Models mimic waste transport underground
Storing nuclear waste below the Earth's surface requires special attention to its transport characteristics in the face of physical, chemical and biological processes within the rock. The EU-backed project Retrock studied the retention and transport of radionuclides for use in PA models of saturated hard fractured rock. Performance assessment of waste disposal sites requires models of radionuclide transport through the rock environment. This means scientists need to develop reliable models that mimic conditions found in these underground repositories. There are many processes that can influence the transport of radioactive material through the rock. Flow field of the radionuclides in fractured rock which takes place in channels in the fractures is one of the main phenomena. Also important is their diffusion between the fractures and the rock matrix. How the radionuclides stick onto rock particles has a major effect on transportation of the radioactive material within the rock. The EU-backed so-called 'WP2' report states that data drawn from the models may not be entirely conclusive. In particular, the report surmises that the extensive data needed for PA models may be a hindrance when actually using the simulations. A major challenge is obtaining relevant data for the main simplified PA models. The findings have fed into subsequent WP reports and had a bearing on acquiring feedback from the Retrock project. Overall, the 'WP2' report has given an accurate description of the present situation surrounding the sensitive issue of radioactive waste repositories and has highlighted some outstanding requirements.