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State-of-the-Art Reactor Consequence Analyses (SOARCA)

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Presentation on theme: "State-of-the-Art Reactor Consequence Analyses (SOARCA)"— Presentation transcript:

1 State-of-the-Art Reactor Consequence Analyses (SOARCA)
OFFICIAL USE ONLY State-of-the-Art Reactor Consequence Analyses (SOARCA) Regulatory Information Conference March 11, 2008

2 Agenda Opening Remarks and Overview Sequence Selection
OFFICIAL USE ONLY Agenda Opening Remarks and Overview Sequence Selection Accident Mitigation Accident Analysis Emergency Preparedness Comments

3 OPENING REMARKS Dr. Farouk Eltawila, Director
OFFICIAL USE ONLY OPENING REMARKS Dr. Farouk Eltawila, Director Division of System Analysis Office of Nuclear Regulatory Research

4 OFFICIAL USE ONLY Overview State-of-the-art more realistic evaluation of severe accident progression, radiological releases and offsite consequences Integrated and consistent analysis of pilot plants (Peach Bottom, Surry) for important sequences (e.g., SBO, ISLOCA) subject to probabilistic considerations Account for plant design and operational improvements, credit existing and newly developed mitigative measures and site specific emergency plans

5 Motivation Plant Design and Operations Severe Accident Phenomenology
OFFICIAL USE ONLY Motivation Plant Design and Operations Severe Accident Phenomenology Emergency Planning 1982 Sandia Siting Study Total CDF: 1x10-4/yr to 1x10-5/yr Alpha Mode Failure Direct Containment Heating Conservative Accident Progression - Large and fast radiological release Generic (including bounding) EP modeling 2008 SOARCA Improved Plant Performance 1x10-5/yr to 1x10-6/yr Additional Mitigative Measures Alpha Mode Failure is remote & speculative DCH resolved Realistic accident progression analysis Improved Site Specific EP Modeling

6 EMERGENCY PREPARDNESS
OFFICIAL USE ONLY SOARCA PROCESS INITIAL SEQUENCE SELECTION MELCOR ANALYSIS SOURCE TERM MITIGATIVE MEASURES ANALYSES DETERMINE CONTAINMENT SYSTEMS STATES STRUCTURAL SITE-SPECIFIC INFORMATION MACCS2 RESULTS METEOROLOGY EMERGENCY PREPARDNESS

7 OFFICIAL USE ONLY SEQUENCE SELECTION
Richard Sherry, Senior Risk Analyst Division of Risk Analysis Office of Nuclear Regulatory Research

8 Sequence Selection Process
OFFICIAL USE ONLY Sequence Selection Process Full Power Operation Internal Initiated Events SPAR model results Comparison with licensee PRA Discussions with licensee staff External Initiated Events Review of prior analyses IPEEE NUREG-1150

9 OFFICIAL USE ONLY Sequence Groups Group core damage sequences that have similar initiating events, Sequence timing and equipment unavailability Initial Screening CDF Initiating Events CDF > 1E-7 Sequences with CDF > 1E-8 Sequences Evolution – Identify and evaluate dominant cutsets (~90% of CDF) Scenario grouping Sequences refined by external events and mitigative measures

10 OFFICIAL USE ONLY Final Sequence Groups Screen in sequence groups with group CDF > 10-6/RY - or - Containment bypass sequence groups with group CDF > 10-7/RY

11 Containment Systems Availability
OFFICIAL USE ONLY Containment Systems Availability Availability of engineered systems that can impact post-core damage containment accident progression, containment failure and radionuclide release and not considered in Level 1 core damage SPAR model Surry and Peach Bottom Availability of containment systems based on support system status Sequoyah Availability of containment systems determined using extended Level 1 SPAR model

12 Sequence Groups Peach Bottom Atomic Power Station
OFFICIAL USE ONLY Sequence Groups Peach Bottom Atomic Power Station Peach Bottom Internal Events None (Dominant below the screening threshold was SBO) Peach Bottom External Events (Seismic) Long Term SBO (RCIC available early) (1x10-6 to 5x10-6 /yr)

13 Sequence Groups Surry Power Station
OFFICIAL USE ONLY Sequence Groups Surry Power Station Surry Internal Events ISLOCA (7x10-7/yr) SGTR (5x10-7/yr) Surry External Events (Seismic) Long-term SBO (TD-AFW available early) (1x10-5 to 2x10-5/yr) Short-term SBO (TD-AFW failed) (1x10-6 to 2x10-6/yr)

14 OFFICIAL USE ONLY MITIGATIVE MEASURES
Robert Prato, Senior Program Manager Division of System Analysis Office of Nuclear Regulatory Research

15 Mitigative Measures Analysis
OFFICIAL USE ONLY Mitigative Measures Analysis Qualitative, sequence-specific systems and operational analyses Licensee identified mitigative measures from EOPs, SAMGs Other applicable severe accident guidelines Input into the MELCOR analyses

16 Mitigative Measures Analysis Process
OFFICIAL USE ONLY Mitigative Measures Analysis Process Consider all mitigative measures Conduct sensitivity analyses to assess the effectiveness of different mitigative measures

17 Mitigative Measures Analysis Process
OFFICIAL USE ONLY Mitigative Measures Analysis Process For each sequence grouping, identify the potential failure mechanisms and determine available mitigative measures Perform a system and an operational analysis based on the initial conditions and anticipated subsequent failures Determine the anticipated availability, capability and the time to implementation (e.g., TSC activation) MELCOR used to determine the effectiveness of the mitigative measures based on capability and estimated time of implementation

18 Structural Analyses Evaluate the behavior of containment
OFFICIAL USE ONLY Structural Analyses Evaluate the behavior of containment structures under unmitigated severe accident conditions to predict the following performance criteria at the selected sites: Functional Failure Pressure - Leakage Structural Failure Pressure - Rupture Develop Leakage Rate and/or Leakage Area as a Function of Internal Pressure Peach Bottom “Mark I – Steel Containment” Surry “Reinforced Concrete Containment”

19 Peach Bottom LTSBO Effectiveness of Mitigative Measures
OFFICIAL USE ONLY Peach Bottom LTSBO Effectiveness of Mitigative Measures Batteries were available for ~ 4 hours RCIC automatically started and prevented loss of RCS inventory Operator, by procedure, depressurizes at ~ 1 hr Portable power supply ensures long-term DC to hold SRV open and provide level indication (allow management of RCIC)

20 OFFICIAL USE ONLY Surry LTSBO Dominant containment dominant failure mode is leakage from cracking around the Equipment and/or Personnel Hatches Effectiveness of Mitigative Measures Batteries were available for ~ 8 hours TDAFW Pump automatically starts to makeup to the SGs SG PORVs operable on DC power for 100 F/hr RCS cooldown Portable power supply ensures long-term DC to provide level indication (allow management of TDAFW) Portable pump provided make up for RCP seal cooling

21 OFFICIAL USE ONLY Surry STSBO Dominant containment dominant failure mode is leakage from cracking (9 in2) around the Equipment and/or Personnel Hatches Effectiveness of Mitigative Measures AC and DC power are unavailable Mechanical failure of TDAFW Pump, fails to start No instrumentation or RCS makeup Portable pump provided containment spray within 8 hours (spray operation 15 hours)

22 Surry SGTR Effectiveness of Mitigative Measures
OFFICIAL USE ONLY Surry SGTR Effectiveness of Mitigative Measures All ac and dc power supplies were available All instrumentation was available Plant response HPI, AFW initiate Turbine stop valves close Steam dump valves throttle and close

23 OFFICIAL USE ONLY SEQUENCE ANALYSIS
Randall Gauntt, Project Manager Sandia National Laboratories

24 OFFICIAL USE ONLY EMERGENCY PREPAREDNESS
Randolph Sullivan, CHP Office of Nuclear Security and Incident Response

25 OFFICIAL USE ONLY Objective Realistically model emergency response during a severe accident Evolutionary improvement over past EP modeling

26 Assumptions Emergency plans will be implemented
OFFICIAL USE ONLY Assumptions Emergency plans will be implemented The public will largely obey direction from officials Emergency workers will implement plans

27 Technical Basis Site, State and local emergency plans
OFFICIAL USE ONLY Technical Basis Site, State and local emergency plans Site emergency classification procedures Aligned with accident progression from MELCOR State/local protective action procedures Precautionary protective actions modeled Evacuation Time Estimate (ETE) Oak Ridge Evacuation Modeling System for evacuation beyond EPZ (if necessary)

28 Identify Cohorts ETE data: Precautionary protective actions:
OFFICIAL USE ONLY Identify Cohorts ETE data: General public “Tail” of public Special needs Precautionary protective actions: Schools Parks, beaches, etc.

29 Identify Cohorts Non-evacuating (0.5%) Shadow evacuation (10%)
OFFICIAL USE ONLY Identify Cohorts Non-evacuating (0.5%) Shadow evacuation (10%)

30 Speed of Travel Determined from ETE and OREMS
OFFICIAL USE ONLY Speed of Travel Determined from ETE and OREMS Modified in space and time “Bottle necks” identified Free flowing areas identified Road loading timing

31 Example ETE - 6.5 hours (from ETE) EPZ Evacuation Times
OFFICIAL USE ONLY Example ETE Region Population Non-Evacuating Evacuated Number of Vehicles 0-10 71,400 400 71,000 41,000 EPZ Evacuation Times hours (from ETE)

32 Speed of Travel MACCS2 does not allow input of road loading function
OFFICIAL USE ONLY Speed of Travel MACCS2 does not allow input of road loading function Median speed of cohort assumed Speeds adjusted for areas of free flow or congestion Distance travelled assumed 50% more than radial Median speed equals dist/time to clear

33 Example Accident Long Term Station Blackout scenario
OFFICIAL USE ONLY Example Accident Long Term Station Blackout scenario General Emergency is declared about 2 hours after loss of all A/C power Evacuation starts at General Emergency No precautionary evacuation of schools (Site specific decision)

34 Comments and Questions
OFFICIAL USE ONLY Comments and Questions

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