ML20080M158

PFHA-2020-3B-3-Vossmar_Stafford-2019_CNS_FCS_Flooding ADAMS Version

ML20080M158
Person / Time
Site:	Cooper, Fort Calhoun
Issue date:	02/21/2020
From:	Mike Stafford, Patricia Vossmar Nebraska Public Power District (NPPD), Omaha Public Power District
To:	Office of Nuclear Regulatory Research
T. Aird
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References
Download: ML20080M158 (29)

Text

2019 Flood at Cooper Nuclear Station and Fort Calhoun Station February 21, 2020 Patricia Vossmar - Cooper SRI (Former)

Mike Stafford - Cooper RI

Agenda 2

• Cooper (CNS) Flood

• Fort Calhoun (FCS) Flood

• Area Flooding Damage

• Unanticipated Aftereffects

• Key Lessons Learned

Flood Prediction - CNS 3

Licensee Preparation

• Flood Plan

• Schedule Scrub

• Survey Levees

• Sandbagging

• River Monitoring 4

Licensee Preparation

• Staged Primary and Secondary Flood Barriers

• Staged FLEX equipment

• Obtained FHRR Crane 5

CNS Event

• 3/15 am - CNS staffed OCC.

• 3/15 am - Notification of Unusual Event (NOUE)

Declared at 899.1; NRC stayed in Normal Mode.

• 3/15 pm - river level rose to 901.5 at CNS and remained stable for a few days.

6

Early Site Flooding 7

CNS Event - Plant Access Road 8

• 3/16 am - Shuttling of employees across access road required due to road flooding caused by overtopping of North plant levee. (901.5)

• 3/16 am - CNS considers shutting down.

CNS Event - Plant Access Road 9

CNS Event

• 3/16 pm - several large levee breaches upstream; river begins to lower ~2in/hr.

• 3/16 pm - With levee relief, CNS decides not to shut down.

• 3/16 - River level hovers at or below 901.5 feet for remainder of event.

• 3/24 1601 - Exited NOUE.

10

11 Before (Looking North)

After (Looking North) 12

West 13

14

Governor Visit 15

National Guard 16

Fort Calhoun Station 2019 - Event 17

• Unit permanently defueled

• Entered Abnormal Flood Procedure 3/13/19

• Staffed OCC

• Water Above Site Grade 3/15/19

• Transferred SFP loads from 161kV to EDG on 3/15-3/16/19

• Restored offsite power 3/21

FCS 2019 - Onsite Transit 18

19

FCS 2019 -DG Fuel Oil tank Water Intrusion 20

Post Flooding Damage - Roads 21

Flooding Damage - Roads 22

Semi trucks on levee near CNS 23

• Road Closures and poor GPS directions led two semi trucks to inadvertently drive and get stuck on the levee near CNS.

Flood Aftereffects - Groundwater

• 10/2/19 - alarms for ground on Div 1 125V DC bus.

• Groundwater inleakage onto Reactor Core Isolation Cooling.

• Elevated groundwater levels exposed deficient flood penetration seals.

24

Flood Aftereffects - Heat Sink

• 12/8/19 - CNS discovers one division of Service Water discharge pipe plugged

• Determines likely cause is silting

• 12/12 - CNS begins dredging discharge

• NRC sends Special Inspection Team 25

Spencer Dam - Nebraska (Before) 26

Spencer Dam - Nebraska (After) 27

28 Key Lessons Learned

• Flood vulnerabilities difficult to predict

- Sandbags, sump pumps (defense-in-depth key)

- DG Fuel Oil flange connection protection

- Conduit and cable vault in-leakage likely

- Elevated groundwater in-leakage into plant

- Levees may overtop or fail

• Must prepare for Latent flood aftereffects

- Groundwater in-leakage; silting of heat sink

• Highly complex flood strategies introduce additional vulnerability

Questions?

29