ML18213A074
| ML18213A074 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/2018 |
| From: | Tammie Rivera NRC/RES/DRA/FRB, Electric Power Research Institute |
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| Download: ML18213A074 (41) | |
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Module III - Fire Analysis Fire Fundamentals Introduction and Overview Joint EPRI/NRC-RES Fire PRA Workshop August 6-10, 2018 A Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES)
Welcome to Module 3 - Fire Analysis Your instructors for the week are:
- Ashley Lindeman EPRI, alindeman@epri.com
- Francisco Joglar Jensen Hughes, fjoglar@jensenhughes.com
- David Stroup US NRC/RES, David.Stroup@nrc.gov and you are 2
Start of Pilot Transitions NFPA 805 LAR Submittals Implementation Start of Non-Pilot Transitions SE Issued 2001 2005 2010 2015 NUGEG-1921 NEI 04 02 Fire HRA FP NUREG/CR-6850 Program NUREG/CR-6850 Supp 1 NUREG-2178 Fire PRA Imp Fire PRA HRR for Methodology Methodology Electrical Fire PRA Cabinets More Standard to come!
NUREG/CR-7150 NUREG-1824 Circuit Failure Fire Model Modes V&V NEI 00 01 Post-Fire SD Circuit Analysis FAQs Figure only include a sampling of key documents associated with analytical methods. Other documents governing NFPA 805 transition and FP programs such as Regulatory Guides etc., are 3
not included. 3
Getting us all on the same page Scope of Module 3 Module 3 covers those aspects of a nuclear power plant (NPP) at-power, internal fire, probabilistic risk assessment (PRA) that support the analysis of fire phenomena
- At-power: the plant is assumed to be operating at steady state, nominal 100% power at the time that a fire occurs
- Internal fire: fires within the boundaries of the plant (which we will define) but not fires outside the plant boundaries (e.g., not forest fires or off-site transportation accidents)
- Fire phenomena: identify fire sources, characterize fire growth and spread, assess impact on the surroundings, credit fire intervention by detection and suppression, predict damage times for important plant components and cables - develop a fire timeline
- Risk: based on how likely it is that a fire will lead to core damage and/or a release of radioactive materials from the plant site 4
Getting us all on the same page PRA elements that we wont cover Module 1: PRA / systems analysis - the analysis of the NPP as an engineered system
- Identification of important systems and components
- Characterization of system dependencies and failure modes
- Development of the post-fire plant response model (PRM) - the event tree / fault tree analysis
- Calculation of conditional core damage probability (CCDP) and conditional large early release probability (CLERP)
- Uncertainty analysis
- Final risk quantification - core damage frequency (CDF) and large early release frequency (LERF) 5
Getting us all on the same page PRA elements that we wont cover Module 2: Electrical/Circuit Analysis - supporting analyses of electrical control and power circuits
- Deterministic analysis of cable failure modes and effects
- Deterministic spurious operation analysis
- Probabilistic failure mode likelihood analysis
- Power distribution system layout
- Circuit protection coordination analysis 6
Getting us all on the same page PRA elements that we wont cover Module 4: Human Reliability Analysis (HRA) - the identification and quantification of human actions important to plant safety
- Review of plant response procedures
- Identification of human failure events (HFEs) to be included in the PRM
- Quantification of the human error probability (HEP) values for important HFEs as a part of PRM quantification 7
Getting us all on the same page PRA elements that we wont cover Module 5: Advanced Fire Modeling - the application of fire modeling tools to predict fire behavior and effects
- Complementary to Module 3
- Covers one more specific topical area in greater detail - the actual use of fire modeling tools
- Covers a range of fire modeling tools from closed-form empirical correlations to 3-D fluid dynamics-based compartment fire models
- We will talk about fire modeling and its role in the overall process of fire analysis, but in far less detail 8
Overall fire PRA structure Module 3 covers tasks in white and white/orange TASK 1: Plant Boundary & TASK 2: Fire PRA Component Partitioning Selection TASK 3: Fire PRA Cable Selection SUPPORT TASK A: Plant Walk Downs TASK 4: Qualitative Screening TASK 5: Fire-Induced Risk Model TASK 6: Fire Ignition Frequencies SUPPORT TASK B: Fire PRA Database TASK 7A: Quantitative TASK 12A: Post-Fire HRA:
Screening - I Screening TASK 8: Scoping Fire Modeling Fire Analysis Module Fire Analysis and Fire Modeling Modules TASK 7B: Quantitative Screening - II PRA/System Module Circuits Module B
HRA Module 9
Overall fire PRA structure Module 3 covers tasks in white and white/orange B
Detailed Fire Scenario Analysis TASK 9: Detailed Circuit Failure Analysis TASK 11: Detailed Fire Modeling A. Single Compartment B. Multi-Compartment C. Main Control Room TASK 10: Circuit Failure Mode &
Likelihood Analysis TASK 12B: Post fire HRA:
TASK 13: Seismic-Fire TASK 14: Fire Risk Quantification Detailed & recovery Interactions Fire Analysis Module Fire Analysis and Fire TASK 15: Uncertainty & Modeling Modules Sensitivity Analyses PRA/System Module TASK 16: Fire PRA Circuits Module Documentation HRA Module 10
Scope of Module 3: Fire Analysis Tasks covered by Module 3 are:
- Task 1: Plant Partitioning
- Task 6: Fire Ignition Frequency
- Task 8: Scoping Fire Modeling
- Task 11: Detailed Fire Scenario Analysis
- Task 13: Seismic/Fire Interactions (briefly)
- Support Task A: Plant Walkdowns In each task we will discuss the requirements of the ASME/ANS PRA Standard, Part 4
- What are the requirements and the expectations
- How they can be met 11
Task 1: Plant Partitioning (1 of 3)
Objectives:
- Define the global analysis boundary of the FPRA
- Divide the areas within the global analysis boundary into fire compartments The fire compartments become the basic units of analysis
- Generally we screen based on fire compartments
- Risk results are often rolled up to a fire compartment level A note on terminology:
- The PRA standard uses physical analysis units rather than fire compartments
- Definitions are quite similar, overall role in analysis is identical Dont let the terminology difference trip you up - intent is the same 12
Task 1: Plant Partitioning (2 of 3)
The global analysis boundary is intended to be a liberal definition of the region potential interest
- It will likely encompass areas of essentially no risk, but that is OK, screening steps will identify these The fire compartments are a matter of analysis convenience
- Fire compartments may equal fire areas if you so choose
- You can also subdivide fire areas into multiple compartments May require cable routing resolution at the compartment level
- The sum of the fire compartments must equal the global analysis boundary No omissions, no overlap between compartments 13
Task 1: Plant Partitioning (3 of 3)
Ultimately, the FPRA is expected to provide some resolution to each defined fire compartment and to all locations within the global analysis boundary Module will cover:
- Guidance and criteria for defining the global analysis boundary
- Guidance and criteria for defining fire compartments Ultimately, there is not a lot of new guidance in this task
- A lot like what was done in the IPEEE days 14
Task 6: Fire Ignition Frequency (1 of 3)
Objective: To define fire frequencies suitable to the analysis of fire scenarios at various stages of the FPRA Fire frequencies will be needed at various resolutions:
- An entire fire area
- A fire compartment (or physical analysis unit)
- A group of fire ignition sources (e.g., a bank of electrical cabinets)
- A single ignition source (e.g., one electrical panel) 15
Task 6: Fire Ignition Frequency (2 of 3)
Task begins with generic industry-average statistics on fire
- EPRI fire event database
- Events filtered for applicability and sorted into ignition source bins
- Plant-wide fire frequency is provided for each bin The real trick is to convert the generic values into values specific to your plant and to a given fire scenario
- Approach is based on ignition source counting and apportionment of the plant-wide frequency based on local population 16
Task 6: Fire Ignition Frequency (3 of 3)
Quite a bit is new relative to fire frequency:
- The fire event data have been re-analyzed entirely to suit the new method That means older IPEEE-vintage frequencies are obsolete
- There has been a switch towards component-based fire frequencies and away from generic room-based fire frequencies
- Some areas have received special treatment e.g., main control room 17
Task 8: Scoping Fire Modeling (1 of 2)
Objective: To identify (and screen out) fire ignition sources that are non-threatening and need not be considered in detailed fire modeling Non-threatening means they cannot:
- Spread fire to other combustibles, or
- Damage any FPRA equipment item or cable 18
Task 8: Scoping Fire Modeling (2 of 2)
Scoping fire modeling introduces a number of key concepts associated with the treatment of fire sources and damage targets
- The Fire Severity Profile approach
- Damage criteria for cables and equipment
- Assumptions associated with specific fire sources 19
Task 11: Detailed Fire Modeling (1 of 3)
Objective: To identify and analyze specific fire scenarios Divided into three sub-tasks:
- 11a: General fire compartments (as individual risk contributors)
- 11b: Main Control Room analysis
- 11c: Multi-Compartment fire scenarios 20
Task 11: Detailed Fire Modeling (2 of 3)
Task 11 involves many key elements
- Selection of specific fire scenarios Combinations of fire sources and damage targets
- Analysis of fire growth/spread Application of fire models
- Analysis of fire damage Time to failure
- Analysis of fire detection and suppression 21
Task 11: Detailed Fire Modeling (3 of 3)
Task 11 comes with a wide range of supporting appendices including:
- Specific fire sources such as high energy arc faults, turbine generator fires, and hydrogen fires
- Treatment of fire severity and severity factors
- Treatment of manual fire suppression
- Treatment for main control board fires Module will cover key appendices 22
Task 13: Seismic/Fire Interactions Objective: A qualitative assessment of potential fire/seismic interactions Module will cover this task briefly
- No significant changes from IPEEE guidance (e.g., the Fire PRA Implementation Guide) 23
Next up: Fire scenarios Before we move on Any questions on where our module fits into the overall fire PRA structure?
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Fire scenarios in risk analysis A key concept Recall that our primary measure of risk is fires leading to core damage
- Off-site release of radioactive materials also calculated, but we can work to the core damage level for our purposes Given that we are looking for fires that may:
- Cause an initiating event - an upset to normal at-power plant operations such that reactor shutdown is required, or
- Damage mitigating equipment - that set of plant equipment that operators would rely on to achieve safe shutdown We do this through fire scenarios that will:
- Represent the range of potential fire sources in the plant,
- Analyze the impact of fires on the surroundings,
- Assess fire protection systems and features, and
- Assess the plant and operators response to fire-induced damage Each fire scenario gives some contribution to total CDF 25
Fire scenarios in risk analysis A key concept A fire scenario is a set of elements representing a fire event:
- The ignition source, e.g., electrical cabinets, pumps
- Intervening combustibles, e.g., cables
- Damage targets (e.g., power, instrumentation or control cables) whose fire-induced failure may cause an initiating event and/or failure of mitigating equipment
- Fire protection features that could mitigate fire damage, e.g.,
automatic sprinklers
- The compartment where the fire is located and its characteristics
- Ultimately an event timeline 26
Fire Scenario Time Line Timeline includes the following elements (not necessarily in this order):
- 1. Scenario starts with ignition of a fire in a specific fire source
- 2. Fire growth involving the affected fuel,
- 3. Heat transfer from the fire to other items within the zone of influence,
- 4. Propagation of the fire to other materials,
- 5. Damage to identified PRA targets (e.g., cables and equipment),
- 6. Detection of the fire
- Detection can actually occur before ignition given an incipient detection system
- 7. Automatic initiation of suppression systems if present,
- 8. Manual fire fighting and fire brigade response,
- 9. Successful fire extinguishment ends the scenario.
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Fire Scenario - Level of Detail In practice, varying levels of detail are used to define the fire scenarios in a typical Fire PRA.
- Level of detail may depend on initial stages of screening, anticipated risk significance of the scenario In principle, at any level of detail, a fire scenario represents a collection of more detailed scenarios.
Screening Detailed 28
Fire Scenario Initial Screening Stage In the initial stages of screening, fire scenarios are defined in terms of compartments and loss of all items within each compartment.
- Assumes all items fail in the worst failure mode
- Detection and suppression occur after the worst damage takes place
- Fire does not propagate to adjacent compartments In multi-compartment fire propagation analysis, a similar definition is used in the initial screening steps for combinations of adjacent compartments.
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Detailed Scenario Identification Process In the detailed analysis tasks, the analyst takes those fire scenarios that did not screen out in the initial stage and breaks them down into scenarios using greater level of detail.
- Level of detail depends on the risk significance of the unscreened scenario
- Details may be introduced in terms of . . .
Sub-groups of cables and equipment within the compartment Specific ignition sources and fuels Fire detection and suppression possibilities 30
Example - Screening Level At the screening level, a fire in this compartment fails all equipment and cables shown in this diagram.
The fire is assumed to be confined to this room 31
Example - Detailed Analysis At the detailed level, a fire in this compartment fails a specific sub-group of components in this room.
The fire may still be confined to this room Scenario #1 Scenario #2 Scenario #3 32
Select and Describe Fire Scenarios Selecting scenarios is dependent on the objectives of the fire risk quantification
- How many fire scenarios are enough to demonstrate the objective?
- Which scenarios are the appropriate ones given objectives?
- What fire conditions are actually modeled?
- Analysis should represent a complete set of fire sources and conditions as relevant to the analysis objectives
- A full-scope fire PRA tries to capture all fire scenarios that may represent contributors to plant core damage risk Selection of scenarios is dependent on the hazard characteristics of the area
- Combustibles, layouts, fire protection The fire scenario should challenge the conditions being considered
- Can the fire cause damage? vs. Which fire can cause damage?
- Fires that dont propagate or cause damage are generally not risk contributors 33
Select and Describe Fire Scenarios
- 1. Scenarios begin with an ignition source - what/where does the fire start and what are the fire characteristics
- 2. Consider intervening combustibles - fire propagation beyond the fire source needs to be considered
- 3. There should be at least one damage target identified. Often it is a set of damage targets rather than just one (e.g., a group of important cables).
- 4. Include fire protection system and features (active or passive) that may influence the outcome of the event (there is a pain/gain decision point here) 34
Select and Describe Fire Scenarios
- 5. Sometimes, multiple ignition sources or targets can be combined into one scenario (e.g., a bank of cabinets all with the same cables overhead)
- 6. Sketch the scenario on a compartment layout drawing and try to qualitatively describe the conditions that a fire might generate. After the analysis, compare this qualitative prediction with the modeling results.
- 7. Do not neglect the importance of details such as ceiling obstructions, soffits, open or closed doors, ventilation conditions, spatial details (e.g.,
target position relative to fire source), etc.
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Scenario Quantification General quantification of CDF is based on a five-part formula:
CDFscenario = W SF Pns CCDP
= Ignition frequency for the postulated ignition source group (e.g., pumps)
W = A weighting factor for the likelihood that the fire occurs in a specific ignition source (this pump) or plant location (this room)
SF = A severity factor reflecting percentage of fires large enough to generate the postulated damage if left unsuppressed Pns = Non suppression probability - the probability that given the fire, it goes unsuppressed long enough that the target set is damaged CCDP = The conditional core damage probability - probability that given loss of the target set, operators fail to achieve safe shutdown and the core is damaged.
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In practice, we often quantify scenarios in a progression of more detailed steps:
A fire in a specific plant location CDFis g Wis 1 1 1 That is severe enough to threaten targets CDFis g Wis SF 11 That goes unsuppressed long enough to cause damage CDFis g Wis SF Pns 1 That prevents safe shutdown CDFis g Wis SF Pns CCDP 37
Training Objectives Our intent:
- To deliver practical implementation training
- To illustrate and demonstrate key aspects of the procedures We expect and want significant participant interaction
- Class size should allow for questions and discussion
- We will take questions about the methodology
- We cannot answer questions about a specific application
- We will moderate discussions, and we will judge when the course must move on 38
Methods - What is Covered in this Module Approved fire PRA Frequently Asked Questions (FAQs);
Supplemental guidance and methods developed as part of the transition to 10CFR50.48(c), NFPA 805 Published NRC or joint industry & NRC methods
- NUREG/CR-6850 and Supplement 1 / EPRI 1011989 & 1019259
- EPRI 3002002936 / NUREG-2169, Nuclear Power Plant Fire Ignition Frequency and Non-Suppression Probability Estimation Using the Updated Fire Events Database: United States Fire Event Experience Through 2009
- NUREG-2178, Volume 1 / EPRI 3002005578, Refining and Characterizing heat Release Rates for Electrical Enclosures During Fire (RACHELLE-FIRE), April 2016 ASME / ANS PRA Standard (RA-Sb-2013) 39
Methods - What is not Covered in this Module Draft FAQs working their way through the process, including;
- FAQ 18-0018, Electrical NSP curve updates On-going research by EPRI and/or NRC
- Treatment of main control room abandonment
- Fire growth profiles and plant personnel suppression
- RF-II Volume 2 (obstructed radiation, cabinet to cabinet fire spread, fire location factor, main control board, and motor and dry transformer heat release rates Working draft of the ASME/ANS PRA Standard Part 4
- Publication planned for mid 2019 40
Questions?
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