ESTABLISHMENT AND DEMONSTRATION OF



　Development of MOX Fuel

Fugen (ATR) is different from LWR in that neutrons are moderated mainly in heavy water. But the operational condition of fuel, such as ATR utilizes light water as coolant, is similar to BWR. Based on that fact, making use of LWR fuel techniques (e.g. using zircaloy-2 for cladding tube), Fugen developed MOX fuel assembly consists of 28-fuel rod. In the course of its development,technical issues derive from ATR characteristics as utilization of MOX pellet or its cylindrical fuel assembly's structure, were focused on to be resolved.
In addition, for the ATR demonstration plant, 36-fuel rod assembly and 54-fuel rod assembly with thinned and increased fuel rods were tried to develop to gain economical efficiency. The 36-fuel rod assembly has almost been developed and proved its integrity at Fugen by irradiating up to 38GWd/t (average of the assembly's burnup). Development of 54-fuel rod assembly, aimed at higher burnup till 55GWd/t, has been completed the basic design stage.
In development of those MOX fuels, various irradiation tests were implemented in Fugen and in testing reactors at home and abroad to acquire irradiation behavior of MOX fuels in normal and abnormal conditions. The performance and safety of ATR MOX fuels were confirmed under those tests and the tests' results were utilized in the safety review of LWR MOX fuels, which have similarity in the operational condition. The data of ATR fuel with diversity as higher liner power and larger fuel rod diameter compared to LWR fuel helps the deep understanding of LWR MOX fuel. At the same time, those data will be organized and disclosed as a systematic database and its contribution to the plutonium utilization in LWR project is expected.
Fugen's MOX fuels were fabricated in the ATR line of "Plutonium fuel fabrication facility(II)" from 1975 to 2001. During this period, total sum of 129 tons of MOX fuel and 772 fuel assemblies were fabricated. The pellet production yield was kept approximately 90% and proved the stability of MOX fuel fabrication in full-scale. Based on these fabrication experiences, plutonium management, MOX pellet fabrication, processing and assembling/inspection and quality assurance technologies have been developed and expected to be utilized in the fabrication of LWR MOX fuel.
Comparison of Specifications for ATR MOX Fuels