05000315/LER-2008-005
| Donald C. Cook Nuclear Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3152008005R00 - NRC Website | |
Conditions Prior to Event Mode 1, 100 percent power.
Description of Event
On July 15, 2008, at. approximately 0220, Operations personnel at Donald. C. Cook Nuclear Plant (CNP), Unit 1, identified that a containment isolation drain valve on the Non-Essential Service Water -(NESW) System (KG) was sealed and capped in the open position rather than sealed and capped in the closed position as required.
This was identified during a monthly'surveillance to verify position of containment isolation valves. There were no inoperable structures, systems, or components that contributed to the event.
When the valve was verified to be out of its required position, Technical Specification Limiting Condition for Operation (LCO) 3.6.3 Condition A, One or more containment isolation flow paths with one containment isolation valve inoperable, was entered. The required action is to verify the affected flowpath isolated within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
On July 15, 2008, at 0242, the valve was closed and verified closed in accordance with the containment isolation surveillance procedure, and LCO 3.6.3 Condition A was exited.
Investigation into the mispositioning of the valve revealed that the mispositioning occurred during restoration of a system clearance on April 23, 2008, near the end of the Unit 1 refueling outage. The clearance correctly directed that the valve be sealed closed and capped; however, it was left partially open and capped.
With the valve partially open and the NESW system pressure at approximately 80 psig, the valve and cap were observed to have no leakage. There was no impact on operation of the NESW system.
Cause of Event
The mispositioning of the valve occurred during restoration of a system clearance near the end of the Unit 1 refueling outage. The apparent cause of the valve mispositioning has been determined to be a failure of the individual performing the positioning to perform adequate review during the self-check process. The apparent cause of the failure of the individual performing the verification to identify the misposition has been determined to be a failure to maintain an adequate questioning attitude regarding the position of the valve stem, which was extended one half inch higher than other similar valves.
During the two monthly surveillances between the April clearance restoration and the July discovery of the mispositioned valve, operators verified the valve seal intact, but did not physically check the valve position. This precluded the identification of the mispositioned valve. Not performing a physical check of the valve position'has been attributed to lack of specific guidance in the containment isolation surveillance procedure for performing the verification of a sealed valve. The expectation was to simply verify the seal intact and not require verification of the actual valve position. The persons involved are Auxiliary Equipment Operators in the. Operations department.
Analysis of Event
The mispositioned NESW valve and associated NESW piping do not support any Probabilistic Risk Assessment (PRA) Risk Significant function for core damage (CD) or Large Early Release beyond that of containment isolation to prevent a Large Early Release condition. In that the valve was found open and capped, and no leaks were noted with NESW system pressure at approximately 80 psig, reasonable assurance exists that there would be no leakage from containment via this path during a Design Basis Accident (DBA) where containment pressure would be expected to be less than or equal to 12 psig.
The Plant PRA Containment Isolation Notebook (PRA-NB-CI, Revision 1) Section 5.1.1, Penetration Screening Analysis, indicates that NESW lines associated with the Unit 1, Number 1 Reactor Coolant Pump (RCP) Motor Air Cooler supply and return lines are not considered significant to the Large Early Release/Containment Isolation function in that they are a closed, NESW filled system/component in containment. Further, the containment leak size necessary to produce a Large Early Release requires an opening in excess of 2 inches in diameter, and the associated NESW valve and line are one half inch in diameter.
The NESW piping for the Unit 1, Number 1 RCP Motor Air Cooler services only that air cooler and has no open connections with the containment interior.
The condition found, the containment isolation drain valve left open and capped with the unit operating in MODE 1, poses no significant plant or personnel risk from a PRA standpoint.
Corrective Actions
The following corrective actions have been taken:
The containment isolation drain valve was closed. An independent verification was performed in order to verify the valve closed, capped, and sealed in accordance with the containment isolation surveillance procedure.
Independent verification of the containment isolation surveillance procedure attachment for manual valves outside containment was performed. All remaining valves were verified to be correctly positioned.
The containment isolation surveillance procedure has been revised to include references to the procedures which provide specific direction for performing position checks of sealed or locked components. The specific direction requires verification of the actual position along with verification that the seal is intact.
The following corrective actions are planned to be taken:
Non-Licensed Operators will receive interactive training to address verification techniques, self-check attributes, mindset, complacency, and questioning attitude.
Previous Similar Events
A review was conducted of Licensee Event Reports (LERs) from January 2003 to the present for mispositioned containment isolation valve LERs. One instance was identified.
November 11, 2004 - CNP submitted LER 50-316-2004-004-00, Failure to Comply with Containment Integrity Requirements. Two NESW drain valves were found open when they were required to be closed. The root cause was determined to be failure to have a comprehensive process to provide positive control of containment integrity or closure through all modes of operation, and inadequate review of clearances for mode change. While the recent mispositioning event is similar to this 2004 event, the cause for the recent mispositioning is not related to the cause or corrective actions of the previous event. Therefore, the corrective action of that LER would not have prevented the event reported in this LER.
A review was performed of all Action Requests (ARs) for the previous two years that were coded with one of the reason codes related to mispositioning. None of the ARs reviewed involved mispositioning or inadequate verification practices related to containment isolation valves. There were no instances identified where a manual valve was placed in position and valve position verification checks failed to discover the error. There was one AR that identified a control switch for a valve that was found out of the required position following a surveillance test. In this case, the procedure required checking the control switch in NORMAL as well as checking the valve closed. The control switch was inadvertently left in the TEST position, but the valve was in the correct, position and closed. The individuals performing the switch verifications missed the out-of-position switch.
This was discovered on a control board walkdown by the oncoming crew, and was determined to be an accountability issue related to human performance. This particular event occurred several weeks prior to the manual containment isolation valve being found out of position that is the subject of this AR. However, the actual valve mispositioning and improper verification of the manual containment isolation valve took place prior to the control switch mispositioning event.
Therefore, there was no corrective action previously taken for the ARs reviewed that should have prevented this event.