ML21146A056

Updated Nextera - Duane Arnold Derecho Event Aug 2020

ML21146A056
Person / Time
Site:	Duane Arnold
Issue date:	05/27/2021
From:	Joel Wiebe NRC/NRR/DORL/LPL3
To:
Wiebe J
References
Download: ML21146A056 (8)

Text

Duane Arnold Energy Center Loss of Offsite Power Due to Derecho May 27, 2021

Outline

• Duane Arnold Overview

• Summary of the Event

• Insights 2

DAEC Overview

• GE BWR/4 - Mark I Containment

• Rated Thermal Power 1,912 MW(t)

• Rated Net Electric Power

~615 MW(e) 3

Plant status prior to event

• Plant Status on August 10, 2020

- Reactor Power approximately 80% in order to maintain Drywell Temperature

- 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 4

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 5

Detailed Event Summary

• August 10 - 13:00 to 24:00

- Operations establishes a controlled cooldown to begin shutdown cooling

- Emergency Service Water strainer differential pressure alarm in Control Room Operations bypassed strainer in accordance with station procedures Emergency Service Water system stable operation throughout the event

- Systems restored to facilitate plant reliability Reactor Water Cleanup Spent Fuel Pool Cooling General Service Water

- Coordinate with ITC to prepare Switchyard for repairs 6

Detailed Event Summary

• August 11 - 02:30

- Operations established cold shutdown conditions

• August 11 - 11:26

- 161kV Vinton line is restored to the switchyard restoring off-site power

- Decision is made to perform a controlled evolution to restore power as the Emergency Diesel Generators are performing well

• 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 7

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 cooling towers did not impact the ability to safely shut the plant down, decay heat removal maintained through the Cedar River

• 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 8