05000352/LER-2008-001
| Limerick Generating Station, Unit 1 | |
| Event date: | 03-16-2008 |
|---|---|
| Report date: | 05-12-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3522008001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 5 (Refueling) at approximately 81 degrees Fahrenheit reactor coolant temperature and zero psig reactor pressure conducting refueling operations.� There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Sunday, March 16, 2008, refueling operations were in progress including preparation for scheduled control rod exercising. The 1C Source Range Monitor (SRM) (EIIS:IG) was inoperable for a scheduled maintenance activity. The reactor operator (RO) was performing the "Pre Control Rod Withdrawal Check Following Core Alterations" surveillance test, which directed verification that the source range monitors were operable. Since 1C SRM was inoperable, the control room supervisor (CRS) requested that the maintenance technicians restore the 1C SRM to service, which was completed. Operations successfully performed the designated post maintenance test (PMT) on the SRM, which consisted of the channel check surveillance test. Following completion of the PMT the 1C SRM was declared operable; however, it was not realized that the 1C SRM was still bypassed. At 0410 hours0.00475 days <br />0.114 hours <br />6.779101e-4 weeks <br />1.56005e-4 months <br />, the RO withdrew control rod 50-19 (which is in the same quadrant as 1C SRM) to the full-out position. During this period the maintenance technician in the auxiliary equipment room had been observing the "Bypassed" light on the 1C SRM channel. The maintenance technician called the back-up CRS to notify him that the "Bypassed" light was still illuminated on 1C SRM. The back-up CRS then identified that the SRM bypass switch (EIIS:SEL) was still in the bypass position for 1C SRM. Core alterations were immediately suspended by the CRS and the SRM bypass switch was restored to the no channels bypassed" position.
Control rod 50-19 was then inserted to the full-in position.
Technical Specification (TS) 3.9.2, Refueling Operations - Instrumentation, requires an operable SRM in the quadrant where core alterations are being performed. If this requirement is not satisfied the operators are required to immediately suspend all operations involving core alterations and insert all insertable control rods.
The SRM in the quadrant where the core alteration was being performed was not operable when the control rod was withdrawn. This condition is contrary to the requirements of TS 3.9.2, which required core alterations to be suspended in that quadrant. Therefore, this event resulted in a condition prohibited by Technical Specifications. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(i)(B).
Analysis of the Event
There were no actual safety consequences associated with this event. The potential safety consequences of this event were minimal. The 1C SRM count rate and period indications remained functional during the event. In addition the 1A, 1B, and 1D SRMs were operable during this period. An operable SRM was located in both adjacent quadrants during the core alteration. In addition, the one-rod-out interlock prevented withdrawal of multiple control rods during the affected period.
Cause of the Event
The root cause of this event was that the CRS and RO failed to ensure the 1C SRM was not bypassed and failed to obtain a peer check by a second senior reactor operator (SRO) prior to declaring it operable.
Corrective Action Completed The SRM channel check surveillance tests have been revised to specify that the SRMs and intermediate range monitors (IRMs) are inserted and not bypassed.
Corrective Action Planned The site Operations procedure for returning equipment to service will be revised to require a peer check for operability decisions when returning equipment to service.
Previous Similar Occurrences There was one previous similar occurrence in the last three years. LER 2-05-001 reported an event where core alterations were performed with the SRMs inoperable, which was caused by a loss of the SRM audible alarm in the control room. The corrective actions for LER 2-05-001 addressed a weakness in the procedure for loss of main control room annunciators and included an evaluation of procedures affected by infrequently used refueling and outage related TS. The weakness in the SRM channel check surveillance tests was not identified during this review.
Component data:
Component Description: 1C Source Range Monitor System: IG((Incore/Excore Monitoring System) Component: DET (Detector) Component Number: 10-S401-40-21 Manufacturer: R220 Reuter Stokes Model Number: RS-C6-0330-201