ML25332A089
| ML25332A089 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 01/14/2026 |
| From: | Kimberly Green Plant Licensing Branch II |
| To: | Erb D Tennessee Valley Authority |
| Green K | |
| References | |
| EPID L-2025-LRO-0031 | |
| Download: ML25332A089 (0) | |
Text
January 14, 2026 Mr. Delson C. Erb Vice President, OPS Support Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR PLANT, UNIT 1 - REVIEW OF THE FALL 2024 STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2025-LRO-0031)
Dear Mr. Erb:
By letters dated May 21, 2025, and October 2, 2025, Tennessee Valley Authority (TVA) submitted information summarizing the results of the fall 2024 steam generator inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 1, during the refueling outage 19.
The NRC staff has completed its review of the information provided and concludes that TVA provided the information required by the Watts Bar, Unit 1, technical specifications and that no additional follow-up is needed at this time. The staffs review summary is enclosed.
If you have any questions, please contact me at 301-415-1627 or via e-mail at Kimberly.Green@nrc.gov.
Sincerely,
/RA/
Kimberly J. Green, Senior Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390
Enclosure:
As stated cc: Listserv
Enclosure REVIEW OF THE FALL 2024 STEAM GENERATOR TUBE INSPECTION REPORT TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 By \
letter dated May 21, 2025 (Agencywide Documents Access and Management System Accession No. ML25141A010), as supplemented by \
letter dated October 2, 2025 (ML25275A045), Tennessee Valley Authority (TVA, the licensee) submitted information summarizing the results of the fall 2024 steam generator (SG) inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 1, during refueling outage 19 (U1R19).
Watts Bar, Unit 1, has four Model 68AXP replacement steam generators, which were designed by Westinghouse, fabricated by Doosan Heavy Industry and Construction, and installed in 2006.
Each SG contains 5,128 thermally treated Alloy 690 tubes. Each tube has a nominal outside diameter of 0.75 inches and a nominal wall thickness of 0.043 inches. The tubes were hydraulically expanded at both ends for the full depth of the tubesheet. The SGs have an integral preheater with small diameter holes (0.29 inch) that prevent the introduction of large foreign objects into the SGs. Stainless steel lattice type advance tube support grids (ATSG) support the vertical section of the tubes. Stainless steel vertical and diagonal structures support the U-bend section of the tubes. The tubes installed in rows 1 through 38 were thermally stress relieved over their entire length after bending.
The licensee provided the scope, extent, methods, and results of the SG tube inspections in the letters referenced above. In addition, the licensee described corrective actions (e.g., tube plugging) taken in response to the inspection findings.
Based on the review of the information provided, the U.S. Nuclear Regulatory Commission (NRC) staff has the following observations:
Eddy current inspection detected tube wear at ATSGs and at U-bend supports. A total of 32 tubes were plugged, all due to wear at ATSGs. In 5 of the 32 tubes, the measured wear depth was greater than the TS plugging limit (40 percent). The remaining 27 plugged tubes were preventatively plugged to support the projected operating cycle until the next SG tube inspection.
The previous operational assessment (OA) supporting five cycles of operation (U1R14 to U1R19) between inspections did not bound the ATSG wear detected in U1R19. SG 1 and SG 4 each had one measured ATSG flaw with a depth greater than the maximum projected depth. The licensees corrective actions, taken in accordance with the industry SG integrity assessment guidelines, included revising the volume-based OA model for the prior inspection cycle and benchmarking it to the U1R19 results, benchmarking wear growth rates to previous projections, and augmenting the U1R19 deterministic OA projections with fully probabilistic and volume-based methods. In its review of the next inspection report, the staff will verify that the modified OA technique projections bound the next SG inspection results.
The licensee concluded that the deterministic, probabilistic, and volume-based evaluations of tube integrity support operation for five cycles until the next planned inspection during U1R24.
In the \
October 2, 2025, letter, the licensee stated that tube integrity limits and OA projections were based conservatively on a flat wear shape; however, two indications were treated as tapered wear in the U1R14 volume-based OA projections and judged to have a tapered shape based on the eddy current array probe data. After re-evaluation for the U1R19 OA, the licensee considers these two indications to have flat wear characteristics in both the U1R14 and U1R19 data.
The NRC staff notes it is important to ensure OA evaluation details are conservative for all degradation mechanisms when projecting degradation over multiple cycles to demonstrate that tube integrity will be maintained until the next planned inspection.
Sludge lancing and foreign object (FO) search and retrieval were performed on the top of the tubesheet in all SGs including visual exams of the tube lane, annulus, and periphery tubes (3 - 5 tubes into the bundle). Of the 21 objects identified, 13 were retrieved and 8 were left in place and evaluated and found acceptable for 5 cycles of operation. Sludge lancing resulted in 42.5 pounds of deposits and debris removed from the four SGs.
The preheater box in each SG was visually inspected for degradation and the presence of FOs. No degradation was found. A total of 31 FOs were found in the four SGs; 26 were removed and the remaining 5 were evaluated and found acceptable for 5 cycles of operation.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by its technical specifications. In addition, the staff concludes that there are no technical issues that warrant additional follow-up action currently since the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.
ML25332A089 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NCSG/BC NAME KGreen ABaxter SBloom DATE 11/28/2025 01/08/2026 11/24/2025 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona KGreen DATE 01/13/2026 01/14/2026