05000272/LER-2004-001
| Event date: | 04-09-2004 |
|---|---|
| Report date: | 10-12-2004 |
| 2722004001R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor (PWR/4) Main Steam / Safety Valves {SB/RV}* * Energy Industry Identification System {EIIS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: April 9, 2004 Discovery Date: April 9, 2004
CONDITIONS PRIOR TO OCCURRENCE
The plant was in Mode 6 (REFUELING OPERATION) at the time of the event.
DESCRIPTION OF OCCURRENCE
On April 9, 2004, PSEG discovered that one of the ten Main Steam Safety Valves (MSSV) {SB/RV) tested during the sixteenth refueling outage (1R16) failed its as-found lift setpoint test. The as-found actuation pressure for the 13MS13 MSSV was found below the lower limit of minus 3% of the nameplate setpoint. Setpoint for this valve is 1110 psig +/ 3% as stated in the Salem Technical Specification Table 3.7-1.
The actual test result of the failed valve was:
Valve Id As found TS Setpoint Acceptable band % Difference (psig) (psig) (psig) (psig) 13MS13 1076 1110 1076.7 — 11433 -3.1% Because the actual lift set point of the 13MS13 was not within the required acceptance criterion of +/- 3% of setpoint, two additional MSSVs were tested as required by ASME OM-1987, Part 1 "Requirements for Inservice Performance Testing of Nuclear Power Plant Pressure Relief Devices." The two additional MSSVs (11MS13 and 11MS14) tested satisfactory and no further testing was required.
The failure to have a successful as-found lift setpoint for the 13MS13 MSSV is reportable per the requirements of 10 CFR 50.73(aX2Xi)(B), Operation or Condition Prohibited by Technical Specifications.
CAUSE OF OCCURRENCE
The 13MS13 MSSV was disassembled at the offsite test facility. The internal parts inspection showed no seat or disc steam cuts or damage, the spindle (stem) total indicated run out (TIR) was within specification, and no spindle or spindle guide galling was noted.
,� 1 .
ti CAUSE OF OCCURRENCE (cont'd) The inspection indicated that both upper and lower spring caps had less than 10% contact with the spring ends. The offsite test facility spring standard (derived from EPRI maintenance training) specifies full contact from three-quarters to seven-eighths of the contact circumference. Additionally, the lower spring end was not in contact with the first coil; and the spring ends were not 180 degrees apart, they were approximately 90 degrees apart.
Based on the internal inspection at the vendor's facility, the cause of the as-found setpoint drift has been attributed to the unsatisfactory condition of the spring and mating spring caps. Although this condition has been previously noted on one Pressurizer Safety Valve, it has never been noted in a Steam Generator Safety Valve. The vendor's repair procedure has inspection attributes and acceptance criteria for the spring and mating spring caps. This condition has not been seen in previous MSSV valve disassemblies.
The Salem MSSVs are Crosby 6R10, Style HA-65W, shown on Crosby Drawings #DS-C-A55100-2&3. The valves are a spring-over-disc, self-actuating design. The 13MS13 serial number is N55100-03-0052.
PREVIOUS OCCURRENCES
A review of LERs at Salem and Hope Creek Generating Stations for the years 2001 through present identified the following prior occurrences; Hope Creek All valves lifted in excess of their allowable 3%.
The corrective actions associated with these LERs would not have prevented his event. The valves failed on the high side of the setpoint due to sticking of the pilot disc. Additionally, the valves are of a different design and manufacturer.
Salem 272/2001-003 dated June 12, 2001. The apparent cause of this event was excessive seat leakage. However, the failure described in this LER would have been acceptable under the current +/- 3 % tolerance. The valve failed on the high side of setpoint and the +/- 1% tolerance.
272/ 2002-006, dated December 12, 2002. The apparent cause of this event was the valve spindle rubbing the spindle guide during lifting due to misalignment.
The corrective actions associated with these LERs would not have prevented his event. In one occasion the valve would have met the current acceptance criterion, and the other failed high due to misalignment.
NRC FORM 366A� U.S. NUCLEAR REGULATORY COMMISSION (1-2001) DOCKET (2)FACILITY NAME (1)
- LER NUMBER6)�PAGE (3)(i
SAFETY CONSEQUENCES AND IMPLICATIONS
There was no safety significance to this event.
There are twenty MSSVs installed in Salem Unit 1. These valves are equally distributed in four Main Steam Headers each containing five MSSVs with setpoints varying from a low of 1070 psig to a high of 1125 psig and a tolerance of +1- 3%. The MSSVs provide over pressurization protection for the Steam Generators on the secondary side and the Main Steam System.
During 1R16 a total of twelve MSSVs were tested, including two additional MSSVs as a result of the failure of 13MS13.
Eleven valves lifted within the setpoint tolerances and one valve lifted earlier by a few tenths of one pound. A MSSV lifting earlier (greater than minus 3%) is an operational transient that would result in depressurizing the main steam lines.
However, the potential consequences of the inadvertent depressurization caused by the lifting of a safety valve are bounded by the Main Steam Line Break analyses. In this case, the small difference between the allowable setpoint and the as found lift setpoint, just a few tenths of one pound, would have had minimal to no impact on plant safety. The ability of the MSSV to provide over pressurization protection for the Steam Generators on the secondary side was never compromised.
This event does not constitute a Safety System Functional Failure (SSFF) as defined in Nuclear Energy Institute (NEI) 99-02, Regulatory Assessment Performance Indicator Guideline.
CORRECTIVE ACTIONS:
1. The failed MSSV was replaced with a pre-tested and certified spare.
2. Expanded scope of MSSV testing to include an additional two MSSVs from another header in accordance with the IST Program. The two additional MSSVs tested satisfactorily.
3. The spring will be replaced in-kind from stores. The replacement spring will be inspected using the same inspection criteria as the original spring by the offsite test facility. The spring caps will be lapped to the spring ends to provide the required contact area. The valve will be re-assembled and tested in accordance with the offsite test facility's approved procedures.
COMMITMENTS
The attached LER contains no commitments.