DISTRIBUTIONS OF RADIONUCLIDES ON AND IN SPENT NUCLEAR-FUEL CLADDINGS OF PRESSURIZED WATER-REACTORS

Radioactivities in Zircaloy-4 cladding of PWR spent nuclear fuel have been examined as a function of fuel burnup in the region of about 7000-40000 MWd/t. The fission products 137Cs and 106Ru in the cladding increased linearly with fuel burnup, whereas the radionuclides 134Cs and 154Eu, which were produced by neutron capture of fission products, increased with the second power of fuel burnup. Tritium and the activation products of alloy constituents and impurities increased in proportion with fuel burnup. The gross activities of α emitters on the inner and outer surfaces of the cladding increased with 3.1 and 1.3 powers of fuel burnup, respectively. The distribution of radionuclides in the cladding has been examined by radiochemical analysis combined with stepwise etching from the inner surface of the cladding. More than 98% of fission products were present within a 10 μm depth from the inner surface of the cladding, while activation products such as 60Co were distributed homogeneously in the interior of the cladding except on the outer surface. The distribution of tritium tended to become heterogeneous with increasing fuel burnup. © 1990.