05000397/LER-2011-001
| Columbia Generating Station | |
| Event date: | 06-29-2011 |
|---|---|
| Report date: | 08-29-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3972011001R00 - NRC Website | |
Plant Condition The plant was operating in Mode 5 at 0% power.
Event Description
On June 28, 2011, during the performance of control rod [ROD] stroke time testing, control rod 34-47 was given a continuous withdrawal signal. The Reactor Operator (RO) at the controls immediately noticed the four rod display initially indicated blank, as expected, then began alternating displays between "00" and "XX". It was noted that the green "full in" light cleared. The RO stopped the rod withdrawal and the display then indicated "XX" with the "full in" light still extinguished. The RO subsequently inserted the control rod to position "00" and its "full in" light was re-energized. The Control Room Supervisor (CRS) consulted the System Engineer and the Station Nuclear Engineer who indicated that that the failure was most likely due to the "00" reed switch being stuck closed. The crew continued with stroke timing achieving an additional full out / full in cycle on the next control rod. A work request was written to replace the rod position indication system (RPIS) probe containing the stuck reed switch on control rod 34-47.
On June 29, 2011, after review of the control rod exercises performed the previous day, it was determined that the "full in" position indication channel for control rod 34-47 was inoperable based on not meeting the requirements of TS SR 3.9.4.1. Since the control rod position indication channel was not declared inoperable and the required actions were not taken before movement of another rod, the station was in non-compliance with Technical Specification Action Statement (TSAS) 3.9.4.A while performing the additional control rod stroke timing following the initial encounter with the indication problems.
Immediate Corrective Actions
Upon discovery of the TS violation, Columbia entered TSAS 3.9.4.A for control rod 34-47 due to the erroneous indication during stroke timing. Control room staff performed the required actions to verify no in-vessel fuel movement, stop all control rod withdrawal and verify all control rods are full in. In addition, the control rod drive (CRD) [AA] for rod 34-47 was disarmed. A condition report was written documenting the failure to comply with TS Limiting Condition of Operation (LCO) 3.9.4. The responsible CRS and RO were removed from standing watch in the control room.
Causes The CRS and SM did not verify and validate the control rod position indication surveillance requirements by reviewing the TS and Bases prior to proceeding with rod movement. A review of the TS and Bases is required prior to authorizing surveillance procedures and other maintenance and clearance order activities in accordance with Operations Department instructions. Failure to meet the requirement to review the TS and Bases was determined to be the apparent cause.
In addition, the RO performing the stroke time testing did not complete the last two steps in the associated procedure for stroke time testing. This presented a missed opportunity for the crew to discuss the control rod position indication and address the TS requirements indicated by the uncompleted procedure steps. This was identified as a contributing cause to this event.
26158 R5 Columbia Generating Station 05000397 30F3 Further Corrective Actions The following corrective actions are planned or have been completed:
- Provided remediation training for the on-duty RO and CRS to address inadequate verification of required TS. (Completed)
- Developed training for licensed operators concerning shutdown TS. (In Progress)
- Reinforced expectations for TS implementation and verification through a night order. (Completed)
- Replaced the control rod RPIS probe for control rod 34-47. (Completed)
Assessment of Safety Consequences
The full-in position indication channel is required to be operable so that the refueling interlocks can ensure that fuel cannot be loaded with any control rod withdrawn and that no more than one control rod can be withdrawn at a time. These restrictions prevent inadvertent criticality during refueling operations. At the time that the rod position indication failed to meet the TS surveillance requirements, Columbia was not moving fuel, only one control rod was being withdrawn, and all other control rods were fully inserted. There was no potential for an inadvertent criticality. The plant remained within the assumptions of the safety analysis at all times.
Withdrawal of control rod 34-47 was suspended and the rod was fully inserted prior to movement of another rod. This event was of low safety consequence.
Similar Events A search of the last ten years of Columbia's condition reports and LERs showed no previous occurrences of a failure to enter the required action statement of TS 3.9.4. However, there have been four similar events in which other TS and their bases were not verified prior to performance of an evolution that resulted in a TS not being met at Columbia within the last ten years. These incidences are documented in LERs 2001-001-00, 2003-004-00, and 2004-001-00.
Energy Industry Identification System (EDS) Information El IS codes are bracketed [ ] where applicable in the narrative.
26158 R5