ML23033A667

Public Call with Constellation January 30, 2023 (Slides)

ML23033A667
Person / Time
Site:	Calvert Cliffs, Byron, Braidwood, Ginna
Issue date:	01/30/2023
From:	Sujata Goetz Plant Licensing Branch 1
To:	Rhoades D Constellation Energy Generation
Goetz, S
References
Download: ML23033A667 (1)

Text

Performance Monitoring Performance monitoring is a necessary component of Risk-Informed Approach (otherwise it is likely risk-based).

When used for justification for inspection relief, performance monitoring relies heavily on volumetric inspection but also includes information from other monitoring techniques, operational experience, research, etc.

Acceptable performance monitoring approach 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 1/30/2023 1

Performance Monitoring Optimization ASME Code required ISI is a form of performance monitoring providing assurance of component integrity.

-Manages known and unknown (novel) degradation Risk insights were provided in the application regarding known degradation and ISI inspection scenarios using PFM.

- Leaves the appropriate vigilance regarding potential future novel degradation as the primary question regarding proposed future inspections.

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Performance Monitoring - Managing Unknowns 1 In assessing the potential of proposed inspections to identify novel degradation, assurance stems from answering, Can the proposed performance monitoring program detect novel degradation in a timely manner?

This question can be addressed statistically.

The staff considered a number of scenarios to evaluate the applicants proposal.

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Performance Monitoring - Managing Unknowns 2 The staff performed statistical analysis to identify an appropriate level of performance monitoring for the subject steam generators.

The staff believe that an acceptable statistical scenario would:

At a 5% population incidence of novel degradation, have a 90%

probability of detecting at least one occurrence in a steam generator sampled For the subject applications this suggests a reduction in the total number of inspections of SGs (not individual welds) can be reduced by 75% (e.g. 1/4 of the total inspections required by ASME)*

• - Previously the NRC has approved 50% reductions for a more significant component, RPVs 4

Performance Monitoring - Managing Unknowns 3 The applicants proposed number of inspections in the September, 2022, RAI supplement would result in nearly no chance of detecting novel degradation in a timely manner.

The proposal consisted of substantially less than a single SG.

1/25/2023 5

Performance Monitoring - Considerations 1 Qualitative considerations:

• Our statistical analysis was conducted on a per-SG basis, e.g. not counting individual welds

• This side-steps complex considerations of weld comparability and focused on the key interest: integrity of SG

• Later inspections are more likely to detect novel degradation (if it is growing), and consequently are more impactful

• Additional time likely to correlate to increased population incidence and detectability

• Early inspections may be more timely, but also less likely to detect rare novel degradation 6

Performance Monitoring - Considerations 2 Qualitative considerations:

• Staff credits multiple full ASME Code interval inspections on subject components

• Other consideration not addressed in this presentation, e.g., OE, other monitoring, are also important in the development of a PM plan

• This presentation presumes credit given for OE, other monitoring (e.g. leak detection), research, etc.

• This presentation presumes that if novel degradation is found, substantial inspection scope expansion would occur 7

Summary Based on the information presented here by the staff, one acceptable proposal could be:

• To perform 1/4 of the ASME Code-required inspections of a component type (SG, PZR) for all of the units covered under the proposed alternative (rounded up to one more component inspection, if necessary)

• To perform each of the remaining inspections on different components (i.e., to not inspect the same SG or PZR more than once), and

• To perform each of the remaining inspections in the 1st Period of the last ASME Code Interval for the unit at which the inspection is to be performed (based on current 10-year intervals).

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