Proving test on the reliability of BWR 8x8 fuel assemblies in Japan

In 1976, a 10 year programme was started to test the reliability of BWR 8x8 fuel assemblies in Japan. The results and conclusions are summarized here. To date, experience with BWR fuel has shown that it has excellent performance and characteristics, but it is still very important to investigate actual fuel behaviour in a commercial reactor in order to confirm the appropriateness of the design method and design data, and the margins to the limits, from the viewpoint of enhancing design techniques and licensing procedures. The programme was planned to verify the reliability of BWR 8x8 fuel assemblies using commercial fuels. As monitoring fuels, 10 fuel assemblies were selected from the first reload fuels for the Fukushima Daiichi No. 3 Nuclear Power Station (BWR 784 MW(e)). These assemblies were well characterized during their manufacture. They were put into the core in 1977, irradiated under normal conditions and operational data were acquired. Seven assemblies were subjected to detailed post-irradiation experiments (PIEs). The burnup of these assemblies ranged from 6 to 29 GW·d/t, covering almost all the burnup regions in which current BWR fuels are utilized. Evaluations of the PIE results were carried out to show the conservatism of design and to quantify the margins. Fuel cladding strength, thermal conductance of crud and nodular corrosion and fuel rod-to-rod spacing were discussed, together with moisture getter and spacer performance. (author)