ENS 46531
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ENS Event | |
|---|---|
21:21 Jan 10, 2011 | |
| Title | Both Trains of Auxiliary Building Ventilation Became Inoperable |
| Event Description | On January 10, 2011, at 1321 PST, Diablo Canyon Power Plant, Unit 2, entered Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3, when both trains of Auxiliary Building Ventilation System (ABVS) became inoperable following closure of damper M-4 and the ensuing loss of both exhaust fans E-1 and E-2. TS LCO 3.0.3 was exited on January 10, 2011, at 1342 following a status reset and selection of fan E-2. This provided a ventilation flowpath and use of both exhaust fans in the Safeguards mode. Both trains of Auxiliary Building Ventilation are operable. This 8-hour non-emergency report is made pursuant to 10 CFR 50.72(b)(3)(v)(D).
The unit is not in a TS LCO. All 3 unit EDG's are operable and offsite power is in the normal lineup. The NRC Resident Inspector has been notified.
On January 13, 2011, at 1603 PST, engineering determined that a single failure design vulnerability exists at Diablo Canyon Power Plant Units 1 and 2. Engineering review of the control logic of the ABVS determined that while in Buildings Only (non-safeguards) alignment or during system realignment from Safeguards Only to Buildings Only alignment, failure of damper M-4A or M-4B (series dampers) could result in the control logic securing both ABVS exhaust fans. This would prevent ABVS actuation on receipt of a valid safeguards actuation signal. When this occurs, a control room alarm is actuated, which requires the operators to reset the control logic from the control room, thereby re-enabling the capability of the ABVS to respond to a safeguards actuation signal. The Unit 2 event on January 10, 2011, at 1321, occurred due to this single failure vulnerability when the control system attempted to restore the ABVS alignment from Safeguards Only to the Buildings Only alignment. This design vulnerability is currently mitigated by maintaining the ABVS in either of the two safeguards alignments (Safeguards Only or Buildings and Safeguards). This single failure design vulnerability is an 8-hour non-emergency report made pursuant to 10CFR50.72(b)(3)(ii)(B) for an event that resulted in the nuclear power plant being in an unanalyzed condition for both Unit 1 and Unit 2. The licensee will notify the NRC Resident Inspector. Notified R4DO (Hagar). |
| Where | |
|---|---|
Diablo Canyon  California (NRC Region 4) | |
| Reporting | |
| 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 | |
| LER: | 05000275/LER-2011-002 |
| Time - Person (Reporting Time:+-1.7 h-0.0708 days <br />-0.0101 weeks <br />-0.00233 months <br />) | |
| Opened: | Paula Gerfen 19:39 Jan 10, 2011 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Jan 14, 2011 |
| 46531 - 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 %) |
Diablo Canyon with 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 | |
WEEKMONTHYEARENS 544172019-11-30T19:00:00030 November 2019 19:00:00
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