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Outline of Modeling and Simulation
for Thermal-Hydraulics Phenomena
in Japan Sodium-Cooled Fast Reactor
Fast Reactor Computational Engineering Department
Japan Atomic Energy Agency
Kei Ito*, Akihiro Uchibori, Norihiro Doda,
Masaaki Tanaka, Shuji Ohno, Hiroyuki Ohshima
Outline of TH R&D Activities in JAEA
Natural Circulation Decay Heat Removal (NC-DHR)
Subassembly Thermal Hydraulics
Gas Entrainment and Vortex Cavitation
High Cycle Thermal Fatigue
(Thermal Striping)
Thermal Stratification during NC-DHR
High Re Flow and Vibration in Piping
Thermal hydraulics in SG
(Sodium-Water Reaction)
Ex-vessel Event Evaluation
(Sodium fire)
Decay Heat Removal in Severe Accident
1
Thermal-Hydraulics-Related Computer Codes
2
Fuel Assembly (F/A)
ASFRE: Subchannel Analysis Code
SPIRAL: Local Detailed Analysis
BAMBOO: Deformation of Fuel Pins
SABENA: Sodium Boiling
Whole Core with Primary system
ACT: F/As + Core Barrel
+ Interaction with Upper Plenum
Plant System Analysis
Super-COPD: Plant Dynamics
(Steady State, Transients, Accidents)
SYRENA: Gas behavior dissolved
in Coolant in Primary System
Sodium-water Reaction (SWR) SERAPHIM: Multi-component & Multi-
phase Flow with Chemical Reaction
TACT: Heat Transfer and Failure of Tubes
RELAP5: Water Side Heat Transfer
Reactor Vessel and Piping
AQUA: General Purpose 3D Code (FDM)
SPIRAL: 3D RANS Code (FEM)
MUGTHES: 3D LES
(Thermal Interaction with Structure)
NERGAL: 3D Two-Phase Flow Code
Japan Sodium-cooled Fast Reactor
(JSFR)
Steam-Generator MSG: Coupling analysis of Sodium Flow
and Water Vapor System
Severe Accident (Core Disruptive Accident) SAS4A: Initiation Phase Analysis
SIMMER: Transition Phase Analysis
Sodium Leakage Analysis SPHINCS: Combustion (Zone Model)
AQUA-SF: Combustion (3D Model)
BISHOP: Chemical Reaction
Containment System Analysis CONTAIN/LMR: Thermal-hydraulics
and Source Term (Zone Model)
Natural Circulation Decay Heat Removal
Passive decay heat removal system with natural circulation in JSFR High reliability by simple DHRS design without pump and blower
High applicability to decay heat removal under accident conditions
Possibly-formed temperature distribution in core (local hot spot in core)
Evaluation of hot spot
DRACS:
1 unit
No Blower
No Pump
No Pony Motor
Redundant Dampers
No Pump
PHX
DHX
*
No Blower
Secondary Cooling System
Primary Cooling System
*) PRACS has a non-safety grade blower connected to a normal
Power Supply.
Air Cooler
PRACS: 2 units
Cooling Systems of JSFR 3
- Plant dynamics analysis code (Super-COPD) - Subchannel analysis code (ASFRE)
Hot Spot Evaluation
STEP1: Plant Dynamics Analysis
Whole core uncertainties are treated
through the values of the BC.
In-Core local uncertainties are treated
through the values of the BC.
STEP2: Plant Dynamics Analysis
STEP3: 3D-simulation in Hottest Assembly
Intra-Assembly uncertainties are treated
through the values of the BC.
Core Condition Init. Condition
Uncertainties
①Whole Core
②In-Core Local
③Intra-Assembly
Subchannel Analysis
Flow rate, Temperature
He
at F
lux
es
B.C.
B.C.
B.C.
Maximum cladding temperature are obtained.
Plant Dynamics Analysis
PRACS A/C
炉容器上部 RV Upper
Prelum
炉容器下部 RV Lower
Plenum ポンプ Pump
IHX
2次系
Secondary
Loop
炉心部
DRACS A/C
Core
A hot channel candidate in the core are identified.
BC of the hottest channel are obtained.
(flow rate, inlet coolant temp.,
heat flux at walls of wrapper tube)
Three-step evaluation method
4
XX10
XX09
Application to EBR-II (IAEA) Benchmark
Blind calculation of PLOF test (SHRT-17) - Flow rates and temperature distributions in primary loop by Super-COPD
- Detailed TH in two experimental subassemblies by ASFRE
Flow network model for PHTS
Core model with all channels of S/A
Super-COPD ASFRE
Achievement of qualitatively-good reproduction of test data
=> Further model improvement
5
Wrapper tube
Fuel pin Wire spacer
Coolant flow
Subchannel
Evaluation of Thermal-Hydraulics in Fuel Assembly
Calculation Meshes
Horizontal Plane
Pin-Surface
: Prism Element: Hexa Element
Wrapper Tube
Fuel Pin
Wire Spacer
Horizontal Plane
Fuel Subassembly Calculation Meshes
Horizontal Plane
Pin-Surface
: Prism Element: Hexa Element
Wrapper Tube
Fuel Pin
Wire Spacer
Horizontal Plane
Fuel Subassembly
Data for
Modeling
Validation
Deformation
Data
Correlations
Boundary
Cond.
Data for Model
ValidationBoundary
Cond.
Experiments Whole Assembly Simulation
Subchannel Analysis Code
ASFRE
Local Detailed Simulation
FEM Code with RANS
SPIRAL
Direct Simulation
Body-Fitted DNS
BAMBOO
Temp.
Data
Fuel Deformation
Simulation Numerical Simulation System
Three TH analysis codes
+
Fuel deformation analysis code
Fuel assembly modeling 6
Simulation
4,638 elements in horizontal plane
Vz/Vm
1.2
0.6
0.0
Experiment (PIV)
Axial velocity distribution
(Averaged
velocity: Vm)
Simulation Results of Flow around Fuel Pin
Coolant
flow
Simulation of three-pins bundle exp.
Simulation Mesh
Very good agreement between
experimental data and simulation result
3D FEM code: SPIRAL Numerical stabilization:
BTD, SUPG
Time integration: Semi-implicit
Pressure solver:
ICCG + LU decomposition
Turbulence model:
Hybrid two-equation
turbulence model
7
Japan Sodium-cooled Fast Reactor (JSFR) : Compact Reactor Vessel (RV) High Coolant Velocity in RV
(Upper Plenum Region)
TH issues in upper plenum:
Complicated flows with non-linearity
(e.g. interfacial flow in GE)
Development of high-precision
numerical simulation code for
each TH issues
Thermal Stratification
Flow Induced Vibration
Thermal Striping
Outlet
Pipe
Inlet Pipes
Interface
Gas Core
Pinch-off
Bubbles
Gas Entrainment (GE)
TH Issues in Upper Plenum of JSFR
8
Development of Interface-Tracking Code for GE
Complicated flow filed
=> Accurate modeling of structural shape
with unstructured mesh scheme
Large interfacial deformation
=> Improvement of high-precision
volume-of-fluid (PLIC) method
on unstructured mesh
Non-linearity of two-phase flow
=> Physically appropriate calculations for
momentum transport and velocity-pressure
coupling at gas-liquid interface
Surface tension modeling
=> Precise curvature calculation algorithm
with grid convergence
Application to large-scale simulation
=> Employment of high-speed matrix solver
and massive parallelization
Conventional Improved
Simulation of static circular bubble
1.0
0.123.0
4.0
2.0
1.0
0.00.0 1.0 2.0 3.0 4.0
x
y
Slotted-disk Revolution*1
Slotted-disk revolution problem
Algorithm Error
Structured
SLIC*
FCT-VOF*
PLIC*
Unstructured
CICSAM
Gauss-Green
Improved
8.38 x 10-2
3.29 x 10-2
1.09 x 10-2
2.02 x 10-2
1.23 x 10-2
0.95 x 10-2
* Rudman, M., Int. J. Numer. Meth. Fluids (1997)
9
Interfacial Dent Caused by Vortex
Entrained Bubble
Gas-Liquid Interface
Suction Pipe
Suction Flow
Outlet Pipe
Gas-Liquid Interface
Bottom Plate
Interfacial Dent
Entrained Bubble
Simulation Results of GE Phenomena
Simulation of GE occurrence
in simple exp.
Simulation of GE in 1/1.8 upper plenum model
Good (qualitative) agreements of
simulation results with experimental data
=> Positive outlook on reproducibility
of GE phenomena in JSFR
with developed simulation code
Application of developed simulation code to GE phenomena
10
Evaluation of GE Flow Rate
Simulation result
Gas flow
Vortex
Gas
Inlet slit
Cylindrical container
Suction pipe
Buffer tank (bubble catcher)
Uniform inlet flow
Outlet flow
Simulation Mesh
Simulation of basic exp. for measurement of GE flow rate
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Experiment
Simulation
Exp. silicone
Sim. silicone
En
trai
ned
gas
flo
w r
ate
m3/s
Outlet liquid velocity m/s
Water Silicone oil
[x 10-5]
Gas entrainment flow rate
- Successful evaluation result
of GE flow rate
- High reproducibility of
fluid property influence
11
High-Cycle Thermal Fatigue
(UIS)
Backup Control Rod (BCR) ChannelPrimary Control Rod (PCR) Channel
Fuel
Subassemblies
Contorol
Rod
Driving
Shaft
1st Baffle Plate
Core Instruments Plate
(CIP)
Upper
Guide
Tube
Flow-hole
Hot
SodiumHot
Sodium
Cold
Sodium
Blanket Fuel
SubassemblyFuel
Subassemblies
Cold
Sodium
Target areas related
to thermal fatigue
(UIS)
Illustration of
Japan Sodium-cooled
Fast Reactor (JSFR)
High-cycle thermal fatigue at core outlet
12
Specification of MUGTHES code
Numerical method: Projection method and Crank-Nicolson scheme
Discretization schemes 2nd order central differential for momentum eq.
for advection terms: High-order upwind scheme with oscillation control for energy eq.
Large eddy simulation: Standard Smagorinsky Model with van Driest function
Wall function: 3 Layer model (Viscous sub layer, Buffer layer, Log-law)
Thermal diffusion: MILES approach (implicit LES without physical model)
Thermal interaction: Conjugated heat transfer between unsteady thermal-hydraulics
module and unsteady heat conduction module for structure
Parallel computing: SPMD (thread parallel with OpenMP)
Validations:
○Fundamental Validation: Back-facing step flow, Cavity flow,
Unsteady heat transfer problem in structure
○Separate Effect Test (SET): T-pipe mixing and jets mixing tests
○Component Effect Test (CET): Five jets experiments (Water/Sodium)
○Integrated Effect Test (IET): 1/3-scale 60˚-sector experiment
MUGTHES : 3D LES (large eddy simulation) code Prediction of thermal mixing phenomena and thermal response of structure
in the field with thermal interaction between fluid and structure
13
- Code verification
(e.g. Convergence tests with benchmark problem)
- Solution verification
(Uncertainty quantification with GCI estimation)
- Fundamental validation with problems in literature
and separated effect tests (SETs)
- Validation with component and integrated
effect tests (CET & IET)
Analysis of High-Cycle Thermal Fatigue
② Local analysis ① Whole upper
plenum analysis
V&V with Uncertainty Quantification
<Spatial connection model>
Whole Domain analysis (with RANS code: AQUA)
→ Local Analysis (with Flow-Structure
Thermal Interaction LES code: MUGTHES)”
→ Transient temperature data in structure
→ Thermal stress analysis (with FINAS code)
Development of Evaluation Methods
Code V&V and Evaluation Methods Development
(PCR) (BCR)
Instantaneous numerical
results of fluid temperature
B.C.
14
Study on Sodium-water Reaction
= Failure propagation
• Occurrence of failure propagation expansion of damage, long-term shutdown, …
• Prevention of failure propagation is major concern in safety assessment of SG
• Development of numerical method to evaluate possibility of failure propagation
occurrence
• Multi-physics phenomena (multiphase flow, chemical reaction, structure, material)
Wastage penetration
Over-heating rupture
Water side: about 15 MPa
Shell side: 0.2 MPa
SG (evaporator) in FR “Monju”
High-velocity & high-
temperature reacting jet Na
Failed tube Adjacent tube
Sodium-water reaction
Water,
vapor
Erosion FAC Combination of them
Strength degradation
Wastage
Over-heating
rupture
15
Numerical Method (Analysis System)
(3) RELAP5 code
(2) TACT code
(1) SERAPHIM code
Evaluate behaviors of reacting
jet & wastage environment
Analysis system consists of multiple computer codes which are based on
mechanistic numerical models.
Compressible multicomponent
multiphase flow model (DM)
Chemical reaction model
Wastage environment
evaluation model
Evaluate heat transfer between fluid and
tube & possibility of failure propagation
Fluid-structure thermal coupling model (DM)
Stress evaluation model (FEM)
Wastage model
Failure judgment model
Evaluate thermal hydraulic
behavior of water inside tube
Two-fluid model (DM)
Heat transfer correlation
B.C. B.C.
(1) (2)
(3)
16
Analysis of SWAT-1R Test by SERAPHIM
400mm
18
00
mm
Tube bundle
Liquid
sodium
Inflow of
water vapor
0.2 sec 0.5 sec 1.0 sec
Iso surface
of α = 0.1
Expansion of gas phase
(void fraction)
Computational domain
Mean temperature
distribution
0.0 1.0 [-] 400 1400 [C]
Analysis (weight
averaged
temperature) Experiment
• High temperature region expands to upper
left both in the experimental result and the
numerical result
• Calculated maximum temperature is almost
equal to measured one
Pressure of sodium : 0.2 [MPa]
Temperature of sodium (initial) : 470 [C]
Pressure of vapor (inflow) : 17.0 [MPa]
Temperature of vapor (inflow) : 352 [C]
17
(%) (oC)
Sodium Fire Analysis
for 3D effect analysis
Simulation System
配管 スプレイ燃焼
プール燃焼
床
液滴燃焼配管配管 スプレイ
燃焼
プール燃焼
床
液滴燃焼Spray fire
Pool fire
Floor plate
Na pipe Droplet combustion
Simulation of spray fire with AQUA-SF
(%) (oC)
Velocity & Temperature
Oxygen concentration
Mechanistic evaluation
of sodium fire with 3D
simulation code
18
Conclusion
In Japan Atomic Energy Agency, simulation codes (simulation systems) have
been developed to evaluate the thermal-hydraulics phenomena in JSFR.
In this presentation, the simulation models for the following phenomena were
introduced.
Natural Circulation Decay Heat Removal (NC-DHR)
Subassembly Thermal Hydraulics
Gas entrainment (Gas–liquid interfacial flow)
High Cycle Thermal Fatigue (Thermal Striping)
Thermal hydraulics in SG (Sodium-Water Reaction)
Ex-vessel Event Evaluation (Sodium fire)
19