Design Options for HLW Repository Operation Technology: Part V—Preliminary Study and Small Scale Experiments on the Method of Removal of Buffer Material With Salt Solution

The Nuclear Safety Commission of Japan stipulates that “When closing a waste disposal site, the validity of safety assessment results should be verified using the data obtained in the construction and operation phases as well. The retrieval of high-level radioactive waste should be made continuously possible during the period before the verification of the validity.”[1] Retrieving high-level radioactive waste requires the removal of the bentonite-based buffer around the emplaced overpack. In this study, focus was placed on a method for reducing the cohesion of bentonite, a major component of the buffer by dipping the buffer in fluid salt solution and dissolving the material into a slurry using fluid salt solution for removal (method of making a slurry). In order to examine the feasibility and the basic characteristics of the method, element tests were conducted using a small specimen of buffer and fluid salt solution (NaCl solution). In order to verify the feasibility of the infiltration and jetting of fluid salt solution, small-scale model tests were conducted using a specimen composed of 1/14-scale overpack and buffer. It was made clear that the infiltration and jetting of fluid salt solution was feasible as a method for removing a buffer.