MELCOR Best Practices - An Accident Sequence Walkthrough L

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
1.02510
2000
2500
Ti
K
Temperature – K
3000
3500
3
3.510
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.