L-24-227, Response to Request for Additional Information for Relief Request RR-A 1
| ML24326A082 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/20/2024 |
| From: | Tony Brown Vistra Operations Company |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-24-227, EPID L-2024-LLR-0037 | |
| Download: ML24326A082 (1) | |
Text
L-24-227 November 20, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Davis-Besse Nuclear Power Station, Unit No. 1 Docket No. 50-346, License No. NPF-3 Davis-Besse Nuclear Power Station Terry J. Brown Site Vice President 5501 N. State Route 2 Oak Harbor, Ohio 43449 419-321-7676 10 CFR 50.55a Response to Request for Additional Information for Relief Request RR-A 1 {EPID L-2024-LLR-0037)
By letter dated June 5, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24158A004 ), Vistra Operations Company LLC (Vistra) submitted a request for relief (RR-A 1) from certain requirements of the ASME Boiler and Pressure Vessel Code Section XI at the Davis-Besse Nuclear Power Station, Unit No. 1. The request applied to the fourth 10-year inservice inspection interval, and RR-A 1 provided the basis for the determination that the inservice examination of certain welds were determined to be impractical.
By electronic mail dated September 30, 2024, the Nuclear Regulatory Commission staff issued a request for additional information (RAI) identifying areas where information is needed to complete its review. On October 31,
2024, a clarification call was held with the NRC to fully understand the request. The Vistra RAI response is attached.
There are no regulatory commitments contained in this submittal. If there are any questions, or if additional information is required, please contact Jack Hicks, Senior Manager, Fleet Licensing, at (254) 897-6725 or jack.hicks@vistracorp.com.
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Terry J. Brown
Attachment:
Response to Request for Additional Information cc:
NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board 6555 SIERRA DRIVE' IRVING. TEXAS 75039 0 714-817 4600 VISTRACORPCOM
Attachment L-24-227 Response to Request for Additional Information Relief Request RR-A 1, lnservice Inspection Impracticality Page 1 of 2 By letter dated June 5, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24158A004 ), Vistra Operations Company LLC (Vistra) submitted a request for relief (RR-A 1) from certain requirements of the ASME Boiler and Pressure Vessel Code Section XI at the Davis-Besse Nuclear Power Station, Unit No. 1. The request applied to the fourth 10-year inservice inspection interval, and RR-A 1 provided the basis for the determination that the inservice examination of certain welds were determined to be impractical.
By electronic mail dated September 30, 2024, the Nuclear Regulatory Commission staff issued a request for additional information (RAI) identifying areas where information is needed to complete its review. The Vistra RAI response is provided below. Each RAI is presented in bold font, followed by the response.
RAl-1 Issue On document page 8 of the subject request L-23-214, the licensee stated that no recordable indications were detected during the ultrasonic (UT) examination of Weld RC-RPV-WR-34 (Lower Shell-to-Bottom Circumferential Weld) with 50.2% coverage achieved during the scan. By letter dated February 27, 2013 (ML13059A315), FirstEnergy Nuclear Operating Company (then licensee of Davis-Besse) submitted relief request L-13-076. This request included a notification of impracticality, RR-A36, to obtain the required examination coverage of "essentially 100 percent" for Weld RC-RPV-WR-34 due to the position of core guide lugs. On document pages 52 and 53 of ML13059A315, a recordable indication within the weld was reported. This indication was determined to be acceptable after the licensee performed an analysis of the size and location of the indication. In the comments for this indication, the previous licensee stated that the indication was recorded during the examination prior to the 2013 submittal.
Request (a) Clarify if the same weld location this indication was detected in the previous two ISi UT examinations was examined as part of the subject request L-23-214.
Response
The location where an indication was found in the previous 2 ISi examinations was also examined as part of the subject request L-23-214.
As communicated in letter dated November 14, 2013 (ML13319A886), Response to Request for Additional Information on 10 CFR 50.55a Request RR-A36, RAl-1, the "identified flaws are embedded and associated with original fabrication versus service induced." The letter further states "For these welds, all of the indications evaluated met the applicable ASME Section XI acceptance standards."
The previous 10-year examination results were reviewed prior to examination, and areas containing previously recorded indications were investigated during the current examination.
Indications were compared with the 2011 final report, and in all instances fewer flaw indications have been recorded during the current examination. This does not mean that the vessel flaw population is changing as the indications are welding fabrication indications and have been there since manufacture or fabrication. Note that the examination performed in 2011 was different in technology, recording methodology, and procedure requirements.
The main difference between the number of indications recorded in the previous examination and the current examination is a difference in recording thresholds and use of Phased Array UT techniques.
There are also cases where previously identified indications have not been detected during the current examination. "Not detected" means that there is insufficient correlation with the flaw location previously reported and the current data or that the indication did not meet the recoding requirements of the procedure. Some of the flaws detected may be close to positions of previously recorded flaws but were not considered close enough to
Attachment L-24-227 Page 2 of 2 positively state that it is the same flaw. Possible reasons for not detecting some of the previously reported flaws include differences in the tool positioning/referencing, differences in applied beam angles or sound field characteristics between focal law groups, or the thresholds between procedures. The latter is particularly evident for flaws of low amplitude that are near recording thresholds. To be considered detected by the current examination, the flaw position and depth had to have reasonable correlation with the previously reported position.
(b) If this weld location could not be examined in the current ISi interval due to impracticality concerns, provide discussion of any dispositioning for possible growth above acceptance criteria between the previous examination and the end of the fourth ISi interval.
Response
This weld location was examined. See response to RAl-1 (a), above.
RAl-2 Issue Within the subject request L-23-214, there is a lack of clarity in the information intended to be conveyed by the figures given in support of examinations of Welds RC-RPV-WR-34 and RC-RPV-WR-35.
Figures for RC-RPV-WR-34 will be used as illustrative examples. Figures 1.1-2 and 1.1-3 are described to show "Area of Interest" and "Area of Coverage - Theta Scan (Cross Section)" respectively. It is unclear what differences exist in the shaded portion of the figures and what information is being communicated.
Figure 1.1-4 appears to be a replication of Figure 1.1-2. Figures 1.1-3 and 1.1-4 give the impression that 100% of the weld volume was able to be accessed, especially in the absence of further explanatory figures as in the case of Weld RC-RPV-WR-35.
Request Please provide updated figures, including necessary information for interpretation of these images such as a legend and more detailed descriptions, in support of weld inspection coverage calculations for RC-RPV-WR-34 and -35.
Response
The figures supporting examinations of weld RC-RPV-WR-34 convey that 100% coverage of the accessible portions (where the lugs did not interfere) were examined. Figure 1.1-5 depicts the transducers and shows the lugs on the inner radius. In the areas of the lugs only partial coverage was achievable. The details of the calculation are in the report shown as Figure 1.1-6. The report details exam angles and beam direction up, down, clockwise, and counterclockwise and indicates that 50.2% of the required examination volume was able to be examined. Calculation of the total aggregate volume examined for RC-RPV-WR-34 was 50.2%.
The figures supporting examinations of weld RC-RPV-WR-35 show the transducers and areas where examinations were limited. Figure 1.2-7 depicts the relationship of the examination area with the instrumentation nozzles that caused coverage limitations. As shown in Figure 1.2-8, the calculation of the total volume examined for RC-RPV-WR-35 was 84%.
The areas that were examined for RC-RPV-WR-34 and RC-RPV-WR-35 had the same interferences as those depicted in letter dated February 27, 2013 (ML13059A315), FirstEnergy Nuclear Operating Company submitted relief request L-13-076. Specifically, Figures 1 through 38 (on pages 46-50 of 66) and Attachment Request RR-A36 (on pages 62-66 of 66). Figure 28 depicts 4 transducers on the inner radius of weld RC-RPV-WR-34, the 2 transducers on the left depict the up and down coverage of the beams and the 2 transducers on the right depict the clockwise and counterclockwise coverage. These figures are still relevant and valid to the latest performance of these exams.