05000237/LER-2008-002

LER-2008-002, Unit 2 High Pressure Coolant Injection System Declared Inoperable

Docket Number
Event date:	04-15-2008
Report date:	06-16-2008
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2372008002R00 - NRC Website

Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electric Company Boiling Water Reactors with a licensed maximum power level of 2957 megawatts thermal.

A. Plant Conditions Prior to Event:

Unit: 02� Event Date: 04-15-2008 �Reactor Mode: 1� Mode Name: Power Operation Power Level: 99 percent Reactor Coolant System Pressure: Approximately 998 psig

B. Description of Event:

On 04-15-08 at 0700 hours0.0081 days <br />0.194 hours <br />0.00116 weeks <br />2.6635e-4 months <br />, Unit 2 HPCI was declared inoperable due to the HPCI FIC 2-2340-1 failing to 60 percent output demand from the expected 100 percent while in Standby Mode of operation. Technical Specification LCO 3.5.1.F (14 day) was entered with the Isolation Condenser (IC) being verified operable. On Line Risk changed from Green to Yellow. Controller failure was discovered by Control Room Operators performing hourly panel checks of panel indications. The controller output demand was observed lower than expected and the HPCI Motor Gear Unit (MGU) was observed below the High Speed Stop (HSS). The MGU normally resides at the HSS since it is fed by the controller output at 100 %.

On 04-15-08 at 1455 hours0.0168 days <br />0.404 hours <br />0.00241 weeks <br />5.536275e-4 months <br />, controller troubleshooting began by the Instrument Maintenance Department (IMD). The controller side display indicated message "PWR ERR". This message occurs with either a low supply voltage or problems with the controller internal power supply. Since the supply voltage was normal, the controller internal power supply was identified as degraded. This condition prevented the controller from being placed into Manual Mode and prevented the controller parameters from being extracted for use in a replacement controller. On 04-16-08 at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br />, a spare re-configured, calibrated controller was installed and at 1213 hours0.014 days <br />0.337 hours <br />0.00201 weeks <br />4.615465e-4 months <br /> following the successful HPCI fast start test, HPCI was declared operable and the LCO was exited.

Additionally, HPCI would have functioned as expected following the controller replacement at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br /> at which time HPCI became available with On Line Risk changing back to Green.

C. Cause of Event:

The Apparent Cause of this event is age degradation of the Model SLPC-271 Yokogawa controller's internal power supply. The examination of the failed controller identified the power supply had failed from aged electrolytic capacitors. An extent of condition review identified that there are twelve similar type controllers in use at DNPS. Actions have been taken to schedule replacement of these controllers prior to the currently scheduled 2010 replacement.

A review determined that the majority of these controllers were installed in the 1990 to 1992 timeframe. This review identified two previous controller power supply failures. One of these failures was in 2006 resulting in replacement of the controller with a refurbished unit. The second was in 2005 resulting in replacement of the controller with a refurbished unit. Based on these results, DNPS will schedule the remaining nine controllers PM due dates prior to the originally scheduled 2010 date.

D. Safety Analysis:

The safety significance of the event is minimal. TS 3.5.1 allows Unit 2 to remain at power for 14 days with an inoperable HPCI if the IC is operable. Unit 2 was in compliance with TS 3.5.1 during this event as the IC was operable and HPCI was inoperable for approximately 1 day. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.

E. Corrective Actions:

The corrective actions to prevent recurrence of this event are:

DNPS will schedule PM refurbishments for the remaining nine controllers prior to the originally scheduled PM due dates of 2010 (Complete)

F. Previous Occurrences:

A review of DNPS LERs for the last three years did not identify any LERs associated with controller failures attributed to age degradation of a power supply.