ENS 52321
ENS Event | |
|---|---|
05:21 Oct 27, 2016 | |
| Title | Loss of Charging and Letdown Systems from the Reactor Coolant System |
| Event Description | At 0021 [CDT] on 10/27/16, Waterford 3 (WF3) experienced a loss of the charging and letdown systems from the Reactor Coolant System (RCS). Technical Specification (TS) 3.0.3 was entered due to the loss of all three charging pumps. Charging Pump AB was restored and aligned to replace Charging Pump A and WF3 exited TS 3.0.3 at 0055 on 10/27/16.
The cause of the loss of charging pumps was due to Refueling Water Storage Pool to Charging Pumps Suction Isolation, CVC-507, not opening as expected following a loss of Static Uninterruptible Power Supply (SUPS) 014AB during electrical troubleshooting. The cause of CVC-507 not opening is being investigated. Power was restored to SUPS 014AB at 0022. WF3 is currently stable in Mode 3 with decay heat being removed by the Steam Bypass Control System. Pressurizer Level was maintained throughout the event. WF3 was previously shut down for reasons unrelated to this event. The NRC Resident Inspector has been notified. Valve CVC-183 closed when the power supply was lost. CVC-183 is the Volume Control Tank outlet isolation valve. Waterford 3 will remain in mode 3 until the issue has been corrected.
This is a retraction of EN 52321 which was reported as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Non-Emergency on October 27th at 0826 EST. At 0021 [EST] on 10/27/16, Waterford 3 (WF3) experienced a loss of the charging and letdown systems due to an electrical transient on a Static Uninterruptable Power Supply that was being worked under a maintenance work order. The cause of the loss of charging pumps was due to Refueling Water Storage Pool to Charging Pumps Suction Isolation, CVC-507, not opening as expected following a loss of Static Uninterruptible Power Supply (SUPS) 014AB. Both operating charging pumps automatically secured due to low suction pressure trips as designed. Post event investigation determined that a relay that had failed affected only the normal suction path isolation valves to the charging pumps and did not impact the safety related flow path that is required during a Safety Injection Actuation Signal (SIAS). Had an SIAS occurred during the period when no active suction path was aligned, the low pressure trip would have been blocked and the pumps selected to start on an SIAS would have auto started. The SIAS would have aligned the Boric Acid Make-up system for Emergency Boration. This would have resulted in the Charging Pumps being aligned to take suction from the Boric Acid Make-up pumps and/or Boric Acid Gravity Feed valves. A function of the charging systems is to inject concentrated boric acid into RCS upon an SIAS. As discussed in FSAR Section 6.3.3.3.1, the injection flow from the charging pumps is not credited in the small break LOCA analysis. Charging is however credited for natural circulation cooldown without letdown in order to meet the safe shutdown requirements of NRC Branch Technical Position (RSB) 5-4. This analysis assumes that the charging source is initially Boric Acid Makeup Tanks followed by Refueling Water Storage Pool. Both sources were available. The charging system was fully capable of performing its safety function following the relay failure. The charging pumps remained capable of starting on an SIAS and the flow path from the Boric Acid Management system remained operable. In addition the flow path from the RWSP was not affected since the outlet isolation valve could be manually opened. The NRC Resident Inspector has been notified. Notified the R4DO (Taylor). |
| Where | |
|---|---|
Waterford  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:+3.08 h0.128 days <br />0.0183 weeks <br />0.00422 months <br />) | |
| Opened: | Ryan Tregre 08:26 Oct 27, 2016 |
| NRC Officer: | Jeff Herrera |
| Last Updated: | Nov 23, 2016 |
| 52321 - NRC Website
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Unit 3 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Standby (0 %) |
| After | Hot Standby (0 %) |