Study of Thermal Evolution of Uranium Oxides Sintered in the Vitrocerus Process

Vitrocerus is a processing method for MTR type fuel plates (Materials Testing Reactor) developed in the laboratory of Nuclear Materials at Bariloche Atomic Center which aims at producing a safe immobilization matrix for the potential provision of interim dry spent fuel from research reactors such type MTR.The present paper deals with the sintering of simulated spent fuel, that is composed of uranium silicide (U3Si2) and aluminum, isotopically diluted in natural U3O8 and also with small additions of borosilicate glass (designated VG98/12), with composition: SiO2 VG98/12 (56.7%), B2O3 (12.4%), Al2O3 (2.6%), Na2O (17.5%), CaO (4.1%), MgO(2.1%) and TiO2 (4.6%) and Tg ∼ 520° C. The glass has the function to induce a liquid phase sintering at low temperatures, resulting in an enhancing of the hardness and densification of the final material. The simulated spent fuel is pre-oxidized before mixing with the glass.Studies were carried out on the thermal behaviour through dilatometry measurements, differential thermal analysis, hot-stage microscopy and X-ray diffraction, resulting in partial expansions at temperatures near 800°C. Then, these system probably densified by the action of a liquid phase from the glass VG98/12 or reaction with the spent fuel that will be immobilized.