ML23255A104
| ML23255A104 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs, Dresden, Peach Bottom, Nine Mile Point, Byron, Braidwood, Limerick, Ginna, Clinton, Quad Cities, FitzPatrick, LaSalle  |
| Issue date: | 08/11/2023 |
| From: | Scott Wall Plant Licensing Branch III |
| To: | Constellation Energy Generation |
| Wall, SP | |
| References | |
| EPID L-2023-LRM-0062 | |
| Download: ML23255A104 (1) | |
Text
Performance Monitoring Requirements In an April 27, 2023, public meeting (ML23114A034), the NRC stated that probabilistic fracture mechanics (PFM) is inherently risk-informed and consequently, any submittal that uses PFM technology as its basis, will be reviewed as a risk-informed submittal. Therefore, performance monitoring must be addressed in any submittals relying on PFM. An acceptable performance monitoring approach must provide:
- Direct evidence of the presence and/or extent of degradation;
- Validation and confirmation of continued adequacy of analysis, and;
- A timely method to detect novel or unexpected degradation.
In the same April public meeting, the NRC stated that a performance monitoring sample of 25% would yield acceptable results, under certain assumptions, for the US fleet of 61 PWRs using a binomial distribution. It was noted that a smaller performance monitoring sample may be acceptable using a Monte Carlo analysis method. This same 25% performance monitoring sample was reiterated during the June 15, 2023, industry technical exchange meetings (ML23158A180). This performance monitoring sample would result in a 75% examination reduction compared to the current ASME Section XI examination requirements. Since the proposed alternative relies on PFM as part of the technical basis, CEGs proposed performance monitoring plan is provided below.
Current Inspection Intervals The dates for the current inspection intervals are defined in Table XXX of the proposed alternative. To satisfy the ASME Section XI requirements applicable to the components covered by the proposed alternative, the seven CEG PWR units would be required to perform a combined 67 examinations each inspection interval. The table below identifies the number of required examinations, by Unit, Examination Category, and Item Number. The Comp. column identifies how many examinations have been completed for each Unit during the current ISI Interval. As shown in the table below, the seven CEG PWR units have completed a combined 22 examinations (~33% of the required 67 examinations) during the current ISI Intervals. These examinations were performed starting in 2017, with the latest examinations performed during the Spring 2023 Byron Unit 1 outage (B1R25). Table XXX of the proposed alternative and Table XXX of Reference XXX provide the complete examination history for each component.
Since the CEG PWR units have completed a sufficient number of ASME Section XI examination in the current intervals to satisfy the requirements of performance monitoring, no additional examinations will be performed during the current inspection intervals for any of the CEG PWR units. The examinations completed during the current, and previous, inspection intervals serve as sufficient performance monitoring and provide direct evidence of the absence of any service induced degradation, validate the adequacy of the PFM analysis, and confirm the absence of any novel or unexpected degradation.
Successive Inspection Intervals Ginna Ginnas current 6th ISI interval began on January 1, 2020, and will effectively end on September 18, 2029, with the expiration of the current operating license. No examinations are proposed to be performed at Ginna during the current 6th ISI interval for the components covered by the proposed alternative which will result in 12.4 to 16.9 years of elapsed time between the completion of the last ASME XI examination and the end of the current operating license. Ginna most recently completed all ASME XI examination requirements for the components covered by the proposed alternative during the 5th ISI interval which started on January 1, 2010, and ended on December 31, 2019. At this time no examinations have been completed during the 6th ISI Interval for the applicable components. Table XXX of the proposed alternative and Table XXX of reference XXX provide the complete examination history for each component at Ginna. The examinations completed during previous ISI intervals, along with the sample of examinations performed by the CEG PWR units during the current inspection intervals, provide sufficient performance monitoring to support the proposed alternative for the remainder of the current interval.
If Ginna pursues subsequent license renewal to operate beyond the end of the current operating license, the ASME Section XI examination requirements would again become applicable at that time. If Ginna desires to use a similar proposed alternative in the second period of extended operation, it is required to be addressed in the license renewal application or a separate proposed alternative will be submitted in accordance with 10 CFR 50.55a(z), either of which will require separate NRC review and approval.
Calvert Cliffs Calvert Cliffs current 5th ISI interval began on July 1, 2019, and is scheduled to conclude on June 30, 2029. During the current interval, Calvert Cliffs Unit 1 has performed 6 steam generator examinations with no unacceptable indications identified. These examinations include 3 Class 1 nozzle-to-vessel welds (Category B-D), 1 Class 2 pressure retaining welds in pressure vessels (Category C-A), and 1 Class 2 nozzle to vessel weld and 1 inside radius section (Category C-B) as shown in the Table above. For Calvert Cliffs, the Unit 1 examinations performed during the current ISI interval, examinations performed during previous ISI intervals, and the sample of examinations performed by the CEG PWR units during the current ISI intervals, provides sufficient performance monitoring to support the proposed alternative for the remainder of the current interval.
During the successive 6th ISI interval, which is currently scheduled to begin on July 1, 2029, Calvert Cliffs Unit 1 and Unit 2 will perform a sample of 25% of the ASME Section XI required examinations as a performance monitoring plan. The performance monitoring sample size is prorated to account for the
fact that the current operating licenses expire midway through the 6th ISI interval. Calvert Cliffs Unit 1 and Unit 2 will operate approximately 5 years and 7 years, respectively, in the 6th ISI interval prior to the expiration of the current operating license. Therefore, as a performance monitoring plan, Calvert Cliffs will perform 5 steam generator examinations during the 6th ISI interval between Units 1 and 2.
14 exams per unit per interval
- 2 units
- 0.25 PM sample
- 12 yr. / 20 yr. proration = 5 exams The examinations to be performed as the performance monitoring sample will be selected during the 6th interval code of record update and scheduled in the ISI database. The components eligible for selection are shown in Table XXX, of the proposed alternative, and Table XXX of reference XXX.
In the unlikely event that any new unacceptable indications (i.e. new indications exceeding the acceptance standards of IWB-3500 or IWC-3500, as applicable, that are accepted by Repair/Replacement Activity or analytical evaluation) are identified during the performance monitoring examinations, the indications will be evaluated as required by ASME Section XI, and CEG corrective action program. The additional examination and successive inspection requirements of ASME Code,Section XI, also apply. Any new unacceptable indications identified as part of the performance monitoring examinations at Calvert Cliffs will result in both Units reverting to ASME Section XI examination requirements for the remainder of the 6th ISI interval for components covered by the proposed alternative.
If Calvert Cliffs pursues subsequent license renewal to operate beyond the end of the current operating licenses, the ASME Section XI examination requirements would again become applicable at that time. If Calvert Cliffs desires to use a similar proposed alternative in the second period of extended operation, it is required to be addressed in the license renewal application or a separate proposed alternative will be submitted in accordance with 10 CFR 50.55a(z), either of which will require separate NRC review and approval.
Braidwood and Byron Given the similarities in design, materials, construction methods, service conditions, and operating strategies between Braidwood and Byron, a common performance monitoring plan is being proposed for the current and successive inspection intervals. As described previously, a sufficient number of examinations have been performed at Braidwood, Byron, and across the CEG PWR fleet to support the proposed alternative for the remainder of the current 4th ISI intervals. The proposed performance monitoring plan, applicable to the 5th and 6th ISI intervals at Braidwood and Byron, is for 1 out of the 4 units to complete all of the required ASME Section XI steam generator examinations. This represents a 25% performance monitoring sample since one (of four required) steam generators worth of examinations will be performed during the 5th and 6th ISI intervals. The unit selected for performance monitoring will distribute the examinations across the interval as required by Table IWB-2411-1 or Table IWC-2411-1, as applicable. This will ensure a continuous stream of data and allow for timely identification of any service induced degradation or the emergence of any novel degradation mechanisms. Given the limited number of examinations performed during the current ISI interval, Braidwood Unit 1 or Unit 2 will be selected for performance monitoring examinations during the 5th ISI interval. The 5th interval is currently scheduled to begin in July and October of 2028 for Braidwood Unit 1 and 2, respectively. The components selected for examination and the timing of examinations will be determined during the 5th interval code of record update and scheduled in the ISI database. The
components eligible for selection are shown in Table XXX of the proposed alternative and Table XXX of reference XXX.
In the unlikely event that any new unacceptable indications (i.e. new indications exceeding the acceptance standards of IWB-3500 or IWC-3500, as applicable, that are accepted by Repair/Replacement Activity or analytical evaluation) are identified during the performance monitoring examinations, the indications will be evaluated as required by ASME Section XI, and CEG corrective action program. The additional examination and successive inspection requirements of ASME Code,Section XI, also apply. Any new unacceptable indications identified as part of the performance monitoring examinations at Braidwood or Byron will result in all four Units reverting to ASME Section XI examination requirements for the remainder of the interval during which the unacceptable indications are identified. If the unacceptable indication is identified during the 5th inspection interval, and no further unacceptable indications are identified during the resumption of ASME XI examinations, then the proposed alternative may continue to be applied for the 6th inspection interval for all Units.
If Braidwood or Byron pursue subsequent license renewal to operate beyond the end of the current operating licenses, the ASME Section XI examination requirements would again become applicable at that time. If Braidwood or Byron desire to use a similar proposed alternative in the second period of extended operation, it is required to be addressed in the license renewal application or a separate proposed alternative will be submitted in accordance with 10 CFR 50.55a(z), either of which will require separate NRC review and approval.
Performance Monitoring Summary The proposed performance monitoring plan for the CEG PWR fleet provides ample opportunity to provide:
- Direct evidence of the presence and/or extent of degradation;
- Validation and confirmation of continued adequacy of analysis, and;
- A timely method to detect novel or unexpected degradation.
A graphical representation of the performance monitoring plan described above is included in Figure XXX.
In addition to the direct evidence provided by the performance monitoring examinations at Calvert Cliffs, Braidwood, and Byron, examination of steam generator welds and components is expected to continue to be performed by other units across the domestic and international PWR fleet. In the United States there are currently 61 operating PWR Units with approximately 200 steam generators in service.
To date, we estimate that 29 of the operating PWR Units in the United States have submitted or received approval to implement an alternative based on EPRI Report 3002015906 and/or 3002014590.
Thirty-two (32) PWR Units or 52% of the domestic fleet, are required by regulation to follow the ASME Code,Section XI, steam generator examination requirements for the foreseeable future. Based on the sampling nature of ASME Code,Section XI, this is an additional 32 steam generators worth of examinations that will provide opportunities to detect known degradation mechanisms and will also provide the opportunity to detect any new or unexpected degradation mechanisms that may occur in the future for the subject components. This estimation does not include any performance monitoring that may be required as part of the approval process for the 29 units seeking similar alternatives. If a
new degradation mechanism is identified during continued industry examinations, CEG will follow the industry guidance to address the new degradation mechanism.
The absence of any new unacceptable indications in the Calvert Cliffs, Braidwood, and Byron performance monitoring examinations and the absence of any unexpected degradation across the operating fleet provides validation that the assumptions and methods of the PFM Model used in the EPRI Reports are adequate to predict the future behavior of the subject welds and components. The strong technical basis provided by the results of the PFM Model and EPRI Report, along with the implementation of the proposed performance monitoring plan, including scope expansion criteria, will provide additional assurance that the steam generator components across the CEG PWR fleet can operate safely for the remainder of the current operating licenses and will continue to provide an acceptable level of quality and safety.
Figure XXX Note: The end dates for the current interval and the start and end dates for successive intervals are estimates based on the current rolling 10-year interval.
Interval start and end dates may be adjusted as allowed by ASME Section XI.