05000339/LER-2001-002

LER-2001-002,

Docket Number
Event date:	03-11-2001
Report date:	04-24-2001
3392001002R00 - NRC Website

1. DESCRIPTION OF EVENT

On March 11, 2001, at approximately 0109 hours0.00126 days <br />0.0303 hours <br />1.802249e-4 weeks <br />4.14745e-5 months <br />, with Unit 2 at 0 percent power (Mode 3) and shutting down for refueling, the control bank "B" group 2 step counter demand position indicator (EIIS System AA, Component CTR) stopped moving at 53 steps while rods were being driven into the core. All other indications of rod motion were normal.

The Limiting Condition for Operation (LCO) for Technical Specification 3.1.3.3 requires the rod group step counter demand position indicator to be within plus or minus 2 steps of the demand position from the logic cabinet for each shutdown or control rod group not fully inserted. The control bank "B" group 2 step counter demand position indicator was greater than 2 steps from the demand position from the logic cabinet. The action requirements of TS 3.1.3.3 require the reactor trip breakers (EIIS - BKR) to be opened within 15 minutes if the LCO requirements cannot be met. Operations personnel continued to insert the control banks into the core. At 0119 hours0.00138 days <br />0.0331 hours <br />1.967593e-4 weeks <br />4.52795e-5 months <br />, a manual reactor trip was initiated by opening the reactor trip breakers, inserting the shutdown banks into the core. At 0428 hours0.00495 days <br />0.119 hours <br />7.07672e-4 weeks <br />1.62854e-4 months <br />, an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> report was made to the NRC Operations Center in accordance with 10 CFR 50.72(b)(3)(iv)(A). This event is reportable per 10 CFR 50.73 (a)(2)(iv)(A) for any event or condition that resulted in the manual actuation of the reactor protection system.

2. SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS

No significant safety consequences resulted from this event since the reactor was already subcritical, with all control banks fully inserted, when the reactor trip breakers were opened and the shutdown banks inserted into the core. Therefore, the health and safety of the public were not affected at any time during this event.

3. CAUSE

The cause of the control bank "B" group 2 step counter demand position indicator not moving was determined to be a defect in the down counter gear such that when the ones column wheel reaches the count of three, the down count coil hammer just misses the gear and is unable to advance the ones column wheel any further.

4. IMMEDIATE CORRECTIVE ACTIONS

Upon discovery of the condition, the "B" control bank group step counter for Group 2 was declared inoperable and the action requirements of TS 3.1.3.3 were entered to open the reactor trip breakers within 15 minutes.

5. ADDITIONAL CORRECTIVE ACTIONS

A manual reactor trip was initiated by opening the reactor trip breakers, inserting the shutdown banks into the core.

6. ACTIONS TO PREVENT RECURRENCE

The control bank "B" rod group 2 step counter and relay driver were replaced during the refueling outage.

7. SIMILAR EVENTS

Unit 2 LER 1998-001-00, dated April 30, 1998, documents that with Unit 2 at 0 percent power (Mode 3) while inserting control rods in preparation for a refueling outage, the "B" control bank group step counter for Group 2 deviated from the actual rod position by more than the allowable Technical Specification limit of two steps. The cause of this event was attributed to a malfunction of the mechanical drive for the step counter.

8. ADDITIONAL INFORMATION

Unit 1 was operating in Mode 1, at 100 percent power, and was not affected by this event.