Irradiation experiments of VHTR reference fuels by in-pile gas loop (OGL-1)

Very High Temperature gas-cooled Reactor (VHTR) reference fuels were irradiated in an in-pile gas loop (OGL-1) and irradiation performance of the fuels taken out from OGL-1 fuel body was studied by post-irradiation examination. In the examination, dimensional and weight changes of the fuel compacts, and failure fraction of coated particles included in the compact were measured, and also ceramographic and X-ray radiographic observations on the fuels were carried out. Major results of the examination are as follows; relation between shrinkage of the compact and fast neutron fluence was obtained, but influence of irradiation temperature on the shrinkage was not detected. Weight change of the compact was hardly recognized. As for failure of the coated particles, the compacts taken out from 3rd fuel body revealed relatively high failure fractions, although the fractions were under the allowable limit in VHTR design. The other compacts showed good performance under irradiation. (author)