRA may be extended to four years after the NRC staff endorsed guidance is available.

The NRC staff could not find the exact expression for the second sentence in SECY-19-0084, Status of Rulemaking to Align Licensing Processes and Lessons Learned from New Reactor Licensing (RIN 3150-AI66) (ML19161A169). The NRC staff found in Enclosure to SECY-19-0084 that, for 10 CFR 50.71(h), This paragraph requires [combined license (COL)] holders to develop a Level 1 and a Level 2 PRA that includes initiating events and modes for which there is the NRC staff endorsed guidance as of 1 year prior to initial fuel loading and 1 year prior to each 4-year update. The NRC staff is considering revising this paragraph to increase the 1 year prior to 4 years prior.

This change would align this requirement with the time frame under which consensus standards are updated and reduce burden. Clarify if this is what X-energy is referring to.

2 NEI 20-09, Performance of PRA Peer reviews Using the ASME/ANS Advanced Non-LWR PRA Standard, Revision 0 (ML20302A115). RG 1.247 endorses it with no exceptions.

12. (Page 14) Section 2.3.5, SECY-15-0002: Updating New Reactor Licensing Policies, Rules, and Guidance, states that The NEI 18-04 process meets these requirements, when discussing the proposed requirements to align 10 CFR Part 50 and 52 regulations related to PRA and severe accidents. The sentence as written is not correct. The NEI 18-04 process is an approach to inform the licensing basis rather than a demonstration of compliance with any specific regulatory requirements. The NEI 18-04 process, however, can be used to develop the bases for complying with applicable regulations or justifying the requests for exemptions. This statement should be clarified.

13. (Page 14) Section 2.3.5 states that The enclosure provides additional detail It is not clear to which the enclosure this statement is referring. It appears that the enclosures to SECY-15-0002, Updating New Reactor Licensing Policies, Rules and Guidance (ML13277A420), do not contain the discussion. Clarify what enclosure X-energy is referring to.

14. (Page 22) Regarding a CPA, Section 3.3.1.1, Construction Permit Application, states that For radiological sources that lack the design detail necessary to address them according to the requirements of the Non-LWR PRA Standard, X-energy will use supplementary analysis and supplementary requirements as described in Section 3 of the Non-LWR PRA Standard. It also states that Low-power modes will be addressed using supplementary analysis and requirements in accordance with Section 3 of the ASME/ANS Non-LWR PRA Standard.

The NRC staff encourages further engagement on the use of supplementary analyses and requirements as discussed in Section 3 of ASME/ANS RA-S-1.4-2021, the non-LWR PRA Standard. The standard states that the use of supplementary analyses and requirements are not within its scope. Areas of interest include the selection and details of the supplementary analyses and requirements as well as whether the supplementary analyses and requirements are based on the NRC staff approved methods or guidance.

15. (Page 22) For the CP PRA, Section 3.3.1.1 states that X-energy does not currently expect to request any design finality as part of a CPA. The Xe-100 PRA scope, level of detail, and degree of plant representation for a CPA will meet requirements selected for this application but will not meet all the requirements of the ASME/ANS Non-LWR PRA Standard. The Xe-100 PRA, however, will still be sufficient to develop a risk-informed licensing basis using the NEI 18-04 process.

The NRC staff acknowledges that the scope and quality of the PRA can vary depending on the type of license application and design maturity. The NRC staff also recognizes that at the CP stage, the PRA may not meet all the requirements of ASME/ANS RA-S-1.4-2021 due to the limited design information available at this stage.

The NRC staff is interested in understanding how the Xe-100 CP PRA, with the limitations discussed, can support the development of its RIPB licensing basis under the LMP process. In addition, the NRC staff is interested in understanding how or whether the use of supplementary analyses and requirements discussed in the previous item are related to this issue. The NRC staff encourages X-energy to clearly define and describe what constitutes the Xe-100 CP PRA, because the limitations and supplementary analysis are outside its scope.

The NRC staff also notes that NEI 21-07 has the following for the CPA content: The discussions in the various sections of [Chapter 3] should provide preliminary assessments of the [anticipated operational occurrences (AOOS), design basis events (DBEs), and beyond design basis events (BDBEs)], and the basis for those preliminary assessments. Any analyses performed and the methods used in those analyses should be described. NEI 21-07 also states that for a CPA the preliminary safety analysis report (PSAR) Chapter 3 should mirror the COL guidance but will reflect the preliminary nature of the design information. The PSAR should describe the methodology to be used in determining the initial set of [licensing basis events (LBEs)]. The discussions should be sufficiently robust so the reader can clearly see how the methodology will lead to a final set of LBEs to be used in developing the final design, safety margins, operational program content, and FSAR content.

Thus, following NEI 21-07, a description of the preliminary PRA or other analyses and methods to inform the preliminary assessments of the LBEs under the NEI 18-04 process is needed as part of a CPA.

16. (Page 22) Section 3.3.1.1 states that the CP PRA will meet Regulatory Position C.3.1 in RG 1.247 by addressing all internal and external hazards in Appendix B of RG 1.247.

The PRA will characterize the hazards that are applicable to the specific site and inform selection of Design Basis Hazard Levels providing the frequencies and consequences of AOOs, DBEs, and BDBEs and implement a fully integrated statement of risk using the Non-LWR PRA Standard.

The NRC staff is interested in additional details on how X-energy plans to develop the frequencies and consequences of a comprehensive list of the Xe-100 LBEs (i.e., AOOs, DBEs, and BDBEs) given the limitations of the CP PRA discussed. Regarding BDBEs, the NRC staff is interested in X-energys approach, or additional engagement on low-frequency and high-consequence external hazards (e.g., seismic) and internal plant hazards (e.g., internal fire) at the CP stage. ANL/NSE-21/56, Regulatory Treatment of Low Frequency External Events under a Risk-Informed Performance-Based Licensing Pathway, discusses some of the challenges and recommendations related to the topic.

The NRC staff is interested in additional details on how X-energy plans to implement a fully integrated assessment of risk using the ASME/ANS RA-S-1.4-2021 at the CP stage.

17. (Page 22-23) Section 3.3.1.1 states that The Xe-100 PRA documentation will identify limitations in the scope and level of detail of the CP-stage PRA and disposition the impact on risk-informed decisions for a CPA.

Section 3.3.1.1.1, Justification for Limiting Scope of POSs Addressed in Xe-100 PRA, discusses the justification for limiting the CP PRA plant operating states (POSs) to only at-power operations. The justification includes insufficient design maturity while discussing future revisions of the PRA that will include all POSs. The section also discusses the supporting requirement of ASME/ANS RA-S-1.4-2021, specifically POS-A1.

The NRC staff observes that clearly identifying and explaining the CP PRA limitations in scope and level of detail and their impacts on the CPA will be important to the NRC staff during its review of the CPA. The NRC staff is interested in additional pre-application interactions on this topic.

ASME/ANS RA-S-1.4-2021 features two Capability Categories (CCs), CC-I and CC-II, for the supporting requirements that are used to distinguish between greater and lesser scopes, levels of detail, plant representation, and realism needed for a given technical requirement. The X-energy WP states that For the PRA supporting the risk-informed applications included in a CPA, the Xe-100 PRA will be limited to at-power operations, which allows X-energy to meet SR POS-A1 at Capability Category I (CC I). The NRC staff also understands that the Xe-100 design, and its associated CP stage PRA are expected to be preliminary. The NRC staff is interested in discussing with X-energy how X-energy plans to meet the CC-I supporting requirements for the expected preliminary design at the CP stage PRA.

The quoted sentence in the previous paragraph has the phrase risk-informed applications included in a CPA. This expression is broad and can be subject to interpretation. For example, is it referring only to the LMP process? Additional clarity to the expression is suggested.

18. (Page 26) In Section 3.3.2, Regulatory Guidance C.3.2, Development and Use of an Acceptable Probabilistic Risk Assessment, X-energy states that it may deviate from some of the guidance in RG 1.247, Appendix A, which the NRC staff published for trial use, and discusses the associated X-energy comments submitted to the NRC staff on the RG. The NRC staff notes that RGs are not substitutes for regulations and compliance with them is not required. Methods and solutions that differ from those set forth in RGs will be deemed acceptable if they provide a basis for the findings required for the issuance of a permit or license by the Commission. The NRC staff encourages additional engagement on the deviations and their bases as applied to Xe-100.

Regarding the stakeholder comments on the RG, the NRC staff has issued a Federal Register Notice 87 FR 62894 in response on October 12, 2022, in which the NRC staff provided discussions on some of the key comments and explained its plan to issue a draft RG for public comments after the trial period.

19. (Page 27) In Section 3.3.2.1, X-energy discusses its position that no peer review of the CP PRA for Xe-100 is to be conducted, based on NEI 21-07 and the NRC staff feedback on the NEI document. As X-energy noted in the section, the RG endorsing NEI 21-07 is under development, which is to be issued for public comments in the future. Thus, X-energy should follow the development of the RG, as discussed in (2.) above.

20. (Page 28) In Section 3.3.2.1.1, Proposed Self-Assessment Approach, X-energy states that Each identified item from the self-assessment (similar to [facts and observations])

will be addressed by dispositioning the item with respect to the risk-informed decisions associated with the license application or by updating the PRA. Clarify what is meant by dispositioning the item with respect to the risk-informed decisions associated with the license application.

21. (Page 30) In Section 3.4.1, Regulatory Guidance C.4.1, Archival Probabilistic Risk Assessment Documentation, X-energy states that, consistent with the ASME/ANS Non-LWR PRA Standard requirements in the Configuration Control technical element, X-energy expects the Xe-100 PRA to meet these requirements prior to the performance of the first peer review.

The NRC staff is interested in whether X-energys CP PRA development is to be under an established quality control process, including configuration management. ASME/ANS RA-S-1.4-2021 states that The objectives of the Configuration Control Program are to ensure that when a PRA is to be used in risk-informed decisions, it represents the as-designed or as-built, as-operated or as-designed, as-intended-to-operate plant at the time of the decision. The CP PRA adequacy may also be supported by the applicant developing the CP PRA under an established quality control process as the design and PRA evolve iteratively consistent with the LMP process.

22. (Page 30) In Section 3.4.1, X-energy states that, consistent with the ASME/ANS Non-LWR PRA Standard requirements in the Newly Developed Methods technical element, the Xe-100 PRA is expected to meet the Newly Developed Methods requirements following the first peer review and it will not meet the Newly Developed Methods requirements prior to the first peer review.

The ASME/ANS non-LWR PRA Standard requirements on the Newly Developed Methods are applicable to PRAs after a peer review. ASME/ANS RA-S-1.4-2021 defines Newly Developed Method as a method used in a PRA that has either been developed separately from a state-of-practice method or is one that involves a fundamental change to a state-of-practice method. A newly developed method is not a state-of-practice or a consensus method. If the Newly Developed Methods are selected and used for the PRAs before a peer review is performed (e.g., a CP PRA), they appear to be subjected to the applicable guidance in place or under development as discussed earlier in (2.)

above and in the WP. The NRC staff encourages X-energy to engage with the NRC staff early if Newly Developed Methods are to be used for its PRA, especially at the CP stage.

23. (Pages 34-35) Section 4, Proposed Xe-100 Approach for Meeting Severe Accident Regulations, states that The Xe-100 license applications will implement NEI 18-04 and NEI 21-07 to analyze the environmental risks of severe accidents and communicate the basis for design alternatives that prevent and mitigate these risks. However, X-energy does not discuss how NEI 18-04 and NEI 21-07, along with the radiological consequence analysis, will be integrated into a cost-benefit analysis for severe accident mitigation alternative/severe accident mitigation design alternative (SAMA/SAMDA) by applying the latest NRC guidance in NUREG/BR-0058, Revision 5, Regulatory Analysis Guidelines of the U.S. Nuclear Regulatory Commission (ML19261A277) and an associated appendix on replacement power in Appendix L (ML22273A162). The NRC staff is interested in obtaining more details on how X-energy intends to address the costs and benefits of SAMAs and SAMDAs, or the basis for not incorporating such alternatives, regarding the guidance in NUREG/BR-0058 based on applying NEI 18-04 and NEI 21-07. The NRC staff would also note that an alternative screening approach to determine whether a SAMA evaluation is necessary is discussed in COL-ISG-029, Environmental Considerations Associated with Micro-reactors (ML20252A076).

Principal Contributor(s): Ian Jung Don Palmrose Hanh Phan