ENS 45119
ENS Event | |
|---|---|
23:52 Jun 9, 2009 | |
| Title | Door for Secondary Containment Boundary Left Open |
| Event Description | This notification is being made pursuant to NRC regulation 10 CFR 50.72(b)(3)(v)(D), any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
At 1852 [CDT] on June 9, 2009, River Bend Station personnel discovered that a normally closed auxiliary building door was open. This door serves as part of the secondary containment boundary. At discovery, immediate action was taken to close the door. This action restored the secondary containment to the design configuration. Investigation determined that the door was last accessed at 1242 on June 9 and was most probably left open at that time. Further action is being taken to investigate the cause of the event. Secondary containment leak tightness is required to ensure that the release of radioactive materials from the primary containment is restricted to those leakage paths and associated leakage rates assumed in the accident analysis, and that fission products entrapped within the secondary containment structures will be treated by the Standby Gas Treatment System prior to discharge to the environment. With the subject door being open, the function of secondary containment would be impacted. A second door is located in the same exterior passage way as the secondary containment door found open. This door was closed during the period of time the secondary containment door was open. This second door serves a security function. However, it potentially could serve to perform the secondary containment function. An evaluation is being performed to determine the actual impact of the condition on the secondary containment function. However, based on the identified condition, this report is being made as a condition that could have prevented fulfillment of a safety function. The licensee has notified the NRC Resident Inspector.
(This event was reported by River Bend Station on 6/10/09 at 0102 [EDT]. This update is being provided for the purpose of retracting that notification.) Subsequent investigation determined that the secondary containment door was left open for unknown reasons some time after 0800 on the morning of June 9. At the 1242 observation by the persons exiting the building, the door was open and it was left in that condition. However, a separate exterior door in that same passageway serves the security function, and it has been confirmed that, other than for routine access, the security door remained closed and locked during the time that the interior pressure boundary door was open. An engineering analysis has determined that the as-found condition did not defeat the function of secondary containment. While the security door is not air-tight, the maximum potential leakage past it under postulated accident conditions has been evaluated. An existing engineering calculation provides a means to determine the maximum size of a breach in the auxiliary building boundary such that the draw-down requirement prescribed by Technical Specifications is maintained. That calculation uses the additional flow area of an identified breach, in addition to the most recent test results of the standby gas treatment system (that system establishes and maintains a negative pressure in the building as part of the its design). Measurements taken on the door found that the potential flow area around it totaled 35 square inches. The current test results indicate that the standby gas treatment system can support the safety function of the auxiliary building with an analytical breach size of 230 square inches. As there is significant margin between the measured gap around the security door and the analytical value, this event was well bounded by the assumptions of the design basis of the building. As such, this event did not constitute a loss of the safety function of secondary containment. The licensee notified the NRC Resident Inspector. Notified the R4DO (D.Powers). |
| Where | |
|---|---|
River Bend  Louisiana (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+1.17 h0.0488 days <br />0.00696 weeks <br />0.0016 months <br />) | |
| Opened: | Mike Mcdaniel 01:02 Jun 10, 2009 |
| NRC Officer: | John Knoke |
| Last Updated: | Jun 29, 2009 |
| 45119 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |