05000387/LER-2020-003, Condition Prohibited by Technical Specifications Due to Inoperable Turbine Stop Valve and Turbine Control Valve Instrumentation
| ML20356A217 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 12/21/2020 |
| From: | Cimorelli K Susquehanna, Talen Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PLA-7913 LER 2020-003-00 | |
| Download: ML20356A217 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3872020003R00 - 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 TALEN
ENERGY 10 CFR 50.73 Docket No. 50-387 Attached is Licensee Event Report (LER) 50-387/2020-003-00. The LER reports an event involving entry into the mode of applicability without meeting the required Limiting Conditions for Operation. The condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's Technical Specifications.
There were no actual consequences to the health and safety of the public as a result of this event.
This letter con ins no new or revised regulatory commitments.
K. Cimorelli Attachment: LER 50-387/2020-003-00 Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. S. Goetz, NRC Project Manager Mr. M. Shields, PADEP/BRP December 21, 2020 Attn: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387/2020-003-00 UNIT 1 LICENSE NO. NPF-14 PLA-7913
Abstract
On May 9, 2020, operators at the Susquehanna Steam Electric Station (SSES), Unit 1, were raising power following a maintenance outage. SSES Technical Specifications (TS) require that certain Turbine Stop Valve (TSV) and Turbine Control Valve (TCV) instrumentation be operable at greater than or equal to 26 percent Rated Thermal Power (RTP). However, at approximately 15:23, Unit 1 reached 26 percent RTP and the TSV and TCV instrumentation was found to be inoperable. Operators declared the TSV and TCV instrumentation inoperable, and entered Conditions A and B of Limiting Condition for Operation (LCO) 3.3.1.1. Control rods were inserted and Unit 1 was brought below 26 percent RTP at approximately 15:37, thereby exiting Conditions A and B of LCO 3.3.1.1. Based on the investigation and identified cause of this event, the inoperable condition likely existed prior to entering the Mode of Applicability. LCO 3.0.4 prohibits reaching 26 percent RTP when the LCO 3.3.1.1 is not met. This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
The cause of the event was determined to be two socket weld failures caused by high cyclic fatigue. Additionally, one of the socket welds was found to be undersized for its application. This condition was corrected by repairing the welds and upgrading the welds to the proper size. There were no actual safety consequences associated with the described condition.
CONDITIONS PRIOR TO EVENT
Unit 1 - Mode 1, approximately 24 percent Rated Thermal Power (RTP)
Unit 2 - Mode 1, approximately 98 percent RTP After the event, two steam leaks were discovered on instrument piping [EIIS System/Component Code:
SB/PSF] leading from Turbine Control Valves (TCVs) 2 and 3 [TA/FCV] to turbine pressure switches [IT/PS]
which feed into the Reactor Protection System [System Code JC]. The steam leaks rendered Unit 1 Turbine Stop Valve (TSV) [TA/SHV] and TCV instrumentation inoperable prior to the start of the event.
EVENT DESCRIPTION
On May 9, 2020, operators at the Susquehanna Steam Electric Station (SSES), Unit 1, were raising power following a maintenance outage. At approximately 15:19, with reactor power at 24 percent RTP, operators withdrew control rods to raise power to approximately 28 percent RTP. SSES Technical Specification (TS)
Limiting Condition for Operation (LCO) 3.3.1.1, Reactor Protection System (RPS) Instrumentation, requires that TSV and TCV instrumentation be operable (i.e., not bypassed) at greater than or equal to 26 percent RTP. However, at approximately 15:23, Unit 1 reached 26 percent RTP and the TSV and TCV instrumentation was still bypassed. Operators immediately stopped withdrawing control rods, declared the TSV and TCV instrumentation inoperable, and entered Conditions A and B of LCO 3.3.1.1. Unit 1 was brought below 26 percent RTP at approximately 15:37, thereby exiting Conditions A and B of LCO 3.3.1.1 after approximately 14 minutes.
Subsequent to reducing power below 26 percent RTP, Susquehanna discovered two steam leaks on instrument piping lines SPDCD117-2 (specifically from Field Weld-10 (FW-10)) and JD-5-3-1A (specifically from FW-60). These leaks resulted in the instrument lines being unable to provide adequate steam pressure to turbine instrument sensing lines, and were determined to have rendered the TSV and TCV instrumentation inoperable during startup. Susquehanna repaired the leaks by installing new socket welds on May 11, 2020, and resumed power ascension.
The Completion Times associated with LCO 3.3.1.1, Required Actions A.1 and B.1 (12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, respectively), were not exceeded. However, SSES TS LCO 3.0.4 prohibits entering a mode of applicability (i.e., reaching 26 percent RTP) without meeting all required LCOs. Based on the investigation and determined cause for this condition, the instrumentation piping likely failed, rendering the TCV and TSV instrumentation inoperable, prior to entry into the Mode of Applicability for LCO 3.3.1.1. As such, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
CAUSE OF EVENT
The cause of the event was determined to be FW-10 and FW-60 socket weld failure due to high cyclic fatigue. Additionally, the weld on FW-10 was determined to be undersized.
ANALYSIS/SAFETY SIGNIFICANCE
The inoperable TSV and TCV instrumentation was limited to a single RPS subsystem; the other subsystem was capable of initiating a valid reactor scram signal. As such, there was no loss of safety function (i.e., a safety system functional failure did not occur). This event did not result in any actual consequences to the health and safety of the public.
CORRECTIVE ACTIONS
Corrective actions for this event included repairing FW-10 and FW-60 by removing the leaking connections and installing new welds.
COMPONENT FAILURE INFORMATION
- 1. FW-10 Component Identification - SPDCD117-2 Component Name - Pressure Lines from Main Steam Line TCV-2 and TCV-3 to Turbine Pressure Instruments Component Description -1 Schedule XXS Instrument Sensing Line Component Manufacturer - Bechtel Socket Weld Location - Downstream end of Valve 101009
- 2. FW-60 Component Identification - JD-5-3-1A Component Name - Pressure Lines from Main Steam Line TCV-2 and TCV-3 to Turbine Pressure Instruments Component Description - 0.5 Flex Hose Component Manufacturer - Senior Flexonics Socket Weld Location - Connection of 0.5 Flex Hose to 0.5 Reducer
PREVIOUS OCCURRENCES
LER 50-388/2015-004-00, Degraded Condition due to Reactor Coolant Pressure Boundary Leakage Caused by Vibration and Stiff Pipe Connection, dated June 10, 2015.
LER 50-387/2014-011-00, Degraded Condition Due to Reactor Coolant Pressure Boundary Leakage Caused by an Inadequate Weld, dated February 11, 2015.
LER 50-387/2012-007-01, Unplanned Shutdown due to Unidentified Drywell Leakage, dated November 20, 2012.