Studies on preparation of (U0.47,Pu0.53)O2 microspheres by internal gelation process

It is proposed to irradiate experimental fuel pins containing 750 μm (U0.47,Pu0.53)O2 microspheres (coarse fraction) and 110 μm UO2 microspheres (fine fraction) in the Fast Breeder Test Reactor at Kalpakkam, with a view to develop sphere-pac fuel for Fast Breeder Reactors in India. This communication describes optimization of the internal gelation process to produce dense sintered (U0.47,Pu0.53)O2 microspheres. Major modifications were incorporated in the feed preparation and the calcination and sintering steps. Use of pre-heated HMTA and urea and plutonium nitrate solution with optimum nitrate to plutonium ratio led to desired gelation kinetics and growth of crystallites which is necessary to obtain good gel microspheres. The calcination process was optimised to remove residual organics without cracking of microspheres. The studies showed that dense crack free sintered (U0.47,Pu0.53)O2 microspheres of about 98% theoretical density (TD) can be prepared using the internal gelation method.