ML23296A088
| ML23296A088 | |
| Person / Time | |
|---|---|
| Issue date: | 10/23/2023 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| References | |
| Download: ML23296A088 (15) | |
Text
NRC PRA Methods Database Development Activities Chris Hunter Sr. Reliability and Risk Engineer Performance and Reliability Branch Division of Risk Analysis Office of Nuclear Regulatory Research 1
2 Key Messages
- The U.S. Nuclear Regulatory Commission (NRC) probabilistic risk assessment (PRA) methods database is being developed as knowledge management tool for NRC staff.
- Aid newer reviewers to efficiently determine the background of a particular PRA method.
- Support graded and focused licensing reviews.
- The database is not a regulatory decision-making tool.
- The NRC made a conscious decision to avoid terminology in the database that may result in its misuse.
- The appropriate disclaimers and limitations will be included in the database.
3 Key Messages (cont.)
The NRC staff is closely collaborating with the Electric Power Research Institute (EPRI) to significantly reduce the duplication of effort.
- EPRI is reviewing NRC PRA methods database information.
- Used EPRIs internal events PRA methods database as starting point for NRC database.
Data Analysis Quantification Human Reliability Analysis
- Shared NRC completed internal fires and seismic PRA methods from NRC database to support EPRIs database.
Will share completed PRA methods for each hazard when completed.
- Additional areas for potential collaboration with EPRI and industry.
High Winds, External Floods, and Other Hazards Database Maintenance Different goals and potential uses necessitate the creation and maintenance of two separate databases.
- Future organizational priorities may change the upkeep and maintenance in one or both databases.
4 Background
- The Office of Nuclear Reactor Regulation (NRR) submitted a research work request to the Office on Nuclear Regulatory Research (RES).
- This request represented an increase in scope from a previous work request, including activities to support non-light water reactor licensing.
- As part of this work, RES was asked to develop a database of probabilistic risk assessment (PRA) methods.
- Additional tasks include:
Development of PRA standards database Update of NUREG-1855 Update NUREG-2122 4
5 Work Overview
- PNNL has vast experience with licensing reviews.
- PNNL complete a report with PRA methods and database fields for each hazard.
- Sandia National Laboratories (SNL) is developing a publicly available database.
- SNL will incorporate PNNLs methods report into the database.
- The PRA methods database will be a part of the public-facing portion of the PRA standards database.
- Reviewers
- RES
- NRR
- EPRI
6 PRA Method Identification Using the Regulatory Guide (RG) 1.200, Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities, Revision 3 (ML20238B871) definition for PRA method.
An analytical approach in the PRA used to satisfy a supporting requirement or collection thereof from a national consensus PRA standard. An analytical approach is generally a compilation of the analyses, tools, assumptions, and data used to develop a model.
PRA methods may include:
Methods formally submitted to the NRC for review Methods that have been used by a licensee or applicant but have not been formally reviewed by the NRC staff or have been used outside of NRC-regulated activities Methods that have been developed by the NRC either via the staff or contractor.
Newly developed methods (NDMs).
Identification of methods is performed by evaluating the high-level requirements (HLRs) and their associated supporting requirement (SRs) for analyses, tools, assumptions, and/or data that form a method needed to model the PRA that satisfies the SRs.
American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) RA-S-1.1-2022 ASME/ANS RA-S-1.2-2014 ASME/ANS RA-S-1.3-2017 ASME/ANS RA-S-1.4-2021 ANS/ASME 58.22-2015
7 Database Fields
- Hazard(s)
- This field contains the applicable hazard(s) for the PRA methods.
- HLR(s)
- This field contain the applicable HLR(s) for the PRA methods.
- SR(s)
- This field contains the applicable SR(s) for the PRA methods.
- Category
- This field identifies the PRA technical element category to which the method belongs.
The categorization of methods attempts to group methods into categories that are readily and clearly understood.
The HLR technical element can be used as the method category if more resolution is not needed to differentiate the category.
8 Database Fields (cont.)
Method
- This field provides a brief description of the method.
Methods are organized and defined according to the requirements prescribed by the PRA standard.
Applicability
- This field provides a brief description of the method that includes how it is applied in the PRA.
This field also identifies the primary technical source (or sources) for the method, including a description of the method, its technical basis, and implementation guidance.
Limitations/Clarifications
- This field provides identification of limitations and clarifications important to implementation of the method.
In some cases, limitation and clarifications are part of the guidance provided by the technical source, and sometimes, they are provided by NRC evaluation of the method.
If the method has been supplemented (but not superseded), then this clarification should be noted.
If the method is limited to a certain situation, design, or condition, then this should be noted and the source of appliable guidance on the limitation identified.
9 Database Fields (cont.)
- Source of Technical Basis
- This field provides a full formal reference for the technical sources for the method identified in the Applicability field and potentially in the Limitation/Clarifications field and a link to the online URL (if available).
- Evidence of Use
- This field provides an indication of the evidence of use of the method.
The method has been formally reviewed and accepted in a published evaluation report.
The technical source for the method states it was developed by NRC or by NRC in collaboration with an industry or laboratory partner specifically to support an element of PRA.
The method is cited as an acceptable approach in the PRA standard or in an NRC regulatory guidance document.
The method is commonly used in risk-informed applications that have been reviewed and approved by NRC without comment on the method.
10 PRA Method Database Examples Hazard(s)
HLR(s)
SR(s)
Category Methods Applicability Limitations/Clarifications Source of Technical Basis Evidence of Use Internal Fires PP-A PP-A1 Plant Partitioning Selection of global plant analysis boundary for the internal fire PRA The global plant analysis boundary for fire PRA is to be selected so that plant partitioning is performed on areas of the plant that contribute to fire risk. This guidance is provided in NUREG/CR-6850, Volume 2, Chapter 1.5.1, Step 1.
No limitations noted NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Volume 2: Detailed Methodology, September 2005 (ML15167A411).
RG 1.205 (ML21048A448) references the fire PRA methodology documented in NUREG/CR-6850, which is widely used in fire PRAs supporting applications, such as NFPA 805, TSTF-505, and 10 CFR 50.69 LARs, that have been accepted by the NRC.
Internal Fires PP-B PP-B1 PP-B2 PP-B3 PP-B4 PP-B5 PP-B6 PP-B7 Plant Partitioning Partitioning of the plant into PAUs for the internal fire PRA Partitioning of the plant into PAUs for the fire PRA involves gathering and characterizing fire compartment boundary information. This guidance is provided in NUREG/CR-6850, Volume 2, Chapter 1.5.2 and 1.5.3, Step 2 and 3, NFPA 805, and PRA standard ASME/ANS RA-S1.1.
Justification of (1) non-fire-rated fire barriers, (2) active features such like water curtains, or (3) spatial separation requires assessment that considers the nature of fire sources in that location.
ASME/ANS RA-S1.1, Table 4-A.2.1-3 states NUREG/CR-6850 provides criteria that may be applied in justifying decisions related to spatial separation, active fire barrier elements, and partitioning features that lack a fire-resistance rating.
ASME/ANS RA-S1.1, SR PP-B3 identifies certain features that should not be credited.
NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities -
Volume 2: Detailed Methodology, September 2005 (ML15167A411).
NFPA 805, Performance-Based Standard for Fire Protection for LWR Reactor Electric Generating Plants, 2001. (Newer version available, but not endorsed for 10 CFR 50.48(c) transition)
RG 1.205 (ML21048A448) references the fire PRA methodology documented in NUREG/CR-6850, which is widely used in fire PRAs supporting applications, such as NFPA 805, TSTF-505, and 10 CFR 50.69 LARs, that have been accepted by the NRC.
10 CFR 50.48(c) establishes the requirements for using NFPA 805 as an alternative to the requirements associated with 10 CFR 50.48(b) (Fire Protection covered by Appendix R).
11 PRA Method Database Examples (cont.)
Hazard(s)
HLR(s)
SR(s)
Category Methods Applicability Limitations/Clarifications Source of Technical Basis Evidence of Use Internal Fires IGN-A IGN-A1 IGN-A2 IGN-A3 Ignition Frequency Estimation Generic fire ignition frequencies and probability distribution data for the internal fire PRA NUREG-2169 provides updated generic fire ignition frequencies from the frequencies provided in NUREG/CR-6850, Volume 2, Chapter 6, and probability distribution data.
Selecting a combination of the lowest frequencies from the two sources main sources of generic fire ignition frequencies has not been allowed in NFPA 805 or TSTF-505 reviews.
Note that the generic fire ignition frequencies promogulated by FAQ 08-0048 (NUREG/CR-6850 Supplement 1, Section 10) have been superseded, in their entirety, by NUREG-2169. By analogy, this would also apply to frequencies for cable fires initiated by welding and cutting that were developed by the EPRI-led Fire PRA Methods Review Panel.
Following the methods outlined in NUREG-2169, Chapter 7 of NUREG-2230 provides updated generic fire ignition frequencies for non-HEAF electrical cabinets (Bin 15).
For HEAF ignition sources (i.e.,
switchgear, load centers and bus ducts),
updated frequencies appear in Chapter 5 of NUREG-2262 (Bins 16.a, 16.b, 16.1, and 16.2).
For the MCB, updated frequencies appear in Chapter 7 of NUREG-2718, Volume 2 (Bin 4).
NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities - Volume 2: Detailed Methodology, September 2005 (ML15167A411).
NUREG-2169, NPP Fire Ignition Frequency and Non-Suppression Probability Estimation Using the Updated Fire Events Database, January 2015 (ML15016A069).
FAQ 08-0048, Close-Out of NFPA 805 FAQ 08-0048, Fire Ignition Frequencies, May 2015 (ML15134A046).
FAQ 12-0064, Close-Out of NFPA 805 FAQ 12-0064, Revision 1 on Hot Work/Transient Fire Frequency Influence Factors, January 2013 (ML12346A488).
NRC-to-NEI Letter, Recent Fire PRA Methods Review Panel Decisions and EPRI 1022993, Evaluation of Peak Heat Release Rates in Electrical Cabinet Fires, June 2012 (ML12171A583).
NUREG-2178, Refining and Characterizing Heat Release Rates from Electrical Enclosures During Fire (RACHELLE-FIRE), Volume 2: Fire Modeling Guidance for Electrical Cabinets, Electric motors, Indoor Dry Transformers, and the Main Control Board, June 2020 (ML20168A655).
NUREG-2230, Methodology for Modeling Fire Growth and Suppression Response for Electrical Cabinet Fires in Nuclear Power Plants, June 2020 (ML20157A148).
NUREG-2262, High Energy Arcing Fault Frequency and Consequence Modeling, April 2023 (ML23108A113).
RG 1.205 (ML21048A448) references the fire PRA methodology documented in NUREG/CR-6850, which is widely used in fire PRAs supporting applications, such as NFPA 805, TSTF-505, and 10 CFR 50.69 LARs, that have been accepted by the NRC.
NUREG-2169, as supplemented by NUREG-2230, NUREG-2262 and NUREG-2718, provide guidance specifically developed by NRC and EPRI to update the frequencies provided in NUREG/CR-6850.
The guidance provided in the closeout memorandum to FAQs, including 12-0064, is acceptable for use by licensees.
Guidance on referenced methods developed by the EPRI-led Fire PRA Methods Review Panel was endorsed by the NRC staff.
PRA Methods Database Demo (SNL)
13 Status
- Completed identification and documentation of PRA methods for internal fires and seismic hazards.
- Incorporated feedback provided by RES, NRR, and EPRI.
- PRA methods for internal floods are undergoing review.
- Currently working on internal events.
- Used completed industry database work on as a starting point.
NRC has shared with EPRI its PRA methods report to be used in industry activities.
- Some difficulties in identifying methods for high winds, external flooding, and other hazards.
- NRC and PNNL do not have access to documentation in these areas.
May consider delaying these elements Is this a potential opportunity to work with industry who may have more experience/access to the necessary documentation?
14 Database Maintenance
- Current contract with PNNL is for an additional 2 years of updates and revisions.
- A plan for long-term maintenance still needs to be determined.
- Need to determine the best way for users to provide feedback for additions and changes.
- In addition, general feedback on the database and its usability and features would be valuable.
- Is the database maintenance a potential area for collaboration of between the NRC and industry?
- Although there are different uses and slightly different information, there could be collaboration to keep the two databases in sync.
Questions?
15