Elucidation of helium behavior in MA-MOX fuel by use of computational science and control of defect formation

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Our study implies that the shape of the negative crystal should change depending on the helium inner pressure enclosed in the negative crystal. The shape of the negative crystal can easily be controlled by the helium injection method. We named the shape controlled negative crystal an image crystal. Our detailed observation indicates that the growth process of the image crystal can be explained by a step free energy model rather than an attachment energy. We could not find a cuboctahedron-type negative crystal of which the surface area is larger than that of a pentacontahedron-type negative crystal with the same volume. In a grain of the raw powder of MA-MOX fuel, helium produced by a-decay is accumulated. The helium may precipitate in the grain-boundary region to form gas bubbles, which will deleteriously affect the sintering process, the formation of gas bubbles poses a serious problem with respect to the quality control of nuclear fuel when MA-MOX is adapted as a standard fuel.