A NEW PROCESS FOR THE REMOTE PREPARATION AND FABRICATION OF FUEL ELEMENTS CONTAINING URANIUM-233 OXIDE-THORIUM OXIDE

A remotely operated pilot piant for the engineering development of the sol-gel---vibratory-compaction procedure is being used to prepare about a thousand Zircaloy-2-clad fuel elements for a zero-power criticality experiment. The feasibility, safety, and economy of remote recovery, preparation, fabrication, and inspection of U/sup 233/O/sub 2/-ThO/sub 2/ fuels are being evaluated. The procedure includes solvent extraction recovery of U/sup 233/ by means of di-sec-butyl phenylphosphonate in diethylbenzene; the sol-gel process, a new procedure for preparing dense oxide fuels; oxide particle sizing; vibratory compaction loading of fuel tubes, followed by end-closure welding, cleaning, and inspecting. Gamma-ray scanning will be used to determine the uniformity of the fuel density. Instruments are provided for remote control of the process and for monitoring the radioactivity and evaluating the hazards to workers at each step of the operation. Twelve pilot-plant runs involving uranium decontamination, sol- gel preparation of 50 kg of oxide, and fuel sizing and ciassification were completed, with only minor difficulties. The results of examination after irradiation of 17 test capsules at burnups to 17,000 Mwd/metric ton of fuel showed the sol-gel-prepared oxide to perform satisfactorily with respect to stability and fission gas release. In laboratory experiments, uranium-thorium dicarbide fragments and microspheres were prepared by the sol-gel process at a maximum temperature of 1600 c- C. (auth