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BWR SAMG EVALUATION
IAEA TECHNICAL MEETING ON THE VERIFICATION AND VALIDATION OF SEVERE ACCIDENT MANAGEMENT
GUIDELINES
JEFF GABOR JENSEN HUGHES
RANDY GAUNTT
SANDIA NATIONAL LABORATORIES
12-14 DECEMBER 2016
2
PROJECT PARTICIPATION/SPONSORSHIP
Technical Input and Review provided by BWROG
3
SAMG HISTORY IN THE US
Generic Letter 88-20 (1988) required Individual Plant Examinations (IPE) to be performed, however, there was no formal requirement for SAMG development
US Industry proposed voluntary effort to develop SAMGs
• NEI 91-04, Severe Accident Issue Closure Guidelines, December 1994
• All plants agreed to SAMG implementation by the end of 1998
• Owners Groups began developing vendor-specific SAMGs
• Technical Basis provided by EPRI
Post Fukushima activities
• Update of EPRI Technical Basis Report (2012)
• Accident reconstruction efforts at DOE and EPRI
4
SAMG HISTORY IN THE US (CONT.)
US NRC Commission endorsed combining all remaining post-Fukushima activities into a single rulemaking – Mitigation of Beyond-Design-Basis Events (Jan 2014)
• The proposed rulemaking does not include an NRC requirement for SAMGs
• NEI Guidelines for development of SAMGs
− NEI 14-01 – Emergency Response Procedures and Guidelines for Extreme Events and Severe Accidents
− NEI 13-06 – Enhancements to Emergency Response Capabilities for Beyond Design Basis Accidents and Events
5
SAMG HISTORY IN THE US (CONT.)
Both BWR and PWR Owners Groups have released updated SAMGs for implementation.
• BWR Emergency Procedures Guidelines (EPG) and Severe Accident Guidelines (SAG) Revision 3 – January 2013
• PWROG developed consolidated guidelines for all US PWRs
6
BACKGROUND
Context for severe accident management
• Set of actions to limit effects of an accident that results in significant damage to fuel
• Focused on stopping progression of fuel damage and limiting releases to the environment
Nature of severe accident management guidelines
• Delineate strategies for response to symptoms of a severe accident
• Traditionally, rely on use of
− Existing equipment
− Existing instrumentation – with alternatives or compensatory measures as necessary
7
SAMGS - BACKGROUND
Nature of SAMGs (cont.)
• Emphasis is on use of Technical Support Center to advise control room staff
• Guidelines, rather than step-by-step procedures, to provide flexibility to address a broad range of possible conditions
Origin of the SAMGs
• Originally developed as part of long-term response to TMI-2 accident
• Overall process:
Technical Basis
Report (EPRI)
Generic SAMGs
by Plant Type
(Owners Groups)
Plant-specific
SAMGs
(Utilities)
Technical foundation for severe accident management
8
WHERE DO SAMGS FIT RELATIVE TO PLANT PROCEDURES?
Support
Procedures
Severe Accident
Management
Guidelines
Emergency
Operating
Procedures
Abnormal
Operating
Procedures
Alarm Response
Procedures
Normal Operating
Procedures
Flex
Support
Guidelines
EDMGs*
* Extensive Damage Mitigation Guidelines, per 10CFR50.54(hh)(2)
9
BWR SAMGS FOCUS ON PRIORITIZATION
Based on plant conditions, set priorities for actions
• Water level in core region
• Core melt is ex-vessel
Actions include:
• RPV pressure control
• RPV injection recovery
• Containment pressure control
• Containment Venting
• Containment Sprays
• Severe Accident Water Addition (SAWA)
• Severe Accident Water Management (SAWM)
10
BWR SAMG DEVELOPMENT AND MAAP
Developed by Emergency Procedures Committee
Consensus process
Targeted technical input
MAAP runs typically performed on a plant specific basis
Confirm that actions produce the expected results
11
SAMG ANALYSIS GOALS
1. Use severe accident analysis accident signatures to probe SAMG actions
2. Address a wide-range of accident signatures and accident mitigation strategies.
3. Use existing severe accident guidance as part of the simulation
4. Assemble a expert panel from industry a. Identify the key scenarios
5. Will take into account : a. Potential failures of operator actions
b. Inaccurate diagnosis of plant conditions
c. Uncertainties in the severe accident simulation
6. Confirm that the SAMGs are robust considering uncertainties
7. Investigate the value of accurately identifying specific plant conditions
12
SEVERE ACCIDENT UNCERTAINTIES
In-vessel hydrogen generation
Melt release characteristics at vessel breach
• Release rate
• Temperature
Ex-vessel debris coolability
Use both MAAP and MELCOR to bound uncertainties
13
STEPS FOR EPRI/DOE PROJECT
Define accident scenario
• Base case assumptions
• Operator actions and diagnosis to represent
Perform analysis in parallel using MAAP and MELCOR
Combine results to provide an assessment of uncertainties and insights on SAMG training
14
SANDIA’S EXPERTISE - MELCOR
Integrated, State of the Art, Severe Accident Analysis • SOARCA
− Peach Bottom (BWR), Surry (PWR – Large Dry Containment)
• SOARCA Uncertainty Analysis − Peach Bottom (BWR) , Surry (PWR), Sequoya (PWR – Ice
Condenser)
Dynamic PRA • Dynamic Event Trees (via the ADAPT code)
− Explores accident progression in a computationally efficient process when compared to simple Monte Carlo
− Evaluates human actions and provides context based human failure probability
» This capability may be critical to take credit for B.5.b. equipment
• SMART-SAMG efforts to automate the identification and response to low probability accident sequences
− Integral Pressurized Water Reactors – Limited Work
− Sodium Fast Reactors – Demonstrated diagnostics of accident sequences
15
JENSEN HUGHES EXPERTISE - MAAP
Containment Protection and Release Reduction Rulemaking - Technical Basis
• In-depth evaluation of a variety of release mitigation strategies
− Severe Accident Water Addition – first step for any strategy
− Severe Accident Water Management – preserve scrubbing via Wetwell vent
Fukushima Technical Evaluation
• Accident reconstruction
• Uncertainty analysis
• Numerous applications and development
Uncertainty Analysis
16
SCENARIO DEFINITION (EXAMPLE)
Step Description Options to be
modeled
Dependency
on previous action
Comments Notes
Initial Conditions
1. Loss of all onsite and offsite AC power
2. Turb Trip 3. MSIVs close 4. Scram
5. Loss of all injection except RCIC
6. Assume total RCP seal leakage of 36 gpm at normal operating conditions (e.g liq break of 5.7E-4 ft2)
None 1
RCIC Injection RCIC auto-start on low RPV
water level Assume suction immediately auto-switched to supp pool
1. Success
2. Failure
None 2
Defeat RCIC interlocks
Defeat RCIC trip logic for low RPV pressure and high turbine
exhaust
1. Success 2. Failure
2
RPV Pressure Control 1
At 10 minutes: using 1 SRV, control pressure in 800-1000 psig range
3. Success 4. Failure
Prevent auto SRV cycling
RPV Pressure Control 2
At 1 hr: using 1 SRV, control pressure in 400-600 psig range
Only assume success if
previous pressure control 1 succeeds
Depress at approx. 80F/hr
RPV Pressure
Control 3
At 2 hr: using 1 SRV, control
pressure in 200-400 psig range
Only assume
success if previous
pressure control 1 succeeds
Hold above 200 psig to maintain
RCIC
Primary Containment
Control 1
Vent containment to maintain adequate core cooling (i.e.
RCIC)
1. Success 2. Failure
Only assume success if initial
RCIC Injection success
Assume vent pressure of 15 psig. We could consider different pressures
in future analysis, but again, focus is on SAG, not EOP.
RPV Level
Control 1
RPV water level drops below min
steam cooling water level limit –
1. Success
2. Failure
None 3
17
CORE DAMAGE EVENT TREE (EXAMPLE)
18
POSSIBLE RESULTS DISPLAY (EXAMPLE)
19
CONCLUSIONS
Joint EPRI/DOE effort to systematically investigate BWR SAMG accident progression using MAAP and MELCOR
Based on Crosswalk findings, these codes should help to address uncertainties in severe accident phenomenology
Event Tree structure, similar to EPRI CPRR, to be used to account for success/failure of specific actions and decision points
Outcome to demonstrate robustness of SAMGs and provide insights for future consideration
20
QUESTIONS?