Transcript EXAMPLE OF DETAILED SYSTEM TH CODE

OVERVIEW - RELAP/SCDAPSIM
Presented Dr. Chris Allison
Outline
• General modeling approaches
• Primary differences between
RELAP/SCDAPSIM and
– RELAP/MOD3.3
– MAAP and MELCOR codes
RELAP5 and SCDAP WERE ORIGINALLY
DEVELOPED BY US NRC
• RELAP5 developed for DBA analysis (Late
1970s)
– SCDAP (Severe Core Damage Analysis
Package) added in 1980s for SA analysis)
• RELAP/SCDAPSIM developed by
ISS/SDTP for commercial applications
– Advanced numerics and programming
– Standard RELAP5/MOD3.2/3.3 and
SCDAP/RELAP/MOD3.2 models
RELAP/MOD3.2 and RELAP/MOD3.3 models
used for system TH analysis
• Non-equilibrium, two fluid models for hydrodynamics
including transport of non-condensable gases
• 2D/3D capability provided through “cross-flow” options
• Convective and radiative heat transfer
• 1D heat conduction in system structures
• Point reactor kinetics
– External 3D kinetics provided through link to user supplied
reactor kinetics packages
• Control system, trip logic, and special system
components such as valves and pumps
SCDAP components/models used for
detailed vessel and core behavior
•
•
•
•
Detailed LWR core components
Upper plenum structures
Core debris and molten pools
Lower plenum debris and vessel
structures
User selects representative fuel rod, control
rod/blade and other components for LWR core
• Bundle convective and radiative heat transfer
– Radiation absorption by fluid
– Bundle deformation/blockage/grid spacer effects on
flow patterns
•
•
•
•
•
2D heat conduction
Grid spacer heating and melting
Bundle deformation/blockage formation
Liquefaction and failure of core components
Debris/void formation
Representative
components can
have different
power levels
Fuel Rod 1
Fuel Rod 2
Control rod
Water Rod
User defines representative assembly for each
flow channel in core
SCDAP fuel rod components use 2D models to
predict temperature (r,z), deformation, chemical
interactions and melting
Zr Cladding
UO2 Fuel Pellet
Gap
SCDAP fuel rod components consider failure due
to spacer grid interactions, metallic and ceramic
melt relocation, and fragmentation
•
•
•
•
2D heat conduction
Fission product buildup and release
Cladding deformation and rupture
Cladding oxidation and hydrogen production
– Effects of steam availability and vapor diffusion considered
•
•
•
•
Zr – spacer grid interactions
UO2 dissolution by molten Zr
Zr melting and relocation
UO2/ZrO2 melting and relocation
SCDAP control rod components use 2D models to
predict temperature (r,z), deformation, chemical
interactions and melting
Zr Guide Tube
SS Sheath
Ag-In-Cd/B4C Absorber
Gap
SCDAP BWR control components use 3D models
to predict temperature (r,z), deformation, chemical
interactions and melting
Gap between absorber
tube and sheath
Zr Guide Tube
SS Sheath
B4C Absorber
Interstitial Gap
SCDAP Ag-In-Cd or B4C control rod/blade
models consider early failure of control
structures
• 2D heat conduction
• Cladding oxidation and hydrogen production
– Effects of steam availability and vapor diffusion
considered
• Zr/SS – control material interactions
• Guide tube, cladding, control material melting
and relocation
SCDAP general 2D shroud model tracks
behavior of other core components
• LWR SCDAP general shroud model used
to model core walls, experimental facility
structures
– 2D heat conduction
– Zr layer oxidation and hydrogen production
• Effects of steam availability and vapor diffusion
considered
– Melting and relocation
SCDAP upper plenum models describe
heating and melting
• Oxidation
– Parabolic rate
– Steam starvation
• Heat conduction
– Lumped parameter
• Relocation of upper plenum structures into
core or lower plenum
SCDAP in-core debris/model pool
models describe later stages of core
failure
• Oxidation
– Parabolic rate
– Steam starvation
• Heat conduction
– Lumped parameter (in rubble)
– 1D (in metallic blockages)
– 1D (molten pool crust perimeter)
SCDAP in-core debris/molten pool
models describe formation, growth, and
failure of in-core molten pools
• Molten pool behavior
– Radial and axial
spreading
– Crust thinning and
mechanical failure
• Side wall versus top
surface
– Transient natural
circulation
– Interactions with
shroud wall
SCDAP in-core debris/model pool
models describe formation, growth, and
failure of in-core molten pools
• Material relocation
– Void formation
– Molten pool upper
crust collapse
• Mixing of debris/molten
pool
– Relocation of upper
plenum structures into
core
– Molten pool slumping
SCDAP uses a detailed 2D model to
describe behavior of lower plenum
debris/vessel
• Heat conduction
– 2D finite element
– gap resistance
(solid/melt)
– 1D model at crust
boundary perimeter
• Molten pool behavior
– Transient natural
circulation
– Interactions with vessel
wall
SCDAP uses detailed 2D model to
describe behavior of lower plenum
debris/vessel
• Creep rupture failure
of vessel wall
• Material relocation
– Relocation of upper
plenum structures
– Relocation of core
component materials
– Molten pool slumping
• Ex-vessel flooding
Primary differences between
RELAP/SCDAPSIM and RELAP/MOD3.3
• RELAP5/MOD3.3 limited to transients that
will not result in core damage
– Peak fuel cladding temperatures < 1500 K
(2200 oF)
– Limited cladding oxidation (< embrittlement)
• RELAP5/MOD3.3 radiation exchange heat
transfer model neglects absorption by fluid
Primary differences between
RELAP/SCDAPSIM and RELAP/MOD3.3
• RELAP/SCDAPSIM has detailed core component
models for typical LWR/HWR designs
–
–
–
–
LWR fuel rod
Ag-In-Cd/B4C control rod
BWR control blade model
Electrically-heated fuel rod simulator
• RELAP/SCDAPSIM has upper and lower plenum models
for typical LWR designs
– Detailed 2D finite element model to describe lower head
• RELAP5/MOD3.3 uses general 1D heat structure model
to describe all structures including core and vessel
Primary differences between
RELAP/SCDAPSIM and RELAP/MOD3.3
• RELAP5/MOD3.3’s 1D heat conduction model to ignores important
phenomena for fuel elements or electrically heated fuel element
simulators
–
–
–
–
Axial conduction
Temperature-dependent electrical resistivity changes on power profile
Burnup/thermal cycling influence on thermal properties
Influence of changes in gap dimensions, fuel rod internal pressure, and
fission product release on fuel-cladding gap conductance
– Steam starvation and vapor diffusion limits for cladding oxidation
– Zircaloy cladding embrittlement
– Fission product release
Note: Boiloff.i sample problem demonstrates differences between RELAP5
and SCDAP fuel rod models (plot)
Primary differences between
RELAP/SCDAPSIM and RELAP/MOD3.3
• RELAP5/MOD3.3’s 1D heat conduction model to ignores important
phenomena for fuel elements or electrically heated fuel element
simulators
–
–
–
–
Axial conduction
Temperature-dependent electrical resistivity changes on power profile
Burnup/thermal cycling influence on thermal properties
Influence of changes in gap dimensions, fuel rod internal pressure, and
fission product release on fuel-cladding gap conductance
– Steam starvation and vapor diffusion limits for cladding oxidation
– Zircaloy cladding embrittlement
– Fission product release
Note: See boiloff example in “Practical Examples of Severe Accident
Analysis” for demonstration of differences between RELAP5 and
SCDAP fuel rod models
Primary differences between
RELAP/SCDAPSIM and more
simplified SA integral codes
• RELAP/SCDAPSIM limited to in-vessel behavior
– Source term and containment provided through links to
IMPACT/SAMPSON Modules from NUPEC
– RELAP/SCDAPSIM/MOD4 being extended for integrated source
term and containment response
• RELAP/SCDAPSIM computation times are longer than
MAAP and comparable to MELCOR
– DBA transients typically run 10-20 times faster than real time
– Typical SA transients run 1-5 times faster than real time
RELAP/SCDAPSIM allows much more
detailed representation of RCS/vessel
• RCS/Vessel nodalization more detailed than historical
DBA analysis using RELAP/TRAC
– 2D/3D core/vessel
– 2D lower plenum/vessel
– Detailed 2D core component modeling
• Typical SA input models use
– Several hundred TH volumes and RCS heat structures
– Five representative assemblies with 2 or more SCDAP
components
– Several hundred volumes in 2D lower plenum/vessel mesh
TML with AM and HPI
4: Tubes
Up Flow
10: Tubes
Up Flow
3: Hot Leg
5: Tubes
Down Flow
Pressurizer
11: Tubes
Down Flow
MAAP4 Nodalization
of RCS
9: Hot Leg
2: Upper
Plenum
1:Core
7: Cold Leg
13: Cold Leg
8: Downcomer
12: Crossover Leg
Intact Loop
6: Crossover Leg
Broken Loop
SCDAP/RELAP5
Nodalization of RCS
12
1
16
14
5 5 5 5 5
8 8 8 8 8
4 3 2 1 0
13
FR O M C O LD
LEG S
TO H O T
LEG S
10
2
59
3
8
75
49
39
29
19
74
73
72
71
6
5
RELAP/SCDAP
nodalization of
4-Loop RPV
2D connections allow
for cross flow due to
natural circulation or
loss of geometry
RELAP/SCDAPSIM models generally more
detailed
RELAP/SCDAPSIM
VS
• 6 equation, nonequilibrium hydro
• 2 D heat conduction
• Relocation of Zr-In, Zr-UO, (U-Zr)-O2
• Grid spacer interactions
• Molten pool (U-Zr)-O2
formation, growth, and
relocation
– Radial, axial (bypass lower
metallic layers)
MAAP/MELCOR
• quasi-equilibrium
hydrodynamics
• 1D lumped parameter
• Relocation of Zr-U-O
–
–
• Core slumping (user
defined temperature)
– Axial
– User defined (MAAP)
SCDAP will predict melting over
wide range of temperatures
Melting of (U-Zr)-O2
MAAP/MELCOR will
predict core slumping at
user specified
temperature
Liquefaction of Zr-O-U
Liquefaction of Structural
and Control Material
SCDAP can predict molten pool
relocation into lower plenum
even if core plate and lower
core intact
MAAP/MELCOR
Lower core and
plate must
slump before
upper material
can relocate
TMI-2 End State
RELAP/SCDAPSIM models generally more
detailed
RELAP/SCDAPSIM
• Reflood
– Oxide spalling
• Accelerated heating,
oxidation, melting
VS
MAAP/MELCOR
• Reflood
– Oxide spalling
(MELCOR)
• Accelerated heating,
oxidation, melting
– MAAP does not
consider oxide spalling
Oxide spalling during
reflood critical to predict
H2 and melt formation
RELAP/SCDAPSIM models generally more
detailed
RELAP/SCDAPSIM
• Reflood
– Debris formation
– Exterior cooling of molten
pool crusts
• Transient 2D lower
plenum debris/vessel
heat conduction and
molten pool convection
– Stratified formation
– Homogenous molten pool
VS
MAAP/MELCOR
• Reflood
– Debris formation (user)
– Exterior cooling of debris
beds (user)
• Steady state
analytic/lumped
parameter lower plenum
debris/vessel
– Stratified formation
– Stratified metallic/ceramic
(MAAP)
Assumptions on lower plenum
debris will impact vessel failure
Layers
formed by
debris/melt
relocation
Molten pool
(mixture)
Gap
cooling
Layers
formed by
debris/melt
relocation
MELCOR
SCDAP
Structural
material
Corium
MAAP
RELAP/SCDAPSIM user defined
parameters are intentionally limited
• System defined through TH nodalization,
selection of representative core and plenum
components and nodalization
– RELAP5 and SCDAP user guidelines and training
• RELAP5 modeling parameters used to control
flow regimes
– Established through RELAP5 validation activities
• SCDAP modeling parameters limited to critical
areas of modeling uncertainties
– Recommended defaults set through validation
activities
MAAP/MELCOR make extensive
use of modeling parameters to
adjust basic processes
• Extensive use of user defined parameters
make evaluation of trends very difficult
• Scaling of code-to-data comparison results
to plant behavior is unclear
– Modeling parameters are unique to facility
– Conservatism or non-conservatism may be
influenced by user choices