05000482/LER-2022-001, Low Steam Generator Level Due to Main Feedwater Valve Failure Caused Reactor Trip
| ML22257A207 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 09/14/2022 |
| From: | Bayer R Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 22-0022 LER 2022-001-00 | |
| Download: ML22257A207 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4822022001R00 - NRC Website | |
text
P.O. Box 411 l Burlington, KS 66839 l 620-364-8831 Robert J. Bayer Plant Manager September 14, 2022 WO 22-0022 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Docket No. 50-482: Licensee Event Report 2022-001-00, Low Steam Generator Level due to Main Feedwater Valve Failure Caused Reactor Trip Commissioners and Staff:
The enclosed Licensee Event Report (LER) 2022-001-00 is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) regarding an Engineered Safety Features Actuation and automatic reactor trip at Wolf Creek Generating Station.
This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4015, or Dustin T. Hamman at (620) 364-4204.
Sincerely, Robert J. Bayer RJB/jkt
Enclosure:
LER 2022-001-00 (
Abstract
Wolf Creek Generating Station 482 4
Low Steam Generator Level due to Main Feedwater Valve Failure Caused Reactor Trip 07 18 2022 2022 001 00 9
14 2022 1
100%
Dustin Hamman, Director Nuclear and Regulatory Affairs (620) 364-4204 B
SJ FCV C635 Y
At 1803 Central Daylight Time (CDT) on July 18, 2022, Wolf Creek Generating Station (WCGS) experienced an automatic reactor trip due to low level in the 'B' steam generator. WCGS was operating in MODE 1 at 100% power when the trip occurred.
ENS notification#56005 was made at 2017 CDT in accordance with 10 CFR 50.72(b)(2)(iv)(B) due to reactor scram, and 10 CFR 50.72(b)(3)(iv)(A) for an auxiliary feedwater system actuation. All control rods dropped, all equipment functioned as designed, and offsite power remained available.
The direct cause of the event was a failure of the valve stem for the 'B' steam generator (SG) main feedwater regulating valve (MFRV), causing the valve to fail closed and resulting in a loss of feedwater flow control to the 'B' SG. The hardware failure analysis performed on the valve stem determined that the failure of the valve stem was due to stress corrosion cracking (SCC) initiating from the external surface within the region contained within the packing area. The root cause investigation found that during the previous valve rebuild, an inappropriate chemical (anti-seize) was applied to the stem for lubrication to assist in the rebuild. It was the presence of this chemical which caused the SSC that led to the failure. All four MFRVs are scheduled to be rebuilt during the upcoming refueling outage in October 2022 with all four valve stems then being sent off to be examined to look for evidence of SCC.Page of 05000-
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
SAFETY SIGNIFICANCE
There were no safety consequences impacting plant or public safety from this event. All control rods dropped, offsite power remained available, and all safety equipment operated appropriately and as designed. There was no loss of any function that would have prevented fulfillment of actions necessary to: shutdown the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
OPERATING EXPERIENCE/PREVIOUS EVENTS On August 18, 2021, WCGS experienced an automatic reactor trip due to Low Level in the 'B' SG (see LER 2021-004-00 dated October 18, 2021). The direct cause of this event was the propagation of a fatigue crack through the valve stem of the 'B' MFRV which caused the stem to fracture resulting in a loss of feed flow control to the 'B' SG. The root cause was determined to be tool marks within the thread root caused local stress risers, which allowed multiple cracks to initiate.
In addition, the thread root was also cut deeper and narrower than allowed by specification. This created an additional stress riser which allowed the cracks to propagate into the body of the valve stem. Though, both failures occurred on the same valve, this condition is not viewed as a repeat event due to differences in the failures. The valve stem that failed in 2021, had ultimately failed after 10 years of operation. The failure in 2022 occurred in the packing area and failed only after 11 months of operation. The hardware failure analysis identified the cause of the failure in 2022 as SCC. There were no signs of SCC in the failure area of the stem in 2021. Therefore, the failure of the stem in 2022 could not have been prevented on what was known during the evaluation of the 2021 failure. Thus, this is not a repeat event.
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Wolf Creek Generating Station 482 2022 001 00