Sorption behavior and inventory of alpha-emitters on the surfaces of spent nuclear fuel cladding

Alpha-emitters on the surfaces of Zircaloy-4 cladding of PWR spent nuclear fuel have been examined at fuel burnup of 6900,29,400 and 38,100 MWd/t. The amount of α-emitter on the inner and outer surfaces of cladding increased with fuel burnup, whereas the amount of plutonium on the outer surface remained roughly constant. The distribution of α-activity in the cladding varied with fuel burnup. The ratio of α-activity on the outer surface to total α-activity of the cladding decreased from about 50% at fuel burnup of 6900 MWd/t to 3% at fuel burnup of 38,100 MWd/t. The inventory of the α-activity in unit weight of cladding was found to be 4.75*102 and 4.35*104 Bq/g-cladding at fuel burnup of 6900 and 38,100 MWd/t, respectively. Adsorptive ability of the outer surface of irradiated cladding was about one order of magnitude greater than that of unirradiated Zircaloy-4 for α-emitters and some of the fission procucts except ruthenium. (author) 5 refs.; 2 figs.; 5 tabs