05000400/LER-2022-003, Manual Reactor Trip Due to Degrading Condenser Vacuum
| ML22179A261 | |
| Person / Time | |
|---|---|
| Site: | Harris  (NPF-063) |
| Issue date: | 06/28/2022 |
| From: | Hoffman D Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-22-0154 LER 2022-003-00 | |
| Download: ML22179A261 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4002022003R00 - NRC Website | |
text
~ ~ DUKE
~ ENERGY David S. Hoffman Plant Manager Shearon Harris Nuclear Power Plant 5413 Shearon Harris Road New Hill, NC 27562-9300 10 CFR 50.73 June 28, 2022 Serial: RA-22-0154 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Shearon Harris Nuclear Power Plant, Unit 1 Docket No. 50-400/Renewed License No. NPF-63 Subject: Licensee Event Report 2022-003-00 Ladies and Gentlemen:
Duke Energy Progress, LLC, submits the enclosed Licensee Event Report 2022-003-00 in accordance with 10 CFR 50.73 for Shearon Harris Nuclear Power Plant, Unit 1 (HNP). On April 29, 2022, with HNP in Mode 1, the reactor was manually tripped due to degrading condenser vacuum. This event had no significance with respect to the health and safety of the public.
There are no regulatory commitments contained within this report.
Please refer any questions regarding this submittal to Sarah McDaniel at (984) 229-2002.
Sincere~ v1 lJ David S. Hoffman Enclosure: Licensee Event Report 2022-003-00 cc:
J. Zeiler, NRC Senior Resident Inspector, HNP M. Mahoney, NRC Project Manager, HNP NRC Regional Administrator, Region II
Abstract
Shearon Harris Nuclear Power Plant, Unit 1 400 3
Manual Reactor Trip due to Degrading Condenser Vacuum 04 29 2022 2022 003 00 06 28 2022 1
100
Sarah McDaniel, Regulatory Affairs Engineer (984) 229-2002 X
SH ISV C665 Y
B SH V
K116 Y
On April 29, 2022, at 04:05 Eastern Daylight Time, with Shearon Harris Nuclear Power Plant, Unit 1 (HNP), in Mode 1 at 100 percent power, the reactor was manually tripped due to degrading condenser vacuum approaching the turbine trip setpoint. The trip was not complex, with all systems responding normally post-trip. The Reactor Protection System and Auxiliary Feedwater System actuated as designed. A monthly swap of the Main Condenser Air Removal System vacuum pumps (CVPs) was in progress at the time of this event. When the 'B' CVP was secured, the suction isolation valve, 1AE-16, and the 'B' CVP discharge check valve, 1AE-19, failed to close, resulting in a rapid decrease in condenser vacuum. The rate of vacuum degradation did not allow time for manual isolation prior to the manual reactor trip. The root cause of this event is the combination of two simultaneous equipment failures, resulting in a large volume of main condenser air-in-leakage. The 1AE-16 failure cause is indeterminate; however, the likely cause is an intermittent malfunction of the control relay associated with the solenoid operated valve (SOV) that controls 1AE-16 actuator operation. The 1AE-19 failure cause is attributed to poor valve construction with the disk arm not being centered, resulting in contact between the disc and valve body. Corrosion product buildup along this contact surface caused valve binding. The CVP operating procedure was revised to close the CVP manual suction isolation valve prior to securing the CVP. Control relays and a circuit breaker mechanism operated cell assembly for 1AE-16 were replaced. 1AE-19 was replaced. The 1AE-16 SOV and the A CVP discharge check valve will be replaced.Page of 05000-
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Within 25 seconds of securing the B CVP, the CVP effluent flow rate had exceeded the flow rate indicator range of 100 standard cubic feet per minute. Within 35 seconds of securing the B CVP, condenser shell pressures begin to increase at a rate of approximately 2.6 inches Hg per minute. Then, less than a minute later, the B CVPs separator tank low-low level alarm was received. The large increase in effluent flow combined with 1AE-16 failing to shut and this low-low level alarm indicate that the A CVP was pulling water out of the B CVP separator tank along with air through the B CVP due to the B CVP discharge check valve, 1AE-19, not being closed.
After the CVP separator tank low-low level alarm was received, with condenser pressure continuing to increase, operations personnel attempted to start the B CVP. B CVP failed to start and the alarm for B CVP trip was received. At 04:03, two minutes after the B CVP was secured, the low condenser vacuum alarm was received that has a set point of 6.5 inches Hg absolute. Condenser pressures continued to increase and reached 8.5 inches Hg absolute, which is the pre-established limit to result in a manual reactor trip in accordance with procedural guidance. At 04:04, the reactor trip was manually initiated by operations personnel.
C. Causal Factors The root cause of this event is the combination of two simultaneous equipment failures, resulting in a large volume of main condenser air-in-leakage. When the 'B' CVP was secured, the suction isolation valve, 1AE-16, and the 'B' CVP discharge check valve, 1AE-19, failed to close, resulting in a rapid decrease in condenser vacuum and a manual reactor trip. The 1AE-16 failure cause is indeterminate; however, the likely cause is an intermittent malfunction of the control relay [RLY]
associated with the SOV that controls 1AE-16 actuator operation. The 1AE-19 failure cause is attributed to poor valve construction with the disk arm not being centered, resulting in contact between the disc and valve body. Corrosion product buildup along this contact surface caused valve binding. Over-reliance by plant personnel on risk mitigation actions instead of an elimination strategy during evolutions was also identified as a cause associated with this event.
D. Corrective Actions
The procedure used for CVP operation was revised to close the CVP manual suction isolation valve prior to securing the CVP being removed from service. Control relays and a circuit breaker [72] mechanism operated cell assembly for 1AE-16 were replaced; forensic analysis on these removed components will be completed to identify any additional actions needed to improve reliability. 1AE-19 was replaced. The 1AE-16 SOV will be replaced; forensic analysis on the removed component will be completed to identify any additional actions needed to improve reliability. The A CVP discharge check valve will be replaced. Personnel will identify any normal operating procedural guidance that contains steps with the words immediately or immediate and will revise applicable procedural guidance to incorporate acceptable completion times.
E. Safety Analysis
The manual reactor trip had no impact on public health and safety. The failure of the condenser vacuum system valves that resulted in degraded condenser vacuum and led to the manual trip did not affect the post-trip response of the feedwater and condensate systems. There was no loss in function of safety systems, structures, or components. There were no significant equipment abnormalities. The condition did not result in a safety system functional failure and had no adverse impact on the health and safety of the public.
F. Additional Information
There have been no events at HNP similar to the event documented in this LER in the past three years.
3 3
Shearon Harris Nuclear Power Plant, Unit 1 400 2022 003 00