05000424/LER-2007-001
| Docket Number(S) | |
| Event date: | 02-19-2007 |
|---|---|
| Report date: | 1-0-5000 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) |
| 4242007001R01 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR 50.73 (a)(2)(i) because the units operated in a condition prohibited by TS when safety-related components were inoperable for longer than allowed by the TS.
B. UNIT STATUS AT TIME OF EVENT
At the time of the discovery of this event, both Unit 1 and Unit 2 were operating in Mode 1 (power operation) at full power. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C. DESCRIPTION OF EVENT
On February 19, 2007 at 1330, a top-mounted auxiliary contact block for the Unit 1 'B' Train SI Pump Mini-flow Isolation valve motor starter assembly was found not completely engaged.
This component was assumed inoperable for longer than allowed by Technical Specifications (TS) as a result of not meeting seismic qualifications. This condition was discovered during a broadness inspection performed on both Unit 1 and Unit 2 as a corrective action to an earlier event on October 14, 2006, where the Unit 2 'A' Train Containment Spray Suction Isolation Valve failed to close as a result of a bound top-mounted auxiliary contact. Upon finding the auxiliary contact block locking tab not engaged during the February 19, 2007 inspection, the seismic qualification of any auxiliary contact block that is not fully seated was called into question, including the Unit 2 'A' Train Containment Spray Suction Isolation Valve, which was found on October 14, 2006. Over 250 motor starter assemblies on both units (including all safety related) have been inspected as a result of the broadness inspection. A total of eight top mounted auxiliary contact blocks on the motor starter assemblies were not completely engaged. Six were determined to be reportable.
On October 14, 2006, the Unit 2 'A' Train Containment Spray Sump Suction Isolation Valve was successfully stroked open and then failed to stroke closed upon demand during a quarterly surveillance. The cause was determined to be a bound top-mounted contact. Later it was determined to be most likely caused by the top-mounted auxiliary contact block not being completely engaged. The condition was initially determined not to be reportable due to repairs being completed and the valve stroked satisfactory within the time allowed by TS. As a corrective action for this event, a broadness inspection was initiated. On February 19, 2007, during the broadness inspection, a top mounted auxiliary contact block for a motor starter assembly was found not completely engaged. This component was assumed inoperable for longer than allowed by TS as a result of not meeting seismic qualifications.
The broadness inspection initiated as a result of the first failure revealed five additional components totaling 6 within TS that were discovered with top mounted auxiliary contact blocks not fully engaged. It should be noted that each of the Motor Operated Valves (MOV)s were successfully functionally tested following the initial installation of each Motor Starter assembly. Four of the MOVs have successfully completed their quarterly surveillances. The Unit 1 Chemical Volume Control System (CVCS) Centrifugal Charging Pump Recirculation to Refueling Water Storage Tank (RWST) MOV has an 18-month surveillance, which is performed during a refueling outage in Mode 5. This MOV has been successfully functionally tested; however, it was installed in the last Unit 1 outage and there have been no subsequent surveillances performed.
D. CAUSE OF EVENT
During performance of the motor starter design change installation, there was not a verification that the auxiliary contacts were fully engaged and secured via the locking tab.
E. ANALYSIS OF EVENT
In the valve's motor starter assembly, the top-mounted auxiliary contact block physically slides into grooves on the contactor and is restrained in the engaged position via a locking tab.
The fully engaged position ensures alignment of the auxiliary contact block and the contactor that physically actuates the auxiliary contact block plunger. The top-mounted auxiliary contact blocks not being secured into place resulted in the inability to meet their seismic qualifications. During a seismic event, the auxiliary contact block could potentially slide to a position which may prevent the starter and associated auxiliary contacts from changing state.
The auxiliary contact block for Unit 2 'A' Train Containment Spray Sump Suction Isolation Valve was successfully stroked open and then failed to stroke closed upon demand during a quarterly surveillance. The cause was determined to be a bound top-mounted contact. Later it was determined to be most likely caused by the top-mounted auxiliary contact block not being completely engaged. Assuming the auxiliary contact block was not completely engaged from installation, would not have resulted in a safety system functional failure. During the time the `A' Train is now assumed inoperable, the '13' Train was available to perform the safety function.
The failure during a seismic event for the auxiliary contact block for the Unit 1 '13' Train SI Pump Mini-flow Isolation Valve would not have resulted in a safety system functional failure.
During a cold leg circulation, the '13' Train SI Mini-flow is required to be isolated and can be accomplished with the common isolation valve.
The failure during a seismic event of the auxiliary contacts for the Unit 1 'A' Train Nuclear Service Cooling Water (NSCW) Tower Return Header Spray MOV would not have resulted in a safety system functional failure. The NSCW System is designed to perform its function `13' Train NSCW Tower was available during the time the Unitl 'A' Train NSCW Tower Return Header Spray MOV was declared inoperable.
The failure during a seismic event for the auxiliary contact block for the Unit 2 'A' Train Residual Heat Removal (RHR) Pump Mini-Flow Isolation MOV would not have resulted in a safety system functional failure. This would not have affected the valve's ability to open.
However, it may have affected the valve's ability to close. Westinghouse performed an analysis that determined the RHR pump was capable of providing the minimum ECCS Cold Leg Injection with the mini-flow valve unable to close.
The failure during a seismic event for the auxiliary contact block for the Unit 1 'A' Train RHR Inlet Isolation Valve would not have resulted in a safety system functional failure. The `A' Train Valve would have been able to open during shutdown cooling and the '13' Train was available for isolation during the time the 'A' Train valve was declared inoperable due to seismic requirements.
The failure during a seismic event for the auxiliary contact block for the Unit 1 '13' Train CVCS Centrifugal Charging Pump Recirculation to RWST MOV would not have resulted in a safety system functional failure. The valve would have opened for mini-flow, protecting the `13' Train Centrifugal Charging Pump during low flow conditions and the 'A' Train Valve can be used to isolate the line to the RWST.
F. CORRECTIVE ACTIONS
1) Procedure revisions to inspect auxiliary contact assembly engagement after installation and mounting were completed following the October 14, 2006 event. The associated procedural step is designated as a critical step and is a sign-off with Independent Verification of auxiliary contact block engagement.
2) A broadness inspection was performed on over 250 motor starter assemblies including all safety related. As a result, 8 top-mounted auxiliary contact blocks were found not fully engaged; 6 were governed under TS. These 8 have been repositioned in the fully engaged position.
G. ADDITIONAL INFORMATION
1) Failed Components: Unit 2 'A' Train Containment Spray Suction Isolation ValveNene 2) Previous Similar Events: None 3) Energy Industry Identification System Code:
Ultimate Heat Sink - BS High Head Safety Injection System — BQ Residual Heat Removal — BP Chemical Volume and Control — CB Containment Spray - BE