ML20080M158

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PFHA-2020-3B-3-Vossmar_Stafford-2019_CNS_FCS_Flooding ADAMS Version
ML20080M158
Person / Time
Site: Cooper, Fort Calhoun  Omaha Public Power District icon.png
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
Shared Package
ML20080M135 List:
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

  • Cooper (CNS) Flood
  • Fort Calhoun (FCS) Flood
  • Area Flooding Damage
  • Unanticipated Aftereffects
  • Key Lessons Learned 2

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 - 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

  • 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.

8

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

Before (Looking North) 11

After (Looking North) 12

West 13

14 Governor Visit 15

National Guard 16

Fort Calhoun Station 2019 - Event

  • Unit permanently defueled
  • Entered Abnormal Flood Procedure 3/13/19
  • 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 17

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

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

23

Flood Aftereffects - Groundwater

  • 10/2/19 - alarms for ground on Div 1 125V DC bus.
  • Elevated groundwater levels exposed deficient flood penetration seals.

24

Flood Aftereffects - Heat Sink

  • 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

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 28

Questions?

29