05000388/LER-2021-004-01, From Susquehanna Steam Electric Station, Unit 2 Main Turbine Pressure Regulator Inoperable for Longer than Allowed by Technical Specifications Due to Inadequate Valve Modification
| ML22307A260 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 11/03/2022 |
| From: | Cimorelli K Susquehanna, Talen Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| PLA-8000 LER 2021-004-01 | |
| Download: ML22307A260 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3882021004R01 - NRC Website | |
text
Kevin Cimorelli Site Vice President Susquehanna Nuclear, LLC 769 Salem Boulevard Berwick,PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com November 3, 2022 Attn: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-388/2021-004-01 UNIT 2 LICENSE NO. NPF-22 PLA-8000 TALEN
ENERGY 10 CFR 50.73 Docket No. 50-388 Attached is Licensee Event Report (LER) Supplement 50-388/2021-004-01. The LER supplement reports an event in which a Unit 2 Main Turbine Pressure Regulator 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.
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 50-388/2021-004-01 Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. A. Klett, NRC Project Manager Mr. M. Shields, PA DEP/BRP
Abstract
At approximately 13:21 on October 11, 2021, the Susquehanna Steam Electric Station, Unit 2, experienced an automatic reactor scram due to a main turbine trip. All turbine bypass valves (TBVs) opened, as expected, to control reactor pressure but did not subsequently re-close. Troubleshooting identified Pressure Transmitter PT-20101B as the cause of the TBVs failure to re-close. To control reactor pressure, operators manually closed the four main steam isolation valves and utilized the main steam line drains and the High Pressure Coolant Injection System. Further analyses showed the Pressure Transmitter PT-20101B failure was caused by failure of the pressure transmitter root valve resulting from main steam line vibrations created by the scram. The root valve was previously modified; however, station personnel did not validate that the modification would perform properly in all plant operating conditions. To correct the condition, the failed valve was replaced and applicable procedures were updated.
Based on failure information, it is likely that Pressure Transmitter PT-20101B was inoperable for longer than allowed by Technical Specification (TS) 3.7.8. Therefore, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
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 95 percent RTP At approximately 13:21 on October 11, 2021, the Susquehanna Steam Electric Station (SSES), Unit 2, experienced an automatic reactor scram due to a main turbine trip. Subsequently, all turbine bypass valves (TBVs) [EIIS System/Component Codes: JI/PCV] immediately opened as expected.
EVENT DESCRIPTION
On October 11, 2021, at approximately 13:21, the Susquehanna Steam Electric Station Unit 2 reactor automatically scrammed due to a main turbine [TA/TRB] trip. The scram event is reported under LER-2021-003. The Unit 2 Control Room received indication of a main turbine trip with both divisions of the Reactor Protection System (RPS) [EIIS System Code: JC] actuated and all control rods inserted. The TBVs opened automatically, as expected, to control reactor pressure but subsequently remained open. Reactor pressure was initially stabilized through manual closure of the Main Steam Isolation Valves (MSIVs) [SB/ISV] and maintained using the main steam line drains [SB/DRN] and the High Pressure Coolant Injection (HPCI) [BJ]
System.
Based on failure information, it is likely that Pressure Transmitter PT-20101B was inoperable for longer than allowed by Technical Specification (TS) 3.7.8, Main Turbine Pressure Regulation System. Therefore, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
CAUSE OF EVENT
Previous to the scram, the root valve (2RV-PT20101B) [RTV] for the B Mains Steam Pressure Secondary Transmitter, PT-20101B, experienced a steam leak on the valve packing. A temporary repair was installed to seal the leak using 2X sealant. During the Unit 2 scram vibrations from the main steam lines caused the 2X sealant to crack and separate from the valve stem. The valve subsequently closed resulting in sustained pressure indication to the TBVs, which remained open longer than required. In preparation of the temporary repair, the station did not validate that 2X sealant would perform properly under all plant operating conditions.
ANALYSIS/SAFETY SIGNIFICANCE
While failure of the pressure transmitter is a potential transient initiator when operating at full power, it is not credited in the mitigation of any accident. The TBVs are credited in multiple Updated Final Safety Analysis Report Chapter 15 analyses, all of which assume the bypass valves will open to mitigate the pressure transient from the event. As noted in the event summary, the failure of the pressure transmitter did not prevent the bypass valves from opening nor was there any other impact to components credited with mitigation. The condition described herein did not result in a safety system functional failure. Accordingly, this event will not be counted as a safety system functional failure under 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
Key Corrective Actions Include:
- 1. Replace 2RV-PT20101B.
- 2. Lessons Learned were shared with applicable departments.
- 3. Revise procedures to restrict use of 2X sealant as applicable.
COMPONENT FAILURE INFORMATION
Component - EHC System Main Steam Pressure Transmitter Root Valve (2RV-PT20101B)
System - Main Steam Manufacturer - Borg Warner Part Number - 74630
PREVIOUS OCCURRENCES
None.