Comparative analysis of borehole interaction in the HAW test field

A comparative finite element study has been performed on 2 models of the HAW test field, which is an underground experimental facility used for the investigation of the effects of storage of nuclear waste in salt formations. The HAW test field consists of 2 parallel galleries in an anticline type of salt formation. From each gallery 4 vertical boreholes have been drilled at equal distance in which electrical heaters or heat producing nuclear sources will be installed. In a former 3D analysis this HAW field has been modelled as if an infinite number of boreholes existed in each gallery which reduced the size of the model due to symmetry conditions. In order to investigate the influence of this assumption a comparison has been made between two models. One uses the actual 8 boreholes and the other is based on two infinite rows of holes. The comparison has been executed for a horizontal plane through the centre of the heat sources in which a state of plane strain has been assumed. From the analysis it appears that maximum compressive stress on the borehole liner can be determined with good accuracy with the model based on an infinite number of holes. For development of the compressive stress after longer periods of time however the comparison shows that the boundary conditions have a larger influence on the evolution of the stress on the liner. A full 3D analysis of the field will be required to account for geometry effects in a correct way. (author). 5 refs.; 21 figs.; 1 tab