ML22140A336: Difference between revisions

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{{#Wiki_filter:WeatherRelated Loss of Offsite Power Trends and Risk Insights Chris Hunter Office of Nuclear Regulatory Research Division of Risk Analysis Performance and Reliability Branch
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Overview
* Evaluations of recent events caused by severe weather conditions have provided important risk insights.
* Severe weather events are most likely to lead to losses of offsite power (LOOPs).
  - A review of current LOOP data and trends can be used to evaluate whether more extreme weather events affect nuclear power plants.
* Key Questions
  - Are the frequency and duration of weatherrelated LOOPs changing?
  - What do the results and insights from recent weatherrelated LOOPs tell us?
 
LOOP Data and Trends LOOP Frequencies
* The overall frequency of all LOOPs is decreasing over the past 15 years (2006-2020).
* There is no statistically significant trend for weatherrelated LOOPs during the past decade (2011-2020).
 
WeatherRelated LOOPs (2006-2020)
Power Ops/ Duration Event Date    Plant          Cause Shutdown  (hours) 8/10/2020 Duane Arnold      Hurricane  Power Ops    25.3 8/3/2020  Brunswick 1      Hurricane  Power Ops    14.0 3/13/2018    Pilgrim    Snow and Wind  Shutdown    12.0 10/8/2016 Shearon Harris    Hurricane  Shutdown      7.4 1/27/2015    Pilgrim    Snow and Wind  Power Ops    0.03 2/8/2013    Pilgrim    Snow and Wind  Power Ops    21.0 10/29/2012  Oyster Creek    High Winds  Shutdown    14.4 4/27/2011 Browns Ferry 1    Tornado    Power Ops    0.03 4/27/2011 Browns Ferry 2    Tornado    Power Ops    0.03 4/27/2011 Browns Ferry 3    Tornado    Power Ops    0.03 4/16/2011    Surry 1        Tornado    Power Ops      5.1 4/16/2011    Surry 2        Tornado    Power Ops      5.1 8/19/2009  Wolf Creek      Lightning  Power Ops    2.2 2/24/2007 Duane Arnold        Ice      Shutdown    17.5
 
LOOP Duration
* The duration of all LOOPs showed an increasing trend during the 1997-2020 period.
* There is no statistically significant trend for the duration of weatherrelated LOOPs during this same period.
 
Durations by LOOP Type Parameter        Plant Switchyard  Grid Weather LOOP event count              16      32      17    19 Mu (µ)                        0.70    0.44    0.35  1.37 Standard error of µ          0.53    0.29    0.33    0.51 Sigma ()                    2.13    1.66    1.36    2.24 Standard error of          0.38    0.21    0.23    0.36 Fitted median, hour          2.00    1.56    1.41    3.94 Fitted mean, hour            19.17    6.21    3.55  48.23 Fitted 95th percentile, hour 66.10  24.03    13.19 156.51 Error factor                32.97  15.42    9.33  39.70
 
Recent Events Brunswick LOOP during Hurricane Isaias
* Stormgenerated debris resulted in a LOOP to Unit 1 in August 2020.
* The LOOP lasted approximately 14 hours.
* The mean conditional core damage probability (CCDP) was 2x105.
  - LOOP transient scenarios dominated risk; station blackout (SBO) risk was minimal.
 
Duane Arnold LOOP during Derecho
* Severe winds (100-130 miles per hour) during a derecho resulted in a LOOP in August 2020.
  - The storm caused severe damage to nonsafetyrelated cooling towers and minor damage to a few buildings.
  - The high winds also resulted in increased debris loading to the essential service water system and resulted in a clogged strainer.
* The LOOP lasted approximately 25 hours.
* The mean CCDP was 8x104.
  - SBO scenarios were the dominant risk contributors.
 
Waterford LOOP during Hurricane Ida
* The high winds, heavy rain, and localized flooding resulted in damage to both sources of offsite power.
* The supplemental diesel generator experienced a failed battery due to rapid discharge after the LOOP occurred.
* The LOOP lasted approximately 53 hours.
* The preliminary analysis indicates a mean CCDP from mid 1x104 to low 1x103.
  - SBO scenarios were the dominant risk contributors.
 
General Risk Insights
* SBO risk is dominant for two emergency diesel generator (EDG) plants for longduration LOOPs.
  - Multiunit sites with shared EDGs typically have much lower risk.
  - Having an EDG not included in the same commoncause component group as the other safetyrelated EDGs can be a significant benefit.
  - Modeling of commoncause failures across the units introduces significant uncertainties because the data do not support this modeling.
* LOOP duration has significant impact on plants that have dominant SBO risk.
* FLEX credit can have significant impact on the results.}}

Latest revision as of 00:43, 18 November 2024

Hunterc-hv-th21
ML22140A336
Person / Time
Issue date: 03/08/2022
From: Christopher Hunter
NRC/RES/DRA
To:
Office of Nuclear Reactor Regulation
References
Download: ML22140A336 (14)
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