The Use of Isostatic Compression to Produce Full-Scale Highly Compacted Bentonite Blocks

Abstract

A feature of the NWMO buffer design concept involves pre-packaging the used fuel container in a rectangular shaped, Highly Compacted Bentonite (HCB) over-pack to form a Buffer Box. The shape and dimensions of the Buffer Box concept are unique to the Nuclear Waste Management Organization. To simplify assembly of the Buffer Box, the over-pack consists of a top and bottom HCB block with cavities for the used fuel container. This requires pressed blocks of approximately 0.5 m x 1 m x 3 m.The NWMO undertook a program to manufacture large blocks by cold-isostatic pressing in order to develop an understanding of the process and to verify that design requirements can be met, specifically a uniform minimum dry density of 1.7 g/cm³. An initial 1⁄4 scale program produced a 700 kg HCB block with an average dry density of 1.745 g/cm³ and a moisture content of 19.7%.Following the success of the 1⁄4 scale block program equipment and tooling were developed to produce rough, near net shape full-size blocks at approximately 0.56 m x 1.07 m x 3.20 m. These dimensions are maximized due to the limitations of available presses. This tooling allowed us to produce full size blocks weighing approximately 4000 kg and with dry densities of ≈1.74 g/cm³ at a bentonite moisture content of ≈20%.