ENS 41567
ENS Event | |
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22:00 Apr 5, 2005 | |
Title | Potential Vulnerability with Alternate Shutdown System (Asds) Isolation Design |
Event Description | The following information was obtained from the licensee via facsimile (licensee text in quotes):
On April 5, 2005 at 1600 [hrs. CDT], Monticello Nuclear Generating Plant during a review of the Alternate Shutdown System (ASDS) as part of the corrective actions for LER 2005-01, submitted on April 4, 2005 (Event Notification#41436) discovered a second breaker affected by a similar cause as identified in the LER. The Bus 16 source (Breaker 152-609) to Load Center #104 has a similar potential vulnerability with the ASDS isolation design that could result in Load Center #104 being locked out in the event of a Control Room or Cable Spreading Room fire. The Monticello Appendix R Safe Shutdown Analysis for Control Room/Cable Spreading [Room] fire assumes a loss of control of Division I and II equipment from the Control room, however safe shutdown is achieved remotely from the ASDS panel. ASDS design is such that a Control Room/Cable Spreading Room fire would not impede the ability to safely shutdown and maintain the plant in a shutdown condition. Contrary to the ASDS design, it was discovered that an unisolated metering circuit could result in Load Center #104 being locked out in the event of a Control Room/Cable Spreading Room fire. The bus lockout is not isolated by the ASDS transfer switches, therefore, this condition could result in failure of Load Center #104 to re-energize during the implementation of the Shutdown Outside Control Room procedure. ASDS is not required to be operable at this time. As a result of this determination, MNGP will issue a revision to LER 2005-01 to the NRC to reflect the new information. This event is being reported as a potential loss of safety function (10CFR50.72(b)(3)(v)(A,B, and D) and as a degraded or unanalyzed condition (10CFR50.72(b)(3)(ii)(B). The NRC [Resident Inspector] has been notified. |
Where | |
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Monticello ![]() Minnesota (NRC Region 3) | |
Reporting | |
10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
Time - Person (Reporting Time:+0.43 h0.0179 days <br />0.00256 weeks <br />5.89014e-4 months <br />) | |
Opened: | Robert Schreifels 22:26 Apr 5, 2005 |
NRC Officer: | Howie Crouch |
Last Updated: | Apr 5, 2005 |
41567 - NRC Website
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Unit 1 | |
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Reactor critical | Not Critical |
Scram | No |
Before | Cold Shutdown (0 %) |
After | Cold Shutdown (0 %) |
Monticello ![]() | |
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