05000458/FIN-2012009-06
From kanterella
Jump to navigation
Jump to search
Finding | |
|---|---|
| Title | Implementation of the Station Cable Reliability Program |
| Description | The team identified an unresolved item associated with the licensees process for ensuring that underground non-safety related power cables whose failure could affect equipment in the scope of the Maintenance Rule were maintained as described in Procedure EN-DC-346, Cable Reliability Program, Revision 3. On May 21, 2012, non-vital 13.8 kV circuit breaker NPS-SWG1A ACB07, the supply breaker to circulating water area transformer STX-XS2A, tripped resulting in a loss of circulating water cooling to the main condenser and a subsequent reactor scram. The licensees investigation discovered that a fault in underground medium voltage cable 1NPSANJ322 had caused the trip of circuit breaker ACB07 and a fire in underground cable vault EMH1A. The licensee wrote Condition Report CR-RBS-2012- 3440 to document the event and the root cause analysis results. The licensees preliminary analysis identified the most probable cause of the cable fault as moisture intrusion at a spliced connection in cable 1NPSANJ322. The team reviewed the licensees root cause evaluation report, dated June 19, 2012. The cause evaluation concluded that the root cause of the cable failure was poor splice crimping and water intrusion at the splice causing accelerated cable insulation degradation. The team determined the report conclusions were appropriate. The NRC issued Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients, in February 2007. The generic letter required licensees to provide a description of the inspection, testing, and monitoring programs they used to detect the degradation of inaccessible or underground power cables that support systems that were within the scope of 10 CFR 50.65 (the Maintenance Rule). The Maintenance Rule required, in part, that licensees monitor the performance or condition of structures, systems, or components in a manner sufficient to provide reasonable assurance that such structures, systems, and components are capable of fulfilling their intended functions. The team determined that the licensee had established a cable monitoring program in December 2009 and had begun diagnostic cable testing in January 2011. Procedure EN-DC-346, Cable Reliability Program, Revision 3, required, in part, that underground power cables whose failure could affect Maintenance Rule equipment be monitored to establish the insulation condition using appropriate testing and evaluation of the test results. The licensee identified approximately 57 in-scope cables, fourteen of which had been tested before the May 21 failure. The licensee used a dielectric loss-dissipation factor test (tan a test) as their method of diagnosing problems in medium-voltage cables. The dielectric loss-dissipation factor test has the ability to detect thermally induced cracking, radiation-induced cracking, mechanical damage, water treeing, moisture intrusion, and surface contamination. Following replacement of the failed cable splice, the licensee performed diagnostic testing on cables 1NPSANJ303, 1NPSANJ304, and 1NPSANJ322 as part of post-maintenance testing and identified that cable 1NPSANJ304 did not have acceptable values for insulation resistance. The licensee cut open a splice on cable 1NPSANJ304 and found water between the cable jacket and insulation. The licensee initiated Condition Report CR-RBS-2012-03590 to document the water intrusion in cable 1NPSANJ304 in the corrective action program. The licensees cable reliability program established a cable risk factor for setting priorities for testing shielded medium voltage cables. The cable risk factor included the number of known splices in the cable and an adverse environment risk factor for cables subject to submergence. The program also included guidance for confirming that underground cable vault maintenance practices and water level trending were sufficient to keep the cables from submergence, if possible, to increase the longevity of the insulation system. The licensee had established a risk ranking for in-scope cables, but had not inspected the in-scope underground cable vaults to determine the number and location of cable splices. The presence of splices would change the ranking of cables. Cables 1NPSANJ304 and 1NPSANJ322 had not been tested before they failed at spliced connections in May 2012. The team identified that several different ranking formats were in use at the station and concluded that the cable ranking system for the scheduling of diagnostic tests was not clearly defined. The licensee performed visual inspections of other underground cable vaults searching for additional splices in the redundant non-safety-related train. No additional splices were found in the redundant train; however, other underground cable vaults needed to be dewatered because the cables were submerged and were not visible until the water had been removed. The team determined that prior to performing the cable vault inspections following the May 21 cable failure, the licensee did not have the information needed to effectively implement the guidance for developing the cable risk rankings described in procedure EN-DC-346, Cable Reliability Program, Revision 3. The root cause evaluation report stated that a testing schedule had been developed for the remaining in-scope cables such that initial dielectric loss-dissipation factor testing would be completed for all in-scope cables by the completion of Refueling Outage 18. The licensee initiated an additional action associated with the root cause evaluation to review the risk-ranking criteria for all in-scope cables. The team concluded further inspection was required to review the effectiveness of the licensees monitoring program for in-scope cables. |
| Site: | River Bend  |
|---|---|
| Report | IR 05000458/2012009 Section 4OA5 |
| Date counted | Sep 30, 2012 (2012Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93800 |
| Inspectors (proximate) | S Graves S Garchow G Miller S Alferink V Gaddya Barrettb Tindell E Uribe B Hagar |
| INPO aspect | |
| ' | |
Finding - River Bend - IR 05000458/2012009 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Finding List (River Bend) @ 2012Q3
Self-Identified List (River Bend)
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||