This paper describes an experimental programme and the corresponding modelling in order to characterise the hydromechanical (HM) behaviour of pellets. At least two levels of porosity can be distinguished in the pellets: microporosity and macroporosity. In general, the microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger-scale structure of the material. In pellets, this concept can be somewhat different as a pellet arrangement creates a large-scale macropore structure. The Barcelona expansive model is proposed to reproduce the material response through infiltration and oedometer tests. In addition to expansive model parameters, a set of hydraulic laws considering the double-structure phenomenon is necessary to perform HM analysis. This paper also describes the effect of macroporosity on the intrinsic permeability changes. To illustrate the general objectives of this research, a full-scale thermohydromechanical calculation has been done to show the capabilities of the approach. The Barcelona basic model (for clays) and Barcelona expansive model (for pellets) have been used in this full-scale calculation.

1 This paper presents a methodology for determining the radial swelling pressure that develops in a cylindrical plastic cell when the bentonite sample it contains is hydrated. Strains in the cylindrical cell wall are measured using strain gauges fixed to its external surface. The plastic cell material is assumed to behave in an elastic manner at the level of strain developed, and a best-fit solution for the pressure that results in the measured strains is calculated using an algorithm of optimisation. Even though the solution obtained is unique, it is also checked to verify that the calculated radial pressure results in the quantity of elastic energy developed in the cylindrical cell wall being a minimum. While the measurements obtained using the strain gauges allow the evolution of swelling pressure to be monitored from a qualitative viewpoint, the precise quantification of swelling pressure is difficult because not all the required pressure measurements were available. This paper demonstrates that the proposed methodology allows the qualitative monitoring of swelling pressures in bentonite cores during hydration. It also provides the basis for a quantitative procedure to be developed in the future.

This paper describes the instrumentation of a full-scale test, known as the Multi-Purpose Test, of the KBS-3H spent nuclear fuel design alternative carried out in the Äspö Hard Rock Laboratory (Sweden). This test is part of the Large Underground Concept Experiments EU project, where Posiva and Svensk Kärnbränslehantering are partners. The test consists of two aspects. The first is that of a ‘demo’ test whose aim is to check the manufacturing and installation process of the different components of the KBS-3H design. The second is the instrumentation and monitoring of the test system. The test is carried out under isothermal conditions and the scope was to measure component displacements, the hydration and swelling pressure of the bentonite material and the water pressure in host rock.