Laboratory development of the grind-leach process for the H.T.G.C.R. fuel cycle, Part 1 - dissolution of urania-thoria fuel particles in nitric acid solutions.

Abstract

The dissolution of 5 w/o UO2 in ThO2 fuel particles in nitric acid — fluoride solutions is a function of the Th02 dissolution rate. The Th02 dissolution rate has an apparent first order dependency on nitric acid concentration and a fractional order dependency on fluoride ion concentration. The apparent activation energy of the dissolution of the Th02 in 13M nitric acid — 0-05M fluoride is 19 kcal/mole. The presence of metal ions such as zirconium, aluminium, and beryllium inhibits the dissolution of the thoria. The order of inhibiting power is ZrlV > AlIII > BeII and this order is the same as the stability of their simplest fluoro — complexes, The addition of small quantities of sulphate also seriously inhibits the dissolution, precipitating thorium as Th(S04)2 , 4H20 and quantitatively removing the fluoride.