[en] Regarding closure technology of underground facilities on geological disposal of the high-level radioactive waste, closure performance of a disposal facility should be assessed from view points of both engineering technology and performance assessment, not only depending on individual technology. Thus, based on closure concept described in H12 report, closure performance of the backfilled repository focused on radionuclides migration from a repository to a major fracture zone was discussed. We aimed at the case of via a connecting tunnel and a minor fracture zone as a potential of migration path other than host rock. Current knowledge on performance of the closure elements as backfill and water stopping plug, hydraulic properties of excavation damaged zone and concrete lining was summarized. Then, a fault tree was analyzed and a closure scenario was discussed for its closure performance. The assessment was concluded that the scenario of existence of the critical path via a connecting tunnel and a minor fracture zone has low potential because the scenario will be prevented by function of closure elements and by low potentiality to meet all necessary conductions simultaneously, and that the scenario of the critical path via host rock in H12 report is relevant. (author)