ENS 46146
ENS Event | |
|---|---|
20:06 Aug 3, 2010 | |
| Title | Potential Safety System Functional Failure of the Accident Mitigating Function |
| Event Description | On 8/3/10 South Texas Project Unit 2 was in a scheduled A Train work week with the following equipment inoperable for planned maintenance; Essential Cooling Water Pump, Essential Chiller, Component Cooling Water Pump, Engineered Safety Function (ESF) Diesel Generator (DG), High Head Safety Injection (HHSI) pump, Low Head Safety Injection (LHSI) pump, and Containment Spray (CS) pump.
At 0754 [CDT] on 8/3/10 the B train sequencer trouble alarm was received. The immediate operability determination was the sequencer remained operable. It was later identified during testing that the sequencer was inoperable. The B train sequencer was declared inoperable at 1506 [CDT] on 8/3/10. Due to loss of the automatic load sequencing support function, all associated train B safety equipment that is sequenced on the B train 14.16 kv bus during a Mode 1 Safety Injection (SI) was also declared inoperable. This condition resulted in an inoperable condition on two out of three safety trains for the accident mitigating function including the A and B train HHSI, LHSI, and CS pumps. All C train safety injection pumps remained operable. Pending a formal operability determination, this is conservatively considered to be a safety system functional failure of the accident mitigating function. This was determined to be reportable within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> as required by 10 CFR 50.72(b)(3)(v)(D). The B train trouble alarm, an auto test feature, was discovered by operators during their rounds. The licensee entered their configuration risk management plan within the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> as required. Currently, the licensee is working on completing the scheduled A train maintenance and restoring operability sometime in the morning. Also, a work package is under development to repair the faulty B train sequencer. The risk based time limit for restoring operability requires completion by 0449 [CDT] on 8/8/10. Unit 1 is unaffected and continues to operate at 100% power. The licensee informed the NRC Resident Inspector.
The purpose of this update is to retract the notification made in ENS Report #46146 (August 3, 2010). Following the ENS notification, troubleshooting determined the cause of the Train B sequencer alarm to be the failure of an Output Mode I Actuation Timing Switch Module. An engineering evaluation of the event has been completed and determined that a failure of this module did not affect the ability of the ESF load sequencer to perform its design function. Therefore, the Train B sequencer and associated Train B ESF equipment remained technically operable during the time that Train A equipment was inoperable due to scheduled maintenance, and a condition reportable per 10 CFR 50.72(b)(3)(v) did not exist. The licensee will notify the NRC Resident Inspector." Notified R4DO (Walker). |
| Where | |
|---|---|
South Texas  Texas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+0.47 h0.0196 days <br />0.0028 weeks <br />6.43806e-4 months <br />) | |
| Opened: | Thomas Dedas 20:34 Aug 3, 2010 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Aug 26, 2010 |
| 46146 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |