05000353/LER-2013-001
| Limerick Generating Station, Unit 2 | |
| Event date: | 04-16-2013 |
|---|---|
| Report date: | 06-12-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 48936 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3532013001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 4 (Cold Shutdown) with reactor coolant temperature at approximately 116 degrees Fahrenheit and reactor pressure at approximately zero psig. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On Tuesday, April 16, 2013, Limerick Unit 2 was in a refueling outage (2R12) with surveillance testing in progress on the reactor protection system (RPS) (EIIS:JC) logic for the main turbine valve (EIIS:VLV) position. The main turbine first stage pressure trip units were placed in the "greater than 26 percent power" condition as required by the "Main Turbine CIV, Stop Valve RPS & EOC-RPT Channel Functional Test" (ST-6-001-660-2). The operating crew made a decision not to restore the first stage pressure trip units to the as-found (zero percent power) condition during the return to normal section of the test since the next test also required the trip units to be in the "greater than 26 percent power" condition. However, the operators failed to properly prepare and technically review the procedure change as required by HU-AA-104-101, "Procedure Use and Adherence", and HU- AA-1212, "Technical Task Risk/Rigor Assessment, Pre-Job Brief, Independent Third Party Review and Post Job Brief".
Subsequent steps in the surveillance test return to normal section directed the operator to depress the "All Valves Closed" pushbutton.
When the pushbutton was depressed the main turbine stop valves closed as designed. When the stop valves closed with power simulated at 100%, the RPS main turbine stop valves closed logic was actuated. The stop valve closure also caused a trip of both reactor recirculation pumps. The mode switch was placed in "Shutdown" as required by the scram procedure (T-100) which caused a valid manual actuation of the RPS system.
An 8-hour NRC ENS notification was required by 10CFR50.72(b)(3)(iv)(A) for a valid actuation of RPS. The ENS notification (#48936) was completed on Tuesday, April 17, 2013, at 0211 ET. This event involved a manual actuation of RPS. Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A).
Analysis of the Event
There was no actual safety consequence associated with this event.
The potential safety consequences of this event were minimal. The reactor was in cold shutdown with all control rods inserted at the time of the event.
The "Main Turbine CIV, Stop Valve RPS & EOC-RPT Channel Functional Test" verifies the operability of the main turbine stop valve closed RPS logic. This trip function is bypassed when reactor power is less than 26 percent since the main steam bypass valves' capacity is greater than 26 percent power. The test directs simulating greater than 26 percent power conditions if as-found power is less than 26 percent. The test section directs simulation of greater than 26 percent power at the main turbine first stage pressure trip units to defeat the bypass of the stop valves closed trip function.
The main turbine control valve test (ST-6-001-766-2) was scheduled following the stop valve test. The control valve test also required simulation of greater than 26 percent power at the first stage trip units. The operators decided to maintain simulated power conditions during the return to normal section of the stop valve test and the initial conditions section of the control valve test. This plan to alter the procedure sequence was not properly performed or technically reviewed per HU-AA-104-101 or HU-AA-1212.
Cause of the Event
The event was caused by a failure to follow the existing procedure change processes.
Corrective Action Completed A corrective action was completed which performed the following:
1) Reinforced the requirements for partial procedure use and temporary procedure changes, 2) Established expectations for the review and approval of partial procedures and temporary procedure changes, and 3) Established expectations for use and performance of technical human performance briefs (HU-AA-1212).
Previous Similar Occurrences There were no similar occurrences of valid manual actuation of the reactor protection system due to surveillance test status control errors in the previous three years.