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