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The Fusion LIQUid Release Experiment (FLIQURE) was designed to study the mobilization behavior of tritium in molten Flibe (2LiF, BeF2) under controlled neutron irradiation and temperature conditions. Nuclear interactions between the source neutrons and the lithium and beryllium atoms in the Flibe will produce tritium while interactions with the flourine will produce a variety of radioactive isotopes, most notably F-18. The experiment will focus on the physical and chemical forms and mobilization rates of the radioactive isotopes and toxic-material species from the Flibe under inert-gas, air, and steam-ingress conditions at fusion-relevant temperatures (500 - 1000 °C). Tritium permeability rates through various fusion reactor structural materials are also of interest as is the mobilization of toxic material, i.e. Be/Be-compound and F/F-compound aerosols.

The FLIQURE design is basically a cylindrical pot filled with molten Flibe surrounded radially by heaters, insulation, and a neutron moderator and shield. A spontaneous fission neutron source (Cf-252) is situated beneath the pot with a fixed neutron emission rate of approximately 1.2E+10 neutrons/second. To efficiently use the source neutrons, the design objective was to maximize the tritium production rate in the Flibe. This objective required parametric neutronic studies for the Flibe geometry and the selection of optimal neutron-moderating materials and thicknesses using explicit 3D MCNP4B model calculations.

An overview of FLIQURE is shown in Figure 1. The pressure vessel or primary test cell containing the molten salt is fabricated from 316L stainless steel. During the experiment, the test cell is heated using a ceramic-fiber radiant heater to temperatures up to 1000 °C. The test cell and heater are surrounded by 5 cm thick, high-temperature, ceramic-fiber thermal insulation. Outside of the insulation, the entire heated zone is enclosed by a water-cooled copper clamshell.

Figure 1: Schematic of FLIQUIRE Experiment

Instrumentation for the test cell includes a thermocouple probe immersed in the molten salt, an electrochemical probe, a liquid-level sensor, and one or more bare-wire thermocouples attached to the outside of the primary vessel. The lid of the pressure vessel was designed to accommodate four penetrations:

• a mobilization gas stream (air, steam, He, N2),
• a hydrogen-permeation carrier-gas stream (He, N2),
• an inlet line for introduction of small quantities of hydrogen or deuterium gas into the molten Flibe,
• a transfer tube for the molten Flibe.

Figures 2 and 3 illustrate the FLIQURE facility's arrangement in the STAR facility building.

Figure 2: FLIQURE Setup (North-South vertical cross section) with illustration of source transfer and shielding configuration and removable shields for experiment assembly and experiment access.

Figure 3: FLIQURE Setup (East-West vertical cross section) with source locations, shield configuration and removable shield for experiment access.