Diffusion of cesium in stainless steel under condition of oxygen potential controlled by Mo/MoO2 or NbO2/Nb2O5 oxygen buffer

The kinetic behaviors of cesium migration in SUS-316 stainless steel for a cladding meterial of fast breeder reactor were studied using radioactive 134Cs as a tracer. The oxygen potential in the atmosphere surrounding the specimen was controlled by Mo/MoO2 or NbO2/Nb2O5 oxygen buffer, which corresponds approximately to the one in fuel-cladding gap during irradiation. The concentration profile of Cs in the specimen was analyzed on the basis of diffusion theory. The temperature dependences of diffusion coefficients of Cs in SUS-316 stainless steel were expressed in the range of 650 -- 8000C by the following equations: In the oxygen potential controlled by Mo/MoO2 oxygen buffer, D = 0.15 exp(-63,500/RT) (cm2/s). In the oxygen potential controlled by NbO2/Nb2O5 oxygen buffer, D = 9.0 x 10-5 exp(-50,300/RT) (cm2/s), where the activation energy is expressed in terms of cal/mol. (author)