05000237/LER-2006-001
| Docket Number Sequential Revmonth Day Year Year Month Day Year N/A N/Anumber No. | |
| Event date: | 02-01-2006 |
|---|---|
| Report date: | 04-03-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372006001R00 - NRC Website | |
Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electric Company Boiling Water Reactor 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 Conditions Prior to Event:
Unit: 02� Event Date: 02-01-2006 � Reactor Mode: 1� Mode Name: Power Operation Power Level: 098 percent Reactor Coolant System Pressure: 1000 psig B. DescOption of Event:
On February 1, 2006, at approximately 1943 hours0.0225 days <br />0.54 hours <br />0.00321 weeks <br />7.393115e-4 months <br /> (CST), with Unit 2 at approximately 98 percent power, Dresden Nuclear Power Station technicians were performing a calibration of the Isolation Condenser (IC) [BL] Steam/Condensate Line High Flow instrumentation when a technician observed an unexpected response during the return to service of the IC Condensate Line High Flow Differential Pressure Switch DPIS 2-1349B. The switch monitors flow in the IC Condensate Return line. The calibration was stopped. The IC was declared inoperable and isolated. Subsequent investigations determined that the observed unexpected response was the result of voids in the instrument sensing lines of the IC Steam/Condensate Line High Flow Differential Pressure Switch.
An ENS call was made on February 2, 2006, at 0043 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br /> (CST) for the above-described event.
The assigned ENS event number was 42300.
The IC was returned to service and declared operable on February 2, 2006 at 1819 hours0.0211 days <br />0.505 hours <br />0.00301 weeks <br />6.921295e-4 months <br /> (CST).
This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident." The IC is a single train system and is credited in the loss of feedwater transient analysis.
C. Cause of Event:
The apparent cause of the voids in the instrument sensing lines of the IC Steam/Condensate Line High Flow Differential Pressure Switch was the failure of Procedure DOP 1300-11, "Unit 2 Isolation Condenser Fill and Vent," to identify that the sensing lines required backfilling after filling of the IC piping.
A review of the activities performed on the Unit 2 IC Condensate Return Line identified an activity performed in the fall of 2005 that could have caused the voids in the sensing lines. The activity involved the refilling of the IC piping in accordance with DOP 1300-11 after the lines had been drained for testing. DOP 1300-11 required the back filling of the sensing lines associated with the IC Steam,'Condensate Line High Flow Differential Pressure Switch prior to completing the refilling of the IC Condensate Return Line. The preferred method is to backfill the sensing lines after completion of the filliig of the IC piping.
A review of the performance of the Unit 3 IC Steam/Condensate Line High Flow Differential Pressure Switches DPIS 3-1349A and DPIS 3-1349B indicate that the sensing lines are filled and operating normally.
D. Safety Analysis:
The safety significance of the event is minimal. The IC during this event was in compliance with the requirements of Technical Specification 3.5.3, "IC System," and subsequent investigations deterrr ined that the IC Steam/Condensate Line High Flow instrumentation was operable with the voids present. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E. Corrective Actions:
Unit 2 Procedure DOP 1300-11 will be revised to require the backfilling of DPIS 2-1349A and DPIS 2 1349B sensing lines after filling of the Isolation Condenser piping.
Unit 3 Procedure DOP 1300-10, "Unit 3 Isolation Condenser Fill and Vent," will be revised to require the backfilling of DPIS 3-1349A and DPIS 3-1349B sensing lines after filling of the Isolation Condenser piping.
Unit 2 IC Condensate Line High Flow Differential Pressure Switches DPIS 2-1349A and DPIS 2- 1349B sensing lines will be backfilled at the next Unit 2 forced outage of sufficient duration.
F. Previous Occurrences:
A review of DNPS Licensee Event Reports (LERs) for the last three years did not identify any similar events.
G. Component Failure Data:
NA