ENS 54338
ENS Event | |
|---|---|
07:07 Oct 18, 2019 | |
| Title | En Revision Imported Date 11/20/2019 |
| Event Description | EN Revision Text: INADVERTENT OPENING OF MAIN TURBINE BYPASS VALVES POTENTIONALLY AFFECTED SAFE SHUTDOWN CAPABILITY
At 0207 [CDT], the Bypass Electro-Hydraulic Control (EHC) system was secured for planned maintenance. When the Bypass EHC pumps were secured, both of the Main Turbine Bypass Valves unexpectedly opened to approximately 4.5 percent. Plant parameters indicated no impact to Turbine Control Valve position, Reactor Pressure, Turbine First Stage Pressure, or Main Steam Line flows. There were no other abnormal indications noted. With the Turbine Bypass Valves partially open, there is a potential to affect instrumentation that trips on high Turbine First Stage Pressure. Therefore, this event is being reported as a potential loss of Safety Function. At 0256, the Bypass EHC system pumps were restored and the Turbine Bypass Valves Closed. No radiological releases have occurred due to this event from the unit. The licensee has notified the NRC Resident Inspector.
This Event Notification was contingent on the Main Turbine Bypass Valves opening which resulted in the inoperability of Turbine First Stage Pressure monitoring instrumentation. A detailed review of system design and plant parameter trends has confirmed that the Main Turbine Bypass Valves remained closed for the duration of the event, permitting the instrumentation systems dependent on accurate Turbine First Stage Pressure to perform their respective design and licensing basis functions. Valve drift in the open direction was observed by position indication when hydraulic control pressure was removed. However, the valves were at an over-travel closed position prior to the event allowing the valves to settle at a position where an internal spring could provide closing force to the valve disc. Multiple plant parameter trends including Turbine First Stage Pressure, Reactor Pressure, Main Steam Line flows, and Main Turbine Bypass Valve discharge line temperatures indicate that the Main Turbine Bypass Valves remained closed for the duration of the event. The licensee has notified the NRC Resident Inspector. Notified R4DO (O'Keefe). |
| Where | |
|---|---|
River Bend  Louisiana (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+3.63 h0.151 days <br />0.0216 weeks <br />0.00497 months <br />) | |
| Opened: | David Dabadie 10:45 Oct 18, 2019 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Nov 19, 2019 |
| 54338 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (75 %) |
| After | Power Operation (75 %) |