Cesium Release and Transport in Biso-Coated Fuel Particles

Theoretical and experimental aspects of cesium release from Biso-coated high-temperature gas-cooled reactor fuel particles are reviewed. Three types of transport are considered: diffusion through the pyrolytic carbon (PyC) coatings under conditions of a constant source potential, transport due to a continuously depleting source, and diffusion from a depleting source following constant source potential transport. Analysis of all of the release data obtained in this laboratory yields the following relations for the diffusion coefficient D_Cs characteristic of cesium transport through PyC coatings:For coatings deposited from propylene or propane at ∼1250°C (1523 K):and far coatings deposited from methane at ∼2000°C (2273 K):where T is the absolute temperature.