ML25227A108
| ML25227A108 | |
| Person / Time | |
|---|---|
| Site: | Electric Power Research Institute |
| Issue date: | 08/22/2025 |
| From: | Licensing Processes Branch |
| To: | |
| References | |
| EPRI TR 3002028939, EPID L-2024-LRM-0062 pre-app, EPID L-2024-TOP-0003 pre-fee, EPID L-2024-NTR-0006 post-fee, Risk-Informed HELB Methodology, EPID L-2024-NTR-0006 | |
| Download: ML25227A108 (5) | |
Text
Enclosure REGULATORY AUDIT REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION IN SUPPORT OF THE REVIEW TECHNICAL REPORT 3002028939, RISK-INFORMED HIGH-ENERGY LINE BREAK EVALUATION REQUIREMENTS ELECTRIC POWER RESEARCH INSTITUTE DOCKET NO. 99902021
1.0 BACKGROUND
By letter dated July 23, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24205A146), as supplemented on June 12, 2025 (ML25164A225) and June 26, 2025 (ML25178A798), the Electric Power Research Institute (EPRI) submitted EPRI Technical Report (TR) 3002028939, Risk-Informed [RI] High-Energy Line Break [HELB]
Evaluation Requirements (also referred to as TR RI-HELB), to the U.S Nuclear Regulatory Commission (NRC) for review and approval. EPRI TR RI-HELB provides an alternative means for assessing and confirming that plant structures, systems, and components (SSCs) that are important to safety are adequate to accommodate the effects of postulated accidents, including appropriate protection against the dynamic and environmental effects of postulated pipe ruptures.
By email dated September 10, 2024 (ML24214A023), NRC staff accepted EPRI TR RI-HELB for review. By email dated August 30, 2024 (ML24241A160), the NRC staff forwarded an audit plan to Fernando Ferrante, Program Manager of Risk & Safety, EPRI, to initiate the audit of the TR.
The audit plan was issued on October 25, 2025, and can be found at ADAMS Accession No. ML24298A056. The audit began with an entrance meeting between the NRC staff and EPRI on November 4, 2024, and ended with an exit meeting on May 23, 2025.
2.0 REGULATORY AUDIT BASES Title 10 of the Code of Federal Regulation (10 CFR) Part 50, Domestic licensing of production and utilization facilities 10 CFR Part 50, Appendix A, General Design Criteria for Nuclear Power Plants General Design Criterion (GDC) 4, Environmental and dynamic effects design bases - Structures, systems, and components important to safety shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance,
testing, and postulated accidents, including loss-of-coolant accidents [(LOCA)].
These structures, systems, and components shall be appropriately protected against dynamic effects, including the effects of missiles, pipe whipping, and discharging fluids, that may result from equipment failures and from events and conditions outside the nuclear power unit. However, dynamic effects associated with postulated pipe ruptures in nuclear power units may be excluded from the design basis when analyses reviewed and approved by the Commission demonstrate that the probability of fluid system piping rupture is extremely low under conditions consistent with the design basis for the piping.
While not explicitly part of the review of EPRI TR RI-HELB, the NRC staff also considered the impact of its application to:
10 CFR Section 50.49, Environmental qualification of electric equipment important to safety for nuclear power plants, (the EQ rule) requires, in part, licensees to establish a program for qualifying the electric equipment important to safety. The electrical equipment under the scope of this section includes safety-related equipment, non-safety-related electrical equipment whose failure under postulated environmental conditions could prevent satisfactory accomplishment of safety functions specified by the safety-related equipment, and certain post-accident monitoring equipment. The equipment should remain functional during and following design-basis events to ensure the integrity of the reactor coolant pressure boundary, the capability to shut down the reactor and maintain it in a safe shutdown condition, or the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures.
3.0 AUDIT SCOPE The NRC staff conducted a virtual audit that included technical discussions pertaining to potential requests for additional information (RAIs) as well as comprehension questions on EPRI TR RI-HELB.
4.0 AUDIT DISCUSSION Summary of Information in the Application: EPRI TR RI-HELB, Risk-Informed High-Energy Line Break Evaluation Requirements, describes an alternative methodology for meeting GDC 4, Environmental and Dynamic Effects Design Bases, by providing an acceptable means for assessing and confirming that plant SSCs that are important to safety are adequate to accommodate the effects of postulated accidents, including appropriate protection against the dynamic and environmental effects of postulated pipe ruptures.
To verify that EPRI provided a basis to support its disposition of the TR, the NRC staff audited the TR. The NRC staff will address the issues identified but not resolved in the NRC staffs safety evaluation.
Audit Activities: During the audit, the NRC staff interviewed the EPRI representatives and reviewed documentation contained in the TR and provided by the applicant via the BOX submittals.
Specifically, the NRC staff from the Piping and Head Penetration Branch (NPHP) were assigned to review Section 2.2, Failure Potential Evaluation, which included Degradation Mechanisms
(DMs) and evaluations, Plant-Specific Service History Review, and DM categories. Additionally, Section 2.3, Risk Characterization, was reviewed as well.
For the operating experience (OE), the NRC staff reviewed the results from a service history and susceptibility review conducted at one of the RI-ISI pilot plants.
Audit Report Section 5 lists the documents that were reviewed by the NPHP staff and were found to be relevant to the TR. These documents were identified in the NRC staff search of the EPRI TR. During the audit of the TR, the NRC staff did not identify any OE that would indicate the EPRI TR for HELB evaluation may not be adequate to manage the effects of postulated accidents, including appropriate protection against the dynamic and environmental effects of postulated pipe ruptures.
During the audit breakout session, the NRC staff discussed the audit questions with EPRI and industry representatives and documentation/responses provided by EPRI.
The NRC staff from the Mechanical Engineering and Inservice Testing Branch (EMIB) were the lead branch for the review of the alternative RI-HELB topical report methodology. EMIB staff examined topics related to operator actions, zone of influence, plant walkdowns and DMs. The NRC staff also audited the risk categorization of high-energy piping and the HELB response strategies. For risk-informed decisionmaking the NRC staff focused on determining whether the licensing basis change meets the current regulations and whether the alternative RI-HELB methodology maintains sufficient safety margins.
During the Probabilistic Risk Assessment (PRA) technical discussions, the NRC staff examined topics related to PRA acceptability and the risk-informed decisionmaking principles. Specifically, the NRC staff audited the description of acceptability of a base PRA in terms of the scope and level of detail. The NRC staff also inquired about the consequence evaluation, internal flooding hazards, operator actions, and external hazards. For risk-informed decisionmaking, the NRC staff focused on determining whether the change is consistent with the defense-in-depth philosophy; maintains sufficient safety margins; and provides adequate performance monitoring strategies.
During a breakout session, the NRC staff and EPRI discussed the potential impact of the proposed TR on the qualification of electric equipment. The applicant noted that it plans to supplement the TR based on these discussions. The NRC staff also issued a request for additional information on this topic.
5.0 DOCUMENTS REVIEWED Document No.
Document Title Revision/Version DR-MISC-070 PRA Application Notebook, RI-HELB Risk Assessment for EPRI 3002028939 Revision 0 DR-PSA-005.08 Probabilistic Risk Assessment, High Pressure Coolant Injection (HPCI) System Notebook Revision 8 DR-PSA-005-05 Probabilistic Risk Assessment, Electric Power (EP)
System Notebook Revision 7
Document No.
Document Title Revision/Version DR-PSA-005-11 Probabilistic Risk Assessment, Low Pressure Coolant Injection (LPCI) and CCSW [Containment Cooling Service Water] System Notebook Revision 8 DR-PSA-005-12 Probabilistic Risk Assessment, Main Condenser (MC) and Main Steam (MS) System Notebook Revision 7 DR-PSA-005-14 Probabilistic Risk Assessment, Reactor Protection System (RPS) System Notebook Revision 4 EPRI TR-1006937 Extension of the EPRI Risk Informed ISI Methodology to Break Exclusion Region Programs 4/4/2002 NRC Safety Evaluation on EPRI TR-1006937 Safety Evaluation of Topical Report TR-1006937, Extension of the EPRI Risk Informed ISI Methodology to Break Exclusion Region Programs 6/27/2002 EPRI TR-112657 Revised Risk-Informed Inservice Inspection Evaluation Procedure Revision B-A NRC Safety Evaluation on EPRI TR-112657 Safety Evaluation Report Related to EPRI Risk-Informed Inservice Inspection Evaluation Procedure (EPRI TR-112657, Revision B, July 1999) 10/28/1999 Draft Responses to Audit Question for Audit Breakout on 2/17/2025 2/17/2025 Draft Update to Section 2.2.1, DM Evaluation 2/17/2025 Draft Responses to Audit Question for Audit Breakout on 3/10/2025 3/10/2025 Draft Responses to Audit Question for Audit Breakout on 4/11/2025 4/11/2025 6.0 TEAM AND REVIEW ASSIGNMENTS The audit team consisted of the following NRC staff:
NAME ASSIGNMENT DIVISION BRANCH Stewart Bailey Chief Division of Engineering and External Hazards DEX Mechanical Engineering &
Inservice Testing Branch (EMIB)
John Bozga Mechanical Engineer DEX EMIB Drew Childs Reliability and Risk Engineer Division of Risk Assessment (DRA)
PRA Licensing Branch A (APLA)
Stephen Cumblidge Mechanical Engineer Division of New and Renewed Licenses (DNRL)
Piping and Head Penetration Branch (NPHP)
David Gennardo Reliability and Risk Engineer DRA APLA Kaihwa Hsu Senior Mechanical Engineer DEX EMIB Lois James Senior Project Manager Division of Operating Reactor Licensing (DORL)
Licensing Projects Branch (LPLB)
Kamal Manoly Senior Level Advisor for Structural Mechanics DEX
NAME ASSIGNMENT DIVISION BRANCH Ching Ng Senior Reliability and Risk Engineer DRA APLA Eric Reichelt Senior Materials Engineer DNRL NPHP Matthew McConnell Senior Electrical Engineer DEX Long Term Operations and Modernization Branch (ELTB)
The EPRI audit team consisted of the following representatives:
NAME AFFILIATION Jenna Burr Constellation Nuclear Fernando Ferrante EPRI Richard Fougerousse EPRI John Fox Constellation Nuclear Doug Kull EPRI Ashley Lindeman EPRI Roy Linthicum Constellation Nuclear Andrew Mante EPRI Jim Moody EPRI Patrick O'Regan EPRI Ryan Tehnant Constellation Nuclear Daniel Thomas Constellation Nuclear Ron Wise Contech Engineered Solutions, Inc.
7.0 CONCLUSION
The audit accomplished the objectives and goals listed in Section 3.0 of the audit plan by allowing direct interaction with EPRI technical experts. The NRC staff were able to obtain clarification on multiple questions, examine notes supporting potential RAI responses, and discuss differences in technical opinion. The clarifications and examinations allowed the NRC staff to assess the need for RAIs and develop the RAIs more efficiently. The discussions on differences in technical opinion will allow the NRC staff and EPRI representatives to obtain alignment on the final safety evaluation.