Advanced Methods for the Fabrication of Mixed Uranium Plutonium Oxide, Monocarbide and Mononitride Fuels for Fast Breeder Reactors

Abstract

The reference fuel for operating and forthcoming prototype and commercial liquid metal cooled fast breeder reactors (LMFBR) all over the world, including India, is mixed uranium plutonium oxide (MOX). Mixed uranium plutonium monocarbide (MC) and mononitride (MN) are considered as advanced LMFBR fuels. “Powder-pellet (POP)” is the conventional method for production of MOX, MC and MN fuel pellets starting from UO2 and PuOa powders. The POP route involves generation and handling of plutonium bearing fine powder or dust particles which has the problem of radiotoxic dust hazard. Further, fine powders have poor flowability which makes automation and remote fabrication difficult. The combination of ammonium uranyl plutonyl carbonate (AUPuC) process and low temperature oxidative sintering (LTS) minimises the radiotoxic dust hazard and the fabrication cost of MOX fuel and is considered as advanced POP route.Vibro-sol (or sphere-pac) and sol-gel microsphere pelletisation (SGMP) are advanced methods for fabrication of MOX, MC and MN fuels. Here, dust-free and free-flowing gel microspheres of the oxide or oxide-carbon are prepared from heavy metal nitrate feed solutions by “internal” or “external” gelation processes. The gel microspheres are subjected to controlled calcination for MOX or carbothermic reduction for MC and MN. Thereafter, the microspheres are either vibropacked in fuel pins or directly pelletised and sintered. These processes minimise radiotoxic dust hazard, facilitate automation and remote processing and ensure excellent microhomogeneity.The present paper summarises the state-of-art of the POP, vibrosol and SGMP processes for the fabrication of MOX, MC and MN fuels, highlighting the author's experience in SGMP process.