05000338/LER-2010-004
| Document Numbersequential Revmonth Day Year Year Month Day Year | |
| Event date: | 10-22-2010 |
|---|---|
| Report date: | 12-20-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3382010004R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT On October 22, 2010, Unit 1 was in Mode 2, with the reactor critical at zero percent power, with personnel performing physics testing in accordance with periodic test (PT) procedure 1-PT-94.0, Refueling Nuclear Design Check Tests. During testing, the rod control in-hold out selector switch (EIIS System AA, Component HS) was observed to not be functioning properly when control rods were moved in the outward direction. At 0636 hours0.00736 days <br />0.177 hours <br />0.00105 weeks <br />2.41998e-4 months <br />, a conservative decision was made to manually trip the Unit 1 reactor, by opening the reactor trip breakers (EllS System AA, Component BKR), in order to perform repairs on the rod control in-hold-out selector switch.
A non-emergency four-hour report was made to the NRC on October 22, 2010 at 0946 hours0.0109 days <br />0.263 hours <br />0.00156 weeks <br />3.59953e-4 months <br />, due to a Reactor Protection System actuation in accordance with 10 CFR 50.72(b)(2)(iv)(B). This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) for a condition that resulted in the manual actuation of the Reactor Protection System.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event posed no significant safety consequences because the control rods remained capable of being tripped. All systems, components and plant parameters responded as expected following the reactor trip. Therefore, the health and safety of the public were not affected by this event.
3.0 CAUSE The direct cause of the malfunctioning rod control in-hold-out switch was attributed to dirt on the push buttons of the switch which resulted in sluggish operation.
In February 2010, a work order was initiated for a sporadic sticking issue of the rod control in-hold-out selector switch during the performance of 1-PT-17.1, Rod Operability. The rod control in-hold-out selector switch was successfully used during subsequent quarterly rod operability tests and ramp of the unit. An error in the work management process prevented the rod control in-hold-out selector switch from being replaced during the 2010 Fall refueling outage. This was a missed opportunity. This issue was entered into the Corrective Action Program to determine and correct process issues.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Control Room personnel responded to the reactor trip in accordance with emergency procedure 1-E-0, Reactor Trip or Safety Injection. Control Room personnel stabilized the plant using 1-ES-0.1, Reactor Trip Recovery.
NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER � 5.0 ADDITIONAL CORRECTIVE ACTIONS The rod control in-hold-out selector switch was subsequently replaced.
An extent of condition review was performed to ensure that no other corrective work orders had been inappropriately cancelled. The review identified one additional corrective work order that was inappropriately cancelled to an open PM work order. A Condition Report was written to generate a replacement corrective work order.
6.0 ACTIONS TO PREVENT RECURRENCE Actions to prevent recurrence from the Apparent Cause Evaluation are being tracked in the Central Reporting System.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION Unit 2 was operating in Mode 1 at 100% power at the time of this event and remained at approximately 100% power for the duration of the event.