ENS 40372
ENS Event | |
|---|---|
20:00 Dec 3, 2003 | |
| Title | Backward Installation of Containment Loop Seal Penetration Vacuum Breakers |
| Event Description | Vacuum breakers 1WL980 and 2WL980 are installed backwards. In their current orientation, the valves will not lift from their seats to break a siphon into the corresponding unit's Ventilation Unit Condensate Drain Tank (VUCDT).
The VUCDT input line is a 6-Inch pipe. There is a loop seal between the outboard containment isolation valve and the VUCDT. Since the VUCDT is vented to the auxiliary building environment, the purpose of the loop seal is to provide a barrier between the containment atmosphere and the auxiliary building atmosphere during normal unit operations. The purpose of the vacuum breaker is to prevent siphoning water out of the loop seal. In its current configuration, the vacuum breaker will not open. The loop seal is not needed to provide a barrier between the containment atmosphere and the auxiliary building atmosphere during a large break Loss of Coolant Accident (LOCA) because valves 1(2)WL867A and 1(2)WL869B will close on a Phase B containment isolation signal on high-high containment pressure (3.2 psig in containment, accounting for instrument error). During certain small break LOCAs, however, a high-high containment isolation signal may not occur, since pressure might not reach the setpoint. In this scenario, the loop seal is needed to isolate the containment atmosphere from the auxiliary building atmosphere. Given the size of the VUCDT inlet piping, the only mechanism that could form a siphon out of the loop seal is a large flow of water that would push the air out of the top of the loop seal. In this instance, a siphon could form and pull water out of the low point of the loop seal. If this were to occur, a vent path from the containment atmosphere to the auxiliary building atmosphere would be open. However, during normal operation, there is not sufficient flow into the tank to make this a plausible scenario. For a large break LOCA, containment pressure would rise quickly to the high-high setpoint; then the inoperable VUCDT loop seal would be isolated by its containment isolation valves. For smaller LOCAs, particularly, for a rod ejection accident resulting in a LOCA, containment pressure would rise slowly- from 2.81 psig (the pressure at which the loop seal isolation function would fail), until 3.2 psig (the maximum high-high containment pressure setpoint, accounting for instrument error), the inoperable loop seal would represent a containment leak path. The rod ejection accident does result in a high level of fuel clad failure; therefore, the unisolated containment leak path represents a source of release to the environment until such time as the high-high containment pressure setpoint is reached (if it is reached). The dose consequences associated with this potential leak path have not been evaluated. Upon discovery of the incorrectly installed vacuum breakers, the containment isolation valves associated with this penetration flow path were closed to isolate the path. The Unit 2 loop seal configuration has since been modified to correct this situation. The Unit 1 loop seal configuration will be modified prior to the completion of the current end of cycle 14 refueling outage. The incorrect installation of the vacuum breakers was identified on 11/03/03, and it is being investigated on how long this condition has existed. It is possible that it has existed since construction. The licensee will notify the NRC Resident Inspector, state and local regulatory agencies.
The subject EN was made on 12/3/03. Following additional review by the licensee, this event was determined to not meet the reportability requirements of 10 CFR 50.72. The event was determined to not result in a degraded or unanalyzed condition, as the consequences of the event were determined to be bounded by transients currently analyzed and described in the Updated Final Safety Analysis Report (UFSAR). In addition, the event did not represent a failure of structures, systems, or components utilized to control the release of radiological material or to mitigate the consequences of an accident. The licensee is therefore retracting the subject EN. The licensee notified the NRC Resident Inspector. Notified R2DO (P. Fredrickson) |
| Where | |
|---|---|
Catawba  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+-4.37 h-0.182 days <br />-0.026 weeks <br />-0.00599 months <br />) | |
| Opened: | Don Bradley 15:38 Dec 3, 2003 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | Jan 13, 2004 |
| 40372 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Catawba with 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded, 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | |
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