Adsorption of Molybdenum Hexafluoride on Magnesium Difluoride for Uranium Purification in FLUOREX Reprocessing

Abstract

The nuclear fuel reprocessing method FLUOREX is a hybrid system based on fluoride volatility and using solvent extraction. Spent nuclear fuel is fluorinated, and most of the uranium is recovered as UF6 gas. UF6 contains some volatile fission product (FP) fluorides, so we considered their elimination from UF6 by adsorbing them on fluoride adsorbents. We experimentally examined the adsorption of MoF6 on MgF2 adsorbent; MoF6 is present as a volatile FP fluoride in UF6 produced by the fluorination of spent nuclear fuel. The adsorption isotherm of MoF6 adsorption on MgF2 was obtained at MoF6 pressures from 10−4 to 50 kPa. The saturated adsorption amount was 1:3 ± 0:4 mg/m2 at MoF6 pressures from 10−4 to 1 kPa. At MoF6 pressure of about 10−3 kPa, the saturated adsorption amount had no dependence on adsorption temperatures from 398 to 463 K. We deduced that MoF6 was adsorbed as a monomolecule layer on the MgF2 surface at MoF6 pressures from 10−4 to 1 kPa, and the MoF6 partial pressure in UF6 could be decreased below 1 × 10−4 kPa, which is the specific MoF6 concentration for the reenrichment process.