05000458/LER-2021-005, Potential Loss of Safety Function Due to Inoperable Reactor Core Isolation Cooling Steam Flow Transmitter
| ML21350A425 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 12/16/2021 |
| From: | Karenina Scott Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48140 LER 2021-05-00 | |
| Download: ML21350A425 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4582021005R00 - NRC Website | |
text
RBG-48140 December 16, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61N St. Francisville, LA 70775 Tel 225-381-4374 Kent Scott Site Vice President 10 CFR 50.73
Subject:
Licensee Event Report 50-458 I 2021-05-00, "Potential Loss of Safety Function due to Inoperable Reactor Core Isolation Cooling Steam Flow Transmitter" River Bend Station - Unit 1 NRC Docket No. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 1 O CFR 50.73, enclosed is the subject Licensee Event Report. This document contains no commitments. If you have any questions, please contact Mr. Tim Schenk at 225-381-4177.
Respectfully, KCS/twf
Enclosure:
Licensee Event Report 50-458 / 2021-05-00, "Potential Loss of Safety Function due to Inoperable Reactor Core Isolation Cooling Steam Flow Transmitter
cc:
NRC Regional Administrator - Region IV NRC Project Manager - River Bend Station NRC Senior Resident Inspector - River Bend Station Louisiana Department of Environmental Quality Public Utility Commission of Texas
Enclosure RBG-48140 Licensee Event Report 50-458 / 2021-05-00, "Potential Loss of Safety Function due to Inoperable Reactor Core Isolation Cooling Steam Flow Transmitter"
Abstract
On October 19, 2021 at 13:40 Central Time (CT) with the unit in Mode 1 at 100% power, wire insulation inside one of the Reactor Core Isolation Cooling (RCIC) Steam Flow Transmitters was found in a degraded condition. The degraded wire insulation could have caused a fault which would have prevented one of the redundant RCIC steam supply line isolations from occurring.
The issue was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(v)(C) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material and 10 CFR 50.73(a)(2)(i)(B) as an operation prohibited by Technical Specifications.
The degraded wire insulation was corrected on October 21, 2021 at 08:38 CT by repair with qualified material. The most probable cause of the wire insulation degradation is moisture intrusion.
EVENT DESCRIPTION
Surveillance test STP-207-4249 performs a channel calibration of the Reactor Core Isolation Cooling (RCIC) [BN]
Steam Flow Transmitter [PDT] E31-PDTN084B as required by Technical Specification Surveillance Requirement 3.3.6.1.5-3.i. This Surveillance Test is performed on a 2-year frequency with the last completion documented on 04/21/2019.
00 On 10/19/2021 transmitter E31-PDTN084B was calibrated, and its performance was determined to be satisfactory by the performance of STP-207-4249. During the performance of the Surveillance Test, Maintenance Technicians identified insulation falling off of the negative wire terminated in the transmitter. The insulation on the positive wire was intact; however, it was discolored. These wires are terminated inside the transmitter and routed through a conduit seal mounted on the transmitter.
This condition could have prevented fulfilment of one of the RCIC steam supply high flow isolation functions. The specified safety function of the transmitter is to detect a break in the common RCIC / Residual Heat Removal (AHR) steam supply line and initiate inboard isolation valve closure. The transmitter provides a 4-20 mA signal to its associated trip unit. The isolation occurs on high steam flow. The degraded insulation did not affect the 4-20 mA signal; however, the transmitter was considered inoperable based on the potential for the bare wire to contact the transmitter housing (ground) during a seismic event. This could result in the signal failing downscale which would prevent the detection of a line break.
A gross failure alarm is received if the signal from the transmitter fails downscale. There were no documented gross failures of E31-PDTN084B over the past three years. There is no work history listed against the transmitter over the past three years other than the surveillance test STP-207-4249 performed on 04/21/2019. Therefore, the only opportunity to observe the wire insulation over the past three years was during the field portion of STP-207-4249 performed on 04/21/2019. STP-207-4249 was satisfactorily completed on 04/21/2019 without any documented degradation of the wiring insulation.
The redundant isolation function, as triggered from RCIC Steam Flow Transmitter E31-PDTN084A, was rendered inoperable for planned surveillance testing on 09/1/2020 from 13:20 to 15:00 CT and again from 15:20 to 16:25 CT.
Therefore, this condition could have prevented fulfillment of the safety function for the for the duration of the time the redundant isolation function was rendered inoperable for testing on 09/1/2020. This issue is reportable in accordance with 10 CFR 50.73(a)(2)(v)(C) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
The degraded wiring insulation on the negative wire was corrected with qualified material on 10/21/2021 08:38 CT.
After the time of discovery, one of the RCIC steam supply high flow isolation functions was determined to be inoperable for 43 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br />. The Technical Specifications allow 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> of operation in this condition. Therefore, this condition is also reported as an operation prohibited by Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
Although this event could have prevented the fulfillment of a safety function, engineering analysis has shown that this condition did not actually prevent fulfillment of a safety function. Therefore, this event is not reportable as a Safety System Functional Failure (SSFF) under the Regulator Assessment Performance Indicator Guideline, NEI 99-02. Page 2 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023
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LICENSEE EVENT REPORT (LEA)
CONTINUATION SHEET (See NUREG* 1022, R.3 for instruction and guidance for completing this fonn https://www.nrc.gov/reading-nn/doc-collections/nuregs/staff/sr1022/r3D
- 1. FACILITY NAME
- 2. OOCKET NUMBER
- 3. LER NUMBER YEAR River Bend Station - Unit 1 05000- 458 2021
SAFETY ASSESSMENT
SEQUENTIAL NUMBER 005 REV NO.
00 The actual consequence of this event was the potential inability to isolate supply steam to the RCIC system with a high steam flow indication on one channel and a concurrent failure of the redundant isolation system.
In this case, the essential safety actions are carried out by equipment of sufficient redundancy so that no single failure of active components can prevent the required actions. The assumption is that the nonaffected channel would perform its safety function during a Design Basis Accident concurrent with a RCIC System Steam Supply Line break. The plant response to this event is bounded by the Updated Safety Analysis Report analysis of a RCIC System Steam Supply Line break concurrent with a Design Basis Accident.
There were no actual Nuclear or Radiological safety consequences due to this event. Thus, this event was of minimal significance to the health and safety of the public.
EVENT CAUSE
The wire insulation degradation was most likely caused by moisture intrusion.
CORRECTIVE ACTIONS
Complete:
The degraded wire insulation condition was corrected with qualified material.
Planned Actions Tracked in Corrective Action Program:
Validate torque on transmitter conduit bolt.
Replace transmitter E31-PDTN084B.
Perform Internal Inspection of E31-PDTN084B and document results.
Update Surveillance Test Procedure to include a visual inspection of internal wiring insulation for E31-PDTN084B and all EQAR qualified transmitters during channel calibration.
PREVIOUS SIMILAR EVENTS
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