EXPERIMENTAL STUDY AND MATHEMATICAL MODELING OF REACTION KINETIC AND TRANSPORT MECHANISM OF U3O8 REDUCTION USING H2 GAS

Reduction of U3O8 by H2 gas is among the important steps in manufacturing
coated UO2
fuel kernels used in High Temperature Reactor (HTR). Most of
previous studies in this area focus on finding operating conditions, such as
temperature and reaction time, which can be used in producing high quality UO2
kernel. The present work deals with experimental study and modeling of the
transport mechanism and reaction kinetic of the U3O8
reduction. The reduction
process was conducted in isothermal condition using a high temperature furnace
namely the Opale furnace. The effects of different reduction temperature (973 K,
1073 K, and 1173 K) and reaction time on the reaction conversion were
investigated. A mathematical model describing H2 diffusion inside the kernel and
the reaction kinetic were proposed and solved numerically. Effective diffusivity
and reaction rate constant were determined by least square method comparing the
conversion obtained from the experiment and that from the simulation. The
experimental result showed most of the reaction took place at the first 60 minutes
and after that the conversion increased slightly as the reaction time proceeded.
Within the temperature range of 973 K and 1173 K, the effect of temperature on
conversion is considerably small. It was found that the reaction rate could be
approximated by the first order reaction to H2 gas and the volume reaction model
for U3O8
reactant consumption in which particle size was allowed to change
during the course of reaction. The effect of temperature on reaction rate constant
(