|Joseph M. Farley Nuclear Plant, Unit 2|
|Reporting criterion:||10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications|
|3642017003R00 - NRC Website|
|Person / Time|
|From:||Madison D R|
Southern Nuclear Operating Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17354A395 (4)|
During the Unit 2 October 2017 refueling outage (2R25), while in Mode 6 and at 0% power level, with the Reactor Coolant System (RCS) at atmospheric pressure and 83 degrees Fahrenheit, a pressurizer safety valve (PSV) was removed as part of the routine In-Service Testing (IST) program and sent to an off-site testing facility. The as-found lift pressure was discovered to be 2455 psig which was outside of the Technical Specification (TS) 3.4.10 allowable lift pressure settings of >1= 2460 psig and Based on the lift pressure meeting the 1ST Program (ASME code) monitored requirements, there was no 1ST scope expansion for the PSV.
During the previous cycle, indications of seat leakage from this PSV was evidenced by tailpipe temperature indication.
Based on review of trends, during the 18-month cycle the tailpipe temperatures were between the minimum and maximum values, 75 and 130 degrees respectively. Additionally, leakage past the seat was identified during testing at the off-site facility. The cause of the valve removed from PSV location lifting low at 2455 psig is setpoint drift which resulted in the seat leakage.
REPORTABILITY AND SAFETY ASSESSMENT:
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." Although seat leakage was identified while online in June of 2016 there is no firm evidence of when the failure to meet the lift setting requirements occurred prior to the time of discovery at the test facility. The setpoint could have drifted below the allowable value at any time between startup from the previous refueling outage (2R24) and the time of discovery.
Since the as-found lift setpoint was lower than the allowed value in the TS, the condition did not have an adverse impact on its over-pressurization function. The as-found lift pressure was 2455 psig, and the valve re-closed following the lift. This is within the safety analysis assumptions that are credited for PSVs, and the plant remained bounded by the accident analyses in the Final Safety Analysis Report (FSAR). Therefore, this condition had no significant effect on the health and safety of the public.
The PSV was replaced during the October 2017 refueling outage. The as-left setpoints were within +/- 1% tolerance.
PREVIOUS SIMILAR EVENTS:
Similar events were reported for Unit 1 in LER 2015-004-00 and LER 2016-003-00. For the 2015 LER, there had been indication of seat leakage during the previous operating cycle based on elevated tailpipe temperatures.
OTHER SYSTEMS AFFECTED:
No other systems were affected by this event.