[B4C-SS Eutectic]
Thermophysical property of eutectic melting material of control rods for severe accident analyses in fast reactors

RESEARCH OVERVIEW

• In the severe accident analysis of sodium-cooled fast nuclear reactors, the simulation of the eutectic reaction between boron carbide (B₄C) as a control rod, and stainless steel (SS) as a cladding material, is very important. In order to develop a physical model for the simulation, the thermophysical properties of the B₄C-SS eutectic mixture is necessary.
• The Thermophysical Property of Eutectic Melting Material of Control Rods for Severe Accident Analyses in Fast Reactors (ELF-B₄C-SS Eutectic) study collects data on the thermophysical properties of the B₄C-SS eutectic mixture, which cannot be obtained on Earth using current available technologies.
• Since this is the first time that this data has been obtained, it will be very useful in creating a database of this material for use around the world. In addition to use in sodium-cooled fast reactors, the information can also be used in basic safety databases for severe accident analysis of existing light water reactors, and has applications in other novel reactor concepts.

DESCRIPTION

In severe accident analyses of sodium-cooled fast reactors, it is considered that boron carbide (B₄C) (as a control rod) comes into contact with stainless steel (SS) (as a cladding material) to cause a eutectic melting reaction, and the resulting substance diffuses into the reactore core. However, the physical model is not currently incorporated into the severe accident analysis code. Therefore, in order to develop a physical model that can simulate the eutectic melting reaction, the thermophysical properties of the B₄C-SS eutectic melting substance are necessary, as they have yet to be obtained. Recently at Tohoku University, thermophysical property data of eutectic melt with low B₄C concentration was obtained by utilizing electromagnetic levitation methods, but the data of eutectic substances with high B₄C concentrations could not be obtained using this same method.

The purpose of the Thermophysical Property of Eutectic Melting Material of Control Rods for Severe Accident Analyses in Fast Reactors (ELF-B₄C-SS Eutectic) study is to measure the thermophysical properties of B₄C-SS eutectic melt with high B₄C concentration under high temperature in the microgravity environment. Under high melting point temperatures, it is difficult to melt and float a sample on the ground. Under microgravity conditions in space, it is possible to “levitate” a sample, which can be melted with a laser, in order to reach the needed high temperatures.

The measurement itself does not require much time to gather data, but several days are required for data processing. Therefore, the process depends on the number of data points collected.

SPACE APPLICATIONS

Attempts have been made to float and melt these types of samples in a high vacuum environment. However, since the liquid phase cannot be obtained due to evaporation of the sample, it is necessary to perform an experiment in a pressurized gas environment on the space station that can suppress evaporation.

EARTH APPLICATIONS

Experiments in this investigation can yield a better understanding of the physical properties controlling the B₄C-SS eutectic melting substance, that can benefit severe accident analysis of nuclear reactors on Earth. These experiments can also improve the reliability of computer codes that simulate liquid mixing, which are useful in many materials science and industrial applications. Results may also benefit research on eutectic melt using levitation technology.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

The Electrostatic Levitation Furnace (ELF) instrument is assembled and installed in the Multi-Purpose Small Payload Rack (MSPR/MSPR2) in Kibo. After setup, the experiment is operated from ground control as required by investigators at Space Station Integration and Promotion Center (SSIPC), Tsukuba Space Center. The experiment procedures:

1. A crew member prepares the experiment by inserting the Sample Holder into the Sample Cartridge, and inserting the Sample Cartridge into the ELF chamber. The ELF is then activated and configured for operation.
2. To begin experiment operations, the sample is released into Experiment Volume by the Sample Release Rod. The Sample is charged, position controlled, heated, and melted using electrodes and Power Lasers. During operations, the sample is measured through sensors and cameras.
3. At the completion of experiment operations, recorded video, pictures, and data are downlinked to Earth.
4. The experiment is closed out by the deactivation of ELF.

YAMANO Hidemasa [JAEA]