05000335/LER-2002-001
| Event date: | 9-28-2002 |
|---|---|
| Report date: | 11-6-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3352002001R00 - NRC Website | |
FACILITY NAME (1) UU 'Ii
Description of the Event
On September 28, 2002, St. Lucie Unit 1 was in Mode 1 and holding at approximately 68 percent reactor power for Technical Specification testing of the main steam safety valves (MSSVs) setpoints. T Two MSSVs met their Technical Specification as-found set pressure requirements and two valves (V8203 and V8214) failed low by small deviations. T Technical Specifications (TS) require the as-found set pressure to be within a tolerance of +1 percent and -3 percent of their set point of 1000 psia (lower bank) and 1040 psia T (upper bank).
Valve Serial Number Trair Set Pressure (psig) As-Found Lift Pressure (psig) TS Lift Setting Limits (+1%, T -3%) (psig) Deviation Set Pressure (psi / % of setpoint) V8203 N55128-00-0003 A 985.3 954.9 > — 955.3 and 0.4 psi low / -3.0854% V8206 N55128-00-0006 B 985.3 988.4 > — 955.3 and V8209 N55128-00-0009 A 1025.3 1034.7 > — 994.1 and V8214 N55128-00-0014 B 1025.3 993.9 > — 994.1 and 0.2 psi low / -3.0625% As the as-found lift pressures of two valves were outside of the TS tolerance limit (TS table 4.7-1), an evaluation is required to assess the potential impact on plant safety analysis and operation during cycle SL1-17.
Cause of the Event
Apparent cause of the deviation is setpoint drift. T Since no valve exceeded a 3 percent positive tolerance of set pressure, a formal root cause is not required by ASME/ANSI OM-1987, Part 1. Per ASME/ANSI OM-1 1.3.3.1(e)(2) T and Code Interpretation 92-8, a Class 1 pressure relief valve with an as-found setpoint outside the acceptance range of the setpoint on the minus side is not considered a failure.
Procedure ADM-29.02, T "ASME Code Testing of Pumps and Valves," generally requires additional testing for valves failing the negative tolerance criteria based upon system functional issues resulting from relief valve seat leakage and premature lift.
Per ADM-29.02, additional testing of valves failing the negative tolerance acceptance criteria may be waived or altered based on an evaluation of the as-found test pressure, valve inspection, system requirements and historical records. T The test expansion was waived based on the acceptable results of the other valve tests with respect to ASME criteria, the absence of recent problems with MSSV seat leakage and premature lift, and the insignificance of the small negative deviations. T The small negative deviations have no practical significance and is not indicative of a generic trend or failure mode.
Analysis of the Event
This event is reportable under 10 CFR 50.73(a)(2)(i)(B) T as "any operation or condition prohibited by the plant's Technical Specifications.
-200 Analysis of Safety Significance The MSSVs must open to provide overpressure protection for the steam generators and relief capacity to remove decay heat. Plant power level and Reactor Trip Setpoints were reduced to 66 percent to allow continued operation with two MSSVs out of service on each train. Since no more than one valve per train was out of service and the Reactor Trip Setpoints were properly adjusted, there were no operability concerns during the performance of the surveillance.
Four St. Lucie Unit 1 MSSVs were tested per Plant Procedure 1-MSP-08.07. Two MSSVs met their Technical Specification as-found set pressure requirements and two valves failed low by small deviations. The only FSARanalyzed events that could potentially be affected by the deviations in the MSSV setpoints are the loss of external load (LOEL) and the small break LOCA (SBLOCA).
The loss of external load event, including the case of inoperable MSSVs, relies on the MSSVs to release the system energy to prevent the primary and the secondary side pressures from exceeding the overpressurization criteria. The analysis of the event conservatively assumes the MSSVs begin to open at the TS allowed maximum lift pressure corresponding to a tolerance of +1 percent. Opening the valves at a pressure lower than that assumed in the safety analysis would be beneficial for this transient and the results would remain bounded by the FSAR results.
In the analysis of the small break LOCA event, it is assumed that the MSSVs begin to open at a lift pressure corresponding to a tolerance of +3 percent. The as-found set pressures therefore would not have any adverse impact on the small break LOCA analysis results, as presented in the FSAR.
Other FSAR events, including the steam generator tube rupture (SGTR) event, are not impacted by the variations in the MSSV lift pressure. The SGTR event analyzed in the FSAR conservatively assumes the opening of the atmospheric dump valves (ADVs) to release the steam from the ruptured steam generators. The identified MSSVs setpoint pressure deviations thus would not impact the FSAR conclusions for this event.
The opening of the MSSVs at pressures lower than the lift pressure corresponding to -1 percent tolerance is thus determined to have no adverse impact on the safety analysis, including deviations outside -3 percent. A much lower negative valve tolerance limit, though acceptable from safety analysis considerations, may have operational impact as the margin to operating pressure is reduced. There are no operational concerns related to the as-found lift-pressures, as these pressures have only minor deviations compared to the negative tolerance limit.
In summary, the MSSVs as-found set pressure values were outside the tolerance limits specified in the St. Lucie Unit 1 TS table 4.7-1. The degraded condition did not compromise plant safety. The evaluation performed using the as-found setpoints concludes that Cycle 17 operation has remained within the design basis of the plant for all analyzed FSAR events. No safety criteria would have been violated due to the identified condition of the MSSVs. The condition is considered to be neither outside the design basis of the plant nor an unanalyzed condition that significantly compromises plant safety. Therefore, this event had no adverse effects on the health and safety of the public.
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Corrective Actions
1. V8203 has been removed, shipped offsite, reworked, re-certified, and reinstalled during the St. Lucie Unit 1 SL1-18 refueling outage via WO 31015590.
2. V8214 has been removed, shipped offsite, reworked, re-certified, and reinstalled during the St. Lucie Unit 1 SL1-18 refueling outage via WO 31015589.
Additional Information
Failed Components Identified None Similar Events Specification Requirements.
Technical Specification Limits.