ENS 51958
ENS Event | |
|---|---|
18:00 May 25, 2016 | |
| Title | Discovery of Non-Conforming Conditions During Tornado Hazards Analysis |
| Event Description | On May 25, 2016, during evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornados, Byron Station identified non-conforming conditions in the plant design such that specific TS equipment on both units is considered to not be adequately protected from tornado missiles. Each of the following reportable conditions is postulated by tornado missiles entering openings through the wall that separates the Auxiliary Building and the Turbine Building:
The following items could be impacted by tornado missiles entering the 0A and 0B [common] MCR [main control room] turbine building intake openings: Main control room pressurization, main control room ductwork and dampers, chilled water to the VC [control room ventilation] coils, main control room radiation monitors. The following items could be impacted by tornado missiles entering the Division 11 and 21 MEER [miscellaneous electrical equipment rooms] rooms: Exhaust from the MEER (affects room cooling and MCR pressure), exhaust from a battery room, conduits and cabinets associated with the battery chargers and DC bus. The following items could be impacted by tornado missiles entering the Division 12 and 22 MEER rooms: Exhaust from the MEER (affects room cooling and MCR pressure), MEER supply fan and ductwork, battery room exhaust, and the instrument inverter cabinets. The RWST [refueling water storage tank] roof access opening Bilco hatch is fabricated from sheet metal that is not designed to prevent all postulated tornado missiles from entering the tank. The tank pressure boundary is 24" thick concrete and is designed to withstand an external tornado missile impact. Thus a missile that enters the tank will not adversely impact the tank pressure boundary. The following items could be impacted by tornado missiles entering the RWST roof access: The 6" RWST recirculation pipe, 3" overflow pipe, and 24" suction pipe. This piping is located inside the tank and they are approximately 130 degrees around the tank away from the hatch opening. This condition creates a potential LOSF [loss of safety function] with the Byron Essential Service Water Cooling Towers (UHS) [ultimate heat sink] with the discovery that the power and control cables to four of eight cooling tower fans can be damaged by tornado missiles penetrating through wall openings. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v)(D) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. These conditions are being addressed in accordance with EGM 15-002 and DSS-ISG-2016-01 [enforcement discretion and interim guidance documents]. The licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
Byron  Illinois (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+-2 h-0.0833 days <br />-0.0119 weeks <br />-0.00274 months <br />) | |
| Opened: | Jim Lynde 16:00 May 25, 2016 |
| NRC Officer: | Howie Crouch |
| Last Updated: | May 25, 2016 |
| 51958 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Byron 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 | |
WEEKMONTHYEARENS 572112024-07-07T19:40:0007 July 2024 19:40:00
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