ML23093A215
| ML23093A215 | |
| Person / Time | |
|---|---|
| Site: | 99902071 |
| Issue date: | 04/12/2023 |
| From: | Michael Orenak NRC/NRR/DANU/UAL1 |
| To: | Chapman T X-Energy |
| Orenak M | |
| Shared Package | |
| ML23093A217 | List: |
| References | |
| EPID L-2022-TOP-0010 | |
| Download: ML23093A215 (6) | |
Text
Enclosure OFFICE OF NUCLEAR REACTOR REGULATION REGULATORY AUDIT REPORT XE-100 PRINCIPAL DESIGN CRITERIA LICENSING TOPICAL REPORT X ENERGY, LLC DOCKET NO. 99902071
1.0 BACKGROUND
X Energy, LLC (X-energy) began pre-application discussions with the U.S. Nuclear Regulatory Commission (NRC) staff regarding its Xe-100 pebble-bed high temperature gas cooled reactor design in September 2018. As part of its pre-application activities, X-energy submitted various topical reports (TRs) and white papers for NRC staff review. By letter dated July 13, 2022, X-energy submitted, Xe-100 Principal Design Criteria: Licensing Topical Report (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22195A260). The TR describes the development of the principal design criteria (PDCs) for the Xe-100 reactor. The NRC staff conducted a regulatory audit as part of its review of the TR and development of the safety evaluation.
The NRC staff provided its audit plan to X-energy on January 19, 2023 (ML23009B755). The audit was conducted from February 6 through 16, 2023, using X-energys Certrec electronic reading room (eRR). The NRC staff held an audit exit meeting with X-energy on February 16, 2023.
2.0 AUDIT REGULATORY BASES The basis for the audit is the regulations in Title 10 of the Code of Federal Regulations (10 CFR)
Part 50, Domestic Licensing of Production and Utilization Facilities, Section 50.34, Contents of applications; technical information. The regulation in 10 CFR 50.34(a)(3)(i) requires, in part, that an applicant for a construction permit to build a power reactor provide PDCs for the facility.
Similar regulatory requirements exist for design certifications, combined licenses, standard design approvals, and manufacturing licenses (10 CFR 52.47(a)(3)(i), 10 CFR 52.79(a)(4)(i),
10 CFR 52.137(a)(3)(i), and 10 CFR 52.157(a), respectively). The PDCs establish the necessary design, fabrication, construction, testing, and performance requirements for structures, systems, and components (SSCs) important to safety that provide reasonable assurance that the facility can be operated without undue risk to the health and safety of the public.
3.0 AUDIT PURPOSE AND OBJECTIVES The purpose of the audit was to allow the NRC staff to: (1) efficiently gain an understanding of the detailed information supporting the TR, (2) verify information, and/or (3) identify information that will require docketing to support the development of the safety evaluation.
2 4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES During the review of the TR, the NRC staff developed preliminary questions and discussed them with X-energy during a public meeting held on November 30, 2022 (ML22321A302). X-energy provided formal responses to the questions on December 30, 2022 (ML22364A293).
Subsequently, the NRC staff and X-energy agreed to have an audit of X-energys documents supporting the information in the TR.
At the start of the audit, X-energy made the following documents available in the eRR:
XE00-P-G1ZZ-GLZZ-W-001279, Xe-100 Required Safety Functions and PRA Safety Functions, Revision 3
XE00-P-G1ZZ-GLZZ-W-001067, Xe-100 Preliminary SSC Classification List, Revision 3
XE00-P-PCDA-RPS-GL-GL-X-005767, Xe-100 Special Treatment for the Reactor Protection System, Revision 1
XE00-P-G1ZZ-GLZZ-X-002327, Xe-100 Integrated Decision-making Process Implementation Guide, Revision 2
XE00-P-G1ZZ-RRZZ-R-002414, Probabilistic Risk Assessment: Phase 1 Event Sequence Analysis - Preliminary, Revision 1 In addition, X-energy subsequently made its draft of Revision 2 of the PDC TR available in eRR to facilitate the audit. The audit focused on the information that was in eRR.
The audit followed the guidance in the Office of Nuclear Reactor Regulation Office Instruction LIC-111, Regulatory Audits (ML19226A274).
Members of the audit team included the NRC staff listed below.
Ian Jung Senior Reliability and Risk Analyst Boyce Travis Senior Nuclear Engineer Margaret Audrain Materials Engineer David Burgess General Engineer Michael Orenak Project Manager On February 16, 2023, the NRC staff held an audit exit meeting with X-energy and summarized the audit purpose, activities, and high-level results. The NRC staff did not acquire any documents during the audit.
5.0
SUMMARY
OF OBSERVATIONS During the audit, the NRC staff reviewed the documents in the eRR and sent questions to X-energy via email. X-energy entered the NRC staff questions and the associated written responses into the Certrec Information Management System to support the interactions between the NRC staff and X-energy. The NRC staff and X-energy held several meetings to discuss the questions and responses as well as other topics that came up during the audit. The summary of NRC observations during the audit is described below.
The Xe-100 reactor design is in progress at the time of the PDC TR review. Similarly, X-energys implementation of the Licensing Modernization Project (LMP) process and its
3 development of the probabilistic risk assessment (PRA) for the Xe-100 reactor design are in progress. The LMP process is laid out in Regulatory Guide (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, Revision 0 (ML20091L698). RG 1.233, Revision 0, endorses Nuclear Energy Institute (NEI) 18-04, Risk-Informed Performance-Based Technology Inclusive Guidance for Non-Light Water Reactor Licensing Basis Development, Revision 1, (ML19241A472). The Xe-100 PDCs are developed based on the implementation of the LMP process along with the use of RG 1.232, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, Revision 0 (ML17325A611). Therefore, the Xe-100 PDCs at the time of a licensing application, such as a construction permit or operating license application, will need to be confirmed or updated based on the more mature design and the further implementation of the LMP process that are sufficient to support the licensing application.
The documents made available during the audit showed X-energys supporting documentation implementing the LMP process including those related to the development of the required functional design criteria (RFDCs) and complimentary design criteria (CDCs)1. The RFDCs and CDCs, corresponding to the required safety functions (RSFs) and safety-significant PRA safety functions (PSFs) of the Xe-100 reactor design, become the PDCs for the design in the TR. The audit allowed the NRC staff to gain a better understanding of how X-energy follows the LMP process including the development of the RFDCs and CDCs and some of the implementation details relevant to the PDC development.
According to NEI 21-07, Revision 1, X-energys RFDCs and CDCs developed through the LMP become the PDCs for the Xe-100 reactor. The NRC staff is developing a RG, currently designated as Draft RG 1404, Guidance for a Technology-Inclusive Content-of-Application Methodology to Inform the Licensing Basis and Content of Applications or Licenses, Certifications, and Approvals for Non-Light-Water Reactors, to endorse NEI 21-07, Revision 1, with clarifications and additions. The NRC staff observed that X-energy is following the development of the Draft RG 1404.
One of the focus areas for the regulatory audit was special treatments2 that are relevant to the development of PDCs. Because RG 1.232, Revision 0, was developed and issued before RG 1.233, Revision 0, the RFDCs and CDCs developed under the LMP, a risk-informed and performance-based approach, can result in the design criteria that are different from the PDCs based on RG 1.232, Revision 0, which is based on a more deterministic approach.
1 CDCs, not discussed in NEI 18-04, Revision 1, are introduced in NEI 21-07, Revision 1, Technology Inclusive Guidance for Non-Light Water Reactor Safety Analysis Report: For Applicants Utilizing NEI 18-04 Methodology, (ML22060A190).
2 NEI 18-04, Revision 1, adopts the definition of special treatment in RG 1.201, Revision 1, Guidelines for Categorizing Structures, Systems, and Components in Nuclear Power Plants According to Their Safety Significance (ML0610906270), which was developed for implementing 10 CFR 50.69, Risk-informed categorization and treatment of structures, systems and components for nuclear power reactors. RG 1.201, Revision 1, defines special treatment as those requirements that provide increased assurance beyond normal industrial practices that structures, systems, and components (SSCs) perform their design-basis functions.
4 The PDC TR under review and X-energys responses to some of the NRC staffs preliminary questions discuss special treatments identified when implementing the LMP process. In developing PDCs under the LMP process, X-energy attempts to separate the design criteria from the special treatments for SSCs. The NRC staff observed that there is a lack of clarity regarding the separation between what are considered design criteria and what are considered special treatments in some of the document reviewed during the audit. The NRC staff also observed that some of the discussions in NEI 18-04, Revision 1, are not always clear regarding the separation between the design criteria and special treatments. For example, NEI 18-04, Revision 1, Table 4-1, Summary of Special Treatments for [Safety-Related] and [Non-Safety-Related with Special Treatment] SSCs, lists RFDCs as one of Additional Special Treatment Requirements to be considered. The NRC staff noted that some of the design criteria in RG 1.232, Revision 0, and the General Design Criteria for Nuclear Power Plants (GDCs) under 10 CFR Part 50, Appendix A, contain special treatments, such as testing, inspection, and quality assurance, within their scope.
As a result of the NRC staffs question and the discussion between the NRC staff and X-energy in this area during the audit, X-energy plans to include special treatment PDCs in Revision 2 of the TR and also identify the PDCs that X-energy considers are special treatments to be met through the LMP process.
The NRC staffs review of the documents led to multiple questions to X-energy for clarification. Some of these questions resulted in opportunities for improvements to the documents, and in response, X-energy will consider such improvements in the future revisions of the documents. These NRC staff questions are not directly related to the NRC staffs development of the safety evaluation for the PDC TR under review; therefore, there is no need for regulatory follow-up from the NRC staff perspective.
X-energy placed a draft of Revision 2 of the PDC TR in the eRR and the NRC staff expanded the scope of its regulatory audit to include the review of this draft TR. This draft TR was intended to address the preliminary questions raised by the NRC staff discussed earlier in the audit. The review of this draft TR led to several questions and discussions between the NRC staff and X-energy regarding multiple subject areas, which is summarized below:
o The NRC staff and X-energy discussed questions on PDCs 6 and 17. As a result, X-energy will add surveillance in addition to monitoring, testing, and inspections to PDC 6. For PDC 17, X-energy will modify it to make it clearer that there is no safety-related electrical equipment for the Xe-100 reactor design. The NRC staff observed that some electrical equipment is classified as non-safety-related with special treatment based on the LMP process.
o The NRC staff raised a question on PDC 10 regarding the deletion of any condition of normal operation based on normal operation being outside of scope of NEI 18-04, Revision 1. Normal operation is used in multiple PDCs already, and as discussed in of NEI 21-07, Revision 1, the NRC staff conveyed its expectation that normal operation, although being outside of the scope of the LMP process, should be within the scope of the PDCs to be submitted as part of a licensing application.
X-energy stated they will review all of the PDCs currently associated with normal operations and clarify the language in that set of PDCs.
5 X-energy also stated that, regarding PDC 10 specifically, specified acceptable system radionuclide release design limits (SARRDLs) must be met during normal operations up to and including anticipated operational occurrences (AOOs).
o The NRC staff and X-energy discussed PDC 12 based on a question raised about SARRDLs, which are not limited to AOO conditions. This is also related to PDC 10 in the previous item. Based on the discussion, X-energy will clarify in PDC 12, and other PDCs as appropriate, that SARRDLs are used as limits for AOOs and normal operation and as an initial condition for design basis accident (DBA) analyses. These revisions are intended to support the position for this fuel design that SARRDLs can be exceeded in response to design basis events (DBEs), beyond design basis events (BDBEs), and DBAs.
o The NRC staff and X-energy discussed PDC 16 based on a question regarding why RFDCs are limited to particles and pebbles in the proposed PDC, which limits the functional containment to only particles and pebbles. The functional containment may consist of more than just the particles and pebbles in the final design, and therefore this PDC may or may not be sufficient; use of more general language is likely to fulfill the same function without the potential for confusion or revision in the future. Based on the discussion, X-energy will revise the wording to maintain the delineation between RSF/RFDC and PSF/CDC and will consider removing any system-level descriptions that link a particular SSC in providing a particular function.
o The NRC staff and X-energy discussed PDC 26 based on a question about the change to the associated RFDC. X-energy will add context to how shutdown is captured in the appropriate portions of the RFDCs associated with PDCs 11, 12, and
- 26. X-energy will provide different language to characterize the requirements for the safety functions associated with PDC 26 as well as context behind what constitutes shutdown for the RFDC and CDC in their proposed design criteria. X-energy will also consider combining the RFDC portions of PDCs 11, 12, and 26 into a single PDC to improve clarity.
o The NRC staff and X-energy discussed the scope of the Licensing Basis Events (LBEs) being addressed by the Xe-100 PDCs based on the observation that the BDBEs, a subset of the LBEs under the LMP process, are not included in the draft Revision 2 of the PDC TR in the eRR. X-energy stated that the BDBEs were not added to the scope of the PDC language given that the GDCs in 10 CFR Part 50, Appendix A and the design criteria in RG 1.232, Revision 0, focused on postulated accidents or accident conditions, which X-energy equates to DBAs. X-energy will clarify the rationale for excluding the BDBEs from the PDC language scope with a focus on the NEI 18-04, Revision 1, methodology.
o The NRC staff identified some editorial items on several PDCs during the review and discussed them with X-energy. X-energy will address them accordingly.
During the audit, the NRC staff identified one follow-up item for the NRC staff. The NRC staff will engage X-energy based on the result of the follow-up.
o The NRC staff will internally discuss X-energys proposed scope of LBEs used for the PDCs provided in the draft Revision 2 of the TR in eRR. This issue arose
6 because the LBEs considered in draft Revision 2 excludes BDBEs. During the previous public discussions regarding the NRC staffs development of the RG to endorse NEI 21-07, Revision 1, the role and scope of PDCs for non-light water reactor (non-LWR) licensing applications were discussed, including the potential need for the exemption request from applicable regulations. The NRC considers the requirement to propose PDCs to include a requirement to address the full scope of criteria for the PDC for non-LWRs. This means that the PDCs must establish the necessary design, fabrication, construction, testing, and performance requirements for SSCs (that is, for SSCs that provide reasonable assurance that the facility can operate without undue risk to public health and safety). The NRC staff also notes that the LMP process, independent of the regulatory requirements related to PDCs, directs the identification of RFDCs and CDCs based on a comprehensive set of LBEs identified. The NRC staff will evaluate X-energys proposal for any regulatory implications it may have and subsequently engage with X-energy to discuss the result of the NRC staff evaluation.
This item is also discussed above and X-energy has committed to clarify the rationale for their proposal.
6.0 REQUESTS FOR ADDITIONAL INFORMATION RESULTING FROM AUDIT As a result of the audit, the NRC staff did not identify any specific items as requests for additional information related to this TR. However, the NRC staff will continue to have interactions with X-energy as part of the TR review process.
7.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS Both the NRC staff and X-energy have follow-up items as discussed above. X-energy will address their follow-up items and submit Revision 2 of the TR for the NRC staff review. The NRC staff will follow up on one item discussed above and engage X-energy for resolution of any identified issues.