A test to demonstrate practical construction technology for underground cavern-type disposal facilities is currently underway. Cavern-type disposal facilities are a radioactive waste repository excavated to a depth of 50 to 100 m below ground and constructed with an engineered barrier system (EBS) that is a combination of low-permeable bentonite material and low-diffusive cementitious material. The disposed materials are low-level radioactive waste with relatively high radioactivity, mainly generated from power reactor decommissioning, and certain transuranic wastes that are mainly generated from spent fuel reprocessing. The project started in fiscal 2005*, and since fiscal 2007* a full-scale mock-up of a disposal facility has been constructed in an actual sub-surface environment. The main objective of the demonstration test is to establish construction procedures and methods which ensure the required quality of an EBS on-site. Certain component parts of the facility had been constructed in an underground cavern by fiscal 2010, and tests so far have demonstrated both the practicability of the construction and the achievement of the required quality. This paper covers the project outline and the test results obtained by the construction of certain EBS components. * All fiscal years end on March 31 of the following calendar year; for example, fiscal 2005 is the year from April 1, 2005, to March 31, 2006.

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