05000237/LER-2001-003
| Dresden Nuclear Power Station Unit 2 | |
| Event date: | 09-02-2001 |
|---|---|
| Report date: | 10-31-2001 |
| 2372001003R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 (If more space is required, use additional copies of NRC Form 366A)(17)
A. Plant Conditions Prior to Event:
Unit: 2 � Event Date: 09-02-2001 Reactor Mode: 4 � Mode Name: Cold Shutdown Reactor Coolant System Pressure: 0 psig
B. Description of Event:
Event Time: 0236 Power Level: 0% On September 2, 2001, at 0236 hours0.00273 days <br />0.0656 hours <br />3.902116e-4 weeks <br />8.9798e-5 months <br /> during a controlled plant shutdown for Dresden Nuclear Power Station, Unit 2, Operations began securing the 2B Recirculation Pump [AD] per station operating procedure. During this evolution, the procedure step following the securing of the 2B Recirculation Pump is to close the recirculation pump discharge motor operated valve (MOV). At the step to close the MOV, the control switch was manipulated but the MOV did not close. Troubleshooting revealed that the normally closed auxiliary contact was stuck open, which prevented the MOV from closing. Electrical Maintenance Department (EMD) personnel were able to free the stuck contact and the MOV was subsequently successfully stroked closed twice. During the investigation, it was identified that the left auxiliary contact plunger arm was off its normal plastic stop, which caused the contact to bind. This was caused by a missing lock washer on the auxiliary contact. A new auxiliary contact assembly, including the plunger assembly with the lock washer, was installed and successfully tested with no evidence of binding.
In the event of a Loss Of Coolant Accident (LOCA), the Low Pressure Coolant Injection [BO] loop select logic determines the appropriate recirculation loop for injection based on differential pressure sensed between the "A" and "B" loops. If, during a LOCA, the "B" loop would be selected for injection, a signal would be sent to the "B" discharge valve to close, allowing the injection path to be completed through the jet pumps and into the core.
Thus, with the "B" discharge valve open, full injection into the core would not be achieved. Therefore, this event is being reported pursuant to 10 CFR 50.73 (a)(2)(v)(B) and (D), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed remove residual heat or mitigate the consequences of an accident.
C. Cause of Event:
The 2B Recirculation Pump Discharge valve did not close upon demand due to a binding auxiliary relay contact in the 480 volt motor control center circuitry due to a missing lock washer on the auxiliary contact. The root cause of this event was determined to be inadequate procedure guidance, which led to the equipment failure. The station procedure does not clearly direct that the plunger be verified tight or to check for the installation of a lock washer.
A contributing cause to the event was inadequate vendor instructions. The vendor instructions that are provided with each auxiliary contact kit do not show the lock washer in the diagram and do not address the lock washer in the written instructions. Corrective actions included revising the station procedure, "DES 7300-05, Maintenance and Surveillance of E.Q. and Safety Related 480 Volt MCC," to clearly identify contact parts including the lock washer, verify the plunger post is tight, and include a picture to further clarify parts configuration. (NRC Cause Code D) LICENSEE EVENT REPORT (LER) burden estimate to the information and Records Management Branch (t-6 and to the Paperwork Reduction Project (3150-0104), Office Of Management And Budget, Washington, DC 20503. If an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17)
D. Safety Analysis:
A Significance Determination Process (SDP) evaluation was conducted for this event. Based on the results of the SDP, this event did not challenge reactor core fuel temperature limits. Additional Emergency Core Cooling Systems were available during this event (Core Spray). The core remained covered at all times, no fuel failure occurred and no offsite dose concerns were created by this event. The reactor was in mode 4, at zero percent reactor power and pressure. Therefore the safety significance of this event has been determined to be minimal.
E. Corrective Actions:
Immediate corrective actions were to troubleshoot and repair the failed auxiliary contact. (Complete) The appropriate station procedure was revised to clearly identify auxiliary contact parts, including the lock washer, verify the plunger post is tight, and to include a diagram to further clarify the configuration for this type of auxiliary contact. (Complete)
F. Previous Occurrences:
A review was conducted via a search of previous condition reports generated. No previous occurrences were identified associated with this type of failure.
G. Component Failure Data
General Electric Series 7700 Motor Control Center Auxiliary Contact