[en] Spent nuclear fuel from nuclear reactors needs to be disposed of in isolation from humans and the environment as much as possible due to high heat and high radioactivity. Among the disposal methods of spent nuclear fuel, deep geological disposal, which is disposed of in the ground more than 500 m underground, is being considered as the most promising method. In the case of deep geological disposal, an engineered barrier is required to prevent radioactive material from leaking from the disposal container and spreading to the natural environment, and structural safety and criticality safety are required. In this study, to secure the structural safety of the disposal container and at the same time increase the handling efficiency, a study was conducted on a method of reducing the weight through structural change. During deep geological disposal, the critical safety evaluation of engineered barriers including the spent fuel copper disposal container was performed to calculate the interval among baskets for the spent fuel required for the design of the disposal cask. And by applying the analytical stress calculation method based on the beam theory, the efficient optimization of the cross-section of the disposal cask was performed. It was confirmed that a design that can have handling efficiency while securing structural and critical safety through the developed optimal design process can be secured