05000400/LER-2021-002, All ECCS Accumulator Isolation Valves Closed in Mode 3 with RCS Pressure Greater than 1000 Psig
| ML21046A031 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 02/15/2021 |
| From: | Dills J Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-21-0022 LER 2021-002-00 | |
| Download: ML21046A031 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4002021002R00 - NRC Website | |
text
John R. Dills Plant Manager Shearon Harris Nuclear Power Plant 5413 Shearon Harris Road New Hill, NC 27562-9300 10 CFR 50.73 February 15, 2021 Serial: RA-21-0022 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 2021-002-00 Ladies and Gentlemen:
Duke Energy Progress, LLC, submits the enclosed Licensee Event Report 2021-002-00 in accordance with 10 CFR 50.73 for Shearon Harris Nuclear Power Plant, Unit 1 (HNP). On December 17, 2020, HNP was in Mode 3 and the reactor coolant system was pressurized greater than 1000 pounds per square inch gauge for approximately 15 minutes with all three cold leg injection accumulator discharge valves closed. The cause evaluation is ongoing and this LER will be supplemented following completion of this evaluation. 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.
Sincerely, John R. Dills Enclosure: Licensee Event Report 2021-002-00 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
All ECCS Accumulator Isolation Valves Closed in Mode 3 With RCS Pressure Greater Than 1000 psig 12 17 2020 2021 002 00 2
15 2021 3
0
Sarah McDaniel, Regulatory Affairs Engineer (984) 229-2002 X
BP ACC W351 Y
3 15 2021 On December 17, 2020, with Harris Nuclear Power Plant, Unit 1 (HNP), in Mode 3, Reactor Coolant System (RCS) pressure was being controlled between 900-1000 pounds per square inch gauge (psig) with all three cold leg accumulator (CLA) discharge valves closed. Only one reactor coolant pump (RCP) was available and operating while RCS pressure was being controlled in manual using a pressurizer spray valve (PSV). With only one RCP in operation, pressurizer spray effectiveness was reduced and RCS pressure began rising at 15:35. Operators took immediate actions to arrest the pressure increase by fully opening the PSV, reducing charging flow, and turning off pressurizer heaters. The RCS pressure rise did not stop prior to exceeding 1000 psig.
HNP Technical Specifications (TS) require each CLA to be operable in Modes 1, 2, and 3 when RCS pressure is greater than 1000 psig. Since all three CLA discharge valves were closed, this TS requirement was not met for approximately 15 minutes, until pressure was reduced to less than 1000 psig.
Causal factors that led to this event will be determined in the cause evaluation, which is still ongoing. The final results of the cause evaluation will be provided in a supplement to this report. Page of 05000-
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
C. Causal Factors The cause evaluation is ongoing. Once the evaluation is complete, a supplemental report will be issued containing the causal factors for this event.
D. Corrective Actions
RCS pressure was lowered below 1000 psig to restore compliance with HNP TS 3.5.1. The operators established margin to the RCS pressure limit by setting a conservative control band and eliminated future concerns by reopening the CLA isolation valves. Additional planned actions will be determined following completion of the ongoing cause evaluation.
E. Safety Analysis
The safety analysis for a LOCA initiating from Mode 1 plant conditions credits three ECCS CLAs being available to function to inject borated water into the RCS. For the limiting large-break LOCA case, the safety analysis assumes that the contents of one CLA are spilled through the break, and that injection from the remaining two ECCS CLAs provides replenishment of RCS inventory to provide cooling to the reactor core. However, in consideration of the actual plant conditions at the time of the event, adequate core decay heat removal and RCS inventory replenishment would have been available to successfully mitigate a postulated LOCA with the CLAs isolated. At the time of the event, the plant was in Mode 3 after being in hot standby (Mode 3) for approximately 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> following a reactor trip on December 16, 2020, from normal RCS operating temperature and pressure. Given these initial conditions, the decay heat load during the event was lower than the limiting Mode 3 LOCA analysis performed by the Pressurized Water Reactor Owners Group (PWROG) which assumes the CLAs are not available. Furthermore, the PWROG analysis for LOCAs in Mode 3 credits one ECCS subsystem train, consisting of one ECCS centrifugal charging pump, one RHR pump, and one RHR heat exchanger.
During the event, both ECCS subsystem trains were operable and available to function to provide injection to the RCS, as required by HNP TS. The availability of RCS injection from a second ECCS subsystem train would provide a risk benefit for the potential consequences of the inability to inject to the RCS from the ECCS CLAs, but is not credited in the deterministic PWROG Mode 3 analysis. In a probabilistic risk assessment (PRA) of the event, it was assumed that all three CLAs were unavailable to inject into the RCS for a 15-minute duration at full power conditions, which bounds the risk impact of this event in Mode 3. The PRA results indicate that this event was of very low risk significance. This condition had no impact on the health and safety of the public.
F. Additional Information
There have been no events similar to the event documented in this LER in the past three years.
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Shearon Harris Nuclear Power Plant, Unit 1 400 2021 002 00