05000364/LER-2020-001, Main Steam Safety Valve Lift Pressure Outside of Technical Specifications Limits Due to Setpoint Drift
| ML20338A131 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 12/03/2020 |
| From: | Erb D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-20-1327 LER 2020-001-00 | |
| Download: ML20338A131 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3642020001R00 - NRC Website | |
text
A Southern Nuclear December 3, 2020 Docket No.:
50-364 U.S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, D. C. 20555-0001 Charles Kharrl Vice President - Farley Joseph M. Farley Nuclear Plant - Unit 2 licensee Event Report 2020-001-00 Main Steam Safety Valve lift Pressure Outside of Technical Specifications limits due to Setpoint Drift ladies and Gentlemen:
Joseph M. Farley Nuclear Plam 7388 Nonh S1a1e Hwy 95 Columbia. Alabama 36319 334.661.2100 tel 33~.661.25 12 fa.~
ckharrl'a. southemco com Nl-20-1327 In accordance with the requirements of 1 O CFR 50. 73(a)(2)(i)(B), Southern Nuclear Company is submitting the enclosed licensee Event Report for Unit 2.
This letter contains no NRC commitments. If you have any questions regarding this submittal, please contact Thomas Campbell, licensing Engineer at (334) 661-2673.
a27Z:
Vice President (Acting)- Farley DE/tec/cbg Enclosure: Unit 2 Licensee Event Report 2020-001-00 Cc:
Regional Administrator, Region II NRR Project Manager - Farley Nuclear Plant Senior Resident Inspector-Farley Nuclear Plant RTYPE: CFA04.054
Joseph M. Farley Nuclear Plant - Unit 2 Licensee Event Report 2020-001-00 Main Steam Safety Valve Lift Pressure Outside of Technical Specifications Limits due to Setpoint Drift Enclosure Unit 2 Licensee Event Report 2020-001-00
Abstract
On October 6, 2020, while in Mode 1 at 95% power level, it was discovered that a Unit 2 Main Steam Safety Valve (MSSV) failed its as-found lift pressure test. The MSSV lifted below the Technical Specification (TS) 3.7.1 allowable lift setting value. Setpoint drift due to spring relaxation is the most likely cause of the MSSV failure.
It is likely that the MSSV was outside of the TS limits longer than the allowable completion times for the associated Required Action Statements during the operating cycle in all applicable modes of operation. Therefore, this condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
The MSSV setpoint was adjusted to within the TS limits and returned to service restoring compliance. The MSSV that failed the surveillance setpoint test was replaced with a refurbished valve during the 2R27 refueling outage and sent to vendor for analysis.
EVENT DESCRIPTION
On October 6, 2020 at 1259 CDT, while operating in Mode 1 and at 95% power level, a C Loop Main Steam Safety Valve (MSSV), Q2N11V0012D [EIIS:SB:RV] as-found lift pressure did not meet the acceptance criteria of+/- 3% of setpoint (1115 psig) as required by Technical Specifications (TS) Surveillance Requirement (SR) 3.7.1.1. The MSSV lifted low at 1065 psig which is 17 psig outside of its acceptance range of 1082 to 1148 psig. The +/- 3% as-found lift pressure requirement is an ASME Section Ill, 1971 edition, and Farley TS requirement to ensure that the MSSV provides adequate protection by preventing the steam pressure from exceeding 110% of the main steam system design pressure.
EVENT ANALYSIS
The valve (Manufacturer: Dresser, Model Number: 3707R, Serial Number: BP09825) was sent to NWS Technologies for failure analysis due to the failed as-found test. The MSSV was disassembled, inspected, and the spring was rate tested.
The spring failed low at 18247 lbf/in. This is below the required tolerance of 18810-20790 lbf/in. The relaxed spring is the most likaly cause of the valve failing the as found test.
REPORTABLITY AND SAFETY ASSESSEMENT:
This failure constitutes a condition that is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." The applicable accident/transient analyses requires five MSSVs per Steam Generator [EIIS:SB:SG] to provide overpressure protection for design basis transients occurring at 102% Rated Thennal Power. On October 6, 2020, MSSV Q2N11V00120 was found outside of its required setpoint range and was declared inoperable. As it is not possible to detennine when the valve exceeded the allowable setpoint range, the MSSV was likely inoperable for greater than the TS allowed completion time. Based on the MSSV as-found lift setpoint being less than 110% of design Steam Generator pressure (1194 psig), and properly reseating, this one MSSV failure did not result in a loss of safety function. There was no release of radioactivity associated with this event.
CORRECTIVE ACTIONS
The C Loop MSSV that failed the surveillance setpoint test was adjusted within tolerance and returned to operable status.
The MSSV was subsequently removed from its location during the 2R27 outage for analysis and was replaced on November 6, 2020 with a refurbished valve that was heat soaked and placed in the Q2N11V0012D location at the required 1115 psig +/-1%.
PREVIOUS SIMILAR EVENTS
A similar event was reported for Unit 2 in LER 2017-002-00.
OTHER SYSTEMS AFFECTED:
No other systems were affected by this event. Page 2
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