05000220/FIN-2012005-03
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Finding | |
|---|---|
| Title | Assessment of Containment Leakage Due to Containment Isolation Valve Failure |
| Description | On December 3, 2012, at 11:31 a.m., Unit 1 established primary containment integrity and commenced a reactor startup from an unplanned outage. The following day at 2:40 a.m., NMPNS commenced injecting nitrogen into the primary containment as part of a planned activity to reduce primary containment oxygen concentration to less than four percent as required by TS 3.3.1, Oxygen Concentration . This activity was completed 10:55 a.m., on December 4. Once an appropriate nitrogen concentration has been achieved in containment, additional makeup is generally not required. However, from December 6 - 8, on three occasions, operators added additional nitrogen to the containment to maintain pressure within procedural limits. This issue was documented in CR 2012-011157, Adverse Trend in Unit 1 Nitrogen Usage. This issue was initially classified as a priority 2 work item and NMPNS commenced initial troubleshooting activities, which included examining systems/components that were possible sources of nitrogen leakage. However, a definitive source for the leakage was not identified. On December 12, following a fourth addition of nitrogen that occurred on December 11, NMPNS increased the importance of the issue to Priority 1, formed an incident response team and staffed the outage coordination center. As part of the investigation process, NMPNS cycled several containment isolation valves in the nitrogen purge and vent system, and attempted to quantify the amount of seat leakage through the valves by opening test fittings located between isolation valves. In parallel with the troubleshooting efforts, NMPNS and vendor personnel began to develop analytical tools that could be used to quantify the amount of containment leakage. On December 13, at 6:47 p.m., after observing a decrease in containment pressure following a fifth nitrogen addition, and receiving preliminary data that a containment isolation valve local leak rate test (LLRT) between reactor containment inert gas purge and fill drywell cooling system isolation valves IV-201-31 and IV-201-32 may fail, NMPNS commenced a plant shutdown because primary integrity as required in TS 3.3.3 could not be assured. The plant reached cold shutdown on December 13 at 11:33 p.m. Subsequent NMPNS testing of containment isolation valves revealed that three valves in the reactor containment inert gas purge and fill drywell cooling system IV-201-10, IV- 201-31 and IV-201-32 had unacceptable seat leak rates. These conditions were documented in several CRs including 2012-011210 and 2012-011288. When the valves were disassembled and examined, NMPNS identified that iron oxide buildup on the valve resilient seats had prevented the valves from closing tightly and adversely impacted seat leakage performance. The reactor containment inert gas purge and fill drywell cooling system is a carbon steel system and the internal piping surface adjacent to the valves had visible signs of iron oxide degradation (rust). NMPNS corrective action included removing the loose surface rust, installing new seats on the valves, and successfully performing as-left LLRTs on the subject valves. Additional corrective actions are outlined in CR 2012-011157. This issue will be tracked as a URI pending NMPNS quantification of the drywell leakage that existed from December 3 - 13, 2012 and NRC review of the NMPNS evaluation to determine whether the issue is more than minor and whether a violation exists. NMPNS intends to complete the evaluation by January 31, 2013. |
| Site: | Nine Mile Point  |
|---|---|
| Report | IR 05000220/2012005 Section 4OA3 |
| Date counted | Dec 31, 2012 (2012Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | D Dempsey K Kolaczyk G Dentel P Presby S Kennedy B Sienel M Schneider E Burket B Dionne E Millerj Lilliendahlp Kaufman D Schroeder K Kolaczyk B Haagensen A Rosebrook J Krafty J Laughlin B Dionne E Miller B Scrabeck |
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Finding - Nine Mile Point - IR 05000220/2012005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Nine Mile Point) @ 2012Q4
Self-Identified List (Nine Mile Point)
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