The Progress and Results of a Demonstration Test of a Cavern-Type Disposal Facility

The cavern-type disposal facilities for low-level waste (LLW) with relatively high radioactivity levels mainly generated from power reactor decommissioning and for part of transuranic (TRU) waste mainly from spent fuel reprocessing are designed to be constructed in a cavern 50 to 100 meters below ground, and to employ an engineered barrier system (EBS) of a combination of bentonite and cement materials in Japan. In order to advance the feasibility study for these disposal, a government-commissioned research project named Demonstration Test of Cavern-Type Disposal Facility started in fiscal 2005, and since fiscal 2007 a full-scale mock-up test facility has been constructed under actual subsurface environment. The main objective of the test is to establish construction methodology and procedures which ensure the required quality of the EBS on-site. By fiscal 2009 some parts of the facility have been constructed, and the test has demonstrated both practicability of the construction and achievement of the quality. They are respectively taken as low-permeability of less than 5×10⁻¹³ m/s and low-diffusivity of less than 1×10⁻¹² m²/s at the time of completion of construction. This paper covers the project outline and the test results obtained by the construction of some parts of a bentonite and cement materials.