05000249/LER-2008-002
| Docket Numbersequential Revmonth Day Year Year Month Day Year N/A N/Anumber No. | |
| Event date: | 10-29-2008 |
|---|---|
| Report date: | 12-23-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2492008002R00 - NRC Website | |
Dresden Nuclear Power Station (DNPS) Unit 3 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: 03 � Event Date: 10/29/2008 �Reactor Mode: 1� Mode Name: Power Operation Power Level: 85 percent Reactor Coolant System Pressure: 1000 psig
B. Description of Event:
On October 29, 2008, at approximately 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br /> (CDT), with Unit 3 at approximately 85 percent power, DNPS operations personnel identified that the OPEN indication light [IL] for the normally open primary containment isolation valve (PCIV) [V] 3-3702 was flickering on and off. PCIV 3-3702 is the Unit 3 Reactor Building Closed Cooling Water (RBCCW) [CC] Drywell Supply Header Isolation Valve to the containment and is designed to receive a manual close signal from the control room during certain accident events. The valve cannot be closed during normal plant operation without a plant shutdown, as it would require securing the Reactor Recirculation System pumps. The bulb was replaced several times but the flickering continued. Operations personnel performed a prompt operability review for valve 3-3702 and concluded that the flickering light indicated that the valve was operable but light socket was failing. The indication light was declared inoperable and actions were taken in accordance with the requirements of Technical Specification (TS) 3.3.3.1, "Post Accident Monitoring (PAM) Instrumentation." TS 3.3.3.1 Required Action (RA) A.1 required the light to be restored to operable within 30 days. An investigation into the flickering of the indication light on November 1, 2008, discovered an intermittent high resistance electrical connection at the motor control center (MCC) for control power to PCIV 3-3702. The intermittent high resistance electrical connection caused the flickering indicator light and also would have prevented valve closure from the control room.
On November 1, 2008, at approximately 1050 hours0.0122 days <br />0.292 hours <br />0.00174 weeks <br />3.99525e-4 months <br />, PCIV 3-3702 was declared inoperable and actions were taken in accordance with the requirements of TS 3.6.1.3, "Primary Containment Isolation Valves (PCIV)." TS 3.6.1.3 RA Al required the valve to be restored to operable status within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or PCIV 3-3702 would have to have been closed, isolating the RBCCW flow. The valve was restored to operable status on November 1, 2008, at approximately 1309 hours0.0152 days <br />0.364 hours <br />0.00216 weeks <br />4.980745e-4 months <br /> within the TS 3.6.1.3 allowed outage time.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." The flickering indication light that was discovered on October 29, 2008, provides evidence that PCIV 3-3702 was historically inoperable for a period of time that exceeded the 4-hour limit of TS 3.6.1.3 RA Al and the PCIV was not closed.
� C.C Cause of Event:
The cause of the event was an intermittent high resistance electrical connection at the MCC for control power to PCIV 3-3702. The cause of the intermittent high resistance electrical connection is indeterminate. The most probable cause is that the electrical connection was marginal at installation and over time, surrounding equipment vibration caused the connection to be intermittent.
Additionally, the cause of not entering TS 3.6.1.3 on October 29, 2008 was a lack of proper procedure guidance that led operations personnel to assume the problem was a faulty light socket.
Troubleshooting was not immediately pursued, as there have been no previous failures of this type, flickering light indicating the valve was inoperable.
The RBCCW system is a closed loop system that in part, cools primary containment critical heat loads. PCIV 3-3702 is one of two isolation valves in the RBCCW supply line to the containment. The second valve is a check valve.
PCIV 3-3702 is a motor operated valve that is normally open during plant operation. The electrical power to the valve motor operator and its associated OPEN indication light is supplied through one electrical bucket in the MCC. The investigation on November 1, 2008, found intermittent voltage to PCIV 3-3702 that was eliminated when a test jumper was placed across the terminal points of the MCC bucket. The MCC bucket was removed to verify the tightness of all screw terminal points and none were found loose. The MCC bucket's terminal spring clips were tightened. The MCC bucket was reinstalled and successfully returned control power to the valve and the indicating light was illuminated.
The MCC bucket referenced above was installed on November 14, 2006, during a refuel outage and successfully passed maintenance testing. PCIV 3-3702 was last successfully cycled on January 17, 2008 during a maintenance outage. A review of Unit 3 operation logs did not find any reference to flickering lights on PCIV 3-307 prior to October 29, 2008.
An extent of condition review was performed on a sampling of similar motor operator valves and no abnormalities were identified.
The procedures used by operations personnel on October 29, 2008, lacks specific guidance to alert users that a failed or flickering indication light associated with a motor operated valve may indicate problems that could effect valve operation and that valve operability must be verified. An extent of condition review of operation procedures identified that revisions to enhance guidance must be made to procedures DGP 03-02, "Normal Control Room Inspection," DOP 0040-01, "Station Motor Operated Valve Operations," DOP 0040-04, "Control Panel Light Bulb and LED Replacement," DOP 6700-20, "480V Circuit Breaker Trip" and DOS 0040-12, "Penetration Flow Path PCIV Position Channel Check and Control Room PCIV Position Verification," to address this event.
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D. Safety Analysis:
The safety significance of the event is minimal. The RBCCW system is a closed loop system that provides a boundary to prevent a radioactive release to the environment during normal plant operation. PCIV 3-3702 is one of two isolation valves in the RBCCW supply line to the containment.
The second valve is a check valve that was operable and capable of isolating the supply line if required. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E. Corrective Actions:
PCIV 3-3702 was restored to operable status.
Procedure DES 7300-05, "Maintenance and Surveillance of E.Q. and Safety Related 480 Volt MCC," was revised to include a step after installation of a MCC to perform a visual inspection of the electrical mating connections and to verify electrical continuity of the mating connection.
A training request was initiated to re-enforce with operations personnel the potential operability issues when valve /light indications are not functioning properly.
Operations revised procedures DGP 03-02, DOP 0040-01, DOP 0040-04, DOP 6700-20 and DOS 0040-12, to add guidance to alert users that a failed or flickering indication light associated with a motor operated valve may indicate problems that could effect valve operation and that valve operability must be verified.
F. Previous Occurrences:
A review of DNPS Licensee Event Reports (LERs) for the last three years did not identify any LERs associated with an intermittent electrical connection causing the inoperability of a TS component.
G. Component Failure Data:
N/A �