Dresden Unit 2 is performing a Technical Specification required shutdown due to the loss of the [120 VAC] Essential Service Bus normal electrical feed. This is reportable per
10CFR 50.72(b)(2)(i), SAF 1.2 "Plant Shutdown Required by Technical Specification". The loss of the feed occurred at 02:10 [CST] on 01/23/04 and power swapped to the backup feed.
Technical Specification 3.8.7. A. was entered and repairs began on the uninterruptible power supply. Repairs were unsuccessful and Unit 2 shut down began at 12:20 [CST] with unit required to be hot shutdown by 22:10 [CST] 01/23/04 and cold shutdown by 22:10 [CST] 01/24/04. Repairs will continue in parallel will unit shutdown.
The licensee notified the NRC Resident Inspector.
- UPDATE on 01/23/04 at 1742 EST by G. Morrow taken by John MacKinnon****
Unit 2 ESS BUS normal feed was restored to OPERABLE, unit shutdown was secured and preparations for load increase are in progress. Preliminary troubleshooting data taken on the ESS UPS show the most likely cause of the UPS power supply transfer was a static switch component that caused the UPS to swap to the emergency supply. The troubleshooting shows the malfunction that caused the initial power supply transfer to the ESS Emergency supply via the ABT at 0210 this morning originated in the static switch circuitry. The static switch is bypassed in the current configuration and therefore the power supply to the ESS bus is assured. The voltage sensing relays investigated during the troubleshooting on the output of the inverter show no indication that an inverter failure initiated the bus transfer. Operations will continue to monitor the output of the inverter. Troubleshooting of the UPS static switch will continue to determine the cause of the malfunction. R3DO (Roger Lanksbury) notified
NRC Resident Inspector was notified of this update by the licensee.
