The demonstration of the disposal of high-level radioactive waste solids has as its objectives the demonstration of required waste-handling equipment and techniques, the determination of the stability of salt under the influence of heat and radiation, and the collection of information on creep and plastic flow of salt which is needed for the design of an actual disposal facility. Fourteen irradiated fuel assemblies from the Engineering Test Reactor will serve as a source of radiation, since high-level solidified wastes do not exist at the present time. The assemblies will be placed in a circular array of holes in the floor of a newly mined area (14 ft above the existing mine floor,) with one can in the center and the othersix canslocated peripherally, spaced 5 ft on centers. During the course of the 2-year test, four sets of assemblies will be used to achieve a peak dose in the salt of about 8 × l08 rad and the temperature of the salt adjacent to the center hole will be maintained at 2000C with supplementary electrical heaters. A second radioactive array, located in the existing mine floor, will receive the fuel canisters which are removed from the main array at the end of each 6-month period. The purpose of this array is to study the problems which may be encountered if the waste containers are located in salt interbedded with water-bearing shale. A third array, consisting only of heaters, will be operated as a control to determine those effects due solely to heat. In addition to the radioactive and control arrays, a rib-pillar located between the main radioactive array and the control array will be heated electrically around its base to produce significant information on salt flow characteristics and mine stability at elevated temperatures. Preparation of the four experimental rooms will involve the mining of approximately 19,000 tons of salt. Placing of the first fuel assembly cans in the mine is expected to take place in November 1965.