MELCOR Best Practices - An Accident Sequence Walkthrough L
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MELCOR Best Practices - An Accident Sequence Walkthrough Larry Humphries, K. Wagner, J. Jun, R. Gauntt (SNL) and Hossein Esmaili (NRC) Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Vg# 1 Best Practices adopted for NRC SOARCA Program • •Introduction •BWR •PWR •Other Best Practices State of the Art Reactor Consequence Analyses (SOARCA) – Realistic evaluation of severe accident progression, radiological releases and offsite consequences • – • Focus on a spectrum of scenarios most likely to contribute to release and subsequent offsite consequences, using a riskinformed approach SOARCA expert review panel meeting – Solicit discussion from experts • – – • • Experts also supplied additional recommendations Discussion of base case approach on some key complex and uncertain events for MELCOR calculations Best Practices distilled from these findings Model defaults updated as result of this work Uncertainty recognized as important – Vg# 2 Provide a more accurate assessment of potential offsite consequences Separate task evaluting uncertainty using uncertainty engine BWR Topics for Consideration •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 3 1. Thermal response and seizure of cycling S/RVs during late phase of in-vessel fuel damage 2. Criteria for representing mechanical failure of highly-oxidized but erect fuel assemblies 3. Volatile fission product speciation 4. Structural (non-radioactive) aerosol generation 5. Aerosol deposition on reactor and containment surfaces 6. Debris heat transfer in reactor vessel lower plenum 7. RPV failure mode and criteria in heads with varied and multiple penetrations 8. Hydrogen combustion and ignition 9. Debris spreading and Mark I shell melt-through 10. Under-cutting of reactor pedestal wall via long-term molten coriumconcrete interaction BWR Walk-through: BWR/4 Mark I LT-SBO •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 4 • Total loss of off-site power • RCIC operation on batteries for 8 hrs • Manual S/RV control available, but partial depressurization not reflected in the example calculation • Containment venting not available due to loss of power BWR/4 Reactor Vessel Model Vg# 5 CV370 (Steam Lines) FL699 CV600 FL359 - FL369 CV350 FL351 CV392 Feedwater source (time independent) FL355 Steam Separators FL345 CV310 FL600 FL357 CV355 Steam Dryers FL352 Downcomer CV394 (time independent keep-full at steady state) FL706 CV345 CV310 Shroud Dome FL376 Downcomer FL374 FL372 CV374 FL311 CV372 FL310 FL387 FW Pump FL386 LOOP B LOOP A Reactor Building RWCU return (not modeled) FL634 CV383 FL657 (LPCI) FL312 CV320 Lower Plenum FL312 FL382 CV384 CV631 FL631 HPCI FL614 CV382 CV385 FL383 CV300 CV300 FL626 SPRSR02 FL606 CV611 FL384 FL399 (RV Breach) FL611 FL633 RCIC CV700 FL391 (RWCU break) FL613 FL385 SPRSR01 FL656 (LPCI) CV652 FL652 CV650 RHR-2 FL653 RHR-1 CV220 CV220 HPSW Core Spray (Loop 1) FL702 B D A C FL704 FL654 (supp. pool cooling) FL655 (supp. pool cooling) CRD Pump FL304 FL910 (Wetwell Vent) CV653 FL650 – Aerial View CV391 Turbine / Hotwell (time independent) S/RV (typical) 11 parallel valves FL648 – Elevation View CST FL371 FL356 – Important features & components – Nodalization • Reactor Coolant System • Cavity Model Inboard MSIVs SVs (2 valves) FL370 CV901 Environment to drywell atmosphere FL358 CV360 Steam Dome FL651 •PWR •Other Best Practices Turbine Building CV200 Drywell CV651 – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI • BWR/4 Reactor Vessel Model FL649 •Introduction •BWR LT-SBO: Early Thermal-Hydraulic Response 1200 •PWR •Other Best Practices S/RV seizes open Local failure of lower core support plate (initial debris relocation into lower head) 800 600 Cooling from automatic cycles of RCIC 400 Containment Failure (drywell shell melt -through) 200 700 Automatic operation of RCIC RPV lower head failure 0 600 0 5 10 15 time [hr] 500 400 Top of Active Fuel Top of Jet Pumps 300 Downcomer Core Region Bottom of Active Fuel 200 Lower core plate failure: debris relocation into lower head 100 Base of downcomer RPV lower head failure 0 0 5 10 15 time [hr] Vg# 6 1 Cycling of lowest setpoint S/RV 1000 Pressure [psi] – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI Water Level [in] •Introduction •BWR Sequence characteristics: • 0 – 8 hrs: RCIC operates to maintain water level • Controlled depress. does not occur to maintain RCIC steam supply 20 25 30 20 25 30 S/RV Seizure at High Temperature 1500 1400 •Introduction •BWR 1.Seizure @ high temperature 2.Valve designs 1.depressurization rate 2.FP transport 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 7 Temperature [K] –LTSBO –Nodalization 1.S/RV 1300 1200 1100 1000 Gases discharged through S/RV(s) 900 Core Exit Gas 800 S/RV seizes (10 cycles over 1000K) 700 1 600 500 0 5 10 15 20 25 30 time [hr] • Automatic S/RV actuation after battery depletion • Typically a single cycling valve • Demand frequency: One cycle every 3-4 min at onset of core damage • Steam/H2 discharge with variable temperatures • Gas temperature exceeds 1000 K close to time of lower core plate failure Valve Design Affects Response •Introduction •BWR –LTSBO –Nodalization 1.S/RV 1.Seizure @ high temperature 2.Valve designs 1.depressurization rate 2.FP transport 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 8 • BWR/3 and /4: 2- or 3-Stage Target Rock • BWR/5 and /6: Spring-actuated, direct-acting Pilot-Operated relief valves relief valves [Crosby or Dikkers] – Valve disk cycles between full-open & full-closed – – Model: Seize in open position at 10th cycle above 1000 K – PBAPS (3-stage TR) Disk opens to position proportional to pressure against spring Model: Seize in last position based on residual lifetime • 60 min @ 1000 K • 30 min @ 1500 K GGNS Depressurization Rate Depends on Valve Position at Seizure 1.Seizure @ high temperature 2.Valve designs 1.depressurization rate 2.FP transport 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 9 Fraction of Full-Open Position –LTSBO –Nodalization 1.S/RV 1.2 Lowest Setpoint SRV Stem Position 1 0.8 1400 SRV seizure 0.6 1200 Reactor Vessel Pressure 0.4 1000 0.2 0 -2 -1 0 time [hr] Pressure [psi] •Introduction •BWR 800 1 600 2 3 4 5 time [hr] 400 6 GGNS (Dikkers spring-actuated) PBAPS (3-stage T-R) 200 0 -2 -1 0 1 2 time [hr] 3 4 5 6 Pressure History Influences Fission Product Transport / Deposition •Introduction •BWR 1.Seizure @ high temperature 2.Valve designs 1.depressurization rate 2.FP transport 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 10 Fraction of Initial Core Inventory –LTSBO –Nodalization 1.S/RV 0.4 Iodine Released from RCS (to suppression pool via open SRV) GGNS [Release fraction normalized to zero at time of SRV seizure] 0.3 0.2 RPV dryout GGNS PBAPS 0.1 PBAPS SRV seizure Vessel breach 0 -2 -1 0 1 2 time [hr] 3 4 5 6 Core Response to Oxidation Transient •Introduction •BWR 2500 Ring 1 –LTSBO –Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Temperature [K] 1.Core Oxidation 2.Damage function 3.Failure model 4.New input 2 Fuel assembly 'failure' at this location (conversion to particulate debris) 2000 1500 Top of Core (axial level 15) Water level in shroud below 2/3 core height 1000 Middle of Core (axial level 12) Bottom of Core (axial level 8) 500 10 11 12 13 14 time [hr] Vg# 11 15 16 17 18 Damage Function for Local Collapse of Fuel Rods •Introduction •BWR –LTSBO –Nodalization 1.S/RV 2.Fuel rod Failure 1.Core Oxidation 2.Damage function 3.Failure model 4.New input 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 12 • Mechanical failure of fuel rods assumed to result from combination of: – Loss of intact, unoxidized clad materal – Thermal stress • Molten Zr ‘breaks out’ from ZrO2 shell at 2400 K • Standing fuel rods collapse (forming particulate debris) based on a cumulative damage function – Concept: Swelling, thermal expansion and mechanical stresses increase with temperature. Insults to fuel integrity build with time at temperature. Fuel Degradation Modeling •Introduction •BWR –LTSBO –Nodalization 1.S/RV 2.Fuel rod Failure 1.Core Oxidation 2.Damage function 3.Failure model 4.New input 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 13 • Molten metallic Zr breakout temperature (2400K) • Fuel rod collapse – Time-at-temperature damage function – Similar to MAAP model – Eliminates single temperature criterion ZrO2 oxide Shell Oxidizing Zr Metal held under Oxide shell Release of Molten Zr (2400K) Fuel Collapse Model Implementation •Introduction •BWR –LTSBO –Nodalization 1.S/RV 2.Fuel rod Failure 1.Core Oxidation 2.Damage function 3.Failure model 4.New input 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 14 • The logic has been implemented within the code (MELCOR 2.1 & 1.8.6) – Require new input records to activate the logic (set of CFs no longer needed) – Different input format between two versions of the code • Added input record: COR_ROD (CORROD in 1.8.6) – Requires two fields • (1) IRODDAMAGE: tabular function name for the residual lifetime of fuel as a function of cladding temperature (tabular function number (integer) in 1.8.6) • (2) RCLADTHICKNESS: minimum un-oxdized clad thickness under which the rod collapse model supplants the default temperature based criterion (default = 1.0E-4 m) 3 The Phebus Experiment Facility •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation –Phebus Facility –Validation –Vapor Pressures –FPT1 Deposition –Booth Parameters 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 15 • Irradiated fuel heated in test package by Phebus driver core – Fuel heatup – Zr oxidation, H2 – Fission product release • Circuit (700 C) transports FP through steam generator tube – Deposits in circuit and SG • Containment receives FP gas and aerosol – – Settling Iodine chemistry Validation of Fission Product Release Models •PWR •Other Best Practices Vg# 16 0.6 0.5 1500 0.4 1000 0.3 2500 0.7 2000 0.6 0.5 1500 0.4 1000 0.3 0.2 0.2 500 2000 4000 6000 8000 10000 0 0 12000 0 2000 4000 Te Release VERCORS 4 VERCORS 4 1 0 12000 2500 3000 0.6 0.5 1500 0.4 1000 0.3 0.8 Release Fraction 2000 Mo Release ORNL Booth CORSOR M Mo data Temperature 0.9 Temperature (K) Release Fraction 0.7 10000 1 3000 ORNL Booth CORSOR M Te data Temperature 0.8 8000 time (sec) time (sec) 0.9 6000 2500 0.7 2000 0.6 0.5 1500 0.4 1000 0.3 0.2 0.2 500 500 0.1 0.1 0 0 0 2000 4000 6000 time (sec) 8000 10000 0 12000 0 2000 4000 6000 time (sec) 8000 10000 0 12000 Temperature (K) 0 500 0.1 0.1 0 Temperature 2000 0.8 Temperature (K) 0.7 2500 3000 ORNL Booth CORSOR M I data COR-TFU.102 0.9 ORNL-Booth data CORSOR-M Temperature 0.8 Release Fraction 1 3000 0.9 –Phebus Facility –Validation –Vapor Pressures –FPT1 Deposition –Booth Parameters 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI VERCORS 4 Temperature VERCORS 4 1 Release Fraction •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation I Release Cs Release Vapor Pressures of Some Important Species NuD k Pk 0 m v ) Afuel ( D fuel RT •Introduction •BWR –Phebus Facility –Validation –Vapor Pressures –FPT1 Deposition –Booth Parameters 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 17 10 10 vapor pressure - atm – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation CsOH P Cs Ti atm P CsI Ti atm • Molybdenum vapor pressure extremely low CsI 1 P CsM o Ti atm Vapor transport rate • Cs2MoO4 considerably higher, but… • Less volatile than CsOH or CsI 0.1 Cs2MoO • MELCOR treatment 4 0.01 P M o Ti atm 1 10 3 0.00011 10 4 – Cs and Mo treated as Cs2MoO4 with respect to volatility – CsI left unchanged Mo 1000 1500 3 1.02510 2000 2500 Ti K Temperature – K 3000 3500 3 3.510 FPT-1 Deposition using Modified ORNL-Booth Release Model FPT-1 Final Dist Cs Distribution as Fraction of Bundle Inventory: O RNL-Booth (m odified) 1 •Introduction •BWR –Phebus Facility –Validation –Vapor Pressures –FPT1 Deposition –Booth Parameters 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 18 0.8 fra c tion of inv e ntory – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation bundle plenum hot leg steam generator cold leg containm ent Total 0.9 0.7 0.6 - total - Containm ent - Plenum 0.5 0.4 0.3 0.2 - Stm G en 0.1 - Hot Leg 0 5000 7500 10000 12500 15000 tim e [sec] • Distribution of transported fission products – Predictions versus experiment – Performance reasonable for application 17500 20000 Booth Parameters for Different Data Fits •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation –Phebus Facility –Validation –Vapor Pressures –FPT1 Deposition –Booth Parameters 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 19 CORSOR-Booth ORNL-Booth Adjusted ORNL-Booth Diffusion coeff. Do 2.5x10-7 m2/sec 1x10-6 m2/sec 1x10-6 m2/sec Activation Energy Q 3.814x105 joule/mole 3.814x105 joule/mole 6 m --1 1 3.3x10-3 1 1 1x10-4 0.001 3.34x10-5 1x10-4 1x10-4 0.05 0.05 6 m --1 1 4x10-4 0.64 0.64 4x10-4 0.0625 4x10-8 4x10-8 3.6x10-7 0.25 0.16 Grain radius, a Class Scale Factors Class 1 (Xe) Class 2 (Cs) Class 3 (Ba) Class 4 (I) Class 5 (Te) Class 6 (Ru) Class 7 (Mo) Class 8 (Ce) Class 9 (La) Class 10 (U) Class 11 (Cd) Class 12 (Sn) 3.814x105 joule/mole 6 m --1 1 4x10-4 0.64 0.64 0.0025 0.2 4x10-8 4x10-8 3.2x10-4 .25 .16 Release of Structural Aerosols •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol –Background –Modeling 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 20 • For BWRs, principal source is tin (alloy material in Zircaloy) – Approx. 70+ MT of Zircaloy in fuel clad + canister – 1.45% of which is Sn • Direct experimental measurements are very limited, but general observations from Phebus tests suggest: – Sn levels greatly reduced in unoxidized Zr – No Sn found in remnants of ZrO2 – Total quantity of Sn on downstream surfaces roughly half of total available mass Release of Structural Aerosols -- Modeling Approach (BWRs) -- – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol –Background –Modeling 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 21 • Create special RN class to track released mass separately from fission product Sn • Invoke ‘non-fuel’ release model in COR Package – – Associate new RN class with releases from core components with Zr and ZrO2 Release rates scaled from CORSOR model for FP Sn Release Mass (kg) 100000 CORSOR-M Birchley FPT-1 multiplier 10000 34,600 3200% 16,700 1550% CORSOR-Booth 1000 CORSOR-Booth 505 CORSOR multiplier = 1.0 47% 195 18% CORSOR-M 100 10 CORSOR-Booth 5 2 Sn as Fission Product CORSOR-M 1 0 1 2 3 4 time (hr) • Sensitivity calculations performed to determine appropriate release rate scalar – Percent of Sn in Zirc Sn from Zircaloy Mass [kg] •Introduction •BWR Results for full-scale plant model compared to similar work by Birchley at PSI 5 MELCOR Aerosol Mechanics MAEROS •Introduction •BWR section mass – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition Time 1 –MAEROS Aerosol mechanics –Deposition –Pool Scrubbing •PWR •Other Best Practices 0.1 1 10 MAEROS sectional model of Gelbard – – • Particles grow in size – – • • Agglomeration Water condensation Particle fallout by gravitational settling Particle deposition processes – – – • 100 10 sections [.1 - 50 m] Condensed FP vapor sourced into smallest section Thermophoresis Diffusiophoresis Brownian motion BWR structural aerosol release (Sn) from Zr cladding and canister – – Significant aerosol mass Affects agglomeration, growth and fallout • Cs chemisorption in RCS modeled – Time 2 0.1 1 10 aerosol diameter [m] Vg# 22 • aerosol diameter [m] section mass 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI Aerosol size distribution evolves in time, depending on sources, agglomeration and removal processes 100 Iodine from CsI revolatilizes when reheated Aerosol Deposition on Reactor and Containment Surfaces •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition –MAEROS Aerosol mechanics –Deposition –Pool Scrubbing 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 23 • All deposition and retention mechanisms available in MELCOR are active in all regions of plant models – Settling, phoretic processes, chemisorption, etc. • Special features added to address mechanisms not captured by default models – “Filters” with filtration efficiencies designed to reflect: • Impaction losses on elbows and surfaces of long-length piping upstream of rupture location in LOCAs • Vapor scrubbing in water pools for species other than iodine • Reactor, containment and auxiliary building surfaces are represented in detail – High level of nodalization: proper temperature distributions and competing transport pathways – Sub-divide complex structures into linked but separate surfaces to properly reflect orientation Enhanced Pool Scrubbing Model •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition –MAEROS Aerosol mechanics –Deposition –Pool Scrubbing 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 24 • Current SPARC90 pool scrubbing model – Fission product decontamination calculated • aerosol Particles • currently, Iodine is the only vapor that is scrubbed • Removal of CsOH and CsI vapors – Typically enter the pool at high temperature in vapor form – Would deposit on the bubble/water surfaces and be scrubbed – Cooling offered by the pool would condense the vapor species to form aerosol particles – Treatment for the scrubbing of these vapor species now available in MELCOR 1.8.6 and 2.1 • Usage – MELCOR 1.8.6: IBUBT or IBUBF field on FLnnn02 must be 2 • e.g., FL10002 0 0 2 2 – MELCOR 2.1: ‘AllScrubbing’ (or 2) accepted as a vaild input for IBUBT or IBUBF on FL_JSW • e.g., FL_JSW 0 AllScrubbing AllScrubbing Debris Mass and Composition in Lower Head 180 •Introduction •BWR 160 – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Debris Mass [MT] 180 Failure of Lower Core Plate 160 140 Debris Mass [MT] –Debris mass in LH –Debris & LH Temperatures –Falling debris quench –Stable debris in LH –HT to LH 140 100 80 60 Zr 40 Failure of Lower Head SS 20 UO2 ZrO2 0 15 120 15.5 16 time [hr] 100 80 SS 60 Zr 40 ZrO2 20 Unoxidized steel 0 10 15 20 25 time [hr] Vg# 25 UO2 120 30 35 40 16.5 17 Debris and Lower Head Temperature •Introduction •BWR –Debris mass in LH –Debris & LH Temperatures –Falling debris quench –Stable debris in LH –HT to LH 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 26 Ring 1 Lower core plate failure (bulk of core debris pours into lower head) 2300 2100 Temperature [K] – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP Early 'dribble' of Inconel 2500 Creep rupture of hemispherical head 1900 Debris temperature 1700 1500 1300 Lower head wall Inner surface Outer surface 1100 900 Lower head dryout 700 500 10 15 20 25 time [hr] 30 35 40 MELCOR Framework for Debris-Coolant Heat Transfer in Lower Head •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP –Debris mass in LH –Debris & LH Temperatures –Falling debris quench –Stable debris in LH –HT to LH 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 27 • Step 1: “Falling Debris Quench” – Parametric model of fragmentation and cooling of a molten jet pouring into pool of water – Free parameters • Vfall (effective fall velocity) • Heat transfer coefficient • Dpart (Dh of final particles) – Dpart and HTC developed from FARO data – Vfall selected to mimic end-state temperature of debris in deep-pool FARO tests. MELCOR Framework (continued) •PWR •Other Best Practices Vg# 28 CV115 516 416 515 415 315 215 CV524 CV523 CV522 CV124 CV123 CV514 CV513 CV113 CV114 509 409 309 CV122 510 410 310 210 209 109 6.637 m CV112 511 411 311 211 111 7.018 m Heated Length 512 412 312 212 112 7.780 m 7.399 m Height of Fuel Assemblies 513 413 313 213 113 8.161 m CV512 514 414 314 214 114 8.542 m 110 5.494 m CV521 CV121 507 407 307 CV511 CV111 508 408 308 208 108 6.256 m 5.875 m 207 • Proposed approach: restore detailed nodalization and disable1-D CCFL to reflect lateral in-flow of water from adjacent ‘rings’ of the debris bed. 316 216 116 115 8.923 m 107 Coarse nodalization required to expose entire debris bed to water Top Guide & Upper tie plate 517 BAF Lower tie plate & nose pieces 106 206 306 406 506 105 205 305 405 505 104 204 304 404 504 103 203 303 403 503 102 202 302 402 502 Lower Core Plate & "Elephant's Foot" 5.218 m 4.685 m 4.152 m 3.619 m CV Lo Ple 3.086 m Control rod guides tubes – Permits calculation of debris temperature distribution Permits more accurate representation of heat transfer to control rod guide tubes 0.0 m 101 201 301 401 501 Penetration - R5 – Penetration - R4 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI – 417 Penetration - R3 –Debris mass in LH –Debris & LH Temperatures –Falling debris quench –Stable debris in LH –HT to LH • Historically limited heat transfer to uppermost region of debris bed 317 Penetration - R2 – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP – Stable debris bed cooling limited by 1-D Lipinsky CCFL correlation 217 Penetration - R1 •Introduction •BWR 117 TAF CV515 9.669 m 9.304 m CV125 • Step 2: Stable Debris Bed Heat Transfer CV525 CV Shrou BWR/4 Core Nodalization Lower head CRD stub tubes CVH Nodalizati COR No MELCOR Framework (concluded) •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP –Debris mass in LH –Debris & LH Temperatures –Falling debris quench –Stable debris in LH –HT to LH 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 29 • Step 3: Heat Transfer to (and failure of) Lower Head – New 2-D curved head model in MELCOR 1.8.6 – Solid debris heat conduction to vessel wall – Heat transfer coefficient between debris & head sensitive to debris temperature and morphology – Creep rupture of hemispherical head based on Larson-Miller parameter and lifefraction rule applied to a 1-D mechanical model Effect of Penetrations on Failure Criteria •Introduction •BWR • Penetration failure can be represented with the following tools: – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations –Modeling –Justification 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 30 – Failure criteria specified via user-defined control function – Distinct temperature of lumped parameter steel mass in contact with debris and inner surface of lower head Baseline Analyses will Not Exercise Penetration Failure Model •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations • Reasons: – – – –Modeling –Justification 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 31 – Experimental/analytical work for BWR penetrations does not conclusively demonstrate high probability of failure at a time that significantly precedes creep rupture of the head Melt penetration into penetration/stub tube structure does not necessarily result in debris ejection from RPV Lumped-parameter penetration model in MELCOR does not account for complexities of melt penetration into structure and local changes in debris state MELCOR sensitivity studies with active model (using reasonable range of penetration masses) indicate penetration failure has small impact on event chronology Hydrogen Combustion & Ignition •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI •PWR •Other Best Practices Vg# 32 • MELCOR (HECTR) combustion models will be active in all calculations – Apply default criteria for steam inerting, combustion efficiency, flame speed, etc. – One non-default option: • Time required for a flame to propagate to neighboring control volume specified on an individual CV basis • Ignition criteria – Use default for sequences with well-defined ignition sources (generally all cases with active ac power) – Defer ignition until vessel breach for total loss of power scenarios. Lateral Debris Spreading in Mark I Drywell •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) –Mark I drywell –Debris spreading –Contact with drywell liner 10.MCCI •PWR •Other Best Practices Vg# 33 • Potential for early drywell failure often dominated by drywell shell melt-through in Mark I containment – Not a factor in some Mark I plants due to deep sumps or curbs • Modeling approach follows basic conclusions of NRC issue resolution – Potential for failure dominated by lateral debris mobility Debris Spreading / Shell Melt-through Criteria •Introduction •BWR – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) –Mark I drywell –Debris spreading –Contact with drywell liner 10.MCCI •PWR •Other Best Practices Vg# 34 • Debris mobility tied to debris temperature and static head (height differential between neighboring areas): – Overflow not allowed if Tdebris < Tsolidus – Above solidus: • • CAV0 to CAV1: 0.5 m when Tdebris > Tsolidus 0.15 m when Tdebris = Tliquidus CAV1 to CAV2: 0.5 m when Tdebris > Tsolidus 0.10 m when Tdebris = Tliquidus • Spreading rate expressed in terms of transit time across single CAV – – When Tdebris = Tliquidus: 10 min for CAV1 30 min for CAV2 When Tdebris = Tsolidus: infinite • 5 min delay to shell failure after debris contact with T > 1811 K Debris Spreading & Contact with DW Liner 2500 In-pedestal (CAV 0) 2000 (L) T-ablation (1750K) (S) 1500 Balance of drywell floor (CAV 2) 1000 Time delay between Vessel Breach and DW melt-through: 14 min 500 In-pedestal (CAV 0) 1.4 1.2 90o sector outside pedestal doorway (CAV 1) 1 0.8 0.6 Balance of drywell floor (CAV 2) 0.4 0.2 0 0 20 30 40 time [hr] Vg# 35 1.8 1.6 10.MCCI •PWR •Other Best Practices 2 90o sector outside pedestal doorway (CAV 1) Debris Depth [m] –Mark I drywell –Debris spreading –Contact with drywell liner CAV 0 Temperature [K] – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) CAV 2 CAV 1 •Introduction •BWR 50 20 30 40 time [hr] 50 MCCI Modeling water •Introduction •BWR •PWR •Other Best Practices dd corium • Enhanced effective corium thermal conductivity (10x) d d – produces 1 to 5 MW/m2 heat flux concrete – Accounts for cracks and fissures and crust failure Corium Crust to Water Heat Flux 5000 4500 Range observed 4000 In MACE3500 Tests Heat Flux (kW/m**2) – LTSBO – Nodalization 1.S/RV 2.Fuel rod Failure 3.Volatile FP speciation 4.Structural aerosol 5.Aerosol Deposition 6.Debris HTF in LP 7.RPV failure with penetrations 8.H2 combustion 9.Debris Spreading (Cavity) 10.MCCI • Corium assumed to be well mixed (default) 1*K 2*K 5*K 10*K 20*K 50*K 100*K 3000 2500 2000 1500 1000 500 0 0 0.1 0.2 0.3 Time (hr) Vg# 36 0.4 0.5 – Consistent with interpretation of MACE tests Summary of Main Points for PWR Discussion •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Vg# 37 Issues Specific to PWR reactors • • • Pump seal leakage and blowout RCS natural circulation treatment Core plate failure Issues Previously discussed (Treated the Same as for BWR reactors) • • • • • • • Safety relief valve cycling and failure Fission product release, speciation, and volatility Fuel degradation and relocation treatment Debris/coolant heat transfer Vessel head failure and debris ejection Hydrogen combustion MCCI Plant and NSS Nodalizations • Plant Buildings •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices – Containment • Elevation View • Aerial view – Other Buildings • Detailed nodalizations of RCS and Core – Capture important 2-D effects – Natural circulation patterns • Core • RCS • Steam generators • Loop seals Vg# 38 Walkthrough of Station Blackout Accident in a PWR •Introduction •BWR •PWR – Nodalization – SBO • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Vg# 39 • Short term station blackout • • • • • Loss of ac power No feedwater injection No ECCS Leaking pump seals Key modeling issues identified in walkthrough Station Blackout High Pressure PWR Sequence Accident Initiation – SG dryout •Introduction •BWR •PWR Primary and Secondary Pressures STSBO - No Mitigation 18 16 – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Vg# 40 Hot leg C creep rupture 14 Pressure (MPa) • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel Pressurizer SG A SG C SG B 12 10 SG dryout 8 6 4 2 0 0 1 2 3 4 5 6 Time (hr) • Initial full loop RCS water circulation removes energy • Main coolant pump seals leak water • Pressurizer safety valve cycling stops 7 8 Steam Generator Secondary Water Accident Initiation – SG dryout SG Downcomer Levels STSBO •Introduction •BWR •PWR 14 12 – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Level (m) • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel SG A SG B SG C 10 8 6 4 2 Bottom of the downcomer 0 0 0.5 1 1.5 2 Time (hr) • Full loop RCS natural circulation period • Good decay heat removal • Secondary dry at ~1.2 hr • Primary RCS pressurization follows Vg# 41 2.5 3 Station Blackout High Pressure PWR Sequence SG dryout – Pump Seal Failure pump seal failure leads to depressurization •Introduction •BWR •PWR cycling reliefPrimary and Secondary Pressures STSBO - No Mitigation valve 18 – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Hot leg C creep rupture 12 10 SG dryout 8 6 4 2 0 0 1 2 3 4 5 6 7 Time (hr) • SG dryout starts RCS re-pressurization to relief valve setpoint • RCS becomes steam-filled challenging pump seals – Seal blowout at 2.8 hrs • Seal failure increases coolant mass loss rate • Cycling relief valve Vg# 42 Pressurizer SG A SG C SG B Pump Seal failure 14 Pressure (MPa) • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel 16 – Same treatment as BWR SRV 8 Station Blackout High Pressure PWR Sequence Core Uncovery – Hotleg failure pump seal failure leads to Primary and Secondary Pressures depressurization STSBO - No Mitigation •Introduction •BWR •PWR 18 – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Hot leg C creep rupture Pump Seal failure 14 Pressure (MPa) • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel 16 Pressurizer SG A SG C SG B 12 10 SG dryout 8 6 4 2 0 0 1 2 3 4 5 6 7 8 Time (hr) • Coolant loss and low core water level leads to RCS depressurization • Core damage phase • PWR valves less susceptible to high temperature conditions Vg# 43 Core Water Level Vessel Water Level STSBO •Introduction •BWR •PWR • SBO definition • Initiation to SG dryout • SG dryout • SG dryout to pump seal failure • Core uncovery to hotleg failure • Core Waterlevel 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices Vessel top 8 Two-Phase Level (m) – Nodalization – SBO 10 6 TAF 4 Accumulators 2 BAF 0 Vessel failure -2 Lower head -4 0 1 2 3 4 5 6 7 Time (hr) • Hot leg and SG natural circulation • Hot leg failure depressurizes vessel – Accumulators dump • Partial core quench and second vessel boildown • Core damage and hydrogen generation as water in core falls Vg# 44 8 Pump Seal Leakage Seal Leakage STSBO - No Mitigation 180 •Introduction •BWR •PWR Total Seal Leakage 160 Seals fail Flow Rate (gpm) 140 – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure 120 100 80 60 40 20 •Other Best Practices 0 0 1 2 3 4 5 6 7 8 Time (hr) • Model based on Rhodes analysis of leakage and likelihood and degree of seal failure – Seals initially leak on loss of site power and back pressure • – 21 GPM Saturation conditions in RCS (high temperature) produces seal failure • Failure can range between 170 and 250 GPM • Assume: – – Vg# 45 21 GPM initially 170 GPM at saturation Natural Circulation Modeling •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 46 • SCDAP/RELAP5 Studies from mid-1980’s to present • COMMIX CFD, 1987 • 1/7th-Scale Westinghouse Test, 1989-1993 • Fluent CFD Work, 2003 to present – Numerical CFD extends work • • • • 1/7th-scale Full-scale Westinghouse designs CE designs • SCDAP/RELAP5 SGTI analysis – FLUENT support Natural Circulation Modeling MELCOR Approach •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 47 • 1/7th Westinghouse Assessment – Steady state tests – Safety valve cycles – Hot leg fission product heating – Hydrogen binding • Comparison to experiment and SCDAP/RELAP5 (where available) – In-vessel – Hot leg – Steam generator 4 •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 48 Natural Circulation Modeling MELCOR Approach • MELCOR vessel and RCS models developed from SCDAP/RELAP5 natural circulation models – 5 ring vessel with 2-D core and upper plenum – Geometry and loss factors from RCS – Zion, Surry, and Calvert Cliffs SCDAP/RELAP5 models – New modeling approach to hot leg and steam generator natural circulation flows • SCDAP/RELAP5 renodalizes model when natural circulation conditions are expected – Special 2-D hot leg and steam generator model • Application of MELCOR includes calculation of source term beyond RCS failure – S/R5 used to predict timing and location of creep rupture failure and not subsequent events Natural Circulation Modeling MELCOR Approach 4 •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 49 • Hot leg counter-current natural circulation tuned to a Froude Number correlation using results from FLUENT CFD analysis where g acceleration due to gravity. Q volumetric flow rate in a horizontal duct r average fluid density (ρ) Δρ density difference between the two fluids CD hot leg discharge coefficient 4 •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 50 Natural Circulation Modeling MELCOR Approach • Steam generator tube to hot leg flow ratio tuned results from the FLUENT CFD analysis • Inlet plenum subdivided into 3 regions for hot, mixed, and cold regions from plume analyses • Steam generator mixing fractions based on FLUENT CFD analysis – M-ratio(steam generator tube to hot leg flow ratio) = 2 Natural Circulation Modeling MELCOR Approach 4 • Explicit modeling of structures in hot leg and steam generator •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 1.Background 2.Assessment 3.MELCOR modeling 4.Hotleg modeling 5.Tube flow modeling 6.Other modeling considerations 3.Core plate failure •Other Best Practices Vg# 51 – Convective heat transfer • Augmented in hot leg based on FLUENT turbulence evaluations – Gas to structure radiative exchange in the hot leg and steam generator – Ambient heat loss through the piping and insulation • Individual modeling of relief valves – When the valves are lumped, it creates a very large flow that non-physically disrupts natural circulation flow patterns and the timing of the valve openings • Creep rupture modeling – Hot leg nozzle carbon safe zone – Hot leg piping – Surge line – Steam generator inlet tubes Westinghouse PWR Core Plate • Weight of core material mass • Engineering stress formulae used (e.g. Roark) • Failure based on exceeding yield stress at temperature • Sequential failure of multiple supporting structures treated •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.RCS natural circulation 3.Core plate failure •Other Best Practices CL Level Lower core plate 6 PLATEG (Level 6) 5 PLATEG (Level 5) Flow plate Flowdiffuser mixer plate Core Coreplate plate supportColumns columns Support 4 COLUMN (Level 4) 3 PLATE (Level 3) Lower core Core support forging plate 2 1 Ring Vg# 52 1 2 3 4 5 Other MELCOR Best Practices • Some standardize some non-default input •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 53 – Porosity of particulate debris • CORZjj01 PORDP 0.4 • Some Numeric in Nature – SC-4401(3); Maximum number of iterations permitted before solution is repeated with a decreased (subcycle) timestep. • Some enable some previously non-default models – RN1002 – enable Hygroscopic model – FLnnnFF – KFLSH=1 enables flashing model • Some new models activated – FLnnn02 IBUBF & IBUBT • -1 Vapor heat transfer in pools for RCS FLs • +2 SPARC scrubbing in pools for spargers, quencher, vents, and BWR downcomers. MELCOR Default Templates •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 54 • New defaults enabled automatically in 2.1 • M1.8.6 defaults enabled as follows: • New defaults disabled automatically in 1.8.6 • M2.1 defaults enabled as follows: ! The following records updates the default by individual package COR_DFT 1.86 CAV_DFT 1.86 RN1_DFT 1.86 HS_DFT 1.86 CVH_DFT 1.86 ! The following records updates the default by individual package CORDEFAULT 2.0 CAVDEFAULT 2.0 RN1DEFAULT 2.0 HSDEFAULT 2.0 CVHDEFAULT 2.0 ! This record restore original defaults all at once EXEC_GLOBAL_DFT 1.86 ! This record restore updates the default all at once DEFAULT 2.0 Note: See User Guide for list of those default items changed in M2.0 default template Other Common Best Practices Item •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 55 Record Field Value(s) 1. BUR000 IACTV 0 (Active) 2. BUR1xx (xx = CV) IGNTR 86 for CVs where ignition is to be prohibited. 3. BUR1xx (xx = CV) TFRAC 1.0 4. FLnnn0T ZBJT0, ZTJT0 = ZBJT0 + Dz ZTJT0 (For axial containment flow paths only) Description Burn package activation Apply to RCS control volumes to preclude combustion. Time fraction of burn before propagation to neighboring CV is allowed. Value of 1.0 means a flame must travel the radius of the control volume before propagating to its neighbor. To insure that MELCOR properly estimates vertical burn propagation in containment, drywell, reactor building, and auxiliary building, it is necessary to define “vertical” flow path “from” and “to” elevations with a small dZ. If the “from” and “to” elevations are set equal (which has been historical practice to ensure complete vertical pool drainage), the MELCOR burn package uses criteria for horizontal burn propagation. 5. FLnnnFF KFLSH 1 Calculate superheated pool flashing for all liquid LOCA connections to initially dry containment regions. KFLSH activates the model. Activate RN1Ikkk as needed for impact into specified heat structures. 6. FLnnn02 IBUBF & IBUBT -1 +2 Vapor heat transfer in pools for RCS FLs. SPARC scrubbing in pools for spargers, quencher, vents, and BWR downcomers. 7. RN2FLTXX00 FPVAPOR 8. COR00001 9. COR00001A Various geometric values MELCOR SPARC pool scrubbing model was modified to scrub all gaseous RN classes for DRGAP 0.0 Thickness of gas gap between fuel pellets and cladding set 0.0 to account for swelling of operating fuel. ILHTYP ILHTRN 0 BWR =0, PWR =1 Lower head is a hemisphere Transition is at RCOR (BWR) or RVES (PWR) Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 56 Item Record Field Value(s) Description 10. COR00009 HDBPN HDBLH MDHMPO MDHMPM TPFAIL CDISPN 100 W/m2-K 100 W/m2-K ‘MODEL’ ‘MODEL’ 9999 K 1.0 This record activates the internal molten pool to lower head heat transfer models and provides reasonable solid debris to lower head heat transfer coefficient. 11. COR00012 HDBH2O VFALL 2000 W/m2-K 0.01 m/s HTC in-vessel falling debris to pool (W/m2-K) Velocity of falling debris (m/s). ). Perhaps not correct for shallow pools and not necessary in deep pools since adoption of no 1-D CCFL limitation via the one-dimensional Lipinski model. 12. CORCR0 IAICON 2 13. CORZjj01 PORDP 0.4 14. CORijj04 DHYPD Core - 0.01 m LP - 0.002 m 15. CORZjjNS TNSMAX 1520 K 1700 K For PWRs only Activate control rod release model, 2 = Model is active, vaporization is allowed from both candling material and conglomerate. Porosity of particulate debris Particulate debris equivalent diameter (LP values for DHYPD, HDBH2O, VFALL tuned to get appropriate end-of-pour debris temperature. 2mm based on FAERO fragmented debris size). Perhaps not correct for shallow pools. Control blades failure temperature (BWR) Core top guide failure temperature (BWR) Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure Item Record Field Value(s) 16. CORijjDX FBYXSS Calculated. 17. SC-1131(2) TRDFAI 2800 K Fuel rod collapse temperature (addressed with CORijjFCL records) 18. SC-1141 (2) GAMBRK 0.20 kg/m-s Molten Zr breakout flowrate parameter to yield 2 mm/s as evidenced in CORA experiments 19. SC-1701 (1) 20. SC-4401(3) XPASMX 15 21. DCHNEMnn00 ELMNAM ELMMAS Use ORIGEN results for core, if available. •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 57 Description 0.01 For BWRs only. Fraction of lower head COR cells normally displaced by control rod guide tubes should be ‘excluded’ from volume available to particulate debris. Volume recovered when tubes (as supporting structure) fails. Open volume fraction for subnode blockage criterion. This is the default setting. Maximum number of iterations permitted before solution is repeated with a decreased (subcycle) timestep. Elemental fission product mass at shutdown for calculation of decay heat. Other Common Best Practices •Introduction •BWR •PWR Item Record Field Value(s) Description Elemental fission product decay heat per unit mass (based on shutdown RN inventory). Define specific decay heat for CsI (Class 16) as 0.51155 of value for Class 2 (Cs) plus 0.48845 of value for Class 4 (I). Define specific decay heat for Cs2MoO4 (Class 17) as 0.7348 of value for Class 2 (Cs) plus 0.2652 of value for Class 7 (Mo). If ORIGEN results are not available for the core, perform an input deck with BE burn-up and cycle history. Redistribute RN mass as follows, Class 2 initial mass represents the NUREG-1465 Cs gap mass not already included in Class 16. Class 4 initial mass is empty (10-6 kg) Class 7 initial mass is remaining Mo mass not included in Class 17. Class 16 has all I and an appropriate amount of Cs mass for CsI stoichiometry. Class 17 has the remaining Cs not included in Classes 2 and 16 plus Mo for Cs2MoO4 stochiometry. 22. DCHNEMnnmm DCHEAT Use pre-combined methodology for Cs, I, and Mo 23. DCHCLSnnn0, DCHCLSnnnm RDCNAM, CLSELM New RN definitions for Classes 1-12, 16-18 – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 58 If ORIGEN results are available, synthesize ORIGEN data to define a single representative element for each class with decay heat data that reflects decay heat for all elements within the class (DCHNEMxxxx input.) Redefine each class to include only the representative element. Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 59 Item Record Field Value(s) Description 24. DCHDEFCLS0 DEFCLS 13, 14, 15 Specifies that MELCOR DCH default classes are to be used. 25. DCHCLNORM CLSNRM ‘No’ when ORIGEN results are available. ‘Yes’ when MELCOR is used to estimate initial inventories. 26. HSccccc400 & HSccccc600 CPFPL CPFAL See discussion Minimum value of CVH pool fraction such that heat transfer is calculated to Pool/Atmosphere. For heat structures within the RPV, use 0.9. For PWR SG Tubes, use 0.1. All other structures modeled use default value of 0.5. 27. HSccccc401 HSccccc601 EMISWL RMODL PATHL 0.27 EQUIV-BAND 0.1 m Mean emissivity of SS type 316 Equivalent band radiation model. Nominal optical distance in steam (m). For SS heat structures within the reactor vessel and those being monitored for creep-rupture failure. 28. HSDGccccc0 ISRCHS ISDIST GASNAM HS # 1 SS New ORIGEN input for elements/classes defines the total core decay heat. Otherwise, let MELCOR normalize the elemental decay heats to the rated power. Do not use RN1DCHNORM. Default behavior normalizes Class 10 (Uranium). Heat structure for application of degas model. Degassing model requires 1 mesh. Name of released gas. For SS boundary structures modeled with the HS package that are coupled to the core. Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure Item Record Field 29. HSDGccccc1 RHOSRC HTRSRC TEMPL TEMPU 30. MPMATxxxx MLT 31. RN1001 NUMSEC NUMCMP NUMCLS Value(s) Description 7930 kg/m3 2.68x105 J/kg 1695 K 1705 K Gas source density. Gas source heat of reaction. Lower temperature for degassing. Upper temperature for degassing. For SS boundary structures modeled with the HS package that are coupled to the core. 2800 K 2800 K Uranium-dioxide Zirconium-oxide Because of the interactions between materials, liquefaction can occur at temperatures significantly below the melt point. The interaction between ZrO2 and UO2 results in a mixture that is fluid at above about 2800 K (compared to the melting temperatures of 3113 K and 2990 K, respectively, for the pure materials). Similarly, although pure B4C melts at 2620 K, interaction with steel produces a mixture that is fluid at above about 1700 K. •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 60 10 2 20 (PWR) 18 (BWR) Default Default For BWR & PWR: 16 = CsI, 17 = Cs2MoO4 Now Class 17 includes default settings for Cs2MoO4. Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 61 Item 32. Record BWR structural tin release RN/DCH data for RN Class 18 Field Value(s) Description For BWR: RN Class 18 = SnO2 (non-radioactive) Define SnO2 (DCHCLSnnn0) 18 = ‘SnO2’ SnO2decay heats (DCHNEMnn00) 0 W/kg (no decay heat) SC(7110) vapor pressures SnO2: Log10(P(mm Hg)) = 15400/T + 8.15 SC(7111) diffusion coefficients SnO2: Sigma = 3.617, E/K = 97 SC(7120) elem./compound molecular weights Sn: MW = 150.7 kg/kg-mole Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure Item Record 33. PWR control rod RN data for RN Classes 18, 19, and 20 Field Value(s) For PWR RN Class 18 = Ag, 19 = In, 20 = Cd Define Ag, In, Cd (DCHCLSnnn0) 18 = ‘Ag-CR’, 19 = ‘In-CR’, 20 = ‘Cd-CR’ Ag, In, Cd decay heats (DCHNEMnn00) 0 W/kg (no decay heat) SC(7110) vapor pressures Ag: Log10(P(mm Hg)) = 1000/T + 1.26x104 + 7.989 In: Log10(P(mm Hg)) = 400/T + 1.27x105 + 8.284 Cd: Log10(P(mm Hg)) = 500/T + 5.31x103 + 7.99 SC(7111) diffusion coefficients Ag: Sigma = 3.48, E/K = 1300 In: Sigma = 3.61, E/K = 2160 Cd: Sigma = 3.46, E/K = 1760 SC(7120) elem./compound molecular weights Ag: MW = 107.8 kg/kg-mole In: MW = 114.8 kg/kg-mole Cd: MW = 112.4 kg/kg-mole •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 62 Description 34. RNCA100 ICAON 1 (Active) Chemisorption model is active (default). 35. RN1002 IHYGRO 1 (Active) Hygroscopic model activation. (RNACOND set to default, 0 = condensation of water onto all aerosols.) Other Common Best Practices •Introduction •BWR •PWR Item Record Field 36. RNCRCLxx SC7100 ICRMT / ICLSS / FRAC (2) Zr (3) ZrO2 (4) steel (5) steel ox. (6) B4C 37. RNFPNijjXX NINP RINP1 RINP2 – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure Value(s) Description 2 / 18 / 0.0145 3 / 18 / 0.0145 0.1 1.0 0.0 0.0 0.0 For BWRs, apply the non-fuel release model. Assign aerosol generated from Zr and ZrO2 to RN Class 18 (SnO2). The mass will be added as a non-radioactive mass to this class. The fraction of material mass available for release as an aerosol from these materials is 0.0145 (Sn fraction in Zirc-2 and -4.) Note: must also add input for the release rate (SC7103) for RN Class 18. Values should be identical to those used (default) for Class 12 (fission product Sn). Multipliers for various structural material types •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 63 Use ORIGEN results, if available. NINP = RN Class, RINP1 = mass, RINP2 = axial peaking factor. Distributes mass based on distribution developed with ORIGEN. If ORIGEN results are unavailable, NINP = 0, RINP1 = axial peaking factor, RINP1 = radial peaking factor. Where, SiSj RINP1 * RINP2 = 1. Other Common Best Practices •Introduction •BWR •PWR – Nodalization – SBO 1.Pump seals 2.Loop seal 3.RCS natural circulation 4.Core plate failure Item Record Field 38. RNGAPijjnn NINP RINP1 RINP2 39. RN2FLTXX00 FPVAPOR Value(s) 1 (Xe) = 0.05 2 (Cs) = 1.00 3 (Ba) = 0.01 5 (Te) = 0.05 16 (CsI) = 0.05 Description Where, NUREG-1465 recommends the following gap quantities, Xe = 5% Cs = 5% Ba = 1% Te = 5% •Other Best Practices – Overview – Default Templates – Tables 1 – Tables 2 – Tables 3 – Tables 4 – Tables 5 – Tables 6 – Tables 7 – Tables 8 – Tables 9 – Tables 10 Vg# 64 Various geometric values For all flow paths entering pools via quenchers or spargers, specify the flow path to scrub all gaseous RN classes.
