ENS 43564
ENS Event | |
|---|---|
19:22 Aug 13, 2007 | |
| Title | |
| Event Description | A condition is being reported as a conservative measure regarding a situation involving potential fire induced circuit failures on associated circuits. Plant Vogtle is considered to be in compliance with its current fire protection licensing basis, Branch Technical Position CMEB 9.5.1 as endorsed by UFSAR Appendix 9B, however, this condition is being reported as the generic industry issues associated with multiple spurious circuit failures have not been resolved to date.
A potential hot short issue exists involving Containment Spray Sump Suction valves 1(2)HV-9002A, 1(2)HV- 9003A, 1(2)HV-9002B, and 1(2)HV-9003B. If a fire were to occur in a location where the control circuit cables for those valves run in the same electrical raceway, a credible condition exists where either flowpath could spuriously open which would cause the Refueling Water Storage Tank (RWST) to drain down to the containment sumps. The fire zones where associated cables are located were placed under a compensatory hourly fire watch until compensatory measures were established. As an interim corrective action, operator manual actions have been specified and incorporated into plant procedures to deenergize and verify closed one valve in the series flowpath upon determination that a credible fire exists. These manual actions are in accordance with RIS 2006-10 for plants which are licensed to operate after January 1, 1979. Southern Nuclear will determine long term corrective actions for this condition. The effects of a fire sufficient to cause a spurious operation of multiple valves is not expected to be immediate and thus will allow sufficient time to perform the manual actions. The licensee notified the NRC Resident Inspector.
An eight hour report (EN#43564) per 10CFR50.72(b)(3)(ii)(B) was conservatively reported based on a fire-induced hot short issue (multiple-spurious) which could result in the spurious opening of Containment Spray Sump Suction valves 1(2)HV-9002A, 1(2)HV-9003A, 1(2)HV-9002B, and 1(2)HV-9003B. HV-9002 and HV-9003 are two valves in series between the containment emergency sump and the containment spray pumps. If a fire were to occur in a location where the control circuit cables for those valves run in the same electrical raceway, it is postulated a condition may exist where either flowpath could spuriously open which would cause the Refueling Water Storage Tank (RWST) to drain down to the containment sumps. The VEGP design basis defines a spurious control signal action/inaction as being caused by a single hot short, open circuit, or short-to-ground for a single component. Since all three conditions are postulated, the assumption that all adverse conditions will happen to the subject component(s) yields a conservative evaluation. Where a hi/low pressure interlace (fire-induced LOCA) is involved, an unlimited number of spurious control signal actions/inactions are postulated. Calculations have been reviewed to ensure these design criteria have been met. At this time, there is no definitive new guidance (Generic Letter, etc.) by the NRC on how licensees are to handle analysis of multiple spurious shorts. The status and history of misunderstanding and confusion relative to the regulatory and design requirements is well documented in NRC EGM 98-002 Rev. 2 and EGM 07- 004. The NRC staff and the industry are currently working to resolve questions raised by the industry about the adequacy of the existing staff guidance concerning fire-induced circuit failures and the consistency of staff interpretations of both the guidance and the underlying regulatory requirements. In summary, VEGP is in conformance with the current design basis. However, as defense-in-depth, actions have been taken that include implementation of hourly fire watches in the affected zones until procedural guidance for performance of manual actions were added to the Annunciator Response Procedures for the Fire Alarm Computer. The manual actions consist of opening the breakers for one of the emergency sump-to containment spray pumps suction isolation valves and then verifying the valves are closed. The licensee will notify the NRC Resident Inspector. Notified R2DO (Ogle). |
| Where | |
|---|---|
Vogtle  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+1.25 h0.0521 days <br />0.00744 weeks <br />0.00171 months <br />) | |
| Opened: | Mark Slivka 20:37 Aug 13, 2007 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | Aug 15, 2007 |
| 43564 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 523192016-10-26T18:39:00026 October 2016 18:39:00
[Table view]10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Tornado Missile Vulnerabilities ENS 435642007-08-13T19:22:00013 August 2007 19:22:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Potential Hot Short Issue with Containment Spray Sump Suction Valves 2016-10-26T18:39:00 | |