ML21130A219

Request for Additional Information Regarding Steam Generator Tube Inspection Reports (EPIDs L2020-LRO-0055, L-2020-LRO-0082, and L2020-LRO-0083)

ML21130A219
Person / Time
Site:	Davis Besse
Issue date:	05/10/2021
From:	Tony Brown Energy Harbor Nuclear Corp
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EPID L-2020-LRO-0082, EPID L2020-LRO-0055, EPID L2020-LRO-0083, L-21-118
Download: ML21130A219 (7)

Text

energy Energy Harbor Nuclear Corp.

harbor Davis-Besse Nuclear Power Station 5501 N. State Route 2 Oak Harbor, Ohio 43449 Terry J. Brown 419-321-7676 Site Vice President, Davis-Besse Nuclear May 10, 2021 L-21-118 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 Request for Additional Information Regarding Steam Generator Tube Inspection Reports (EPIDs L2020-LRO-0055. L-2020-LRO-0082. and L2020-LRO-0083)

By letters dated October 31, 2016, and August 21, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML16306A262 and ML18233A451, respectively), FirstEnergy Nuclear Operating Company submitted the reports for the steam generator (SG) tube inspections performed at Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse) during the spring 2016 refueling outage (1R19) and spring 2018 refueling outage (1 R20), respectively. By letter dated September 15, 2020 (ADAMS Accession No. ML20260H057), Energy Harbor Nuclear Corp. submitted the report for the SG tube inspection performed at Davis-Besse during the spring 2020 refueling outage (1 R21 ). The spring 2016 SG tube inspections were the first inspections following SG replacement at Davis-Besse in 2014.

Davis-Besse Technical Specification (TS) 5.5.8, "Steam Generator (SG) Program,"

provides specific requirements for the structural and leakage integrity, repair, and inspection of SG tubes. In addition, TS 5.6.6, "Steam Generator Tube Inspection Report," requires a report summarizing the results of each SG inspection to be submitted to the U.S. Nuclear Regulatory Commission (NRC). The NRC staff is currently reviewing the SG tube inspection reports for the spring 2016, 2018, and 2020 refueling outages at Davis-Besse and has determined that additional information is required to complete its review.

By electronic mail dated February 10, 2021 (ADAMS Accession No. ML21041A545),

the NRC staff issued a request for additional information to complete its review. The Energy Harbor Nuclear Corp. response is attached.

Davis-Besse Nuclear Power Station, Unit No. 1 L-21-118 Page 2 There are no regulatory commitments contained in this submittal. If there are any questions, or if additional information is required, please contact Mr. Phil H. Lashley, Manager - Fleet Licensing, at (330) 696-7208 .

Attachment Request for Additional Information Regarding Steam Generator Tube Inspection Reports cc: NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board

Attachment L-21-118 Request for Additional Information Regarding Steam Generator Tube Inspection Reports Page 1 of 5 By letters dated October 31, 2016, and August 21, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML16306A262 and ML18233A451, respectively), FirstEnergy Nuclear Operating Company submitted the reports for the steam generator (SG) tube inspections performed at Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse) during the spring 2016 refueling outage (1R19) and spring 2018 refueling outage (1 R20), respectively. By letter dated September 15, 2020 (ADAMS Accession No. ML20260H057), Energy Harbor Nuclear Corp. submitted the report for the SG tube inspection performed at Davis-Besse during the spring 2020 refueling outage (1 R21 ). The spring 2016 SG tube inspections were the first inspections following SG replacement at Davis-Besse in 2014.

Davis-Besse Technical Specification (TS) 5.5.8, "Steam Generator (SG) Program,"

provides specific requirements for the structural and leakage integrity, repair, and inspection of SG tubes. In addition, TS 5.6.6, "Steam Generator Tube Inspection Report,"

requires a report summarizing the results of each SG inspection to be submitted to the U.S. Nuclear Regulatory Commission (NRC). The NRC staff is currently reviewing the SG tube inspection reports for the spring 2016, 2018, and 2020 refueling outages at Davis-Besse and has determined that additional information is required to complete its review.

By electronic mail dated February 10, 2021 (ADAMS Accession No. ML21041A545), the NRC staff issued a request for additional information to complete its review. The Energy Harbor Nuclear Corp. response is below.

Request for Additional Information

1. Provide the scope of the array probe and rotating-coil probe special interest inspections performed during 1R21.

The array probe special interest examinations were performed to either characterize selected bobbin probe indications of tube support plate (TSP) wear of tubes or to further characterize bobbin probe proximity indications. As provided by letter dated September 15, 2020 (ADAMS Accession No. ML20260H057), no rotating-coil probe special interest examinations were performed in 1R21.

2. Discuss the results of the channel head visual inspections performed on each SG in 1R21.

The general visual examination of all four channel heads was performed during 1R21 to address industry concerns with steam generator channel head and tubesheet degradation.

The results of these examinations were satisfactory; no degradation was identified.

Attachment L-21-118 Page 2 of 5

3. Provide the scope and results of any secondary side inspection and maintenance activities performed in each SG during 1R21.

The scope of the secondary side inspection included visual examinations performed from the tube bundle periphery of the first span, between the lower tubesheet and the first TSP, in selected locations of SG 2A. These examinations were performed to verify the suspected cause of the proximity indications observed during electromagnetic testing (ET) examinations. The results of the examination confirmed the existence of tie rod bowing conditions at the selected locations visually examined. There was no secondary side inspection in SG 1B during 1R21.

Secondary side maintenance activities performed during 1R21 included adjustment of the orifice plates in both SG 1B and SG 2A. The result of this maintenance was that the steam generator orifice plates were opened to reduce feedwater downcomer level during operation.

4. Sections 2 and 4 of the spring 2018 SG tube inspection report stated that one foreign object wear indication was found in SG 2A in Row 147, Tube 12, during 1R20. No tubes were plugged during 1R20 due to foreign object wear.

Discuss whether the foreign object was still present at the time of the inspection and if it was removed from the SG.

The foreign object was not present at the time of the inspection in 1R20. The small size and location of the indication below TSP 15S made classification difficult during 1R20, and as a result, the most conservative sizing quantification, associated with foreign object wear was used. However, Energy Harbor Nuclear Corp. concluded from the 1R21 examination results that the indication was not associated with foreign object wear and the indication was reclassified as tube wear at a drilled TSP location, as provided the 1R21 report dated September 15, 2020 (ADAMS Accession No. ML20260H057.)

5. Section 2 of each SG tube inspection report identifies the number of broached tube support plate (TSP) wear indications found during the associated refueling outage. This information is summarized in the table below.

Steam Broached TSP Wear Indications Generator 1R19 1R20 1R21 SG2A 627 1337 1912 SG1B 67 194 703

Attachment L-21-118 Page 3 of 5 During an April 12, 2016, teleconference {ADAMS Accession No. ML16130A750) with the NRC staff, the licensee stated that the higher number of wear-like indications in SG 2A were believed to be due to a different length of secondary side piping that runs into SG 2A and that similar differences had been seen with the previous SGs.

Provide any additional insights {e.g., location, wear rate) regarding the higher number of broached TSP wear indications in SG 2A. In addition, provide any insights {e.g., location, wear rate) regarding to the higher number of broached TSP wear indications in SG 1B in 1R21.

The location of broached TSP wear indications continues to be primarily in the periphery of the upper tube bundle in both steam generators. This is expected because of the high crossflow conditions in this region combined with reduced damping due to the superheated steam also present in this region. The upper 95th percentile growth rate of broached TSP wear indications has decreased in 1R21 compared with 1R20 in both steam generators. The higher number of reported broached TSP wear indications in SG 1B from 1R21 are nearly all attributable to very small (<15 percent through-wall) indications first being detected in 1R21.

6. Sections 1, 5, and 6 of each SG tube inspection report provides the number of previously installed tube plugs, the number of tubes plugged during the associated refueling outage, and the total number of tubes plugged in SG 2A.

However, there appears to be discrepancies in the numbers reported. This information is summarized in the table below.

Tubes Steam Refueling Previously Plugged Total Generator Outage Installed Tube During Plugged Plugs Refueling Tubes Outage SG2A 1R19 2 10 11 1R20 22 16 27 1R21 27 78 105 Confirm the total number of previously installed tube plugs and the total number of tubes plugged in SG2A for 1R19, 1R20, and 1R21.

The reporting method changed in the 1R21 report compared with previous 1R19 and 1R20 reports.

The 1R19 and 1R20 Section 1 reports indicate the tube plug examinations as one examination for each plug. With the tubes being plugged at both ends, this resulted in two

Attachment L-21-118 Page 4 of 5 examinations reported for each plugged tube. The two examinations reported in 1R19 were for 1 plugged tube. The 22 examinations reported in 1R20 were for 11 plugged tubes.

However, the Section 1 reporting from the 1R21 report only reported one examination for each plugged tube. In 1R21, both the examination of the hot leg plug and cold leg plug were recorded as one examination, as opposed to two examinations previously.

The 54 previously installed plugs, both hot leg and cold leg, were examined in 1R21. The results of all examinations were satisfactory. The revised table below shows the number of plugs inspected and the number of tubes plugged for each inspection for SG 2A for 1R19, 1R20, and 1R21.

Previous Tubes Steam Refueling Previously Number of Plugged Total Generator Outage Installed Plugged During Plugged Plugs Tubes Refueling Tubes Outage SG2A 1R19 2 1 10 11 1R20 22 11 16 27 1R21 54 27 78 105

7. A drilled TSP wear indication (22 percent through-wall) was reported in Row 142, Tube 1, of SG 2A for 1R20, but no tubes were plugged due to drilled TSP wear indications during 1R20. However, drilled TSP wear indications were only reported in Row 36, Tube 1, and Row 147, Tube 12, of SG 2A for 1R21.

Discuss if a reportable indication was detected in Row 142, Tube 1, of SG 2A during 1R21.

Row 142, Tube 1 of SG 2A was plugged in 1R20 due to a broached TSP wear indication at TSP 16S; therefore, the tube was no longer in service and unable to be examined in 1R21.

8. Section 6 of the spring 2020 SG tube inspection report states that 78 tubes in SG 2A and 66 tubes in SG 1B were plugged during 1R21. The report only noted that one tube in SG 2A was plugged due to broached TSP wear.

Confirm that proximity indications were the reason for plugging the additional tubes. Provide any additional insights regarding the tube proximity indications.

The additional 77 tubes in SG 2A and 66 tubes in SG 1B, which were plugged during 1R21, were preventatively plugged due to the observed proximity indications. As stated in

Attachment L-21-118 Page 5 of 5 response 3 above, selected locations with ET indications of tube proximity in SG 2A were examined visually from the secondary side. The results of the examination confirmed the suspected tie rod bowing conditions. The tie rod bowing condition observed in 1R21 was not associated with any tube-to-tie rod wear or tube-to-tube wear indications. Tube-to-tube wear and tube-to-tie rod wear have been considered potential degradation mechanisms and examinations have been performed to detect them. The proximity indications detected during the 1R21 examinations were discovered during the examinations performed to detect tube-to-tube wear and tube-to-tie rod wear.