ENS 56054
ENS Event | |
|---|---|
01:08 Aug 18, 2022 | |
| Title | Safety System Inoperability |
| Event Description | The following information was provided by the licensee via email:
At 2108 EDT on August 17, 2022 the Division 2 Mechanical Draft Cooling Tower (MDCT) fans were declared inoperable due to failure of the over speed fan brake inverter. The brakes prevent fan over speed from a design basis tornado. The MDCT fans are required to support operability of the Ultimate Heat Sink (UHS). The UHS is required to support operability of the Division 2 Emergency Equipment Cooling Water (EECW) system. The Division 2 EECW system cools various safety related components, including the High Pressure Coolant Injection (HPCI) room cooler and Division 2 Control Center HVAC (CCHVAC) chiller. An unplanned HPCI inoperability occurred based on a loss of the HPCI Room Cooler. At the time of the event, Division I CCHVAC was inoperable for maintenance (but was running for a maintenance run) and the event caused an inoperability of Division 2 CCHVAC. This resulted in an inoperability of both divisions of CCHVAC. Failure of the Division 2 MDCT Fan brake inverter occurred due to a trip of the DC input breaker. The breaker was reset at 2128 EDT restoring Division 2 UHS Operability. This report is being made pursuant to 10CFR50.72(b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfilment of the safety function of structures or systems that are needed to mitigate the consequences of an accident based on a loss of a single train safety system and loss of both divisions of a safety system. The Senior NRC Resident Inspector has been notified
The following information was provided by the licensee via email: On 8/17/22 at 2108 EDT the Division 2 (Div. 2) mechanical draft cooling tower (MDCT) brake inverter input breaker tripped for an unknown cause. The result of the loss of power was the inoperability of the MDCT fan brakes which impacts the ultimate heat sink (UHS) (TS 3.7.2). The UHS cascades to the EECW (emergency equipment cooling water) (TS 3.7.2) which is a support system for Div. 2 CCHVAC (Control Cell) Chiller A/C system (TS 3.7.4). This resulted in the inoperability of the Div. 2 CCHVAC Chiller. The cause for the breaker to trip is an intermittent electrical transient. Immediate corrective action was to reset the breaker, and the long-term action is to implement a modification to mitigate susceptibility to voltage variations. Div. 1 has implemented this long-term mod and no unexpected trips have occurred to date. Div. 1 CCHVAC Chiller was previously inoperable from equipment issues which was repaired, and the unit was in service for a 24-hour confidence run. Although licensed personnel had not completed the administrative actions for documenting operability during the 24-hour confidence run to monitor parameters, the (post maintenance test) PMT related to the maintenance was already completed, which included a 4-hour run in accordance with surveillance 24.413.01, Div. 1 and Div. 2 Chilled Water Pump and Valve, to verify normal operation and motor current. These PMT's were completed prior to the identified inoperability of the Div. 2 UHS due to the tripped breaker on the brake power supply. At the time of the MDCT brake inverter trip, the Operations' Senior License and the Night Shift Manager were aligned that, although still operating as part of the 24-hour confidence run, the unit was in service and capable of performing its safety function, but the administrative tasks were not completed, the Limited Condition of Operation (LCO) sheet had not been cleared, and no log entries were made. Since the Div. 1 Chiller was, in fact, operable at the time of the trip of the breaker on the inverter, this would allow the use of Technical Specification (TS) 3.0.9 'Barriers'. Per Operations Department Expectation (ODE)-12 `LCOs' (standard guidance and expectations for preparing and implementing an LCO), Operations determined that the MDCT brakes are barriers to a tornado event and TS 3.0.9 could be utilized. By invoking TS 3.0.9, as long as all other supported systems in the other division are operable, Div. 2 supported systems relying upon the UHS can remain operable and the Automatic Depressurization System (ADS) and Reactor Core Isolation Cooling (RCIC) system can be used as backup to the High Pressure Coolant Injection (HPCI) system. Based on this information, there was no loss of safety function with CCHVAC A/C system or HPCI. Therefore, the NRC non-emergency 10CFR50.72(b)(3)(v)(D) report was not required and the NRC report 56054 can be retracted. The NRC Resident Inspector has been notified. Notified R3DO (Orlikowski) |
| Where | |
|---|---|
Fermi  Michigan (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+0.2 h0.00833 days <br />0.00119 weeks <br />2.7396e-4 months <br />) | |
| Opened: | Greg Miller 01:20 Aug 18, 2022 |
| NRC Officer: | Brian Lin |
| Last Updated: | Sep 8, 2022 |
| 56054 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |