This paper provides the outline of trial repository designs and specific design examples of underground facilities for the SDMs in NUMO safety case. Purposes of the repository design in this study are as follows.

· To show methodologies for developing flexible repository designs, tailored to various site conditions and changes in the social environment.

· To emphasize progress of the practical application of engineering technologies related to construction, operation and closure of a repository, based on technology developments for the manufacture and construction of engineered barrier systems.

· To confirm that the repository concepts developed here are capable of ensuring pre- and post-closure safety for the potential host rock formations defined in this safety case and meet the requirements in terms of practicality.

In designing the underground repository layout, the functions and design requirements of the key tunnels constituting the underground facilities were first identified, then the layout of them was designed taking into consideration discontinuous geological structures, i.e., faults and bed boundaries, and the groundwater flow. Regarding the shapes of the disposal panel for the highlevel vitrified waste, the through type and the dead-end type were adapted for the vertical emplacement concept and for the horizontal emplacement concept, respectively. The layouts of the underground facilities were provided for each emplacement concept. As the results of comparison among these design options, the underground facility combined with the horizontal emplacement concept and the dead-end type panel was identified as a relatively efficient and economical approach which is flexibly applicable to the geological structure.