05000237/LER-2013-003
| Dresden Nuclear Power Station, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 2372013003R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Dresden Nuclear Power Station (DNPS) Units 2 and 3 are General Electric Company Boiling Water Reactors with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as (XX).
A. Plant Condlti9ros Prior to iverit:
Unit: 02 .
- Event Date: 09-23-2013 Reactor Mode: 1 Mode Name: Power Operation Unit: 03. Event Date: 09-23-2013 Reactor Mode: 1 Mode Name: Power Operation Event Time: 1655 hours0.0192 days <br />0.46 hours <br />0.00274 weeks <br />6.297275e-4 months <br /> CDT Power Level: 100 percent Event Time: 1655 hours0.0192 days <br />0.46 hours <br />0.00274 weeks <br />6.297275e-4 months <br /> CDT Power Level: 100 percent B. litasdillatutrant From 16:55:5910 16:56:04 on September 23, 2013, indication was received in the control room that two secondary containment [NG] doors leading to the Unit 2/3. EDG. room were opened ,.
simultaneously. An individual was traveling from the 2/3 EDG Room into the Reactor Building at the time of the event. As the individual proceeded to leave the interlock from the reactor building side door, the reactor building side door and the EDG side door opened simultaneously. The individual stated that they had heard clicking noise, from the interlock relays, at the time of the interlock failure.
The individual then proceeded to CiOSO the EDG side door and exit the interlock. After challenging the reactor building tide door, the individual walked to a phone located at the unit 2 reactor building, near the equipment hatch; to inform the control room.
This event is being reported in actordance with 10 CFR 50.73(eX2)(vXC), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
cfintittent:
Initial troubleshooting of the interlock circuit was performed by the electrical maintenance department (EMD). The troubleshooting scope included a voltage test of circuit relays, visual inspection of connections in the junction box, resistance readings across all applicable relay contacts, and monitoring the relays voltage via a chart recorder while performing functional tests of the door circuit. The functional test monitored all applicable relays while operating the interlock approximately 500 times over five day duration. The doors were challenged in all operation scenarios, but a failure could not be replicated. The troubleshooting performed by EMD was indeterminate.
During this event, the operator in the interlock at the time of failure reported excessive relay chattering in the relay panel. It is believed that intermittent relay malfunction in the circuit degraded the voltage to the diesel side door strike causing this failure to occur.
C.
D. Adtkandaill:
The Secondary Containment interlock doors were open for approximately five seconds and based upon the short duration of the secondary containment doors being opened simultaneously and that the Secondary Containment differential pressure remained negative during the course of this event, this event is of low safety significance.
E.
As a result of the June 28, 2013, and September 23, 2013 events, site engineering performed an apparent cause evaluation that identified the need to develop a modification to improve the interlock door circuit. Dresden engineering has completed the engineering change, and the modification is currently in the process of being installed.
F. fritgiallagNM:
A search was performed to determine the number of previous occurrences for this event over the past two years. The following table presents these results for the Unit 2/3 Interlock:
IR Date Sort Description 1493171 3/27/2013 Unit 2/3 Interlock Failure 1530208 6/28/2013 Unit 2/3 Interlock Failure 1562854 9/23/2013 Unit 2/3 Interlock Failure The search revealed that there were two prior occurrences, within the past two years, that specifically relate to a failure of the Unit 2/3 Interlock.
G. Aornixonent Failure Dita:
Not Applicable