Characterization of high-temperature materials behavior in a neutron environment will be required to develop reliable performance prediction models for high-temperature gas-cooled, space power, and fusion reactors. One vehicle by which material behavior in a fast neutron environment can be studied is the Materials Open Test Assembly (MOTA) in the Fast Flux Test Facility (FFTF). Until recently, irradiation temperatures in the MOTA were limited to 1075 K. A recent successful experiment, however, has extended the temperature capability in the MOTA to 1500 K.

This report describes the design and performance of high-temperature capsules that were used in that experiment. Each of eight uniquely designed instrumented capsules (which contained refractory metal specimens) operated at an irradiation temperature between 1290 and 1500 K. Temperatures within ± 10 K of target were maintained in seven of the eight capsules during the 335-day irradiation. Data obtained during the experiment clearly showed the advantages of having a temperature control system for high-temperature irradiation capsules.