The basic idea of the HPF field experiment is to alter a portion of a shear zone (a permeable planar structure) in the GTS by percolating a hyperalkaline fluid for a long period of time (over two years) and examine the effects on the primary mineralogy, hydrology, and transport properties of the shear zone.

This is achieved by setting up a dipole flow field, with continuous monitoring of fluid chemistry, performing of intermittent tracer tests (with and without radionuclides) within the dipole, a final injection of safety relevant radionuclides, followed by excavation (resin injection and overcoring) and laboratory-based analysis (radiochemical, mineralogical and structural) of the shear zone.

This challenging experiment employs novel materials and techniques for on-line monitoring of hydraulic parameters, electrochemical parameters and spectrometric detection of gamma emitting tracers under the extreme high pH conditions of around 13.2.

The experimental concept can be summarised by the diagram below.