ENS 41108
ENS Event | |
|---|---|
23:45 Oct 9, 2004 | |
| Title | Reactor Building Pressure Decreased Below Specified Limits |
| Event Description | The following information was obtained from the licensee via facsimile:
On October 9, 2004 at 1945 hrs. EST, Operators discovered that Oconee Nuclear Station Unit 3 Reactor Building pressure decreased to less than the limit specified in Oconee Selected Licensee Commitment 16.6.13, 'Additional Requirements to Support Low Pressure Injection (LPI) Operability'. This initial Reactor Building Pressure is used in the NPSH Analysis for the LPI Pumps in the Sump Recirculation phase of post-LOCA operation. In addition to effecting LPl, this condition also affects the Reactor Building Spray system. Engineering Evaluation performed on May 25, 2004 identified that guidance contained within the Selected Licensee Commitment may be inadequate and as a result, the Reactor Building Spray and Low Pressure Injection systems were determined to be Operable But Degraded/Nonconforming. For the interim, until appropriate changes are made to the Selected Licensee Commitment, Engineering recommended that Oconee Operations enter Technical Specification 3.0.3 any time that the limits of Selected Licensee Commitment 16.6.13 are exceeded. At the time of discovery, Oconee Unit 3 was cooling down for refueling outage. Unit 3 was in Mode 4 at approximately 235 degrees, 275 psig with one train of Reactor Building Spray deactivated per the Controlling Procedure for Unit Shutdown. When it was identified that the limits of Selected Licensee Commitment 16.6.13 were exceeded, Operations began increasing Oconee Unit 3 Reactor Building pressure. Oconee Unit 3 Reactor Building pressure was restored to within the limits of Selected Licensee Commitment 16.6.13 on October 9, 2004 at 2023 hrs. EST. Initial Safety Significance: The NPSH analysis for the Low Pressure Injection pumps in the sump recirculation phase of post-LOCA operation credit reactor building overpressure of 2.2 psig as permitted by a license amendment granted July 19, 1999 and supplemented August 19, 1999. Operation with Reactor Building pressure less than the limits specified in Selected Licensee Commitment 16.6.13 cannot ensure that 2.2 psig overpressure will always be available. Corrective Action(s): Actions were taken by Operations to restore Unit 3 Reactor Building pressure to within the limits of Selected Licensee Commitment 16.6.13. These actions were successful in restoring Reactor Building Pressure to within limits of Selected Licensee Commitment 16.6.13 approximately 38 minutes from time of discovery. The licensee has informed the NRC Resident Inspector.
This report is retracted based on the following: Event: Withdrawal of Event Number 41108 On October 9, 2004 at 1945 hrs. EST, Operators discovered that Oconee Nuclear Station Unit 3 Reactor Building (RB) pressure decreased to less than the limit specified in Oconee Selected Licensee Commitment (SLC) 16.6.13, 'Additional Requirements to Support Low Pressure Injection (LPI) Operability'. This initial RB Pressure (Containment overpressure) is credited in the NPSH Analysis for the LPI and RB Spray Pumps in the Sump Recirculation phase of post-LOCA operation. Engineering recommended that Oconee Operations enter Technical Specification 3.0.3 any time that the limits of SLC 16.6.13 are exceeded. Operations exited the condition after taking actions which raised RB pressure within the SLC limit. The ENS was reported as a loss of safety function under 50.72(b)(3)(v)(D) - ACCIDENT MITIGATION. Justification for conclusion that there was no loss of safety functions: An engineering analysis determined that, at the time of this event, the worst case post-LOCA RB sump temperature would be approximately 170F. From a July 19, 1999 SER for the license amendment which credited containment overpressure, the NRC Staff concurred that containment overpressure credit was only needed for sump temperatures above 208F. Therefore, for the conditions which existed during this event, there was adequate NPSH, and no reportable loss of safety function existed. The licensee informed the NRC Resident Inspector. Notified R2DO (Tom Decker). |
| Where | |
|---|---|
Oconee  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+1.1 h0.0458 days <br />0.00655 weeks <br />0.00151 months <br />) | |
| Opened: | Kevin Moses 00:51 Oct 10, 2004 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Nov 18, 2004 |
| 41108 - NRC Website
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Unit 3 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Shutdown (0 %) |
| After | Hot Shutdown (0 %) |