05000425/LER-2007-001
| Docket Number(S) | |
| Event date: | 01-01-2007 |
|---|---|
| Report date: | 1-0-5000 |
| 4252007001R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR 50.73 (a)(2)(i)(B), any operation or condition which was prohibited by Technical Specifications (TS). TS LCO 3.5.4 requires these valves to automatically close on an Refueling Water Storage Tank (RWST) low-level signal, and the valves were incapable of closing.
B. UNIT STATUS AT TIME OF EVENT
The RWST sludge mixing valves were determined to have been in a condition prohibited by TS on January 1, 2007 at 1310 EDT. At the time of the event, Unit 2 was at 100% power.
C. DESCRIPTION OF EVENT
Unit 2 RWST sludge mixing valves 2HV-10957 and 2HV-10958 were placed in the jack open position and tagged using a clearance to help facilitate maintenance on another component. After maintenance was completed, the tagout was released and operations performed an independent verification on the valves.
The first operator did not fully understand the term "Available Ensure Off the Jack" as stated on the clearance release sheet. The operator assumed that this meant the hand wheel on the valve needed to be full up. Also, he was not aware that the jacks on these valves hold them open.
When the second operator independently verified the position of the valves, he made the same assumption as the first operator. He turned the hand wheel to the closed position to verify the valve was open and then returned the hand wheel to full open. The clearance was returned to the control room, and signed off as removed. Operability was determined by stating that the tagout had been released and LCO 2-2006-157 was exited. This determination of operability was incorrect and left the valves inoperable for 24 days.
� On January 1, 2007 surveillance 14825-2 was attempted and valves 2HV-10957 and 2HV-10958 did not stroke. This is when the valves were discovered jacked open, and were removed from the jack returning them to operable status.
D. CAUSE OF EVENT
The primary cause of this event was no procedural guidance was given to verify the valves were operable following the valves being placed on the jack.
E. ANALYSIS OF EVENT
Per TS 3.5.4, the RWST sludge mixing isolation valves are required to automatically close on an RWST low-level signal. The contents of the RWST are protected from freezing by a sludge mixing system which includes an electric circulation heater. However, the sludge mixing pump and the electric circulation heater connected to the tank are not safety grade or seismically qualified.
Therefore, an isolation capability is provided to prevent loss of the RWST water volume. Two train-oriented, air operated, seismically qualified valves mounted in series are provided on the suction line to the sludge mixing pump. These are the valves that were inoperable for longer than allowed by the TS. Had a seismic event occurred during this time, the non-seismic portion of this line could have broken causing a loss of RWST inventory. Operators would have been made aware of this loss of inventory by the RWST low-level alarm. In addition, the engineering evaluation determined that at least an hour would have been available following the RWST low-level alarm for operator action to identify the loss of inventory and isolate the broken line.
If a design basis event requiring safety injection had occurred at the same time that the seismic event occurred, adequate inventory would have been available in the RWST so that the injection function of the Emergency Core Cooling System (ECCS) could have been accomplished as determined by an engineering evaluation using design pump flows without operator intervention. � Therefore, the injection function of the ECCS would have been maintained.
No event occurred requiring the RWST ECCS injection function during the time that the valves were inoperable. There was no adverse effect on the health and safety of the public.
F. CORRECTIVE ACTIONS
1. The "Conduct of Operations" procedure was revised to include operability requirements for Safety Related Air-Operated Valves (A0Vs) placed on the jack to defeat the fail safe operation. That is, the valve should be stroked using remote service prior to declaring it operable.
2. The Operations Manager has covered this and other mispositioning events in Requalification Training, emphasizing the use of HU tools and the importance of making sure the plant is in a normal alignment to ensure safe reliable operation of the plant.
3. Lessons learned regarding this event were included in Licensed Operator and Non-licensed Operator continuing training with an emphasis on the operation of various AOVs that can be placed on the jack, the purpose of the jack, and how to restored valves from the "jacked" position.
4. "Operation of valves with Jacks" will be included as part of the Initial and Continuing core tasks for licensed and non-licensed operators. Estimated to be included by May 23, 2007.
G. ADDITIONAL INFORMATION
None 2) Failed Components:
None 3) Previous Similar Events:
None 4) Energy Industry Identification System Codes:
Chemical and Volume Control Makeup and Purification System — CB High Pressure Safety Injection System - BQ Residual Heat Removal / Low Pressure Safety Infection System — BP Containment Spray System - BE