ENS 40311
ENS Event | |
|---|---|
13:20 Nov 10, 2003 | |
| Title | Bypassing the Pressure Suppression Function of the Torus |
| Event Description | On 11/10/2003 at 07:20 CST it was discovered, during a control room panel walk-down, that Dresden U2 had primary containment valves 2-1601-56 Torus Purge valve and 2-1601-21 DW (drywell) Purge valve open simultaneously. This valve alignment created a flow path from the Drywell to the Torus, effectively bypassing the pressure suppression function of the torus water volume during a LOCA (Loss of Coolant Accident) condition. This condition placed U2 containment in an unanalyzed condition, not capable of performing the intended design function, which is to mitigate the consequences of a LOCA. The proper valve alignment was restored at 07:26 CST which restored U2 primary containment to operable status per TS (Tech. Spec) 3.6.1.1.
A review of plant data identified that this valve arrangement, which bypassed primary containment, had been in effect when U2 entered Mode 2 (Startup) from Mode 4 (Cold Shutdown) at 12:01 on Nov 9, 2003. In addition, this valve line-up existed for a duration greater than that allowed by TS 3.6.1.1 A.1 and B.1 (1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />). The NRC Resident Inspector was notified of this event by the licensee.
Dresden has performed an engineering evaluation that bounds the plant conditions that existed while the two valves were simultaneously open. The evaluation concluded that the valves would have automatically closed in sufficient time to prevent exceeding the design limits of the primary containment during a postulated Design Basis Accident. Therefore, Dresden retract the ENS call associated with this event. This event will be the subject of an Licensee Event Report in accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B), 'Any event or condition which was prohibited by the plant's Technical Specifications.'" R3DO (Ken Riemer) notified. The NRC Resident Inspector was notified of the above retraction by the Licensee. |
| Where | |
|---|---|
Dresden  Illinois (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.73 h0.114 days <br />0.0162 weeks <br />0.00374 months <br />) | |
| Opened: | R. Buckley 16:04 Nov 10, 2003 |
| NRC Officer: | John Mackinnon |
| Last Updated: | Dec 31, 2003 |
| 40311 - NRC Website
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