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The second Japan/US Program on Irradiation Tests for Fusion Research (JUPITER-II) began on April 1, 2001. Part of the collaborative research centers on the study of the molten salt 2LiF2-BeF2 (also known as Flibe) for fusion applications. Flibe has been proposed as a self-cooled breeder in both magnetic and inertial fusion power plant designs over the last twenty years. The key feasibility issues associated with the use of Flibe are

• corrosion of structural materials by the molten salt,
• tritium control in the molten salt blanket system,
• safe handling practices and releases from Flibe during an accidental spill.

The neutron irradiation of Flibe will deplete the lithium and produce free fluorine and/or TF (tritiated hydrofluoric acid). Both of these materials are extremely corrosive to structural materials. Thus, a redox agent is needed to control the free fluorine in the system and minimize the overall corrosion in a fusion blanket.

For fusion applications, Be is a natural choice for a redox agent because of the need to have Be in the blanket for neutron multiplication. Accordingly, the first phase of the MSTCE research is directed at examining Be as a redox agent in both dissolved and solid phase molten salt. Electrochemical and traditional tritium measurement techniques will be used to:

• record the change in tritium's chemical state (T2 versus TF) when Be is introduced,
• elucidate chemical reactions occurring in the molten salt,
• determine tritium transport properties in the molten salt.

Once successful redox control has been demonstrated for short time periods in a small volume, the second phase of the experimental program will focus on longer duration time periods using the derived redox control technique and selected fusion materials of interest (e.g. SiC, V, ferritic steel, etc.). Beyond the corrosion/tritium control experiments, separate experiments will concentrate on using a variety of electrochemical and traditional tritium measurement techniques to record the diffisivity, solubility, and permeability of tritium in the molten salt.

The key safety issue associated with Flibe is the interaction of air, moist air, or steam with the molten salt and the consequential mobilization of vapors and aerosols. In order to quantify this mobilization, experiments on Flibe-air, Flibe-moist air, and Flibe-steam interactions will be performed. These interactions will be created by introducing the reacting gas (air, moist air, steam) into the Flibe and characterizing the resulting vapors and aerosols in terms of:

• total and elemental mobilization,
• mass, volume, and chemical form of the aerosols,
• non-condensible gas species.

Figure 1 shows a “pot” that will be used for the mobilization studies. Figure 2 presents an exploded view of the pot components. In the figure, one sees the copper cooling jacket and lid, the heating structure, and the stainless pass-thru's for the gas.

Figure 1: Assembled “pot” for the MSTCE mobilization experiment

Figure 2: Cooling and heating components of a pot.

The final phase of the MSTCE experiments will be the Fusion Liquid Release Experiments (FLIQURE). FLIQURE will use a Cf-252 source to irradiate the Flibe. This irradiation will induce via nuclear transmutation tritium, free fluorine, and F-19. The presence of F-19 isotopes is of significant importance due to its radiological implications. Mobilization of the tritium, free fluorine, and F-19 will be studied by creating an air or steam ingress.