05000482/LER-2021-003, Re Automatic Reactor Trip Due to Low Steam Generator Level
| ML21193A078 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 07/12/2021 |
| From: | Bayer R Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 21-0024 LER 2021-003-00 | |
| Download: ML21193A078 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4822021003R00 - NRC Website | |
text
P.O. Box 411 l Burlington, KS 66839 l 620-364-8831 Robert J. Bayer Plant Manager July 12, 2021 WO 21-0024 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Docket No. 50-482: Licensee Event Report 2021-003-00, Automatic Reactor Trip Due to Low Steam Generator Level Commissioners and Staff:
The enclosed Licensee Event Report (LER) 2021-003-00 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 Ron Benham at (620) 364-4204.
Sincerely, Robert J. Bayer RJB/rlt
Enclosure:
LER 2021-003-00 cc:
S. S. Lee (NRC), w/e S. A. Morris (NRC), w/e N. OKeefe (NRC), w/e Senior Resident Inspector (NRC), w/e
Abstract
Wolf Creek Generating Station 482 4
Automatic Reactor Trip Due to Low Steam Generator Level 05 12 2021 2021 003 00 07 12 2021 1
8%
Ron Benham, Director Nuclear and Regulatory Affairs (620) 364-4204
On 5/12/2021, Wolf Creek Generating Station was performing initial reactor startup following Refueling Outage 24 (RF24). With reactor power at approximately 8%, steam generator levels began to oscillate while in automatic control. Operators took manual control of the main feedwater regulating bypass valves but were unable to stabilize steam generator levels prior to reaching the C steam generator low level reactor trip setpoint. At 1125 Central Daylight Time (CDT), the reactor tripped and an auxiliary feedwater actuation occurred. All equipment responded as expected. ENS notification#55252 was made at 1441 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 a specified system actuation.
The cause of the event was determined to be during the 7300 modification, improper utilization of main feedwater regulating bypass valves inherent valve curves did not take into consideration system flow characteristics. The result was an inaccurate correlation of feed flow with valve position within the system. This led to a mismatch in feed flow demand and actual feed flow to the steam generators. Due to improper gain settings, the mismatch began to diverge and led to a reactor trip on low steam generator water level. Following tuning of control parameters, operators were able to commence reactor startup and reached full power on 5/15/2021. 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. The operating crew responded appropriately to lowering steam generator levels. 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 LER 2015-003-00 describes an event that occurred at Wolf Creek on May 3, 2015, during startup from RF20. While swapping feedwater control from the MFRV bypass valves to the MFRVs a high steam generator level was recieved on C steam generator resulting in a turbine trip, feedwater isolation signal, and eventual reactor trip. This specific event was caused by a lack of a reliable and consistent standardization between the operating crews to control the transfer of the steam generator feedwater flow between the MRFV bypass valves and the MFRVs. This previous event is related to the current occurence as it is associated with steam generator level oscillations during low power ascensions and difficulties with bypass valve control. However, it is specific to the old analog feedwater control system.
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Wolf Creek Generating Station 482 2021 003 00