Argentine experience on immobilization of simulated high-level liquid wastes in sintered borosilicate and aluminoborosilicate glasses

A research and development program on sintering for the immobilization of high-level liquid wastes (HLLW) is carried out since 1984 at the Division Materiales Nucleares of the Centro Atomico Bariloche. Sintered samples were produced with glasses from diverse sources and with different compositions: a German borosilicate glass (VG98/12), its local counterpart (Simil VG) and a German aluminoborosilicate glass (SG7). Simulated HLLW, light water reactor (LWR) and heavy water reactor (PHWR) types, were immobilized in these glasses with a waste loading of 10 wt.%. The behavior, including thermal stability and chemical corrosion, was studied for the sintered glasses with and without simulated HLLW. Borosilicate and aluminoborosilicate glass samples were obtained by cold pressing and sintering (CP+S), also known as pressureless sintering. Borosilicate glass samples were also produced by uniaxial hot pressing (UBP), also known as pressure sintering, in graphite dies or in the final metal container (in-can). Devitrification studies were carried out on SG7 and VG98/12 with and without simulated PHWR wastes. The microstructure of both cold pressed and sintered VG98/12-10LWR and Simil VG-IOLWR, in which calcined waste particles were immobilized, shows that the particles did not dissolve in the glass, but were homogeneously dispersed. Leaching tests (MCC-IP) were carried out at temperatures lower than 373 K. The gamma radiation damage was produced by a 60Co gamma field (Division Fuentes Intensas, Centro Atomico Ezeiza, C.N.E.A.). The dose rate was 4.34x 104 Gy/h and the total doses ranging from 1.4 x 106 GY to 2.0 x 108 Gy. The density, the degree of devitrification, the microstructure and the leaching rate in ADI remained unaffected by the gamma irradiation. After leaching tests, the waste zones were more affected than the glass matrix and there was no global difference with the irradiation dose