ML25344A037
| ML25344A037 | |
| Person / Time | |
|---|---|
| Issue date: | 12/19/2025 |
| From: | Beverly Smith NRC/RES/DRA |
| To: | Mark Franke, Jason Kozal, Philip Mckenna, Shilp Vasavada, Patricia Vossmar, Blake Welling Office of Nuclear Reactor Regulation, Region 1 Administrator, Region 2 Administrator, Region 3 Administrator, Region 4 Administrator |
| References | |
| Download: ML25344A037 (0) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 MEMORANDUM TO:
Those on the Attached List FROM:
Brian Smith, Director Division of Risk Analysis Office of Nuclear Regulatory Research
SUBJECT:
REVISION 3 OF RISK ASSESSMENT OF OPERATIONAL EVENTS (RASP) HANDBOOK VOLUME 1 - INTERNAL EVENTS Enclosed for your information and use Revision 3 of the Risk Assessment of Operational Events (RASP) Handbook Volume 1 - Internal Events. Staff from the Office of Nuclear Regulatory Research (RES) and the Office of Nuclear Reactor Regulation (NRR), with support from regional senior reactor analysts (SRAs), revised this handbook as part of periodic efforts to improve and update guidance associated with performing event and condition assessments (ECAs) to support the Significance Determination Process (SDP), the Accident Sequence Precursor (ASP) Program, Management Directive (MD) 8.3, NRC Incident Investigation Program, and notices of enforcement discretion. In addition, User Need Request NRR-2022-001, Support in the Development and Enhancement of NRC Risk Analysis Tools, (ML22139A073), dated May 5, 2022, directs RES to develop new guidance for the application of new and enhanced risk tools/methods for incorporation into the RASP Handbook and to revise existing guidance based on lessons learned.
This revision of the RASP Handbook has revised the section numbers to increase ease of reference and reduce the excessive use of bullets. In addition, Appendix A, Road Map for Risk Analysis of Operational Events, was eliminated because material contained within was never considered formal guidance and was rarely (if ever) used by the SRAs.
Many relatively small revisions, including editorial changes, were made in this revision of Volume 1 of the RASP Handbook to add clarity and to improve the readability of the document.
However, it was determined that some sections needed more substantial revisions, including new guidance. The following are a list of the key changes made in this revision:
Section 4 - Mission Time Updated the guidance for the various cases on revising mission times.
CONTACT: Christopher Hunter, RES/DRA/PRB 301-415-1394, christopher.hunter@nrc.gov December 19, 2025 Signed by Smith, Brian on 12/19/25
Those on the Attached List 2 Section 5 - Common-Cause Failure (CCF) Modeling This section was completely rewritten to update guidance and increase readability.
Added background material on the key CCF models (e.g., Alpha, Multiple Greek Letter, Beta).
Added background material on how common cause component groups (CCCGs) are modeled in the SPAR models and new guidance on CCCG modeling that reduce overcounting/overestimation of potential CCF.
Added new guidance on treatment of intersystem CCFs including cross-unit CCF along with an interim approach for adjusting cross-unit CCF parameters.
Provided information on how different CCF parameters are calculated.
Added section on causal alpha factors, including their limitations, and the recommendation that they should not be used in most cases.
Replaced the CCF ground rules with updated key principles from NUREG-2225, Basis for the Treatment of the Potential CCF in the SDP.
Updated the CCF examples and included a detailed example of how SAPHIRE calculates the revised CCF probability.
Section 8 - Initiating Events Reordered the three cases. Eliminated Case 4 which was associated with support system initiating event (SSIE) component failures (covered in Section 11).
Revised language to be inclusive of the three programs (SDP, ASP, and MD 8.3) and to match what is currently done in the SDP.
Section 9 - Human Reliability Analysis Updated this section to include information on IDHEAS-ECA and the IDHEAS dependency method.
Section 10 - Loss of Offsite Power (LOOP) Events This section was completely rewritten to expand guidance for all LOOP events (i.e., not just LOOP initiating events) and increase readability.
Added key LOOP definitions.
Added section on modeling of FLEX mitigation strategies in the base SPAR models, along with several key areas that analysts may need to revise on a plant-specific basis or at least understand the uncertainties associated with the existing approach.
Added section that provides guidance for analyzing the various LOOP events.
Section 11 - SSIEs Revised and expanded the examples for the various SSIE ECAs.
Enclosure:
- 1. RASP Handbook Volume 1 - Internal Events, Revision 3
ML25344A037 OFFICE RES/DRA/PRB RES/DRA/PRB RES/DRA NAME C. Hunter J. Evans B. Smith DATE 12/10/2025 12/12/2025 12/19/2025
MEMORANDUM TO THOSE ON THE ATTACHED LIST DATED:
SUBJECT:
REVISION 3 OF RISK ASSESSMENT OF OPERATIONAL EVENTS (RASP)
HANDBOOK VOLUME 1 - INTERNAL EVENTS Shilp Vasavada, Director, Division of Risk Assessment, Office of Nuclear Reactor Regulation Shilp.Vasavada@nrc.gov Phil McKenna, Director, Division of Reactor Oversight, Office of Nuclear Reactor Regulation Philip.McKenna@nrc.gov Blake Welling, Director, Division of Operating Reactor Safety, Office of the Regional Admin, Region 1 Blake.Welling@nrc.gov Mark Franke, Director, Division of Operating Reactor Safety, Office of the Regional Admin, Region 2 Mark.Franke@nrc.gov Jason Kozal, Director, Division of Operating Reactor Safety, Office of the Regional Admin, Region 3 Jason.Kozal@nrc.gov Patricia Vossmar, Director, Division of Operating Reactor Safety, Office of the Regional Admin, Region 4 Patricia.Vossmar@nrc.gov December 19, 2025
DATE Memo - Completion of RASP Handbook, Volume 1, Revision 3 December 19, 2025 DISTRIBUTION:
CHunter, RES/DRA/PRB JEvans, RES/DRA/PRAB BSmith, RES/DRA RFelts, NRR/DRO JTappert, RES/DRA JGroom, R-IV/ACES MFranovich, NRR JPelton, NRR/DORL DCollins, R-I/DRP JLara, R-II JGiessner, R-III MShuaibi, R-III JMonninger, R-IV SVasavada, NRR/DRA KHsueh, NRR/DRA PMcKenna, NRR/DRO BWelling, R-I/DRP RMcKinley, R-I/EAGLT PVossmar, R-IV/DRP/RPB-D APatz, R-II/DORS/RPB4/HARO DAird, NRR/DRO/IRAB KCoyne, RES/DRA MFranke, R-II/DORS JKozal, R-IV/DRP/RPB-C GSuber, R-II/DORS BDickson, R-III/DRP/B2 SWeerakkody, NRR/DRA AGarmoe, NRR/DRO/IRAB MKichline, NRR/DRA/APOB QPan, RES/DRA/PRAB MLeech, NRR/DRA/APOB FArner, R-I/DRS CBickett, R-I/DRS/EB2 ARosebrook, R-II/DORS/RPB6 SSandal, R-II/DORS/TSAB TStephen, R-II/DORS/OB1 5
Memo ML25344A037 OFFICE RES/DRA/PRB RES/DRA/PRAB RES/DRA NAME CHunter JEvans BSmith DATE Dec 10, 2025 Dec 12, 2025 Dec 19, 2025