ML18213A096
| ML18213A096 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/2018 |
| From: | Tammie Rivera NRC/RES/DRA/FRB, Electric Power Research Institute |
| To: | |
| Shared Package | |
| ML18213A072 | List: |
| References | |
| Download: ML18213A096 (20) | |
Text
Joint EPRI/NRC
-RES Fire PRA WorkshopAugust 6-10, 2018Module III
-Fire AnalysisTask 11b: Main Control Room Fire Analysis and Appendix LA Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES) 2Main Control Room Fire Analysis ObjectivesThe objective of this presentation is:Describe the recommended approach for detailed fire modeling in the main control room. Specifically:
-Differences between the main control room and other compartments
-Criteria for abandonment due to fire generated environmental conditions
-Description of how to analyze:Conditional probability of damage to a target set Forced control room abandonment time 3Main Control Room Fire Analysis What is Different in the MCR?The control and instrumentation circuits of all redundant trains for almost all plant systems are present in the control room. -Redundant train controls can be within a short distance of each other
-Small fires within control panels could be risk
-significant
-Related SR: FSS
-A6The room is continuously occupied, which provides the capability for "prompt detection and suppression."Evaluating control room abandonment conditions is necessary-Abandonment refers to situations in which control room operators are forced to leave due to untenable fire generated conditions (temperature, toxicity, and visibility).
-Related SRs: FSS
-B and its two SRs 4Main Control Room Fire Analysis Recommended StepsStep 1: Identify and characterize main control room featuresStep 2: Estimate control room fire frequencyStep 3: Identify and characterize fire detection and suppression features and systemsStep 4: Characterize alternate shutdown featuresStep 5: Identify and characterize target setsStep 6: Identify and characterize ignition sourcesStep 7: Define fire scenariosStep 8: Conduct fire growth and propagation analysisStep 9: Fire detection and suppression analysis and severity factorStep 10: Estimate failure probability of using alternate shutdown featuresStep 11: Estimate probability of control room abandonmentStep 12: Calculate scenario frequenciesStep 13: Document analysis results 5Main Control Room Fire Analysis Step 1: Identify and Characterize MCR FeaturesThe specific features of the control room and the control board areidentified. Control room dimensions Other adjacent compartments included in the MCR properLocation, shape, dimensions and special features of the control panels and other electrical panelsMain control board layout and location of various controls and displaysCable penetration into the control room and into the control panelsVentilation system characteristics False ceiling features and the ceiling above it 6Main Control Room Fire Analysis Step 4: Characterize Alternate Shutdown FeaturesThe features of alternate shutdown capability vary widely amongNPPsIn general, a control panel is installed at a location away from the control room where the operators can control and monitor key core cooling functions and parameters independent of the MCR. In other plants, alternate shutdown capability is achieved through a set of control points and control panels located at various points of the plant requiring coordinated actions of several operators.It is necessary for the fire risk analysts to understand the alternate shutdown capability of the plant.
-For example, the analyst may select safety
-related target sets on the panel that are not backed up by an alternate shutdown control or instrumentation circuit.
7Main Control Room Fire Analysis Step 5: Identify and Characterize Target SetsThe target sets can be identified by systematically examiningcombinations of control and instrumentation items found on thecontrol panels, electrical cabinets, wireways, and cable racewaysinside the MCR. Examine the control panels from one end to the otherGroups of adjacent controls and instrumentation Cursory and conservative estimation of the CCDP/CLERP as the basisElements of a set are located within the reach of a potential fireExposure fire affecting multiple cabinetsCorresponding PRA Standard SRs: FSS
-A2 through A4 8Main Control Room Fire Analysis Step 6: Identify and Characterize Ignition SourcesThe final product of this step is a list of ignition sources, theirrelevant characteristics, and fire ignition frequenciesassociated with each sourceSimilar to Step 3.a of single compartment analysisType, quantity, dimensions and heat release rate profile of each sourceMain control board as ignition sourceAssume fire might occur at any point on a control panelOther control panels, electrical cabinets, wireways, and cable racewaysKitchen appliances and other electrical devices?Transient combustible fires 9Main Control Room Fire Analysis Step 7: Define Fire ScenariosFour types of fire scenarios are specifically recommended forevaluationFire inside the main control board and stand
-alone electrical cabinets that open into each other, Fires affecting two adjacent electrical cabinets that do not open into each other,Fires affecting two non
-adjacent electrical cabinets, andTransient firesCorresponding PRA Standard SR: FSS
-A6 10Main Control Room Fire Analysis Steps 8 and 9: Non
-SuppProb& Severity Factor The non-suppression probability and severity factors arecalculated as recommended in the approach for singlecompartment firesFor fires inside a control panel, use the method described in Appendix L (covered previously)
W H d h w 11Main Control Room Fire Analysis Step 10: Estimate Failure ProbUsing ASPTwo approaches may be followed:An overall failure probability is estimated representing the failure of successful usage of alternate shutdown means. The alternate shutdown procedure is integrated in the plant response model (i.e., the fault trees and event trees). The core damage sequences are adjusted to include failures associated with alternate shutdown means, and the human error probabilities are reevaluated based on the alternate shutdown procedures.This is an area of ongoing research!
12Main Control Room Fire Analysis Step 11: Estimate Probof Control Room AbandonmentThe final decision to abandon the control room is assumedto depend on habitability conditions. The analyst may postulate that the alternate shutdown procedure would be activatedThe time to activate the alternate shutdown procedure is suggested to be established based on plant operating procedures rather than control room habitability conditionsAbandonment possibility should be examined for all postulated target damage scenarios 13Main Control Room Fire Analysis Step 11: Estimate Prob of Control Room AbandonmentAbandonment criteria based on habitability conditionsTemperature, or heat flux
-2. This can be considered as the minimum heat flux for pain to skin. A smoke layer of approximately 95°C (200°F) could generate such heat flux.Visibility
-Optical density of the smoke is less than 3.0 m
-1light-reflecting object would not be seen if it is more than 0.4 m away. A light
-emitting object will not be seen if it is more than 1 m away.2 4 0.1 mkW T q sl&
14Main Control Room Fire Analysis Step 11: Estimate Probof Control Room AbandonmentThe conditional probability of abandonment can be estimatedbased on the calculated evacuation timeDetermine the heat release rate generating abandonment conditionsCalculate the severity factor for fires of this sizeDetermine the time for abandonment
-Time to reach untenable conditions such as 200 oF hot gas layer or smoke density conditions of 3.0 m-1Calculate non
-suppression probabilityMultiply the severity factor and non
-suppression probability to determine conditional abandonment probabilityCorresponding PRA Standard SRs: FSS
-B1 and FSS
-B2Note that this is typical HRR distribution discretization approach-15Main Control Room Fire Analysis Step 11: Estimate Probof Control Room AbandonmentProbability of abandonment due to habitability can be determined based on:
-The criteria for abandonment due to fire conditions
-Fire modeling analysis using field models, zone models, or hand calculations. (Field models and zone models are the tools usually selected for this)NUREG-1934 includes a detailed example of a control room evaluation (Discussed in Module 5) 16Main Control Room Fire Analysis ExampleCredit prompt detectionSuppression by fire brigade
-Pnsfrom CR suppression curveSF from probability distribution for vertical cabinets with unqualified cable and fire propagating to more than one bundle.InputsAmbient temperature [C]
20Duration [sec]Opening area [m2]
4Height of opening [m]
2Room length [m]
20Room width [m]
15Room height [m]
60.0014Density [kg/m3]
2000Specific heat [kJ/kg]0.880.15Temperature for abandonment [C]
93 17Main Control Room Fire Analysis Example -(alternate discretization approach based on abd. time)0.0E+005.0E-021.0E-011.5E-012.0E-012.5E-01 0 10 20 30 40 50 60 70Time for a 200 F HGLProb 0 100 200 300 400 500 600 700 800 900SFPnsDuration [Min]SFPnsSF*Pns 5 7943.2E-021.9E-016.1E-03 10 6684.8E-023.7E-021.8E-03 15 6036.0E-027.1E-034.2E-04 20 5616.9E-021.4E-039.4E-05 25 5317.7E-022.6E-042.0E-05 18One related current activityMCR abandonment analysis methodsMCR abandonment is a complex issue
-Abandonment may arise from loss of habitability or control
-How is abandonment decision made for loss of control?
--will it be timely?
-Partial abandonment
-Operators stay in the MCR to supplement alternate shutdown operations (control maintained from the MCR)
-Quantifying transfer and alternate shutdown actionsA FAQ was proposed by industry to address operations from alternate shutdown including abandonment
-FAQ 13-0002 -only available in draft form
-Proposed a framework for abandonment, containing relatively simple set of alternate shutdown conditions and related discussions 19Continued-NRC Staff agrees that questions are important and need resolution
-Staff put out interim staff guidance as could not come to agreement on FAQ approachML14080A028Ongoing EPRI/RES research effort
-First phase addressing qualitative considerationsPublished in 2017 by EPRI, NRC publication in progress
-Publicly available at epri.com, 3002009215 (NUREG
-1921 Supplement 1)Second phase to address quantification
-Completed peer review
-Comment resolution processOne related current activityMCR abandonment analysis methods 20Main Control Room Fire Analysis Concluding RemarksThe main control room has unique characteristics that areaddressed in detail in Task 11b.Recommended fire scenarios for the MCR Evaluation of MCR abandonment due to fire generated conditions
-Loss of MCR habitability
-Loss of control functions due to fire in MCR or elsewhere