CNL-17-076, Bellefonte Nuclear Plant, Unit 2 - Containment Vertical Tendon (V281) Failure - Second Interim Report
| ML17158B336 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 06/07/2017 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNL-17-076 | |
| Download: ML17158B336 (4) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga , Tennessee 37402 CNL-17-076 June 7, 2017 10 CFR 50.55(e)
ATTN : Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Bellefonte Nuclear Plant, Unit 2 Construction Permit CPPR - 123 NRC Docket No. 50-439
Subject:
Bellefonte Nuclear Plant Unit 2 - Containment Vertical Tendon (V281)
Failure - Second Interim Report Reference(s) 1. U.S. Nuclear Regulatory Commission Operations Center Event Notification No. 52476, dated January 6, 2017
- 2. Letter from TVA to NRC, CNL-17-004, "Bellefonte Nuclear Plant Unit 2-Containment Vertical Tendon (V281) Failure - First Interim Report," dated January 6, 2017.
The purpose of this letter is to provide the NRC with the second interim report on the subject defect initially reported to the NRC Operations Center on January 6, 2017, and referenced Bellefonte Condition Report 1239343. TVA submitted the initial interim report on this matter via Reference 2.
This interim report was originally scheduled to be submitted on May 25, 2017 . During the conversation with Mr. Robert Schaaf of your staff on May 24, 2017, it was agreed that TVA would submit the second interim report on or before June 9, 2017. Enclosure 1 of this letter contains the second interim report. Enclosure 2 provides the list of commitments made in this submittal. TVA will submit the next report by October 31, 2017 . Please address any questions regarding this response to Gordon P. Arent at 423-365-2004.
J.
President, Nuclear Licensing Enclosures cc: See Page 2
U.S. Nuclear Regulatory Commission CNL-17-076 Page 2 June 7, 2017 Enclosure(s) 1. 10 CFR 50.55(e) Second Interim Report Bellefonte Nuclear Plant Containment Vertical Tendon Coupling Failure
- 2. List of Commitments cc (Enclosure):
NRC Regional Administrator - Region II Deputy Regional Administrator for Construction NRR Project Manager - Watts Bar Nuclear Plant
10 CFR 50.55(e) SECOND INTERIM REPORT BELLEFONTE NUCLEAR PLANT (BLN)
CONTAINMENT VERTICAL TENDON COUPLING FAILURE Description of Deficiency The additional inspection of the failed Bellefonte Nuclear Plant (BLN) Unit 2 Reactor Building Containment Vertical Tendon V281 coupling indicated a potential for an unknown common mode failure mechanism for BLN Containment vertical tendon rock anchor couplings. On December 6, 2016, the Unit 2 Reactor Building Containment Vertical Tendon V281 rock anchor/
tendon anchor coupling was found failed during a routine weekly inspection. The anchor coupling appears to have sheared in the threaded portion allowing the anchor head for the vertical tendon and the anchor head for the rock anchor tendon to separate.
The failed tendon coupling was inspected on October 19, 2016, and showed no signs of component specific damage or improper installation creating the potential for an unknown common mode failure.
Safety Significance The cause for the failure of the V281 rock anchor/tendon anchor coupling has been determined to be Environmentally Influenced Corrosion Cracking. An extent of condition including grease testing of 18 additional tendons, has determined that no detectable hydrogen sulfide was found and that there would come a time, where the remaining tendons would have an insufficient amount of water present to support corrosion and its associated hydrogen induction. Based on this conclusion, additional tendon failures of this type are not anticipated.
Cause of Deficiency The cause of the failure of the V281 rock anchor/tendon anchor coupling is Environmentally Influenced Corrosion Cracking. Chemical analysis of the coupling grease and metallurgical analysis of the failed coupling was performed.
Interim Progress Upon discovery, access to the BLN Unit 2 tendon gallery was restricted. The area of the V281 tendon failure has been cleaned. Grease samples have been obtained and sent to TVA Central Labs for analysis. The coupling from the rock anchor and tendon anchor locations has been removed and was sent to TVA Central Labs for metallurgical analysis. The subsequent Central Labs report was sent to Sargent and Lundy for further evaluation Grease samples have also been taken from adjacent tendons (V272 through V290) to evaluate if conditions are similar to the samples from tendon V281.
A third party consultant performed a vendor review which indicated that the failure was similar to the Unit 1 tendon V-9 failure that occurred in 2009. The analyses performed for the current coupling failure have determined that the failure mechanism is the same for both failures.
Additional corrective actions will be determined after review of both reports. The results will be contained in Corrective Action documents CR 200119, 1239343 and 225287.
Future Updates TVA will provide an update to this report by October 31, 2017.
CNL-17-076 E1 1 of 1
ENCLOSURE 2 LIST OF COMMITMENTS
- 1. TVA will submit an update to this interim report prior to October 31, 2017.
CNL-17-076 E2 1 of 1