05000387/LER-2010-004
| Susquehanna Steam Electric Station Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3872010004R00 - NRC Website | |
On March 11, 2010, during local leak rate testing (LLRT) of Main Steam Line Isolation Valve (MSIV) [EIIS Code: SB] Penetration Number X-7D, the Unit 1 "D" Main Steam Line Boundary, the Unit 1 "D" Outboard Isolation Valve exceeded 71 standard liters per minute (SLM). This condition, which was considered to have existed during the previous operating cycle, was a failure to meet Technical Specification 3.6.1.3. As a result, this condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
The sequence of events leading up to the LLRT failure is as follows:
- March 11, 2010 at 0350 - "D" Outboard (OB) MSIV leakage exceeded 71 SLM during testing March 24, 2010 at 0700 — the "D" OB MSIV was reworked in accordance with procedures March 25, 2010 at 1800 - after rework, the As-Left LLRT for the "D" OB MSIV was 33.28 SLM
- The event should have been reported in accordance with 10 CFR 50.73(a)(2)(i)(B) in 2010 but was not reported as required due to less than adequate guidance in the Susquehanna reportability procedure. This event was originally reported in LER 50-387/2012-006-00, dated July 12, 2012 with a similar 2012 event. Since this event should have been reported separately, this LER is being submitted.
CAUSE OF THE EVENT
The causes of the event were determined to be as follows:
The valve body seat had poor contact area at the lower segment (6 o'clock location).
- The X-7D as-left penetration leakage having minimal margin to the TS limit, contributed to the as-found testing failure in the next refueling outage.
Following initial analysis of the events and submittal of the LER, a root cause analysis was performed to analyze the failure to properly evaluate the testing failures. This analysis identified the following root causes:
- Station Engineering management and supervision had not exercised Technical Authority over the Appendix J Program to prevent MSIV LLRT failures.
- The Leak Rate Test Program procedure did not establish "maintenance limits" for As-Found and As-Left MSIV LLRT test results for each valve.
- The station reportability procedure inappropriately stated that exceeding the MSIV 100 scfh leak rate limit is not reportable.
ANALYSIS/SAFETY SIGNIFICANCE
Actual Consequences:
The actual safety consequence of the "D" inboard MSIV LLRT failures is minimal. The MSIVs have a safety function to close to prevent a large release of radiation to the site boundary under accident conditions. As-Found and As-Left LLRTs of "D" Main Steam Line Penetration X-7D demonstrated that "D" inboard MSIV penetration would have performed satisfactorily to prevent the release of radioactive materials through penetration X-7D.
Potential Consequences:
The potential consequence is that, in the event of a LOCA combined with a failure of the "D" Inboard MSIV to isolate, the "D" Outboard MSIV would not have isolated Penetration X-7D sufficiently to prevent fission products from being released. This potential consequence involves multiple safety system failures both to cause the LOCA and then to create the release path.
1. The Conduct of Station Engineering procedure was revised to include the Technical Conscience obligation statement from INPO 10-005, Principles for Maintaining an Effective Technical Conscience.
2. The Leakage Rate Testing Program procedure has been revised to establish administrative maintenance limits for as-found and as-left MSIV LLRT results for each valve. These administrative maintenance limits identify when as-found corrective maintenance needs to be performed as well as what the as-left limit must be achieved prior to returning the valve back to service after maintenance.
3. The station reportability procedure was revised to provide correct guidance associated with reportability of MSIV leakage.
PREVIOUS SIMILAR EVENTS
A cause of this LER was a less than adequate procedure. The following recent LERs identified similar causes:
instructions as one of the causes.
unclear procedure requirements and less than adequate reinforcement of management expectations for work package content as one of the causes.
test procedures that did not test all aspects of the system that were relied upon for operability.