Development of Impregnated Agglomerate Pelletization (IAP) process for fabrication of (Th,U)O2 mixed oxide pellets

Highlights: ► A new fabrication technique Impregnated Agglomerate Pelletization (IAP) has been developed for making (Th,U)O2 pellets. ► Useful technique for fabrication of highly radioactive (Th,233U)O2 fuel for AHWR. ► Reduces powder handling, man-rem, number of process steps requiring shielding. ► Improvement in microstructure and homogeneity of (Th,U)O2 pellets fabricated by IAP process. ► Results from IAP process are better than CAP route and it is comparable with POP route. - Abstract: Impregnated Agglomerate Pelletization (IAP) technique has been developed at Advanced Fuel Fabrication Facility (AFFF), BARC, Tarapur, for manufacturing (Th,233U)O2 mixed oxide fuel pellets, which are remotely fabricated in hot cell or shielded glove box facilities to reduce man-rem problem associated with 232U daughter radionuclides. This technique is being investigated to fabricate the fuel for Indian Advanced Heavy Water Reactor (AHWR). In the IAP process, ThO2 is converted to free flowing spheroids by powder extrusion route in an unshielded facility which are then coated with uranyl nitrate solution in a shielded facility. The dried coated agglomerate is finally compacted and then sintered in oxidizing/reducing atmosphere to obtain high density (Th,U)O2 pellets. In this study, fabrication of (Th,U)O2 mixed oxide pellets containing 3–5 wt.% UO2 was carried out by IAP process. The pellets obtained were characterized using optical microscopy, XRD and alpha autoradiography. The results obtained were compared with the results for the pellets fabricated by other routes such as Coated Agglomerate Pelletization (CAP) and Powder Oxide Pelletization (POP) route.