Modelling hygro-thermo-mechanical behaviour of engineered clay barriers — validation phase

The Canadian Nuclear Fuel Waste Management Program (CNFWMP) is evaluating the concept of disposal of nuclear fuel waste in an engineerted vault at a depth of 500 to 1000 m in the plutonic rock of the Canadian Shield. In common with engineered barrier system designs being developed in other countries, the waste would be contained within durable containers that, in turn, would be isolated from the host rock by clay-based materials.

The objective of the CNFWMP is to develop a disposal concept that will protect human health and the natural environment far into the future. Assessments of the conceptual vault designs are based on system theory in which an attempt is made to correlate experiences with theoretical concepts of planned systems in such a way that the resulting coordination is sound and convincing. By necessity, since experiments with a total disposal system can never be performed, both the design and the performance assessment rely on experiments performed on physical models of vault elements over relatively short times and on information inferred from calculations (mathematical models) that simulate the probable behaviour of the system in the space-time domainof interest. For a simulation model to be successful, that is applied within a real world situation, the model must provide information regarding the behaviour of the system of interest that is clearly better, in some way, than the mental image or other abstract model that would be used instead. The results of a series of tests performed within the activity known as validation serve as tangible evidence regarding the success of a model in representing the system of interest.

This paper focusses on the validation of the models that describe the hygro-thermo-mechanical behaviour of the engineered clay-barriers proposed for application in the Canadian disposal system concept. The strategy being used to address the key issues in modelling to minimize the model error and to maximize the usefulness of the simulation model, based on testing procedures, is reviewed. Finally, a concept of the validation of codes/models that describe the unsaturated behaviour of engineered clay barriers, is described.