05000368/LER-2008-001
| Arkansas Nuclear One - Unit 2 | |
| Event date: | 3-13-2008 |
|---|---|
| Report date: | 5-8-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3682008001R00 - NRC Website | |
A. Plant Status At the time this condition occurred, Arkansas Nuclear One, Unit-2 (ANO-2) was in Mode 1 at approximately 100 percent power. At the time this condition was discovered, the plant was shutdown in Mode 5 for Refueling Outage 2R19.
B. Event Description
On March 18, 2008, with the plant shutdown in Mode 5, the outside containment isolation valve [ISV] for the chill water system [KM] did not fully close during "as-found" stroke time testing. Investigation by Operations personnel revealed that a scaffold pole was interfering with the close stroke of the valve, resulting in it remaining approximately 30 to 40 percent open. The obstruction was removed and the valve was successfully stroke tested.
C. Root Cause
The cause of this event was human error in that the walkdown conducted by Operations personnel and the scaffold crew before the scaffold was installed did not identify the subject valve as a work site interference issue. This was, for the most part, due to the unique valve design. The valve has a large air cylinder on the top with four rods and springs connecting it to the valve body. Between the cylinder and the rods/springs, there is a flat plate that moves when the valve operates. When the valve is open, the plate rests against the bottom of the air cylinder and appears to be an integral part of the cylinder, which does not move during valve operation. The plate also extends approximately 1 to 2 inches beyond the edge of the cylinder. When the scaffold was installed, special care was taken to ensure that the scaffold was not close enough to the springs and rods to interfere with valve operation (approximately 1 1/2 inches). However, the crew did not recognize that the subject plate was a movable part of the valve assembly. Due to the unique design of the valve associated with this event, it was determined to be an isolated occurrence.
D. Corrective Actions
The obstruction was removed and the valve was successfully stroke tested.
Even though this event was an isolated occurrence, a "lessons learned" discussion will be conducted with the Operations staff of both ANO units regarding this event to stress the importance of walkdowns with scaffolding personnel in identifying all potential interference issues.
E. Safety Significance
Considering that this condition existed for a short period of time and the fact that the redundant containment isolation valve remained operable during this time, the significance of this event is considered to be minimal.
F. Basis for Reportability ANO-2 Technical Specification 3.6.3.1 requires that each containment isolation valve be operable in Modes 1, 2, 3, and 4. If unable to restore an inoperable containment isolation valve to operable status or isolate the affected penetration within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, the specification requires that the plant be taken to Hot Standby within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
The scaffold was constructed on March 13, 2008, while the plant was in Mode 1 at 100 percent power. The plant was shutdown for Refueling Outage 2R19 on March 16, 2008, and entered Mode 5 at 1503 on that date, at which time containment integrity was no longer required. Since the subject containment isolation valve was inoperable for a period of time longer than allowed by the Technical Specifications, this event is reportable pursuant to 10CFR50.73(a)(2)(i)(B) as operation prohibited by Technical Specifications.
G. Additional Information
There have been no previous similar events reported by ANO.
Energy Industry Identification System (El IS) codes are identified in the text as [XX].
Attachment 2CAN050801 List of Regulatory Commitments Attachment 1 to 2CAN050801 List of Regulatory Commitments The following table identifies those actions committed to by Entergy in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
TYPE
COMMITMENT (Check One)
ONE TIME CONTINUING
SCHEDULED COMPLETION
DATE
ACTION COMPLIANCE (If Required) Conduct a lessons learned discussion with the Operations staff of both ANO units regarding this event to stress the X 6/30/2008 importance of walkdowns with scaffolding personnel in identifying all potential interference issues.