Debris remelting experiments and simulations

Lu Zhao, Andrei Komlev

Division of Nuclear Science and Engineering (NSE)

Royal Institute of Technology (KTH)

Half-time webinar. June 4^th

Outline

• Introduction
• Single Particle Slice (SPS) melting tests
• MPS preliminary simulation of debris bed melting
• Conclusion and outlook

2

Introduction

Simplified  in-vessel accident progression

3

Debris remelting process and significance

• Debris remelting, dynamic of melt formation and relocation, heat transfer in the lower plenum provide the conditions for determining thermo-mechanical loads on the lower head wall and structures (such as IGTs and CRGTs).

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• The evolution of in-vessel debris bed plays an important role in accident progression, including vessel failure mode and melt discharge upon vessel failure.

4

Debris melting study approach

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Particulate bed melting tests

Focus of current study: Particulate bed melting in a local geometry to obtain data for validation of debris melting models (e.g., MPS modeling)

Particulate bed under dry condition

A particulate bed with a thickness of Single Particle in Slice geometry (SPS)

Corium debris bed simplification:

• Uniform spherical and cylindrical particles
• Uniform particles distribution
• Low temperature simulant materials: Paraffin and SnBi
• No chemical interaction between particles

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SPS-1 test section concept

Sphere of oxidized Carbon steel AISI1010

(D = 6 mm)

Cylinders of paraffine wax

(D = 6.0; H = 6 mm)�(T_melting = 65 °C)

FBG connection

Test section

Inductor

300 mm

Component ratio:

14 steel layers

15 paraffin layers

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SPS-2 test section concept

Sphere of Sn-Bi alloy �(D = 5.9 mm) �(T_melting = 139 °C)

Cylinders of paraffine wax

(D = 5.9 mm)�(T_melting = 65 °C)

Component ratio:

22 SnBi layers

7 paraffin layers

to keep specific hight between molten layers

8

SPS-1 experiment performance

Melting

(20 times speeded up)

Solidification

(40 times speeded up)

Level of molten paraffin

9

SPS-1 temperature map

2 min

3 min

4 min

5 min

6 min

7 min

°C

160

140

120

100

80

60

40

20

10

SPS-2 experiment performance

Melting

(40 times speeded up)

Solidification

(40 times speeded up)

Level of molten paraffin

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SPS-2 temperature map

5 min

10 min

15 min

17.5 min

20 min

25 min

30 min

35 min

°C

160

140

120

100

80

60

40

20

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• Moving particle semi-implicit (MPS) method is employed

MPS modelling approach

Example: water column collapse

• Lagrangian approach for incompressible free surface flow
• The computation domain is represented by particles
• Pressure term is calculated implicitly

• What is MPS method?

• Why choose MPS method here?

• Allows large deformation of interfaces
• No convection term
• Easier to generate particle configuration

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• Nuclear Engineering

Application of MPS code developed at KTH

• Chemical Engineering

• Vehicle Engineering

Melt dry spreading

Melt underwater spreading

Melt penetration into debris bed

Powders mixing in a roller

Car driving through a shallow water pool

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• This simulation is pre-design which does not represent debris structure in the experiment.
• This simulation assumes 50vol% paraffin and 50vol% carbon steel particles are initially relocated in a rectangular geometry (L=0.15 m, H=0.15 m).
• Paraffin and carbon steel particles are assumed to be in the form of sphere with a diameter of 7 mm and 6 mm, respectively.
• The volumetric power distribution is nonuniform, lower at the top and bottom of the debris bed.

3D simulation of debris bed remelting

Note: The power is artificially increased to reduce computational time which does not represent the reality.

Thermophysical properties and initial conditions

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Debris bed remelting and relocation

• With gradual remelting of paraffin, liquid paraffin drains downward to fill gaps among solid particles. Both the carbon steel and paraffin particles migrate downward due to change of support forces.
• With further melting, carbon steel particles continue to move downward in the molten pool. Some of the paraffin particles float in the molten pool, while others are trapped between carbon steel particles.
• Finally, carbon steel particles settles at the bottom of the molten pool.

Time: 20 s

Time: 50 s

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Conclusion and outlook

• SPS-1 and SPS-2 tests were performed to provide data for modelling and MPS debris melting model validation

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• The data includes particles melting dynamics, melt infiltration, temperature distribution, and molten pool formation

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• The MPS code is employed to perform simulation of particulate bed melting, and preliminary results show its capability in capturing the key characteristics of particulate bed melting

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• The next step is to perform more tests, and to validate the MPS code against SPS tests

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Thank you for your attention

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Main equations

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