ML21146A183
| ML21146A183 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 05/27/2021 |
| From: | NextEra Energy Duane Arnold |
| To: | Joel Wiebe NRC/NRR/DORL/LPL3 |
| Wiebe, J. | |
| References | |
| EPID L-2020-PPM-0015 | |
| Download: ML21146A183 (8) | |
Text
Duane Arnold Energy Center Loss of Offsite Power Due to Derecho May 27, 2021
2 Outline Duane Arnold Overview Summary of the Event Insights
3 DAEC Overview GE BWR/4 - Mark I Containment Rated Thermal Power 1,912 MW(t)
Rated Net Electric Power
~615 MW(e)
4 Plant status prior to event Plant Status on August 10, 2020 Plant was operating normally Diesel Driven Fire Pump inoperable due to maintenance Dry cask storage campaign under way in the spent fuel pool Weather Forecast for August 10, 2020 National Weather Service Storm Prediction Center issued Moderate Risk Outlook At 11:38 the National Weather Service Issued a Severe Thunderstorm Watch for the DAEC area which was upgraded to a Severe Thunderstorm Warning at 12:02
5 Detailed Event Summary August 10 - 12:30 to 12:35 High sustained winds cause perturbation in the power lines feeding DAEC At 12:35 voltage drop is significant enough to automatically start the diesel generators, but they did not tie on to their respective buses as offsite power was still available August 10 - 12:49 Sustained high winds damage all power lines leading to the plant causing a loss of offsite power The plant responded as designed The reactor tripped and all control rods fully insert Emergency Diesel Generators (already operating) automatically connect to and power their respective essential buses Operators enter their emergency response procedures Notice of Unusual Event Reported to the NRC
6 Detailed Event Summary August 10 - 13:00 to 24:00 A plant cooldown to Mode 4 was initiated Emergency Service Water strainer differential pressure alarm in Control Room The B ESW strainer was bypassed in accordance with station procedures Both Emergency Service Water systems were stable throughout the event Systems restored to facilitate plant recovery Reactor Water Cleanup Spent Fuel Pool Cooling General Service Water Coordinate with ITC to prepare Switchyard for repairs
7 Detailed Event Summary August 11 - 02:30 The plant reached Mode 4, Cold Shutdown August 11 - 11:26 161kV Vinton line is restored to the switchyard restoring off-site power to available status August 11 - 12:15 Startup transformer is reenergized from offsite power August 11 - 13:12 to 13:24 Safety Bus A and B reenergized from offsite power August 11 - 16:00 Notice of Unusual Event Terminated
8 Insights There was never an impact to public health or safety The plant operated as designed when offsite power was lost The loss of the non-safety cooling towers did not impact the ability to safely shut the plant down or remove decay heat.
Operators responded in accordance with plant procedures Plant achieved safe shutdown Subsequent actions Assisted SRA and SRI with risk significance Engaged owners group to provide insights for generic impact Provided comments to NRC ASP report