ML22061A104

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4A-4_of_4-Leech-DAEC_LIC504_for_PFHA_Workshop-SLIDES
ML22061A104
Person / Time
Site: Duane Arnold NextEra Energy icon.png
Issue date: 02/15/2022
From: Matthew Leech
NRC/NRR/DRA
To: Thomas Aird
NRC/RES/DRA
Aird, Thomas - 301 415 2442
Shared Package
ML22061A095 List:
References
Download: ML22061A104 (13)
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Text

Duane Arnold Derecho PFHA Research Workshop - 2022 Matthew Leech Reliability and Risk Analyst Office of Nuclear Reactor Regulation Division of Risk Assessment 1

Overview Re-cap of the event and its risk significance Description of the LIC-504 Risk Insights and Sharing the Operating Experience (OE) 2 2

Re-cap of the Event

  • A Loss of Offsite Power Occurred - and was not restored for 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />
  • The plant scrammed offline and shutdown safely, power was provided by their EDGs until offsite power was restored
  • Transmission towers knocked down and damage occurred to a standby transformer in the switchyard

- complicated offsite power recovery

  • One FLEX building was damaged, but equipment inside remained functional.
  • Hours later ESW was challenged by debris clogging the strainers, one train of ESW and its EDG was declared INOP but still functional 3 3

Risk Significance of DAEC event

- Why was the risk so high?

Single unit site without the ability to crosstie power from another unit No Station Blackout diesel It took about 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore offsite power Ultimate Heat Sink and Service Water Intake were vulnerable to debris generated by derecho Another insight was that the risk was significantly improved due to FLEX.

4

LIC-504

  • The NRCs LIC-504 process is a risk-informed decisionmaking process that the NRC uses for emerging issues.
  • One of the recommendations from regional feedback of the DAEC event was that the NRC should evaluate the event for any generic implications to the nuclear fleet.

- Is there a population of plants that could have unacceptable risk?

- Are there risk insights that would be useful to share?

  • The NRC decided to perform a LIC-504 in October of 2020.

5

The LIC-504 Analysis vs the ASP LIC-ASP 504 Conducted by the office of Nuclear Reactor Regulation Conducted by Office (NRR) examined of Research focuses several plants by on examining the risk running a similar from the specific scenario to the one event for the Duane Duane Arnold Arnold Plant. experienced during the derecho and examining the risk results.

6

LIC-504 in Two Main Steps

  • The first step of the LIC-504 analysis is to determine if the risk from the issue warrants any immediate action:

- Do any plants need to be shutdown immediately?

- Are there any immediate compensatory actions or orders that need to be issued?

  • The second step involves a more detailed analysis to assess the risk and develop recommendations.
  • Its also used to formally document how the NRC arrives at a decision.

7 7

Getting Started with the LIC-504

  • To get started the NRC took a population of plants that had the same generic traits as DAEC.

- Single unit sites

- No station blackout diesels

- Potentially vulnerable ultimate heat sinks*

  • Plants were chosen to gain a representative look at the overall fleet vulnerability to a similar derecho using the characteristics identified as being risk significant from the event at DAEC.
  • First step concluded that there was no immediate safety issue.

8

Second Step of the LIC-504

  • Eight different plants were chosen for the analysis.
  • They were a representative population of plants: PWR Westinghouse, PWR Combustion Engineering, BWR4 plants, and a BWR6.
  • They were evaluated for the same conditions present during the DAEC derecho:

- A weather-related loss of offsite power that was not recoverable for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />

- Challenge to the ESW system 9

Second Step of the LIC-504 (Cont.)

  • The second analysis differs from the first in that it was a more detailed analysis and designed to increase accuracy and reduce conservatism.

- Provided credit for FLEX actions and equipment

- More scrutiny and detail looked at each plants service water modeling

- Lessons learned from the DAEC ASP analysis was applied to this phase of the analysis.

10

LIC-504 Risk Insights

  • When the risk analysis for the LIC-504 was completed some common plant design attributes were found to have an impact on plant risk.

- Plants with extra diesel generators not dependent on service water cooling had significant benefit

- Plants that had the ability to bypass a degraded strainer had improved risk

- Some plants have alternate cooling strategies to their diesel generators in case ESW isnt available (like fire protection water for instance) and that helps risk

- Plants that have ESW traveling screens on an emergency power source that will still be available during a loss of offsite power have improved risk

- FLEX equipment and strategies, demonstrated a significant safety benefit from this type of event 11

LIC-504 Follow Up Actions Issued internal OE Held a public communication with webinar with the more information, industry to discuss the including updated ASP, the LIC-504 and risk insights from the the results.

LIC-504.

Issued an Information Notice to share the OE, the results of the ASP &

the LIC-504 & share the risk insights with the industry.

12

References and Contact Info

  • The Duane Arnold Energy Center LIC-504 recommendations:

ML21078A127

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