05000269/FIN-2008003-02
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Finding | |
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| Title | AVR Maintenance Procedure Resulted in a Loss of Inventory While on Decay Heat Removal |
| Description | On April 15, 2008, Unit 1 experienced a generator lockout, which caused a loss of normal power through the back charged main transformer to main feeder bus (i.e., N breakers and generator output breakers PCB 21 and 20 opened). This caused a momentary loss of power to the LPI and low pressure service water (LPSW) pumps, and AP-26 (Loss of Decay Heat Removal) was entered by the operators. The main feeder bus (MFB) power was restored in 1.8 seconds via the slow transfer logic from the E breakers (as expected) and power to the LPI and LPSW pumps was restored (non-load shed). MFB re-energization should have re-energized motor control center (MCC) 1XP, but did not, as the alternate feeder breaker to 1XP tripped on high in-rush current. MCC 1XP supplies power to air operated valves 1HP-8 (Unit 1 Purification Demineralizer Inlet Isolation), 1HP-17 (1A Letdown Filter Inlet Isolation) and 1HP-18 (1B Letdown Filter Inlet Isolation). These valves closed due to the loss of power to each valves respective control solenoid valve, which isolated the letdown flow path. The valves should have reopened upon the restoration of power, but the loss of power to MCC 1XP prevented this from occurring. The isolation of the letdown flow path coupled with the LPI pump restart caused 1HP-43 (letdown line relief valve) to lift open as the relief valve now saw LPI pump discharge pressure. This resulted in a loss of RCS inventory to the Mixed Waste Holdup Tank (MWHUT)
Operators initiated makeup to the LPI system from the borated water storage tank (BWST) by throttling 1LP-21 (BWST isolation) and 1LP-96 (LP Supply to Purification IX block) was closed to isolate LPI from the purification lineup per AP-26. This allowed 1HP-43 to shut and effectively stop the inventory loss. Specifically, RCS level dropped from 70 to 54 inches on LT-5 (approximately 2000 gallons of inventory was dumped to MWHUT). Level was restored to 79 inches on LT-5 approximately 30 minutes from initiation of the event. The generator lockout was a result of ongoing automatic voltage regulator (AVR) preventive maintenance, IP/0/B/2005/001, Main Generator Automatic Voltage Regulator Maintenance and Channel Transfer, where as part of the AVR procedure, the AVRs measuring unit board (part of each AVR channel) was replaced and powered up. Unrecognized by the procedure, this power up resulted in the actuation of the K31 relay in the AVR, which sends a lockout signal to the main generator. The root cause was determined to be a failure of procedure preparers and reviewers of IP/0/B/2005/001, to recognize the system interaction between the AVR trip circuitry and the backcharge power path. This issue is unresolved pending further NRC review of the licensees procedures, operator actions, and risk management associated with this event. This item is identified as URI 05000269/2008003-02, AVR Maintenance Procedure Resulted in a Loss of Inventory While on Decay Heat Removal. This issue is in the licensees corrective action program as PIP O-08-2056. |
| Site: | Oconee  |
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| Report | IR 05000269/2008003 Section 4OA3 |
| Date counted | Jun 30, 2008 (2008Q2) |
| Type: | Finding: White |
| cornerstone | Initiating Events |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | A Hutto B Collins E Riggs L Lake R Chou R Mackowski S Rosec Evansl Wert V Mccree W Rogersg Gullaj Mitman J Moorman S Rose A Hutto C Evans |
| CCA | H.7, Documentation |
| INPO aspect | WP.3 |
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Finding - Oconee - IR 05000269/2008003 | |||||||||||||||||||||||||||||||||||||||||||
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Finding List (Oconee) @ 2008Q2
Self-Identified List (Oconee)
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