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

我们的研究表明，负极晶体的形状应随负极晶体中氦的内压而改变。用氦注入法可以很容易地控制负极晶体的形状。我们将这种形状可控的负片晶体命名为图像晶体。我们的详细观察表明，图像晶体的生长过程可以用台阶自由能模型来解释，而不是用附着能来解释。我们没有发现相同体积的立方八面体型负晶体的表面积比五面体型负晶体的表面积大。在一粒MA-MOX燃料的原始粉末中，积累了α衰变产生的氦。氦在晶界区析出形成气泡，对烧结过程产生不利影响，当MA-MOX作为标准燃料时，气泡的形成对核燃料的质量控制是一个严重的问题。

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.