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| Entered date | Event description | |
|---|---|---|
| ENS 45878 | 28 April 2010 14:32:00 | This telephone notification is provided in accordance with 10 CFR 50.73(a)(1) to report an invalid actuation reportable under 10 CFR 50.73(a)(2)(iv)(A). On March 5, 2010, at 0539 hours, during the Unit 1 refueling outage (L1R13), the inboard and outboard Main Steam Isolation Valves (MSIVs) closed as a result of an invalid partial Group 1 PCIS (Primary Containment Isolation System) isolation signal generated during the performance of station surveillance LOS-TG-SR2 'Operability of Main Turbine Valves and Controls Following an Extended Outage.' Investigation revealed that during the resetting of the main turbine, the Group 1 PCIS logic received a signal that one of the Turbine Stop Valves (TSVs) was open. This caused the logic for Group 1 PCIS logic to be made up and the MSIVs to shut. Review of the data indicates that at no time did any of the TSVs open during the testing. This issue occurred as a result of the vibration seen by the relays in the trip logic during the resetting of the main turbine. The apparent cause of this event was attributed to a lack of questioning attitude during testing. The surveillance has multiple actions for cycling all the turbine valves, as well as performing various trips and resets of the main turbine. The surveillance has a prerequisite to ensure during performance of the various sections, that the MSIVs are shut or jumpers are installed to prevent an inadvertent closure of the MSIVs should the TSVs be cycled. The operating crew had concluded that the section of the procedure they were performing did not require the MSIVs to be shut or the jumpers to be installed. When the turbine was reset, the Reactor Protection System (RPS) Channels A1 and B2 actuated. Based upon these actuations, plant response to the partial Group 1 PCIS isolation signal was as expected. This actuation was invalid since the conditions required to bypass the low condenser vacuum Group 1 PCIS isolation were all met. With the mode switch not in run, the condenser low vacuum bypass keys in bypass and the main stop valves not full open, the Group 1 PCIS isolation is bypassed. These conditions were all met when the partial Group 1 PCIS isolation was received. The TSVs remained closed as indicated on the Digital Electro-Hydraulic Control (DEHC) system. Corrective actions include enhancements to the surveillance procedure and preparation of a case study on the circumstances, which led to this event. (Corrective actions also include presentation) to all operating crews in LORT (Licensee Operations Requalification Training) Cycle 10-4 and various site training advisory and curriculum review committees. The licensee has notified the NRC Resident Inspector. |