Safe and durable solutions for nuclear waste disposal
For short-lived low- and intermediate-level nuclear waste, disposal at or near the surface is the preferred solution. For long-lived medium- and high-level radioactive waste, disposal in stable geological layers is internationally recognised as the most promising solution.
Although the new fuel cycles studied for, for instance, the Generation IV nuclear reactors and Partitioning and Transmutation can strongly reduce the volume and heat output of high-level radioactive waste, a geological repository will still be required for the remaining radioactive waste.
The Waste and Disposal expert group
Already in 1974, SCK•CEN started a project to study the Boom clay as potential host rock for nuclear waste disposal. Since the early eighties the National Institute for Radioactive Waste and Fissile Materials, NIRAS/ONDRAF has taken over the responsibility to develop the long-term nuclear waste management. Since then, SCK•CEN is the main research partner of NIRAS/ONDRAF in this domain. This research was and still is embedded in the European Commission framework programmes on nuclear research.
The Waste and Disposal expert group conducts research on the behaviour of nuclear waste, its surrounding engineered and natural barriers, and their interactions. It is composed of a multi-disciplinary team of engineers and scientists specialised in material sciences, geology, radionuclide chemistry, geochemistry and mass transport phenomena.
The main research subjects are:
- The behaviour of vitrified high-level radioactive waste
- Spent fuel and bituminised waste under repository conditions
- The anaerobic corrosion of steel containers
- Geochemical processes in clays (especially the Boom clay)
- The chemical behaviour of the radionuclides and other contaminants once released from the waste (dissolution-precipitation; sorption-desorption) under different geochemical conditions
- The migration of radionuclides and gases in clays
- The chemical and hydromechanical perturbations of the clay host rock
Since NIRAS/ONDRAF selected the supercontainer design, using a thick-walled concrete container and a cement-based backfill, the Waste and Disposal expert group has extended its research to strongly alkaline conditions caused by cement.
3 research units
The W&D expert group is composed of three units:
- R&D Waste unit: focuses on the waste and engineered barrier behaviour.
- R&D Disposal unit: focuses on the natural clay barrier.
- Process Support unit: the main activity is the co-ordination of a large EC Integrated Project NF-PRO concerning near-field (i.e. the waste and its engineered barriers) processes. Besides this project it also co-ordinates other international activities of the W&D expert group.
The Waste & Disposal Expert Group has elaborated a dedicated infrastructure for the study of the chemical stability of waste forms and of the geochemistry and migration behaviour of radionuclides in clay. We therefore are using a number of gloveboxes (see photo) and other infrastructures for operating in the conditions simulating the underground environment (very low pO2, controlled pCO2 and redox potential), both for working with non-radioactive and radioactive materials. This is needed to reproduce the potential interactions in a future underground disposal repository in Boom Clay in Belgium, in particular since the geochemistry (solubility, speciation, sorption) of long-living radionuclides in clay are very sensitive to the environmental conditions. We have also developed a dedicated infrastructure for (thermo)hydromechanical and gas transport experiments on clays in specific stress conditions.
Our infrastructure and equipment are regularly updated or upgraded, as the scientific approaches change with time, and programmes evolve. Such a recent evolution was for example the development of an infrastructure for monitoring the swelling and swelling pressure developed by bituminized waste upon contact with water.
The main experimental facilities are the following:
- Leaching / dissolution tests on vitrified high-level waste and spent fuel
- Water uptake (see photo) and ageing (due to thermal or radiation effects) of bituminized waste
- Corrosion tests (electrochemical, immersion) on candidate container materials (carbon steel, stainless steel)
- Solubility tests on radionuclides
- Different kinds of migration tests on radionuclides
- Determination of various characteristics (hydraulic conductivity, (thermo)hydro-mechanical and self-sealing properties, gas transport properties) of clay
In the framework of studies related to the properties of Berylium either as waste from material testing reactors such as the BR2 or as a material used in future Fusion reactors, the Waste & Disposal Expertise Group has a quite unique infrastructure for performing chemical reactivity tests on Berylium requiring special protection measures due to the high chemotoxicity of especially Beryllium dust.
Our expert group also has developed through the many years before, in cooperation with the EURIDICE expert group many experiments in the HADES underground research laboratory in clay.
We also refer to the expert groups Radiological Impact and Performance Assessments and EURIDICE, that also contribute strongly to the R&D at SCK•CEN on waste and disposal.
The reader can find a comprehensive overview of the many technical and scientific expertises developed through these programmes in the section 'research projects'.
Head of Expert Group: Christophe Bruggeman