Experience in barc on the preparation of gel microspheres of uranium, thorium and plutonium fuels

Sol-gel process provides an attractive fuel fabrication route having advantages over the conventional powder metallurgical processes. Work in BARC started in the late 70s and was concentrated on the development of sol dehydration process (ORNL route) for the preparation of ThO2 and ThO2-UO2 microspheres. Work on the use of this process for UO2 had to be discontinued because of the problems encountered in the preparation of sols for this purpose. Since then, studies have been mainly concentrated on the development of internal gelation process. After initial success on preparation of small quantities of UO2 microspheres using static columns the work was extended to the development of the chemistry of the process and of continuously operating gelation systems. Based on detailed studies, a gelation field diagram has been defined using which it is possible to prepare UO2 microspheres of good quality from uranium solutions having a wide range of uranium concentration. Continuous gelation systems have been developed and gradually scaled up from initial 500 g/day to about 2.5 kg/hour level. All steps up to the preparation of green gel are either automatic or semi-automatic. Efforts are in progress to develop a continuous belt drier which would lead to further automation of the process. Simultaneously, work has been taken up on the preparation of (U,Pu)O2 microspheres and laboratory scale equipment for this purpose is successfully operating. In the field of advanced fuels, efforts are on for the preparation of UC and UN microspheres and these advanced fuel microspheres have been prepared with fairly low amounts of oxygen and nitrogen for carbides and oxygen and carbon for nitrides. (author) 20 refs., 6 figs