05000266/LER-2012-005
| Point Beach Nuclear Plant 05000266 | |
| Event date: | 10-8-2012 |
|---|---|
| Report date: | 06-27-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2662012005R01 - NRC Website | |
Description of the Event
On October 8, 2012, Point Beach Nuclear Plant (PBNP) Unit 1 was operating in a steady state condition Containment INOPERABLE due to a Service Water (SW) leak into Containment. Unit 1 entered Technical Specification Action Condition (TSAC) 3.6.1.A, with Required Action A.1 to Restore Containment to OPERABLE status with a Completion Time of one hour. On October 8, 2012, at 2355, Unit 1 entered TSAC 3.6.1.B, with Required Action B.1 to Be in MODE 3 with a Completion Time of six hours AND Required Action B.2 to Be in MODE 5 with a Completion Time of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
NextEra Energy Point Beach, LLC (NextEra) personnel entered containment to determine the source of the SW leak, and found the leak to be on the common return piping for the B Train reactor cavity cooler.
The leak was isolated by shutting the outside containment isolation valves. The leak was stopped, as verified by local observation inside containment. Containment was then declared OPERABLE, and the appropriate TSACs were exited.
NextEra determined the Containment Leak Rate Testing Program (CLRT) excludes these valves from Local Leakage Rate Testing (LLRT) requirements. The valves that were closed could be credited for the containment isolation function with sufficient documentation to support operability. The immediate operability determination provided sufficient justification for operability based on verification of the leakage stopping when the valves were closed. However, a prompt operability determination was not requested at the time to provide justification for the use of non-tested valves. Therefore, Unit 1 should have been placed in MODE 3 by October 9, 2012 at 0555, and MODE 5 by October 10, 2012 at 1155.
Instead Unit 1 remained at full power. The degraded pipe was repaired and returned to service on October 26, 2012 at 2119. A prompt operability determination was subsequently requested on October 18, 2012 and completed on October 23, 2012 at 20:51. The POD determined that the penetration was operable but degraded. The POD did not provide sufficient information to justify containment operability requirements for allowable containment leakage La.
Cause of the Event
There was insufficient guidance provided in the Technical Specification Bases and CLRT program for the Shift Manager to determine a prompt operability determination was required to provide additional information justifying meeting containment operability requirements regarding allowable leakage La. The CLRT program document did require that an engineering evaluation be performed for the use of these valves but did not provide adequate guidance on requiring containment leakage to be addressed.
Analysis of the Event
NEI 94-01, which was endorsed by the NRC via Regulatory Guide 1.63, provides methods acceptable to the NRC staff for complying with Option B of 10 CFR 50 Appendix J. Section 6.0 General Requirements of NEI 94-01 states An LLRT is not required for the following cases: Primary containment boundaries that do not constitute potential primary containment atmospheric pathways during and following a Design Basis Accident (DBA)..." This exception for not performing LLRT was assumed to be applicable to manual isolation valves of the SW system because the SW system is a closed system inside containment with no potential for a primary containment atmospheric pathway to outside containment.
However, when the closed system is degraded with a pathway to outside containment, an engineering evaluation of potential leak path was required. While the CLRT program required an evaluation, it did not provide details on the content of the required evaluation and the TS bases makes no reference to the need for an engineering evaluation or the CLRT program.
Analysis of Safety Significance containment that is normally closed was open to containment atmosphere due to a through-wall leak. The SW pipe was isolated by the closure of the isolation valves outside containment. Closure of the valves does not adversely affect any key safety function.
This plant configuration does not increase the likelihood of a core damaging event. According to WCAP-16378-P, Westinghouse Owners Group Definition for Large Early Release Frequency (LERF), a general rule is that containment isolation failures with an equivalent diameter of greater than 2 inches are considered large. Because the size of the degradation in the pipe is much smaller than this, a release through this hole would not be considered large, and there would be no increase in LERF due to this issue.
Since the SW supply header remains pressurized above containment pressure during the period of an accident when fission products may be actively evolved from the core, leakage into the pressurized SW system is not considered to be a credible release path.
In addition to the immediate visual verification of leak-tightness by operators, SW return isolation valves in are also considered an insignificant potential release path.
Given the unlikely combination of a core damage event and a subsequent failure of either the pipe or valve, the release to the environment via the hole in the SW piping would not be classified as a large early release event. Therefore the issue is not significant.
Corrective Actions
The degraded piping was repaired and the closed system integrity was verified on October 26, 2012, restoring the closed system boundary.
Revise the CLRT program to improve the level of detail for prompting timely evaluations in support of immediate operability determinations regarding isolation valves used for isolation that are not tested via the CLRT program.
Revise TS Basis to improve the level of detail used in support of operability determinations regarding isolation valves used for isolation that are not tested via the CLRT program.
Similar Events None
Failed Components
None