05000316/LER-2010-002

LER-2010-002, Containment Divider Barrier Seal Mounting Bolts Not Properly Installed

Docket Number
Event date:	1-5-2010
Report date:	12-07-2010
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3162010002R00 - NRC Website

Conditions Prior to Event Mode 6

Description of Event

On October 15, 2010, during performance of the surveillance of the Donald C. Cook Nuclear Plant Unit 2 containment divider barrier seal in accordance with the Technical Specification (TS) surveillance requirement, personnel identified two divider barrier seal retaining bolts missing, one retaining bolt with a loose nut and one retaining bolt missing its nut. This condition constitutes a noncompliance with the TS surveillance which requires the divider barrier seal and seal mounting bolts to be properly installed. Investigation of the condition concluded that the nut has been missing for the duration of the recently completed operating cycle, the bolts have been'presumed missing since replacement of the divider barrier. seal in 1990 and the loose nut was not properly tightened following removal of a seal sample coupon during a previous outage.

The condition described above constitutes a non-compliance with the Technical Specification (TS) requirement to ensure seal bolting is properly installed and therefore is reportable as a condition prohibited by TSs.

Cause of Event

The cause of the event has been determined to be an inadequate containment divider barrier seal surveillance procedure.

The procedure lacks clear guidance and specificity in details to ensure TS surveillance requirements are satisfied when completing the inspection. Additionally, the procedure format directs completing the inspection of the entire seal, which occurs over a period of several days by several different persons, prior to signing for completion. This procedure format can lead to errors due to not providing a method or process to track completed portions of the surveillance and document discrepancies as the inspection progresses.

Analysis of Event

A Past Operability Determination Evaluation (PODE) concluded that the as-found condition of the seal did not affect the ability of the divider barrier and the containment building to perform their design functions. The divider barrier seal would have performed its safety function adequately.

The safety function of the divider barrier seal is to provide separation between the upper containment and lower containment volumes' atmospheres. Performance of this safety function following a Loss of Coolant Accident (LOCA) assures that high pressure/high temperature gas/steam released into the lower containment from the reactor coolant system must flow from the lower containment volume through the ice condenser before reaching the upper containment volume. Steam flowing through this path is condensed by the ice bed, thereby reducing the total volume of gas reaching the upper containment and maintaining overall containment pressure below its design value.

Divider barrier seal performance is credited in the Probabilistic Risk Assessment (PRA) model. Degradation of divider barrier seal performance could affect the risk results of the PRA model due to possible impact on containment pressurization characteristics. For a large loss of cooling accident (LOCA), and possibly even a medium LOCA, extensive degradation of the divider barrier seal would result in a much larger initial containment pressure spike. However, since the divider barrier seal was capable of performing its function with the identified condition, the actual discovered, minor degradation of the divider barrier seal would have no effect on the PRA model results.

Corrective Actions

Completed Corrective Actions

The identified divider barrier seal retaining hardware conditions were corrected prior to Unit 2 ascending to Mode 4, the Mode of applicability for TS 3.6.13. The seal retaining bolts and the missing nut were replaced, and the loose nut was tightened.

Planned Corrective Actions

The containment divider barrier seal surveillance procedure will be revised to provide guidance that is commensurate with the complexity of the surveillance task and documentation needs.

A qualification will be developed and personnel performing the containment divider barrier seal surveillance will be qualified to the task.

The Pre-Job Brief Database for containment divider barrier seal surveillance inspections will be enhanced for the surveillance pre-job brief.

Previous Similar Events

A search of Licensee Event Reports (LER) for the past 10 years identified one LER documenting missing divider barrier seal retaining bolts.

On October 5, 2006, following an inspection of the Donald C. Cook Nuclear Plant Unit 1 containment divider barrier seal, Indiana Michigan Power Company (I&M) personnel discovered that, contrary to TS 3.6.13, Divider Barrier Integrity, one divider barrier seal retaining bolt was missing and a second divider barrier seal retaining bolt was missing its associated nut. The investigation of this condition determined the missing components had previously been identified in November 1998. However, the 1998 evaluation of the'condition failed to identify the TS noncompliance and subsequent corrective actions failed to correct the condition.

The condition evaluation for this issue prescribed a corrective action to conduct training. However, a corrective action to conduct training was not developed due to human error.

Additional Information

A survey of the Corrective Actions database revealed that a condition report dated October 16, 2007, documented a number of loose and missing bolts for the containment divider barrier and the divider barrier seal. The PODE in the condition report concluded that the identified issues constituted a violation of TS, but incorrectly concluded that the divider barrier was operable since the identified condition did not prevent the divider barrier from performing its safety function. The condition was then incorrectly determined to be not reportable. The disposition of the condition should have been inoperable due to a surveillance requirement not being met, and an LER submitted at that time.

While this condition is reportable in an LER, this condition was identified as reportable greater than three years after it was discovered. In accordance with 10 CFR 50.73(a)(1), an LER is not required because this issue occurred greater than three years earlier than the date of discovery.