The diffusion of fission products in thorium metal

A study was performed of the diffusion in α-thorium of fission products representing impurity atoms with a diversity of size and valence differences with respect to the solvent lattice. The atoms were recoil injected into thorium disks. Diffusion coefficients were determined for 133Xe by monitoring its release during annealing, and for the other isotopes by post-annealing concentration profile analysis. The Arrhenius constants D0(cm2/sec), resp. Q(kcal/mole) were obtained for the diffusion coefficients where, D=D0 exp(-Q/RT);99Mo: 7.6 X 10-4 and 37.6; 132Te: 1.32 X 106 and 95.6; 133I: 2.7 X 10-1 and 66.2; 133Xe: 3.6 X 102 and 82.3; 140Ba: 2.3 X 10-2 and 59.4; 141Ce - 143Ce: 1.8 X 10-2 and 60.0. The fission product diffusion behavior, in general, fit either the vacancy or the substitutional-interstitial diffusion mechanisms for impurity atoms in a fcc metal. Both valence and ionic radius correlations were found. The data indicate low rates of diffusion for the operating temperatures at which α-thorium-based fuel might be used. (Auth.)