ML23158A180
| ML23158A180 | |
| Person / Time | |
|---|---|
| Issue date: | 06/15/2023 |
| From: | Dan Widrevitz NRC/NRR/DNRL/NPHP, NRC/NRR/DNRL/NVIB |
| To: | |
| References | |
| Download: ML23158A180 (1) | |
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Performance Monitoring DAN WIDREVITZ JUNE 15, 2023
Performance Monitoring Performance monitoring provides direct measurements of real-world indicators.
Acceptable performance monitoring approaches must provide:
- Direct evidence of presence and/or extent of degradation
- Validation/confirmation of continued adequacy of analyses
- Timely method to detect novel/unexpected degradation 2
Performance Monitoring Optimizing ISI The NRC has received numerous submittals seeking to optimize ISI inspections such as for pressurizers and steam generators.
Approved submittals include substantive performance monitoring, generally in the form of extending the ISI interval from 10 to 30 years (e.g. doing 33% of what would otherwise be required by ASME Code).
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Performance Monitoring Site vs. Fleet NRC presented example sampling method in a March 27th, 2023 meeting (ADAMS Accession No. ML23114A034.)
Sampling on a per-site basis may result in larger overall percentage of the subject welds being sampled than a coordinated fleet-based sampling program could justify.
NRC staff believe that a more effective and efficient solution path for individual site submittals would require an approved topical report approach.
NRC staff note that such an approach was previously taken for reactor vessel inspections.
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Use of RIDM Language NRC staff have been relying on the conceptual framework of risk-informed decision making to provide scope and depth of review for PFM supported ISI optimization submittals.
Why?
What does this mean?
When is it RIDM?
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RIDM - Why Topic How a materials engineer addresses problem using RIDM How a risk analyst addresses problem using RIDM What can go wrong?
Degradation can impact component structural integrity Component/system failure How likely is it?
Degradation initiation frequency estimated from data or models Frequency of component/system failure - data or analysis What is the consequence?
Component failure proxy (leakage, rupture, LOCA etc.)
Core damage, etc.
Defining risk/risk metric Increase in risk of component failure due to alternative Increase in risk of core damage due to alternative Calculating Risk PFM PRA Risk acceptance criteria Does the alternative significantly increase the risk of component failure? No prescriptive guidance.
Per RG 1.174 6
RIDM - Why Topic How a materials engineer addresses problem using RIDM How a risk analyst addresses problem using RIDM Safety margin Change in ASME code requirements impacts safety margins of component - less inspections yields less margin assurance Similar Performance monitoring Need monitoring to ensure PFM remains valid over time period alternative is approved and protection continues against unexpected degradation Same, but also required for PRA Regulations If staff finds the alternative provides acceptable level of quality and safety, the regulations are met Same Defense in Depth Failure of Class 1 component may impact Defense in Depth, but other barriers to release are unaffected.
Same 7
When probabilistic, risk, and risk-proxy results are used as part of justification for proposal, the RIDM framework provides substantive and defined language to discuss review aspects.
All aspects of RIDM predate PRA and RG 1.174 in regulatory application (use of safety margins, defense in depth, uncertainty, performance monitoring, etc.) though may have been discussed in other terms.
RIDM - What does it mean?
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Formal risk-informed submittals require PRA results and include NRC DRA review scope.
Submittals with substantial probabilistic, risk, and risk-proxy information supporting proposals can be approached in terms of scope and depth of review under intellectual framework of RIDM approach.
LIC-206, Rev. 1 ML19263A645 9
QUESTIONS 10