Manufacturability Estimation on Burnable Poison Mixed Fuel For Improving Criticality Safety of HTGR Fuel Fabrication

Abstract

Abstract Manufacturability of the BP-mixed uranium dioxide (UO2) kernel for burnable poison (BP) credit concept was estimated to ensure criticality safety in 14 wt% enrichment fuel fabrication facility for commercial high temperature gas-cooled reactor (HTGR). The case of the coating process has not been examined, so this study is different from manufacturability estimation on Tri-ISOtropic (TRISO) coated fuel. As a BP, boron, gadolinium, erbium, and hafnium were investigated. It is essential that mixing BP does not affect the shape of the fuel kernel, and that BP does not melt or vaporize during the heat treatment in the reduction process. We determined to add BP as a nitrate by considering the existing kernel fabrication process. The results of thermodynamic equilibrium analysis showed boric acid would melt and vaporize during the heat treatment processes. On the other hand, it was found that gadolinium, erbium, and hafnium nitrate would change to solid oxides that do not melt even at 2000 °C. These results indicate the existing external sol-gel method could be applied for the fabrication of the UO2 fuel kernel mixed with gadolinium, erbium, or hafnium.