05000298/LER-2004-001
| Cooper Nuclear Station | |
| Event date: | 02-11-2004 |
|---|---|
| Report date: | 04-08-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2982004001R00 - NRC Website | |
PLANT STATUS
Cooper Nuclear Station (CNS) was in Mode 1 (Run) at 100 percent power when the condition prohibited by Technical Specifications (TS) was discovered.
BACKGROUND
The Service Water (SW) System [EllS:B1] is designed to provide cooling water for the removal of heat from equipment, such as the diesel generators (DGs) [EllS:DG] and Reactor Equipment Cooling System [EllS:CC] heat exchangers, and to provide a supply of water for the Residual Heat Removal (RHR) [EIIS:BO] heat exchangers through the Residual Heat Removal Service Water Booster System pumps, required for a safe reactor shutdown following a Design Basis Accident or transient.
The SW System consists of the Ultimate Heat Sink and two independent and redundant subsystems.
The two subsystems are separated from each other so failure of one subsystem will not affect the operability of the other system.
Each set of SW pumps has a water bearing lubrication (Gland Water) supply utilizing the safety-related discharge of the SW pumps as the normal line-up. The gland water supply originates down stream of the SW pump discharge strainer and can be divisionally cross-connected to maintain bearing lubrication from the opposite division during maintenance and cleaning of the pump discharge strainer.
With one SW subsystem inoperable, the SW subsystem must be restored to operable status within 30 days. Additional Limiting Conditions for Operation (LCOs) must be entered and Required Actions taken if the inoperable SW subsystem results in an inoperable DG or RHR shutdown cooling subsystem.
EVENT DESCRIPTION
On February 11, 2004, during validation of a valve line-up on the Service Water Gland Water system, CNS discovered that the gland water piping was cross-connected with SW subsystem "A" safety related pump discharge supplying gland water to both SW subsystems. This resulted in SW subsystem "B" being declared inoperable due to loss of subsystem separation, and required entry into a 30 day LCO.
DG 2, which is cooled by SW subsystem "B", and the Control Room Emergency Filter System (CREFS), which was aligned to the DG 2 emergency bus, were declared inoperable, and required entry into 7-day Shutdown LCOs. The LCOs were entered at 0310 hours0.00359 days <br />0.0861 hours <br />5.125661e-4 weeks <br />1.17955e-4 months <br />. The gland water line-up was returned to the required configuration and the Shutdown LCOs were exited at 0340 hours0.00394 days <br />0.0944 hours <br />5.621693e-4 weeks <br />1.2937e-4 months <br />. Further investigation determined that the cross-connected configuration had existed since restoration of the system from planned maintenance performed 21 days earlier.
BASIS FOR REPORT
DG 2, and CREFS were inoperable for 21 days, exceeding the TS 7-day shutdown LCO. This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as "Any operation or condition which was prohibited by the plant's Technical Specifications.
CAUSE
The cause of this event was determined to be a process weakness in the Clearance Order program.
The process for development of the clearance order to restore the cross-connected configuration of the SW gland water to the required configuration allowed the use of a note in the clearance order referring the operator to use the system operating procedure (SOP) for system restoration instead of a specific step to direct use of the SOP.
SAFETY SIGNIFICANCE
An evaluation of this event concluded that it was not risk significant. The change in the core damage probability was calculated as less than the threshold for classification as risk significant. The risk assessment included assumptions that the Service Water pumps can run 30 minutes with a loss of gland water flow, and that the average response time to restore the flow in the event of a low gland water flow condition is 20 minutes.
This event is not considered a Safety System Functional Failure as defined in NEI 99-02, Revision 2, Regulatory Assessment Performance Indicator Guideline.
CORRECTIVE ACTIONS
Immediate actions:
The system was restored to the proper configuration at 0340 hours0.00394 days <br />0.0944 hours <br />5.621693e-4 weeks <br />1.2937e-4 months <br /> on February 11, 2004.
Issued instructions for the work control process to require a separate entry for confirmation of clearance order release and an additional entry for confirmation of system configuration restoration. This action was completed February 13, 2004.
The Service Water system operating procedure was revised to include placement and removal of "Crosstied" tags for the pump control switches, and verification of valve lineups. The procedure revision was effective February 24, 2004.
Long Term actions:
The station procedure for development of clearance orders was revised to eliminate the possibility of improperly using notes instead of numbered steps, and to require the release sequence be coordinated with the applicable system operating procedure sequence. This action was completed on April 8, 2004.
PREVIOUS EVENTS
No previous reportable events resulting from mis-positioned components within the last three years were identified.