Project Structure

In a geological repository for the disposal of high-level vitrified waste and spent fuel, the waste matrix constitutes the first barrier confining the disposed radionuclides. Various factors and processes such as radiation, thermal, hydraulic and geomechanical processes influence the stability and the evolution of the waste matrix. For example, interactions with repository groundwater as well as with engineered barriers forming part of the disposal system might affect the isolation capacity of the waste matrix and may lead to the slow dissolution of the waste matrix and the release of radionuclides. NF-PRO’s research component 1 investigates key processes having an effect on the isolation capacity of the waste matrix Work performed under NF-PRO concentrates on two main waste types: vitrified radioactive waste and spent fuel.

The engineered barrier system consists of a sequence of man-made structures encompassing the disposed vitrified waste or spent fuel. The engineered barrier system plays an important role in ensuring the overall safety of disposal since it isolates the disposed radioactive waste chemically and physically from the natural environment over very long periods of time. Interactions with repository groundwater and various components of the disposal system will lead to chemical changes and the build-up of concentration gradients affecting radionuclide retention and retardation. NF-PRO’s research component 2 investigates chemical processes and alterations in the near-field including impact on radionuclide immobilisation.

In most repository concepts under investigation of EU Member States, the engineered barrier system includes buffer materials, which are emplaced around the disposed waste canisters. Clay-based buffer materials will progressively hydrate and act as a low permeability barrier and play an essential role in ensuring the overall performance of the repository since they control and limit the migration of radionuclides released from the disposed waste after closure of the repository. However, various factors and processes such as thermal gradients in the area surrounding heat-producing waste, changes in the mechanical conditions of the near-field, groundwater inflow-outflow and the movement of gases produced as a result of radioactive decay and the corrosion of steel will induce changes in the mechanical conditions of the near-field. An important part of the work performed by NF-PRO concentrates on processes affecting the properties and the behaviour of the buffer. Main emphasis is on the investigation of the combined effects of thermal, geomechanical and hydrodynamic processes on the performance of the buffer. To this end, experimental work is carried out on different types of buffer material (bentonite, salt), at different scales (from laboratory to real scale), and under different degrees of saturation and thermal conditions.

The characteristics of the host rock may be locally altered due to the excavation of disposal galleries and access shafts. Parts of the rock that have been affected by the excavation are known as the Excavation Damaged Zone (EDZ) and form the transition between the engineered barriers and the intact host rock. NF-PRO’s RTD Component 4 investigates the key process leading to the development and the evolution of the Excavation Disturbed/Damaged Zone including their potential impact on overall performance of the disposal system.

In evaluating the overall performance of a geological repository for the disposal of radioactive waste, very long timescales have to be considered. Over such timescales, the disposal system will evolve due to interactions between the different near-field components as well as with the host rock. Also, the relative importance and impact of dominant processes controlling the evolution of the disposal system determine will advance with time. NF-PRO’s RTD Component 5 integrates information from the investigation of detailed processes and individual near-field components into assessments of the overall performance of the near-field system.