MC3D Premixing Analysis using X-Ray Radioscopy ... · PDF fileRESEARCH ERMSAR 2017 MC3D Premixing Analysis using X-Ray ... •KROTOS Radioscopy Data Analysis for KFC Test and KS-Series

May16-18, 2017

Warsaw, Poland

8TH CONFERENCE

ON SEVERE ACCIDENT

RESEARCH

ERMSAR 2017

MC3D Premixing Analysis using X-Ray

Radioscopy Experimental Data

of KROTOS-SERENA Tests

M. Leskovara, V. Centriha, M. Uršiča,

N. Cassiaut Louisb, C. Brayerb, P. Pilusob

aJožef Stefan Institute, Ljubljana, Slovenia

bCEA Cadarache, France

ERMSAR 2017, Warsaw, May 16-18, 2017

Outline

• Introduction

• Experimental observations

• KROTOS-SERENA X-ray radioscopy experimental data

• New insights for MC3D modelling

• MC3D premixing simulations

• Melt jet release and breakup modelling

• Lateral premixture extension analysis

• Conclusions

2


Introduction

• Steam explosion

• During a severe accident, molten core may be released from failed reactor vessel into flooded

reactor cavity → Fuel-Coolant Interaction (FCI)

• Important condition for possible steam explosion is premixture formation

• OECD SERENA Phase 2 project

• Experimental and analytical part

• 12 complementary tests in KROTOS (CEA) and TROI (KAERI) facilities

• 6 KROTOS-SERENA (KS) tests performed (KFC, KS-1 to KS-6)

• Goal: Improving understanding and modelling of FCI processes, increasing the capabilities of FCI

models/codes for use in reactor analyses

• Comprehensive report on KROTOS X-ray data analysis by CEA:

• KROTOS Radioscopy Data Analysis for KFC Test and KS-Series Tests, N. Cassiaut-Louis & D.

Grishchenko, 2016

• Objective of the work: Improve understanding and modelling of premixing processes based on X-ray data

3


KROTOS KS Experimental Data

• KROTOS experimental facility – melt poured into water pool

4

KFC KS-1 KS-2 KS-4

Water level

Water depth

0.00 m

0.15 m

0.30 m

0.45 m

0.60 m

KS-5

KS-6

Water: 1145 mm

• Pressure transducers, Video

camera, Pyrometer, Water level

transducer, Thermocouples -

water temperature, Sacrificial

thermocouples - detection of

melt propagation

• X-ray radioscopy (200 x 300 mm

window) – position varied


KROTOS KS X-Ray Data

• KROTOS radioscopy data analysis

• X-ray images analysed and post-processed (KIWI software, CEA)

• Qualitative and quantitative data for corium and void obtained

• Results of image analysis:

1. Corium volume and surface area per fragment

2. Cumulative corium volume in the premixture

3. Velocity of corium fragments and jet characteristic points

4. Void volume and surface area

5. Void volume distribution in Cartesian and axisymmetric

cylindrical coordinates (provided only at triggering time)

• Important for our MC3D (IRSN) analysis:

• Evolution of corium passing through X-ray window

• Evolution of void volume and fraction within X-ray window

• Void volume distribution at triggering time

5

Post-processed:

Void

Post-processed:

Melt & Void


Experimental Observations - Corium

• Experimental data for melt jet release determination

• Sacrificial thermocouples

• X-ray corium data: KFC and KS-1 test

Image position near water level – not so complex premixing

Better estimation of mass flow rate

• Cumulative delivered mass (X-ray corium data in diagrams)

6

0

0,5

1

1,5

2

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Cum

ula

tive

co

riu

m m

ass

[kg

]

Time [s]

Total

Inframe

Below

KFC

0

0,5

1

1,5

2

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Cum

ula

tive

co

riu

m m

ass

[kg

]

Time [s]

Total

InFrame

Below

KS1

KFC KS-1 KS-2 KS-4

Water level

Water depth

0.00 m

0.15 m

0.30 m

0.45 m

0.60 m

KS-5

KS-6

Water: 1145 mm

• KFC test

No fusible disc → fast initial

droplet spray

• KS-1 test

Fusible disc → suspended

melt release, gravity pour

Slope → melt mass flow rate


Experimental Observations - Corium

• Three main melt jet parameters may be revised based on X-ray corium data analysis

1. Melt mass flow rate

From jet diameter & velocity at water level → 4.4 kg/s

Slope of KS-1 cumulative corium evolution → 3.6 kg/s Slight under-prediction expected (smallest droplets not seen)

Estimation ~ 4.0 kg/s

2. Jet impact velocity

From thermocouples: all tests 3.3 to 4.1 m/s KS-1 → 3.6 m/s

KS-4 → 3.3 m/s (additional guide tube)

X-ray data: KS-1 → 3.6 m/s

3. Jet breakup length

From thermocouples: 35 – 46 cm

From X-ray images: 25 – 30 cm

7

KS1 rate = 3,6135

KFC rate1 = 6,7601

KFC rate2 = 2,2374

0,0

0,5

1,0

1,5

2,0

0,2 0,4 0,6 0,8 1 1,2

Cu

mu

lati

ve c

ori

um

mas

s [k

g]

Time [s]

KS1

KFC

KS1 rate

KFC rate1

KFC rate2


MC3D Modelling

• MC3D (IRSN) mesh and calculation conditions

• Only premixing phase simulated

• KS-4 test conditions applied

8

Corium

Water

Calc. mesh20 x 120 cells

MC3D v3.8

KS-4 x-rayframeposition

Experimental KS-4 conditions

Initial melt temperature 2963 K

Melt mass 3.2 kg

Water temperature 333 K

Ambient pressure 0.21 MPa

Sub-cooling 60 K

Material properties

80% UO2 / 20% ZrO2 Near eutectic

Liquidus/solidus temperature 2920 K / 2870 K

Latent heat 280 kJ/kg

Specific heat (liquidus/solidus) 510 / 450 J/kg∙K

Density 6866 kg/m3

MC3D modelling conditions

Jet fragmentation model Global model

Fragmentation rate coefficient 0.075 m3/m2/s

Sauter diameter 2.5 mm

Release nozzle diameter, exp. / sim. 30 mm / 25 mm

Calculation time 2 s

Release nozzle


Premixing Modelling – Melt Jet Release

• Mass flow rate

• May be adjusted by release system geometry corrections

• → adjusting release nozzle diameter: 3 cm → 2.5 cm

• Mass flow rate: 4.0 kg/s

9

D30 ... 5,0633

D27 ... 4,4691

D25 ... 4,0081

D24 ... 3,6433

D22 ... 3,2702

0,0

0,5

1,0

1,5

2,0

2,5

3,0

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Cu

mu

lati

ve

co

riu

m m

ass

[k

g]

Time [s]

D30

D27

D25

D24

D22

KS1

3

3,5

4

4,5

5

5,5

2,2 2,4 2,6 2,8 3M

ass

flo

w r

ate

[k

g/s

]Nozzle diameter [cm]

Mass flow rate

Experimental

boundaries

Mass flow rate 4.0 kg/s at

2.5 cm nozzle diameter


Premixing Modelling – Melt Jet Release

• Jet impact velocity

• May be controlled by release system height adjustments

• Simulations in good agreement with analytical solution

• Experimental height 1.9 m gives 3.8 m/s impact velocity

• Not changed

• Jet fragmentation length

• MC3D global jet fragmentation model - fragmentation rate

coefficient (FR)

• FR = 0.075 m3/m2/s (default)

• Jet breakup length: 28 cm

corresponds to X–ray data results

• FR kept default

10

3,1

3,2

3,3

3,4

3,5

3,6

3,7

3,8

3,9

4

1,65 1,70 1,75 1,80 1,85 1,90 1,95

Imp

act

ve

loci

ty[m

/s]

Release height [m]

Simulation impact velocity

Analytical solution

5

10

15

20

25

30

35

0,05 0,1 0,15 0,2 0,25 0,3

Jet

bre

aku

p le

ng

th [

cm]

Fragmentation rate [m3/m2/s]

D = 3 cm

D = 2.5 cm

3,1

3,2

3,3

3,4

3,5

3,6

3,7

3,8

3,9

4

1,65 1,70 1,75 1,80 1,85 1,90 1,95

Imp

act

ve

loci

ty[m

/s]

Release height [m]

Simulation impact velocity

Analytical solution

5

10

15

20

25

30

35

0,05 0,1 0,15 0,2 0,25 0,3

Jet

bre

aku

p le

ng

th [

cm]

Fragmentation rate [m3/m2/s]

D = 3 cm

D = 2.5 cm


Comparison with Experimental Data

11

• Melt jet propagation

Initial good agreement, but ovepredicted melt

penetration in simulation after full jet breakup

Melt bottom contact: Sim 0.86 s, Exp 1.18 s

• Void fraction evolution

Global (full line) and within X-ray

window (dashed line)

Similar void fraction development,

but shifted (delayed) in simulation

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Fro

nt

jet

po

siti

on

[m

]

Time [s]

Experiment

Melt Front

water height at 1.15 m

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Void

frac

tio

n

Time [s]

Exp. Total

Exp. Frame

Sim. Total

Sim. Frame


Comparison with Experimental Data

• Lateral premixture extension

• Defined as radius inside which 80% of void in each horizontal slice is present

12

initial water level

0,745

1,045

0 0,1

KS-4 test (extension yellow curve) Simulation (extension blue curve)

• Results presented at time of MBC (similar premixture state but not same time)

• Not very reasonable to compare such complex phenomena based on a single snapshot in a time → averages

Added experimental results

(extension yellow curve)


Lateral Premixture Extension – Parametric Analysis

• X-ray data indicated influence of subcooling on lateral premixture extension

• Premixture more focused around corium stream at higher subcooling (120 K in KFC, KS-1) than at

lower subcooling (60 K in KS-4)

• Parametric analysis: Water subcooling varried from 30 K - 120 K

• Decreasing trend in void and melt lateral extension

• Lateral premixture extension probably corresponds to global void differences

13

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

Mat1

Mat2_R

Mat3

Mat4

MATERIAL Global void fraction

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

T=30K

T=60K_R

T=90K

T=120K

SUBCOOLING Global void fraction

0

0,01

0,02

0,03

0,04

0,05

Mat1 Mat2_R Mat3 Mat4

Vo

id e

xten

sio

n r

adiu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

0

0,01

0,02

0,03

0,04

0,05

T=30K T=60K_R T=90K T=120K

Vo

id e

xten

sio

n r

adiu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

0

0,01

0,02

0,03

0,04

0,05

Mat1 Mat2_R Mat3 Mat4

Mel

t ex

ten

sio

n r

adiu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT

0

0,01

0,02

0,03

0,04

0,05

T=30K T=60K_R T=90K T=120K

Mel

t ex

ten

sio

n r

adiu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT


Lateral Premixture Extension – Parametric Analysis

14

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

V=0.0

V=0.1

V=0.3

V=0.5_R

V=0.7

V=0.9

V=1.0

VEJDR Global void fraction

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

TURB=0.0_R

TURB=0.5

TURB=1.0

TURB=2.0

TURB. DIFFUSION Global void fraction

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

FR=0.075_R

FR=0.1

FR=0.2

FR=0.25

FRGFLM Global void fraction

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Vo

id f

ract

ion

Time [s]

Experiment

D=1.5 mm

D=2 mm

D=2.5 mm _R

D=3 mm

D=4 mm

DIACRE Global void fraction

0

0,01

0,02

0,03

0,04

0,05

TURB=0.0_R TURB=0.5 TURB=1.0 TURB=2.0

Vo

id e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

0

0,01

0,02

0,03

0,04

0,05

D=1.5 mm D=2 mm D=2.5 mm _R D=3 mm D=4 mm

Vo

id e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

0

0,01

0,02

0,03

0,04

0,05

V=0.0 V=0.1 V=0.3 V=0.5_R V=0.7 V=0.9 V=1.0

Me

lt e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT

0

0,01

0,02

0,03

0,04

0,05

TURB=0.0_R TURB=0.5 TURB=1.0 TURB=2.0

Me

lt e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT

0

0,01

0,02

0,03

0,04

0,05

FR=0.075_R FR=0.1 FR=0.2 FR=0.25

Me

lt e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT

0

0,01

0,02

0,03

0,04

0,05

D=1.5 mm D=2 mm D=2.5 mm _R D=3 mm D=4 mm

Me

lt e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

MELT

0

0,01

0,02

0,03

0,04

0,05

V=0.0 V=0.1 V=0.3 V=0.5_R V=0.7 V=0.9 V=1.0

Vo

id e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

0

0,01

0,02

0,03

0,04

0,05

FR=0.075_R FR=0.1 FR=0.2 FR=0.25

Vo

id e

xte

nsi

on

ra

diu

s [m

]

Simulation

R_water

R_x1

R_x4

VOID

1. Radial melt droplet velocity VEJDR coefficient varied: 0.0 – 1.0

Increasing trend reflected only in lateral melt extension

Initial increase in void extension, later slight decrease - too

diluted melt droplets cannot produce large void in outer regions

2. Turbulent diffusion term Coefficients varied: 0.0 – 2.0

Decreasing trend in void extension, probably related to melt

droplet dilution

3. Jet fragmentation rate FRGFLM coefficient: 0.075 – 0.25

A rather stochastic influence observed

4. Melt droplet diameter Sauter diameter: 1.5 – 4.0 mm

Distinct decreasing trend, probably related to global void

Sa

ute

r d

iam

ete

r

F

rag.

rate

co

ef.

T

urb

. d

iffu

sio

n

R

ad

ial ve

locity


Conclusions

• Post-processed innovative X-ray radioscopy data of KROTOS-SERENA tests provide important new insight

into complex premixing process and opened various possibilities for improved analytical work

• Premixing analysis with MC3D performed

• X-ray data enabled appropriate modelling of melt release and more accurate determination of jet

breakup length → prerequisite for reliable experiment calculations

• Influence of experimental conditions and model parameters on lateral premixture extension analysed

• Analysis confirmed X-ray data indications that lateral premixture extension decreases with

increasing water sub-cooling

• Lateral premixture extension is driven mainly by amount of local produced vapour → emerging

vapour pushes water and melt droplets towards tube wall

• Influence of individual parameter complex → not straightforward to establish appropriate

modelling parameters even if some local experimental data is available

• Experiments with larger X-ray window and higher spatial resolution would be beneficial

15

Documents

MC3D Premixing Analysis using X-Ray Radioscopy ... · PDF fileRESEARCH ERMSAR 2017 MC3D Premixing Analysis using X-Ray ... •KROTOS Radioscopy Data Analysis for KFC Test and KS-Series