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 (ks) and effective diffusivity of the initial solid (de0) was estimated using the arrhenius equation resulting the following equations ks=422.843exp(formula presented) and de0=1.98x10-6exp(formula presented) the value of thiele modulus was about 6 suggesting that the diffusion regime controls the overall reduction process © school of engineering,taylor’s university.