05000316/LER-2010-003
| Docket Number | |
| Event date: | 3-0-2010 |
|---|---|
| Report date: | 01-28-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3162010003R00 - NRC Website | |
Conditions Prior to Event Mode 5
Description of Event
On November 30, 2010, at 1749 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.654945e-4 months <br />, Donald C. Cook Nuclear Plant (CNP) Unit 2 Operators determined that the containment divider barrier was inoperable. This occurred approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after Unit 2 ascended from Mode 5 to Mode 4 at 1255 hours0.0145 days <br />0.349 hours <br />0.00208 weeks <br />4.775275e-4 months <br />. A modification of the containment divider barrier seal [SEAL] had been completed prior to entering Mode 4, but the seal was not recognized as having been reassembled incorrectly at that time. As a result, the entry-into Mode 4 was made with the Technical Specification (TS) required containment divider barrier inoperable, and without meeting Limiting Condition for Operation (LCO) 3.0.4 conditions to do so.
During a walkdown of the divider barrier seal modification following ascension to Mode 4, the configuration of a portion of the divider barrier seal directly adjacent to the modification was questioned. This walkdown identified one missing nut and one nut with improper thread engagement. The divider barrier was determined to be inoperable because it did not meet TS 3.6.13 Surveillance Requirement 3.6.13.5, which specifies that the "Seal and seal mounting bolts are properly installed...
Ascension to Mode 4 with the Containment Divider Barrier inoperable without meeting LCO 3.0.4 conditions to do so is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), Operation or Condition Prohibited by Technical Specifications.
Cause of Event
The cause of this event was personnel exceeding their work scope by disassembling a section of the divider barrier seal adjacent to the area being modified, and failure to properly restore the section of the divider barrier seal that had been disassembled. The disassembly of the adjacent section of the divider barrier seal was neither communicated to job oversight personnel nor documented in the work package.
Contributing causes were lack of adequate oversight of the field work such that exceeding work scope was not identified, and a failure of the modification and work control processes to implement the TS Surveillance requirement as a post-modification test/inspection to verify the divider barrier was operable prior to entering Mode 4.
Analysis of Event
The safety function of the divider barrier seal is to provide separation between the upper containment [NH] 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 [AB] flows from the lower containment volume through the ice condenser [BC] before reaching the upper containment volume. Steam flowing along this flow path condenses on 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 LOCA, and some medium LOCAs, extensive degradation of the divider barrier seal would result in a much larger initial containment pressure spike. However, an evaluation of the identified condition determined that the maximum potential divider barrier bypass flow area resulting from this event would be less than the design basis value. Therefore, the divider barrier seal was capable of performing its function while degraded, and, as a result, the actual degradation of the divider barrier seal would have no effect on the PRA model results.
Corrective Actions
Completed Corrective Actions
In the affected area, the divider barrier seal assembly was corrected by reworking the seal plate, adding a new nut where
- one was missing, and tightening the nut that did not have adequate thread engagement.
Performed surveillance of the divider barrier seal areas worked during the modification, and on the section of the divider barrier seal adjacent to the modification.
Planned Corrective Actions
Revise appropriate procedure to ensure that applicable surveillance will be used as post-modification test/inspection for work on safety-related components, including inspection of passive structures. TS surveillance requirements must be used where applicable to verify as-found conditions prior to work and verify as-left conditions via post maintenance/modification test (PMT) after completion of work.
Procedure guidance will be developed to ensure that work performed by contractor personnel must only be within the scope of the work package, and that any difficulties, obstacles, interferences or concerns need to be communicated to oversight personnel for resolution.
Future outage work scope performed by contractor personnel will be reviewed for activities that impact safety-related structures, systems, or components, high risk activities, or where human error poses elevated risk. Activities identified will have a CNP supervisor hold placed on them for oversight to verify all work is complete, the equipment worked or potentially impacted by the work has been fully restored for return to operations, and/or post maintenance inspection or test activities are adequate to verify completion or identify any deficiencies.
Previous Similar Events
The issue reported in this Licensee Event Report (LER) is related to entry into a Mode or condition of Applicability without either having all TS required equipment operable, or complying with the provisions of LCO 3.0.4. A search of LERs for the past 5 years identified the following:
between these two LERs are that both involve non-compliance with a TS LCO and both lacked procedural guidance to help ensure compliance. Specifically, LER 2008-003-00 documents that procedures did not effectively cross-reference the aspects of the Safety Function Determination Program. The current LER documents a failure to perform Post-Modification Testing on TS-related equipment.
Because of the difference in the specific LCOs involved, and that the procedure direction that was lacking in each instance was very different, the corrective actions resulting from the incident reported in LER 2008-003-00 could not have prevented the event identified in this LER.
retaining bolt with a loose nut; and one retaining bolt missing its nut. This was determined to be a non-compliance with the Divider Barrier LCO, which was not recognized when it occurred. This is similar in that it is another unrecognized non-compliance with the Divider Barrier LCO. Specifically, LER 2010-002-00 documents that the procedure used to perform the TS Surveillance on the divider barrier lacked the necessary specificity. The current LER documents a failure to perform Post Modification Testing on TS required equipment, which was the divider barrier seal.
Because of the difference in the mechanisms of these two non-compliances related to the divider barrier seal, corrective 'actions regarding how the surveillance is performed would not have prevented the event identified in this LER.