05000281/LER-2008-001
| Surry Power Station, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 2812008001R00 - NRC Website | |
REPORTABLE
TO EPIX
DAY YEAR
On May 2, 2008 with Unit 2 shut down for a refueling outage, a pressurizer safety valve (PSV) 2-RC SV-2551C as found lift setting was 2368 psig, which is 4.7% below the nominal value of 2485 psig.
Technical Specification (TS) 3.1.A.3.b specifies the as found tolerance shall not exceed +- 3% (2410 2510 psig).
On May 9, 2008, PSV 2-RC-SV-2551B failed to lift within the as found set pressure requirement. The as found lift setting also did not meet the +/- 3% tolerance allowed by TS 3.1.A.3.b. This PSV exhibited an as found lift setpoint of 2399 psig which was 3.51% below the nominal value of 2485 psig.
The as found PSV lift settings were evaluated and it was determined that the PSVs were capable of performing their safety function and operation with the low as found lift setpoints was within the limits assumed in the accident analysis. Therefore, the health and safety of the public were not affected.
There were no significant safety consequences associated with this event. This report is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) "Any operation or condition prohibited by the plant's Technical Specifications".
NRC FORM 366 19-2007) PRINTED ON RECYCLED PAPER 1.0 DESCRIPTION OF THE EVENT On April 27, 2008, Unit 2 was shut down to start a refueling outage. As part of the outage scope, pressurizer safety valve (PSV) 2-RC-SV-2551C was sent to Wyle Laboratories in Huntsville, Alabama for setpoint testing. The PSV was tested in accordance with station testing procedures developed pursuant to the Surry Power Station ASME Section XI Testing Program for Pumps and Valves. This PSV failed to lift within the +/- 3% requirement (i.e., 2485 +/- 3% (2410-2510 psig)) for as found setpoint (TS 3.1.A.3.b); 2-RC-SV-2551C as found lift setting was 2368 psig which is 4.7% below the nominal value of 2485 psig. In accordance with requirements of ASME Section XI, the remaining two PSVs were subsequently sent to Wyle for setpoint testing.
On May 9, 2008 PSV 2-RC-SV-2551B failed to lift within the as found set pressure requirement.
The as found lift setting, did not meet the +/- 3% tolerance allowed by TS 3.1.A.3.b. (i.e., 2485 +/ 3% (2410-2510 psig)). This PSV exhibited an as found lift setpoint of 2399 psig which was 3.51% below 2485 psig.
The as found setpoints were evaluated and it was determined that the PSVs were capable of performing their safety function and operation with the low as found lift setpoints was within the limits assumed in the accident analysis.
This event is reportable pursuant to 10 CFR 50.73(a)(2)(i) )(B) "Any operation or condition prohibited by the plant's Technical Specifications".
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The lower PSV lift pressure would have continued to provide overpressure protection. An evaluation was conducted regarding the as found bench test lift of PSV 2-RC-SV-2551C being found 2 psig lower than the nominal high pressure reactor trip setpoint (2370 psig). Events that would increase pressure in the reactor coolant system are a loss of load or loss of all feedwater flow. Redundant trip signals of the turbine trip and steam generator low level trip signals would have actuated before the PSV as found setpoint would have been reached. Although not credited in the safety analysis, pressurizer spray and pressurizer PORVs would keep pressure lower than the bench test setpoint achieved. Thus, there is no concern regarding this as found setpoint from a safety analysis standpoint as the current safety analysis remains bounding.
3.0 CAUSE An apparent cause evaluation was performed and determined that, while there was no clear indication that the PSV as found setpoint was directly attributable to a specific cause, the most likely cause is aging of the valve components.
4.0 IMMEDIATE CORRECTIVE ACTION(S) PSV 2-RC-SV-2551C was completely disassembled and the valve internals were VT-3 inspected.
The valve internal components were cleaned and polished. The valve internals were visually and dimensionally inspected. The valve internals (i.e. nozzle seat step, spindle ball, disc holder angle, disc insert and nozzle seating areas) were reworked, machined and lapped. PSV 2-RC-SV-2551C was reassembled for the steam set pressure and steam seat tightness testing. PSV 2-RC-SV 2551C satisfactorily passed both steam set pressure and steam seat tightness testing.
In accordance with the requirements of ASME section XI, the remaining two PSVs were sent to Wyle labs for setpoint testing.
5.0 ADDITIONAL CORRECTIVE ACTIONS The other two PSVs on Unit 2 were setpoint tested.
PSV 2-RC-SV-2551B as found set pressure was 2399 psig which is 3.5% lower than the TS required range of 2410 - 2510 psig. PSV 2-RC-SV-2551B was completely disassembled and valve internals were VT-3 inspected and dimensions verified. The disk insert was replaced due to the disc seat step being near minimum tolerance. The spring assembly was replaced and the valve re assembled and satisfactorily tested.
PSV 2-RC-SV-2551A was tested satisfactorily and subsequently re-installed.
6.0 ACTIONS TO PREVENT RECURRENCE The PSV test program is based on Section XI of the ASME Code. The EPRI Safety and Relief Valve Testing and Maintenance Guide lists several factors as potential causes of lift low. All but two of these factors, aging and spring relaxation, do not apply in this case. Failure rate of as found set pressure testing can be reduced if the valves are rebuilt prior to actual failure. The PSV maintenance strategy will be revised prior to the next refueling outage to address aging issues.
7.0 SIMILAR EVENTS None.
8.0 MANUFACTURER/MODEL NUMBER Crosby, HB-BP-86E