Scale-model test for disposal pit of high-level radioactive waste and theoretical evaluation of self-sealing of bentonite-based buffers

Bentonite is attracting greater attention in Japan and some other countries as a buffer for use in repositories of high-level radioactive waste (HLW). Bentonite-based buffers for HLW disposal are expected, because of their swelling deformation, to fill spaces between buffers and walls of disposal pits or between buffers and waste containers designated as overpack. Bentonite has a self-sealing capability. This study conducts scale-model tests simulating the relation between the buffer and interstitial space. It also investigates the validity of theoretical equations for swelling presented by Komine and Ogata (published in 2003 and 2004) to evaluate buffer self-sealing capabilities by comparing calculated and experimentally obtained results of scale-model tests. Results of the experimental work and calculations described herein highlight bentonite's self-sealing capability and demonstrate the high applicability of these Komine and Ogata equations to quantify filling of interstitial spaces by bentonite-based buffer swelling.