ML22061A106

4A-2_of_4-Hanna-Duane_Arnold-rev0-SLIDES

ML22061A106
Person / Time
Site:	Duane Arnold
Issue date:	02/18/2022
From:	John Hanna Division Reactor Projects III
To:	Thomas Aird NRC/RES/DRA
Aird, Thomas - 301 415 2442
Shared Package
ML22061A095	List: ML22061A099 ML22061A104 ML22061A105 ML22061A106 ML22061A107 ML22061A116 ML22061A137 ML22061A138
References
Download: ML22061A106 (20)

Text

The NRCs Regional Response to the Duane Arnold Derecho John David Hanna Senior Reactor Analyst US Nuclear Regulatory Commission, Region III Office Division of Reactor Projects February 18, 2022

Overview of the Presentation

• General Information

• Regional response to the event

- Immediate event response

- Management Directive 8.3 assessment

- Other regional actions

• Risk insights from this event

• Comments/Questions 2

General Information

• My Background and Experience 3

Duane Arnold derecho

• 10 August 2020 storms/high winds hit large sections of Midwest US with little warning

• Widespread destruction including damage to the electrical grid occurred 4

DAEC Immediate Event

Response

• Operators performed well

• NRC inspectors responded to the site

- On-site within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />

- Rapid assessments of immediate actions, plant stability, SM, DID, etc.

• Rapid risk assessment was done to inform the inspectors event response, i.a.w., what should they review?

• Initial response to the site was supplemented with regional inspectors with EP and Ops expertise

• The storm had impacts on IE and MS and lesser effects on BI and EP 5

Duane Arnold (continued) 6

DAEC Management Directive 8.3 Assessment

• RIII immediately realized the PRA risk from the event was very high.

• CCDP was approx. 2E-4 to 2E-3 range.

• MD 8.3 process was entered.

• RIII performed a focused baseline inspection under IP 71153 and supplemented the RIO with other inspectors (ML20314A150), but did not perform a Special Inspection.

7

MD 8.3 Assessment -

Continued ICCDP Results Given Various 'B' ESW Strainer Failure Probabilities 6.00E-03 5.00E-03 4.00E-03 3.00E-03 IIT AIT 2.00E-03 1.00E-03 0.00E+00 0.00E+00 1.00E-01 2.00E-01 3.00E-01 4.00E-01 5.00E-01 6.00E-01 Series1 Series2 Series3 Linear (Series1) Linear (Series2) Linear (Series3) 8

Regional Response -

Miscellaneous Items

• Requested that the LIC-504 Integrated Risk-Informed Decisionmaking Process for Emergent Issues process be entered

• Risk analysis paper written looking at commonalities between several events involving external hazards, including DAEC

• Supported the ongoing revisions to the MD 8.3 and IMC-0309, Reactive Inspection Decision Basis for Reactors 9

Risk Insights - what are these events telling us?

• Sunny day events can happen with little warning but relatively high-risk impact

• Synergistic effects are non-trivial

• Operator actions may be required in order to respond to the event which will initially INCREASE the risk during the event

• Small changes in the weather could have had disproportionately large impacts on the event 10

Questions or Comments?

11

Backup Slides 12

References &

Additional Material

• Paper Characterizing Previously Unknown Dependencies in Probabilistic Risk Assessment Models of Nuclear Power Plants, ML21103A355

• NRC Inspection Report - ML20314A150

• MD 8.3 assessment document ML21022A415

• Non-Concurrence document ML21022A418

• John Hanna - John.Hanna@nrc.gov 13

Back up slides - DAEC Storm damage from the derecho -

State of Iowa, 10 August 2020 14

Back up slides - DAEC Pictures of damage to Duane Arnold Energy Center due to derecho - 10 August 2020 15

Back up slides - DAEC Cooling Towers North FLEX Building 69 kV Electrical Transmission Yard Tower

Back up Slides - DAEC Plant Automatic Response

• Immediate Response

• Generator Trip, Turbine Trip, Rx Scram

• Diesel output breakers immediately closed to safety related busses; no loss of RPS; no Group I Isolation

• 2 Safety Relief Valves lifted for approximately 10 sec

• Reactor Water Level decreased to Level 2, Lo-Lo Level

• HPCI and RCIC started

• Reactor water level restored to Level 8, High Level Trip

• HPCI and RCIC Tripped (as designed)

• Two Minutes Later:

• Plant parameters were stable

• A and B EDGs supplying power to their respective safety busses

Back up Slides - how do these events compare to others?

Risk Significance 2002 Davis Besse vessel head leakage:

6x10-3 of DAEC Derecho compared to 2020 Duane Arnold Derecho:

8x10-4 other High SWGR Fires (2010 Robinson, 2011 Fort Calhoun):

Profile US Events 4x10-4 since 2000 Earthquake induced LOOP (2011, North Anna Unit 1):

(Conditional Core 3x10-4 Damage Trans. & breaker failure induced LOOP (2012 Byron):

Probabilities) 1x10-4

Where is LOOP/SBO risk highest and/or where does FLEX make the most difference?

• Single unit sites

• Fewer EDGs +/or no SBO EDG

• No crosstie capability at multi-unit sites

• Absence of low leakage RCP seals

• Small DC batteries

• Higher LOOP likelihood

• Higher (LOOP/SBO or electrical) risk from internal events

General Info- Reactor Safety Cornerstones 20