Modeling the UO₂ ex-AUC pellet process

Studies on modeling uranium dioxide (UO₂) powder and pellet processes from ammonium uranyl carbonate (AUC)- derived uranium dioxide powder (UO₂ ex-AUC powder) were reported in the paper. A mathematical model describing the effect of the fabrication parameters on specific surface area (SSA) of UO₂ powders was built up. To the best of our knowledge, the Brandon model is used for the first time to describe the relationship between the essential fabrication parameters [reduction temperature (T_R), calcination temperature (T_C), calcination time (t_C) and reduction time (t_R)] and SSA of the obtained UO₂ powder product. The Brandon model was tested with Wilcoxon's rank sum test, showing a good agreement with the experimental parameters; the model can be used to predict and control the SSA of UO₂ powder. Response surface methodology (RSM) based on face centered (CCF), one type of quadratic central composite design (CCD), was used to model the pellet process. The experimental studies on the UO2 pellet process determined region of experimental planning as follows: conversion of AUC into UO₂ powder at various temperatures of 773 K, 823 K and 873 K and sintering of UO₂ pellets at temperatures of 1923 K, 1973 K and 2023 K for times of 4 h, 6 h and 8 h. On the base of the proposed model, the relationship between the technological parameters and density of the UO₂ pellet product was suggested to control the UO₂ ex-ADU pellet process as desired levels. The studies on the modeling were implemented at Nuclear Fuel Technology Center (ITRRE). (author)