Sealing materials proposed for use in a deep geologic repository for used nuclear fuel: tests conducted using bentonite-based materials at AECL's URL (1988-2004)

The development of a robust concept for deep geologic isolation of used nuclear fuel includes the selection and application of sealing systems that will ensure that the containers holding the used fuel are effectively isolated from the biosphere. The emplacement-room sealing system is required to provide a number of isolating functions as well as a means of transmitting the heat generated by the used fuel to the surrounding geosphere. While laboratory simulations to assess sealing system performance provide a starting point, ultimately their performance needs to be demonstrated and assessed at, or near full-scale and in a real geologic environment. Such large-scale simulations also provide a means of testing the capabilities of numerical simulation tools being developed for use in predicting longer-term repository performance. Atomic Energy of Canada Limited (AECL) constructed and operated an Underground Research Laboratory (URL) in a previously undisturbed granitic rock mass near its Whiteshell Laboratories in Eastern Manitoba between 1983 and 2005. During the Operating Phase of the URL, a wide range of valuable experiments and demonstrations were conducted on two main testing levels (240-m and 420-m depth), to simulate the performance of sealing materials for potential application in a deep geologic repository. These included the following in situ engineered barriers simulations. -The Buffer/Container Experiment (1990-1993) - The Isothermal Test (1992-1996) - The Tunnel Sealing Experiment (1998-2005) - The Composite Seal Experiment (2001-2005). Each of these studies is briefly described and the key results are presented in this paper. (author)