Processing of large-Scale radwaste-containing blocks using exothermic metallic mixtures

Abstract

AbstractThe parameters of processing of large-scale (50-100 kg) radwaste-containing blocks were studied. Batches consisted of exothermic mixture, oxidizer, mineral additive, and radwaste surrogate. Such mixtures provide process temperature up to ˜2400 K. In the present work exothermic mixtures composed of Ca-Fe silicide, zirconium, silicon, and boron were intermixed with oxidizer (mixture of KMnO4 and V2O5), natural zircon concentrate as mineral additive, and cerium oxide (actinide surrogate). Tests were carried out in a bench-scale plant. Burning of the reaction mixture was remotely initiated from electric supply unit. Melt formation started in the nearbottom area sustained upwards frontally, The melt temperature ranged between 1600 and 1900 K. The melt formation rate during the tests ranged between 0.7 and 2.5 kg/s. Melt cooling after reaction completion was kept for about 15-18 hours. Volatile aerosols were essentially retained in the bulk. The initial volume of the mixture was reduced after reaction by factors of 2 to 3. The densities of the blocks were ranged between 3.2 and 3.9 kg/dm3.Samples of the materials obtained were examined by optical microscopy, X-ray diffraction, and scanning electron microscopy. The product consisted of glass-like body with metallic spheres (˜0.5-1.5 mm) distributed within. The base was composed of glass (˜60-80 vol.% of total) and crystalline phases (mainly zirconia). Monoclinic baddeleyite was found to be the major crystalline phase. The minor phase was tetragonal zirconia. Cerium (actinide surrogate) was partitioned among the glass and zirconia. The Ce2O3 concentration in glass ranged between ˜0.4 wt.% and ˜0.8 wt.% whereas its content in zirconia was found to be lower (up to ˜0.3 wt %). The metallic constituent consisted of vanadium and Fe-V-Si alloy whose average composition wasFe7O2V19.3Mn1.1 Si9.4.