05000440/LER-2020-002-01, Standby Liquid Control System Rendered Inoperable Due to Valve Misposition
| ML21131A168 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 05/11/2021 |
| From: | Penfield R Energy Harbor Nuclear Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2020-002-01 | |
| Download: ML21131A168 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4402020002R01 - NRC Website | |
text
energy Energy Harbor Nuclear Corp Perry Nuclear Power Plant 10 Center Road Perry, Ohio 44081 Rod L. Penfleld 440-280-5382 Site Vice President, Perry Nuclear 724-462-0816 (cell)
May 11,2021 L-21-132 10 CFR 50.73(a)(2)(v)(A) 10CFR50.73(a)(2)(v)(D) 10CFR50.73(a)(2)(i)(B)
ATTN:
Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Perry Nuclear Power Plant Docket No. 50-440, License No. NPF-58 Licensee Event Report Submittal Enclosed is revision 1 to Licensee Event Report (LER) 2020-002, "Standby Liquid Control System Rendered Inoperable due to Valve Misposition", which is being submitted to provide additional information regarding the subject occurrence.
The changes are marked with a revision bar in the margin.
The original LER was submitted in accordance with 10 CFR 50.73(a)(2)(v)(A) and 10 CFR 50.73(a)(2)(v)(D).
There are no regulatory commitments contained in this submittal.
If there are any questions or if additional information is required, please contact Mr. Glendon Burnham, Manager - Regulatory Compliance, at (440) 280-7538.
Sincerely, Rod L. Penfield
Enclosure:
LER 2020-002-01 cc:
NRC Project Manager NRC Resident Inspector NRC Region III Regional Administrator
Enclosure L-21-132 LER 2020-002-01
Abstract
i.e., approximately 15 single-spaced typewritten lines)
On August 20, 2020, while performing testing on the Standby Liquid Control (SLC) system, water was inadvertently added to the SLC storage tank causing an unintended dilution of the boron solution. On August 21, 2020 at 0953 hours0.011 days <br />0.265 hours <br />0.00158 weeks <br />3.626165e-4 months <br />, sampling of the boron solution concentration revealed that Technical Specification (TS) Limiting Condition of Operation (LCO) 3.1.7 was not met, and Action Condition B was entered for two SLC subsystems INOPERABLE. Boron addition and sampling were performed, with SLC returning to OPERABLE on August 21, 2020 at 1307.
The direct cause of the unintentional addition of water to the SLC Storage Tank during testing was a valve mis-position due to human error. A corrective action will add independent verification to the procedure for closing of the Transfer Line Isolation valve.
The safety significance of this event is considered to be of very low safety significance, in accordance with the Regulatory Guidance. This event is reported in accordance with 10 CFR 50.73(a)(2)(v)(A) and 10 CFR 50.73(a)(2)(v)(D) as an event or condition that prevented the fulfillment of the safety function of the Standby Liquid Control System. The event was also found to be reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications.
Energy Industry Identification System (ElIS) codes are identified in the text as [XX].
INTRODUCTION
The purpose of the Standby Liquid Control (SLC) System [BR] is to provide an alternate method of shutting down the reactor, independent of the Control Rod Drive System [AA]. This is accomplished by pumping a neutron absorbing solution into the reactor in sufficient concentration and quantity to provide the required shutdown margin without control rod movement and to overcome the maximum positive reactivity resulting from cooldown and xenon decay.
EVENT DESCRIPTION
On August 20, 2020, while the plant was at 100 percent rated thermal power, Periodic Test Instruction, PTI-C41-P0001, Standby Liquid Control Transfer System Pump and Valve Operability Test, was being performed on the Standby Liquid Control (SLC) system. During the test, the Transfer Line Isolation valve [ISV], was directed to be closed, but instead was left open due to a human performance error by a plant operator. The error led to the inadvertent addition of approximately 226 gallons of demineralized water to the existing 4872 gallons of boron solution in the SLC Storage Tank [TK].
Subsequently, preparations were made to perform sampling of the boron solution in the tank to verify SLC system operability.
On August 21, 2020, at 0953 hours0.011 days <br />0.265 hours <br />0.00158 weeks <br />3.626165e-4 months <br />, while the plant was at 100 percent rated thermal power, the SLC system was declared INOPERABLE due to the sample for the SLC storage tank boron solution concentration not meeting Technical Specification (TS) criteria. Condition B of TS 3.1.7 was entered for two SLC subsystems being INOPERABLE.
SLC was declared OPERABLE on August 21, 2020 at 1307 hours0.0151 days <br />0.363 hours <br />0.00216 weeks <br />4.973135e-4 months <br />, following boron addition to the SLC Storage Tank and sample verification that the boron solution concentration was within TS limits.
CAUSE
Direct Cause:
The direct cause of the unintentional addition of approximately 226 gallons of water to the SLC Storage Tank during the performance of PTI-C41-P0001 was a valve mis-position due to human error. A procedure step in the PTI directed the Non-Licensed Operator (NLO) to Unlock and Close the Transfer Line Isolation valve. The NLO unlocked the valve but failed to close the valve. A subsequent step opened the Transfer Line Outboard Containment Isolation valve aligning the discharge of the running transfer pump to the SLC Storage Tank, which caused the Storage Tank to fill with water from the Transfer Tank.
Contributing Cause
A contributing cause to the event was a latent procedural risk evaluation error that occurred in 2011. The Maintenance Plan for PTI-C41-P0001 was classified as a GREEN RISK activity, however, a single error resulted in the inoperability of a safety system. Per procedure NOP-OP-1007, Risk Management, an "activity if performed incorrectly (i.e. any single unrecoverable error) that would cause a loss or defeat of a safety system.
If yes, this activity shall be Yellow Risk". Had the PTI been classified as a Yellow Risk activity, increased oversight and monitoring usually associated with Yellow Risk activities may have eliminated or minimized the impact of the error.
A subsequent interview with the NLO found that there was no time or situational pressure related to the incident.
EVENT ANALYSIS
The event was reported to the Nuclear Regulatory Commission (NRC) on August 21, 2020 at 1242 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.72581e-4 months <br />, as an event or condition that at the time of discovery could have prevented the fulfillment of a system needed to shut down the reactor and maintain it in a safe shutdown condition (10 CFR 50.72(b)(3)(v)(A)) and mitigate the consequences of an accident (10 CFR 50.72(b)(3)(v)(D)).
Based upon the event timeline, this event was also found to be reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications, due to exceeding the completion time for Limiting Condition of Operation of TS 3.1.7, Condition B, Two SLC subsystems inoperable.
A Probabilistic Risk Assessment (PRA) evaluation was performed for the August 21, 2020 Standby Liquid Control Inoperability event. The analysis of this event results in delta Core Damage Frequency (CDF) and delta Large Early Release Frequency (LERF) values that are well below the acceptable thresholds of 1.OE-06/yr and 1.OE-07/yr, as discussed in Regulatory Guide 1.174, An Approach for using Probabilistic Risk Assessment in Risk Informed Decisions on Plant-Specific Changes to the Licensing Basis. Therefore, this event is considered to be of very low safety significance in accordance with the Regulatory Guidance.
A Reactor Engineering evaluation was performed, following the event. The analysis showed that the reactor would have been shut down had the SLC tank been injected with a 2.6% boron concertation with sufficient margin to the analytical requirement. As such, the reactor would have been shut down with the measured SLC tank boron concentration of 2.73%.
This event is reportable under 10 CFR 50.73(a)(2)(v)(A) and 10 CFR 50.73(a)(2)(v)(D) as an event or condition that prevented the fulfillment of the safety function of the Standby Liquid Control System, and 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications.
CORRECTIVE ACTIONS
The immediate corrective action for the personnel error was handled through station performance management.
A planned corrective action will change procedure PTI-C41-P0001 to add an independent verification step for the closure of the Transfer Line Isolation valve.
PREVIOUS SIMILAR EVENTS
A review of Condition Reports for the past three years was performed, and no similar issues were identified.
COMMITMENTS
None(08-2020)
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