ENS 47884
ENS Event | |
|---|---|
13:41 Mar 2, 2012 | |
| Title | Potential Degradation of Reactor Containment Electrical Penetration Seals |
| Event Description | During a review of environmental qualification records for reactor containment building electrical penetrations, six penetrations were identified that may not provide an adequate seal during worst case (Design Basis Accident (DBA)) conditions as required. These penetrations are through wall from the containment into the auxiliary building. The conditions that could cause degradation of the electrical penetration seals are not applicable to this operating mode. The station is currently in a refueling mode. This event was identified on March 2, 2012. The reportability was confirmed on May 1, 2012 at 1502 CDT.
The current penetration configuration has existed since the plant was built. The area of concern is that the Teflon connections may degrade under conditions of high radiation and high temperature during a DBA event. The licensee is investigating the extent of the condition and repair techniques. The licensee notified the NRC Resident Inspector.
On review of CR 2012-01947 by a new Project Manager, who was brought in as a subject matter expert on HELB/EEQ, and issue was identified with the 530 primary containment electrical penetration feed-throughs used for non-CQE devices. The CR [Condition Report] correctly notes that under the original accident testing, the Teflon seals failed, and water was noted leaking from these penetrations. On further review, the following was noted: Due to the design of the penetration feed-throughs, when the inboard Teflon seal fails (as it is expected to, due to high level of radioactivity in the primary containment, following a Loss of Coolant Accident (LOCA)), the atmosphere of the primary containment will be introduced to the penetration assembly, first through the failed seal or seals, and then through the weep hole between the inboard and outboard seals of the feed-through. This will put the same high level of radioactivity in direct contact with the outboard seals, resulting in the failure of its Teflon Seal. This would result in approximately 530 breaches of the Primary Containment during post LOCA conditions. The existing vendor analysis does not assume any contribution to the outboard seal exposure from the mixing of containment atmosphere with the penetration air after the failure of the inboard seal. This is probable, as each feed-through has a weep hole. Once the inboard seal fails, the penetration will be filled with containment atmosphere to equalize the pressure, which will bring the associated noble gas and Iodine fraction in proportion, into the penetration. The licensee notified the NRC Resident Inspector. Notified R4DO (Clark)
During the extent of condition review for CR 2012-01655 and 2012-01947 additional penetration feed-through assemblies were identified that are subject to the same failure mechanism. These penetrations are associated with the containment sump recirculation isolation valves, and also associated with the personnel air lock. The licensee notified the NRC Resident Inspector. Notified R4DO (Walker). |
| Where | |
|---|---|
Fort Calhoun  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| LER: | 05000285/LER-2012-002 |
| Time - Person (Reporting Time:+1445.08 h60.212 days <br />8.602 weeks <br />1.979 months <br />) | |
| Opened: | Erick Matzke 17:46 May 1, 2012 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Jul 17, 2012 |
| 47884 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Cold Shutdown (0 %) |
| After | Cold Shutdown (0 %) |
WEEKMONTHYEARENS 522012016-08-25T20:23:00025 August 2016 20:23:00
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