ML25006A117
| ML25006A117 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 01/10/2025 |
| From: | Kimberly Green Plant Licensing Branch II |
| To: | Erb D Tennessee Valley Authority |
| Green K | |
| References | |
| EPID L 2024 LRO 0022 | |
| Download: ML25006A117 (1) | |
Text
January 10, 2025 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 2 - REVIEW OF THE FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT (EPID L-2024-LRO-0022)
Dear Delson Erb:
By letters dated May 16, 2024, and November 4, 2024, Tennessee Valley Authority (TVA) submitted information summarizing the results of the fall 2023 steam generator inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 2, during the Cycle 5 refueling outage.
The NRC staff has completed its review of the information provided and concludes that TVA provided the information required by the Watts Bar, Unit 2, technical specifications and that no follow-up is needed at this time. The staffs review 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. 50-391
Enclosure:
As stated cc: Listserv
Enclosure REVIEW OF THE FALL 2023 STEAM GENERATOR TUBE INSPECTION REPORT TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 By letters dated May 16, 2024, and November 4, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML24137A267 and ML24309A265, respectively), Tennessee Valley Authority (the licensee) submitted information summarizing the results of the fall 2023 steam generator (SG) inspections performed at Watts Bar Nuclear Plant (Watts Bar), Unit 2, during the Cycle 5 refueling outage (RFO 5).
The licensee replaced the Watts Bar, Unit 2, SGs during RFO 4. The replacement SGs are a similar design to the original SGs that contained U-bend tubes and an integral preheater. The four replacement SGs are Westinghouse Model 68AXP, which each contain 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. All tubes were hydraulically expanded through the full thickness of the tubesheet. The lower row U-bend were stress relieved after tube bending. The straight leg portion of the tubes are supported horizontally by stainless steel advanced tube support grids (ATSGs). The upper bundle tube support is provided by stainless steel vertical and diagonal strip assemblies. Each SG has an integral preheater section with a feedwater flow distribution box with small diameter holes to prevent the intrusion of significant foreign objects from the feedwater system. The preheater contains a flow distribution plate designed to develop a uniform upward flow along the tubes in the preheater section.
The licensee provided the scope, extent, methods, and results of their SG tube inspections in the document referenced above. In addition, the licensee described the corrective actions 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:
There are a total of 380 eddy current inspection indications of tube wear at ATSGs with six of these ATSG wear indications having a measured depth between 20 and 28 percent through-wall. There are a total of six indications of tube wear at U-bend supports in all SGs.
Based on the inspection results, 56 tubes with wear at ATSGs and one tube with wear at U-bend supports were plugged. Most of the plugged tubes (47 of 57) were in SG No. 2.
The licensee conducted an apparent cause evaluation for the tube wear at ATSGs in the replacement SGs. The licensee determined that there was higher local crossflow velocity in the preheater region from the recirculation window and leakage from the feedwater box, likely increased above calculated values due to local gaps. These local crossflows, coupled with a potentially ineffective ATSG support (due to fabrication anomaly not detected) are the apparent causes.
The licensee stated it is planning to reinspect the Unit 2 SGs at the next refueling outage (currently scheduled for spring 2025).
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 there are no technical issues that currently warrant additional follow-up action since the inspections appear to be consistent with the objective of detecting potential tube degradation.
ML25006A117 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NCSG/BC NAME KGreen ABaxter SBloom DATE 01/06/25 01/07/25 12/12/24 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona KGreen DATE 01/08/25 01/10/25