05000388/LER-2007-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| 3882007001R00 - NRC Website | |
EVENT DESCRIPTION
On March 9, 2007 at 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br />, with Susquehanna Unit 2 in Mode 5 (Refueling) at 0% power, it was determined that the as-found minimum pathway Secondary Containment Bypass Leakage (SCBL) Technical Specification (TS) limit had been exceeded during regularly scheduled Local Leakage Rate Testing (LLRT). The TS SCBL limit is 9 scfh (4247 sccm). At the time the limit was surpassed, the station was testing the Unit 2 'A' Residual Heat Removal (EllS Code: BO) Containment Spray penetration. Despite work history that suggested leak rate failures at this penetration were not usually attributable to the isolation valve being tested (HV251 F01 6A) but were often caused by a leaking test boundary valve (HV251F021A), PPL lubricated and stroked the tested isolation valve before boundary valve repairs could be made.
This action required PPL to accept the higher than desired as-found LLRT results. Analysis has concluded that the boundary valve was, in fact, primarily responsible for the unsatisfactory LLRT results and that the event was caused by PPL's failure to rework the boundary valve and perform a second as-found leak rate test.
Total bypass leakage was determined to be 5892 sccm at the completion of the outage leak rate testing effort. The as left SCBL total was reduced to 953 sccm following maintenance. This is well below the TS limit of 4247 sccm.
10CFR50 Appendix J minimum pathway limits were not exceeded.
CAUSE OF EVENT
The higher than desired leak rate experienced at the Unit 2 'A' Residual Heat Removal Containment Spray penetration was primarily attributable to a leaking test boundary valve. The event was caused by PPL's failure to rework the boundary valve and perform a second as-found leak rate test.
ANALYSIS / SAFETY SIGNIFICANCE
This event was determined to be reportable in accordance with 10CFR50.73(a)(2)(ii)(A) in that the total as-found minimum pathway leakage rate exceeded the TS limit.
Actual Consequences:
The purpose of primary containment (EIIS Code: NH) isolation valves is to limit fission product release during and following postulated Design Basis Accidents. The SCBL TS value is established to limit the release of radioactive materials outside of secondary containment to ensure offsite and main control room doses remain within regulatory limits. No event occurred during the SCBL testing (Mode 5) or during any other plant condition over the past operating cycle to challenge 10CFR100 or 10CFR50, Appendix A, GDC 19 dose limits. As such, there were no actual safety consequences resulting from this event.
Potential Consequences:
Analysis has concluded that, during a postulated design basis accident, any increase in dose related to the elevated SCBL leak rate would not have exceeded either 10CFR100 or 10CFR50, Appendix A, GDC 19 dose limits.
CORRECTIVE ACTIONS
Following valve maintenance activities, as-left SCBL values meet established TS limitations.
Corrective Actions are planned to more clearly identify those leak rate tests that contribute to SCBL in procedures, maintenance work plans, and station schedules. Troubleshooting plans will be pre-staged for SCBL related LLRT activities.
ADDITIONAL INFORMATION
Failed Components Information:
Component HV251F016A; 12 inch globe valve Model:�W8522332B Manufacturer: Anchor Darling Valve Co.
Past Similar Events: