05000387/LER-2021-004, Loss of 1B RHRSW Pump Due to Cable Damage During Excavation Activities
| ML21335A100 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 12/01/2021 |
| From: | Cimorelli K Susquehanna |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PLA-7974 LER 2021-004-00 | |
| Download: ML21335A100 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 3872021004R00 - NRC Website | |
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Kevin Cimorelli Susquehanna Nuclear, LLC Site Vice President 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com December 1, 2021 Attn: Document Control Desk 10 CFR 50.73 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387/2021-004-00 UNIT 1 LICENSE NO. NPF-14 PLA-7974 Docket No. 50-387 Attached is Licensee Event Report (LER) 50-387/2021-004-00. The LER reports an event in which the Unit 1 B Residual Heat Removal Service Water Pump was inoperable for longer than allowed by Technical Specifications (TS). The condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as condition prohibited by TS and 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented fulfillment of a safety function.
There were no actual consequences to the health and safety of the public as a result of this event.
This letter contains no new or revised regulatory commitments.
K. Cimorelli Attachment: LER 50-387/2021-004-00 Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. A. Klett, NRC Project Manager Mr. M. Shields, PA DEP/BRP TALEN~
ENERGY
Abstract
At approximately 15:19 on October 7, 2021, operators at the Susquehanna Steam Electric Station, Unit 1 observed current oscillations during a run of the Unit 1 B Residual Heat Removal Service Water (RHRSW) Pump (1B RHRSW Pump). Following shutdown of the pump, operators entered Technical Specification (TS) 3.7.1, Condition B for an inoperable RHRSW subsystem. Troubleshooting identified the cause of the current oscillations to be a ground on the B-phase power cable for the pump, which was likely damaged on September 23, 2021 during excavation activities, thereby rendering the pump inoperable at the time. The power cable was replaced, and the RHRSW System was declared operable at 07:33 on October 11, 2021. Therefore, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS. The Unit 1, A RHRSW subsystem was determined to be concurrently inoperable on September 29. Therefore, this event is also being reported in accordance with 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented fulfillment of a safety function.
The cause of the event is under investigation and will be provided in a supplement to this report with associated
corrective actions
There were no actual safety consequences associated with the described condition.
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CONDITIONS PRIOR TO EVENT
Unit 1 - Mode 1, approximately 100 percent Rated Thermal Power (RTP)
Unit 2 - Mode 1, approximately 100 percent RTP On September 23, 2021, during excavation activities to support future unrelated piping replacement work, personnel at the Susquehanna Steam Electric Station (SSES) punctured a 4 conduit line. Work was immediately stopped, and an investigation commenced. On October 7, the damaged conduit was positively identified as F1F104 [EIIS System/Component Code: BI/CND]. F1F104 contains cable FF1S0601A [BI/CBL],
which is the power cable for Pump 1P506B [BI/P], the Unit 1, B, Residual Heat Removal Service Water (RHRSW) Pump (hereafter referred to as the 1B RHRSW Pump).
EVENT DESCRIPTION
At approximately 15:19 on October 7, 2021, operators at the Susquehanna Steam Electric Station, Unit 1 observed current oscillations during a run of the 1B RHRSW Pump. The operators shut down the 1B RHRSW Pump entered Technical Specification (TS) 3.7.1, Residual Heat Removal Service Water (RHRSW) System and the Ultimate Heat Sink (UHS), Condition B, for the inoperable Unit 1 B RHRSW subsystem.
Troubleshooting identified the cause of the current oscillations to be a ground on the B-phase of cable FF1S0601A. Troubleshooting also determined that the likely cause of the ground on cable FF1S0601A was damage to the cable when conduit F1F104 was punctured on September 23. Therefore, the 1B RHRSW Pump is considered to have been inoperable from the time of cable damage on September 23, 2021.
Cable FF1S0601A was replaced, conduit F1F104 was repaired, and the 1B RHRSW pump was returned to service at 07:33 on October 11. Therefore, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS. Further, on September 29, the Unit 1 A RHRSW subsystem was declared inoperable due to UHS spray array and bypass valve alignments to support UHS nozzle cleaning. Thus, both subsystems of the Unit 1 RHRSW System were concurrently inoperable.
Therefore, this event is also being reported in accordance with 10 CFR 50.73(a)(2)(v)(B) as condition that could have prevented the fulfillment of the safety function of structures, systems, or components that are needed to remove residual heat.
CAUSE OF EVENT
The cause of the event is under investigation and will be provided in a supplement to this Licensee Event Report (LER).
ANALYSIS/SAFETY SIGNIFICANCE
An Engineering Evaluation was performed for the time period for which the Unit 1 B RHRSW subsystem was inoperable. On September 29, the Unit 1 A RHRSW subsystem was declared inoperable due to spray array and bypass valve alignments to support spray array inspection and nozzle cleaning. The associated RHRSW pump and motor could have started and provided flow to the RHR heat exchangers in case of an emergency with the flow path for RHRSW through the open bypass valve to the spray pond (i.e., bypassing L...
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the spray arrays). This has the potential to adversely impact the design basis spray pond temperature analysis due to the loss of evaporative and convective cooling of the water droplets when discharged through the spray arrays. However, the valves could be re-positioned under operator direction during a design basis accident. Such a manipulation within three hours from the onset of an accident is assumed in the SSES accident analyses, as approved by the NRC in ADAMS Accession No. ML081000255. Therefore, the Unit 1 A RHRSW subsystem would have been able to perform its safety functions during a postulated design basis accident despite the valve alignment which renders the RHRSW system inoperable. Further, the initial spray pond temperature assumed in the design basis analysis is 85°F; the pond temperature was below this value.
The initial spray pond temperature would allow an even greater timeframe for operators to perform the required actions which assures the actions could be completed consistent with the design basis.
Based on the above discussion, only the Unit 1 B RHRSW subsystem was incapable of performing its design function during the subject timeframe. The SSES design basis analyses assume a single failure of an RHRSW subsystem which is consistent with the condition that existed. Since the remaining RHRSW subsystem could perform its design basis function, the event did not represent a safety system functional failure (SSFF). This will not be counted as an SSFF in the Reactor Oversight Process Performance Indicators.
There were no actual consequences to the health and safety of the public as a result of this event.
CORRECTIVE ACTIONS
Corrective actions will be provided in a supplement to this LER.
COMPONENT FAILURE INFORMATION
Component failure information will be provided in a supplement to this LER.
PREVIOUS OCCURRENCES
Previous similar occurrences, if any, will be provided in a supplement to this LER.
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