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Qualitative Assessment for Crediting Mitigating Strategies Equipment in RI Decision Making
NEI FRIDM Task ForceDecember 9, 2015
NRC Public Meeting at Three White Flint
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Purpose
• The qualitative assessment process ensures that important considerations are evaluated by licensees during risk informed decision making
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Assessment Considerations
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Feasibility Assessment (Section 5)
• The purpose of the Feasibility Assessment is to:- Ensure that the equipment can be used to meet the needed
success criteria- Identify key issues that need to be resolved
• This includes an evaluation of key aspects of the:- Scenario (Section 5.1)- Function (Section 5.2)- Equipment Capability (Section 5.3)
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Availability and Reliability of Equipment (Section 6)
• The purpose of this section is to establish confidence in the availability, reliability, and deployment capabilities of the necessary equipment.
• This section evaluates:- Equipment Availability (Section 6.1)- Reliability, Testing, and Maintenance (Section 6.2)- Location and Transportation Capability (Section 6.3)
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Time Availability & Margin (Section 7)
• This sections evaluates if there is adequate time margin to confidently accomplish necessary steps
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Command and Control (Section 8)
• The purpose of this section is to evaluate the quality of knowledge of when and how to use the equipment in a given scenario
• This section includes:- Procedures and Written Instructions (Section 8.1)- Training (Section 8.2)- Staffing and Communications (Section 8.3)
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Environmental Challenges (Section 9)
• The purpose of this section is to evaluate how environmental conditions may impact deployment, timing, or implementation:- Identify applicable environmental conditions- Identify potential challenges- Assess how those challenges are addressed
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Example Use of Qualitative Assessment
Turbine Driven AFW Pump NOED
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Example Case
• Plant Type: PWR • Issue:
- The single Turbine Driven AFW pump is out for maintenance - Time necessary to complete repairs beyond Tech Spec
Requirements• Resolution:
- Request for additional 36 hours for repair through NOED- Credit FLEX portable pump to support RI decision making
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FEASIBILITY ASSESSMENTQualitative Assessment Example
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Scenario Assessment
• Scenarios and timelines- Some identified relevant scenarios that rely on Auxiliary
Feedwater are:• Loss of off‐site power (LOOP)• Station Blackout (SBO)• Loss of Feedwater (LOFW)
- Timeline for most scenarios would preclude necessary time to deploy portable pump
• Pre‐deployment would be required to meet available time
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Scenario Assessment (cont.)
• Equipment needed- Diesel‐driven portable pump- Hoses to align to suction source and discharge path
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Scenario Assessment (cont.)
• Operations and procedures- Operators have been trained to use the portable pump to feed
the steam generator- Installation and use of the pump has been validated- Written instructions are available to the operator
• Strategy: FLEX Support Guidelines (FSGs)• Pump Operation and Alignment: Placards on pump
- Additional written instructions would be developed to use equipment for this specific application
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Function Applicability
• The ability to use the portable pump to feed steam generators has been established and validated through the FLEX program
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Equipment Capability Evaluation
• Systems conditions:- The portable pump can provide sufficient flow at a pressure of 500 psi.
- Steam generators will need to be depressurized to allow feed from pump
• Available connection points:- Suction source: Condensate Storage Tank- Discharge path: Feedwater line to steam generators
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Equipment Capability Evaluation (cont.)
• System alignment- Manual alignment of isolation valves is required
• Suction source capacity- CST will provide 8 hours of water to the steam generators- Procedures are available to refill CST beyond 8 hours
• Normal instrumentation will be available in the Control Room
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Equipment Capability Evaluation (cont.)
• Pump capability validated by FLEX program:- The portable pump can provide sufficient flow at a pressure of 500 psi.
- Additional analysis has shown that the portable pump provides sufficient flow immediately after plant trip (Not explicitly addressed by FLEX validation)
- All hoses and connections can handle shutoff head pressure of the portable pump
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Initial Feasibility Assessment Summary
• Use of the portable pump to feed steam generator is determined to be feasible given:- Steam generator is depressurized- Portable pump is pre‐deployed prior to the initiating event- Additional written instructions are created to address the specific application
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AVAILABILITY AND RELIABILITYQualitative Assessment Example
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Equipment Availability
• Multiple sets of equipment are available:- The FLEX program requires N+1 sets of equipment where N = number of units on site
• Normal and alternate connections points as established by the FLEX program are available
• Total time is well within the 90 day unavailability monitoring limits of the FLEX program
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Reliability, Testing and Maintenance
• The plant performs periodic testing to ensure that the pump is reliable
• Additionally, the pump will be tested prior to installation to ensure it will successfully start and run
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Location and Transportation Capability
• The portable pump is currently in its normal FLEX storage location
• Pump will be transported and pre‐deployed to the proper location prior to exceeding AFW completion time
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TIME AVAILABILITY & MARGINQualitative Assessment Example
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Time Availability and Margin
• Two actions required for success:1. Initiate feed to steam generator with portable pump2. Depressurize the steam generator
• Actions can be performed concurrently
Note: Example timeline is based on station blackout scenario. Other scenarios would require a similar approach
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Time Availability and Margin
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Timeline Feed Steam Generator with Portable Pump
Steam Generator Depressurization
Initiating Event Time ZeroTime to Mitigate 60 Minutes (SG Dryout)
Delay Time 5 minutes
Time to Deploy N/A(Pre‐Deployed)
N/A(Deployment not Necessary)
Time to Install 15 Minutes N/A(Installation not Necessary)
Time to Execute 5 Minutes 30 Minutes
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Time Availability and Margin (cont.)
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Start Portable Pump
Depressurize Steam Generator
System Time Window (60 min)
Limiting
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COMMAND & CONTROLQualitative Assessment Example
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Procedures and Written Instructions
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FLEX Support Guidelines:Steps to feed SG with the
portable pump
ECA 0.0 (Loss of AC):Steps for Steam Generator
Depressurization
Specific Written Instructions for NOED
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Training
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FLEX Support Guidelines:Steps to feed SG with the
portable pump
ECA 0.0 (Loss of AC):Steps for Steam Generator
Depressurization
Specific Written Instructions for NOED
Existing
Training
Just In
Tim
eTraining
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Staffing and Communications
• A dedicated operator will be at the location of the portable pump for the duration of the NOED
• The dedicated operator will have normal radio communications with the Control Room
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ENVIRONMENTAL CHALLENGESQualitative Assessment Example
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Environmental Challenges
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Potential Environment Challenge Resolution
Internal Fire and Flooding Pump and associated hosing staged outside
Seismic Event Equipment Tie‐downs used to reduce failure potential
External Flooding , High Winds, and Extreme Temperatures
Weather forecast shows low likelihood of potential events for duration of the NOED
Evaluation of Environmental Challenges is based on pre‐deployed location of the pump and not its normal FLEX Storage Location
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Qualitative Assessment Example Summary
• The process has shown that the example plant has evaluated important considerations and addressed issues in using a portable pump to back up feedwaterto the steam generator
• Justification for crediting the portable pump and the details of this assessment would be included in the risk assessment portion of the NOED submittal
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Streamlined Approach for Crediting Mitigating Strategies Equipment in RI Decision Making
NEI FRIDM Task ForceDecember 9, 2015
NRC Public Meeting at Three White Flint
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Purpose• FLEX capabilities can help reduce the risk from some contributors in
plant‐specific PRAs, e.g., station blackout scenarios • It is desirable to have a means to get numerical credit for FLEX in
regulatory interactions, e.g., SDPs, NOEDs, etc.• The streamlined quantitative approach provides a mechanism to
get credit in the near term and avoids need to add in PRA model in advance
• Provide foundation for eventual guidance for crediting FLEX in PRA directly
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Streamlined Quantitative Approach
• Mirrors factors considered in qualitative assessment- Feasibility Assessment- Time Margin- Command and Control- Environmental Factors- Equipment Availability
• Implemented using post quantification techniques in a decision tree format
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Process for Streamlined Credit
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Factors to be Considered
• Time Available / Time Required• Leverage Validation Studies
• Command and Control• Procedures, Cues, and Indication• Training• Staffing and Communication
• Environmental Factors and Accessibility• Equipment Availability (N, N+1)
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Decision Tree Approach
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Example Use of Streamlined Approach
Emergency Diesel Generator SDP
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Example Case• Plant Type: BWR • Issue:
- SDP for representative BWR with EDG fail to start with one month exposure time- The internal events and internal fire PRA models were quantified to represent the
SDP boundary conditions. - The internal events PRA model results were similar to that obtained with the site
SPAR model. - The impact from seismic and other external events hazards was determined to be
negligible and would not impact the characterization of the SDP evaluation.- Results indicate a White finding is likely with no credit for FLEX mitigation strategies
• Credit for FLEX is desired to get more realistic evaluation of finding using best available information
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Initial Results
• SDP for representative BWR with EDG fail to start with one month exposure time
43Streamlined Approach for Crediting FLEX
Initial PRA Model Results (No Credit for FLEX)
Figure of Merit Internal Events Internal Fires Total
Increase in CDF (∆CDF) 5.7E‐06 / yr 2.3E‐05 / yr 2.8E‐05 / yr
Increase in LERF (∆LERF) 9.0E‐09 / yr 2.4E‐07 / yr 2.5E‐07 / yr
Exposure Time (T) 1 month 0.083 yr
SDP CDF (∆CDF * T) < 1.0E‐06 for Green 2.4E‐06 (White)
SDP LERF (∆LERF * T) < 1.0E‐07 for Green 2.1E‐08 (Green)
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FEASIBILITY ASSESSMENTStreamlined Quantitative Approach Example
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Scenario Assessment
• Credit for FLEX would be highly feasible in dominant sequence for ∆CDF evaluation - SBO scenario with initial operation of HPCI or RCIC- Core damage predicted after battery depletion- Aligns with ELAP design for the FLEX mitigation strategy
• Exclude other early scenario contributors (< 6 hours) and certain fire scenarios
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Potential Impact on Risk‐Informed Decision
• Will credit for FLEX impact regulatory decision?
• Probably, but need to estimate impact and provide basis
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TIME AVAILABILITY & MARGINStreamlined Quantitative Approach Example
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Time Availability and Margin
• Key actions required for success:1. Deploy and install two backup generators for
prolonged DC availability within 6 hours, and 2. Deploy and install one FLEX pump to provide RPV
injection or suppression pool makeup within 6 hours.
• Actions are performed concurrently
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Time Availability and Margin
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Timeline Deploy and Install Two 480VAC Generators Deploy and Install Flex Pump
Initiating Event Time ZeroTime to Mitigate 6 hours (Battery depletion)
Delay Time 60 Minutes (120 mins for fire)
Time to Deploy 45 Minutes 23 Minutes
Time to Install 81 Minutes 16 Minutes
Time to Execute 7 Minutes 5 Minutes
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Time Availability and Margin
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Deploy and Install Flex Pump
Deploy and Install Two 480VAC Generators
System Time Window (6 hours)
Limiting
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Time Margin Assessment• Time Margin (TM, expressed as a percentage) =
100 * [(TSW ‐ TDelay ‐ TDebris) – (TTrans + TInstall + TExe)] / (TTrans + TInstall + TExe)
• Internal EventsTM = 100% * [(6 – 1 ‐ 0) – (0.75 + 1.35 + 0.12)] / (0.75 + 1.35 + 0.12) = 126% “Expansive” in Decision Tree (TM = 0.5)
• Internal FiresTM = 100% * [(6 – 2 ‐ 0) – (0.75 + 1.35 + 0.12)] / (0.75 + 1.35 + 0.12) = 80%“Nominal” in Decision Tree (TM = 1.0)
51Streamlined Approach for Crediting FLEX
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COMMAND & CONTROLStreamlined Quantitative Approach Example
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Procedures and Written Instructions
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FLEX Support Guidelines:Steps to align generators for prolonged DC availability
FLEX Support Guidelines:Steps to align FLEX pumps for RPV injection or suppression
pool makeup
• FSGs specifically directed in EOPs when in ELAP or when required for adequate core cooling
• EOPs also include steps for RPV depressurization and containment venting
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Training, Staffing and Communications
• Existing training for EOPs and use of FSGs• Staffing and communications confirmed as part of FLEX validation studies
• Command and Control in Decision TreeCC = 1.0 for internal eventsCC = 1.0 for internal fires
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ENVIRONMENTAL FACTORSStreamlined Quantitative Approach Example
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Environmental Factors Assessment
• No adverse conditions expected in response to an internal event or internal fire initiating event
• Nominal Factors exist for internal events and internal fires
EF = 1.0 for internal eventsEF = 1.0 for internal fires
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AVAILABILITY AND RELIABILITYStreamlined Quantitative Approach Example
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Equipment Availability and Reliability
• Multiple sets of equipment are available:- The FLEX program requires N+1 sets of equipment where N = number of units on site
• Maintenance and Testing of FLEX pumps and generators consistent with EPRI templates
• Credit dictated by decision tree pathEA = 0.01 for internal eventsEA = 0.1 for internal fires
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DECISION TREE SUMMARYStreamlined Quantitative Approach Example
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Decision Tree Results Summary
• Internal EventsFFPIE = 0.1 * TMFPIE * CCFPIE * EFFPIE + EAFPIEFFPIE = 0.1 * 0.5 * 1.0 * 1.0 + 0.01 = 0.06
• Internal FiresFFIRE = 0.1 * TMFIRE * CCFIRE * EFFIRE + EAFIREFFIRE = 0.1 * 1.0 * 1.0 * 1.0 + 0.1 = 0.20
• Incorporate numerical adjustments to credit FLEX for applicable sequences
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Adjusted Results using Streamlined Approach
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Adjusted PRA Model Results (With Credit for FLEX)Figure of Merit (∆CDF) Internal Events Internal Fires Total
Initial Increase in CDF 5.7E‐06 / yr 2.3E‐05 / yr 2.8E‐05 / yr
Applicable Scenarios (No Credit for FLEX) 5.2E‐06 / yr 1.9E‐05 / yr 2.4E‐05 / yr
Excluded Scenarios 4.7E‐07 / yr 3.4E‐06 / yr 3.9E‐06 / yr
Applicable Scenarios (Credit for FLEX)
5.24E‐06 / yr * 0.06 = 3.1E‐07 / yr
1.91E‐05 / yr * 0.20 = 3.8E‐06 / yr 4.1E‐06 / yr
Total Adjusted ∆CDF 7.8E‐07 / yr 7.3E‐06 / yr 8.0E‐06 / yr
Exposure Time (T) 1 month 0.083 yrSDP CDF (∆CDF * T) < 1.0E‐06 for Green 6.7E‐07 (Green)
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Streamlined Approach Summary• Performed in the context of key contributors to the decision • Narrows the scope. Focuses the issues.• Allows more realistic assessment (compared to no credit for
FLEX)• Can be performed without needing detailed modeling• Focus on the key performance attributes for the key
contributors- Leverage attributes of FLEX V&V process
• Simple decision tree look up of quantitative factors
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Proposed Path Forward
• Comments on white papers from NRC by January 15, 2016 before next RISC meeting
• NEI submittal of final white papers by February 29, 2016• NRC endorsement of white papers via ISG by April 29,
2016• Full Draft NEI guidance with PRA considerations to be
developed by June 2016
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