The long term function of repository barriers is an essential consideration in a safety case, and needs to be studied for different scenarios. Kemakta has carried out several of the key assessments of the function and degradation of the SFR concrete barriers over the repository lifetime for SKB. These studies model the leaching of cement minerals and the chemical interactions of the concrete with the waste and groundwater. They have also provided quantitative mechanistic models of fracture formation and analysis of the impact of barrier degradation on the barrier performance and radionuclide migration over time. Furthermore, we have used modeling to investigate the impact of highly alkaline conditions on bentonite barrier performance. A PDF version of each report can be accessed by clicking on the title.
The impact of concrete degradation on the BMA barrier functions (2014). SKB R-13-40
Reactive transport modelling have been performed of concrete degradation in 2/3-dimensional concrete barrier structures considering the impact of thin fractures that constitute areas of locally increased leaching by groundwater. The leaching and degradation processes have been modelled over a period extending for more than 50 000 years in order to investigate the ultimate fate of the concrete interacting with the groundwater. Changes of groundflow conditions as well as the changes of the chemical composition as a result of landrise have been studied. Simple analytical models have been developed to study the impact of fractures and porosity changes on the overall barrier performance over time.
Model codes: Phast, PHREEQC and Comsol
Project SAFE – Modelling of long-term concrete degradation processes in the Swedish SFR repository (2001). SKB R-01-08.
Reactive transport modelling was performed of the interaction between concrete barriers and groundwater over time. Mineral transformations leading to porosity changes in the barrier materials were studied, as well as the gradual depletion of alkaline minerals of importance for the ability to maintain a high pH to ensure good sorption of radionuclides in the repository.
Model code: PHREEQC
EU research project ECOCLAY-II. EU and SKB (2000-2003).
The research activities combined predictive modeling, advanced experimental research and development of mechanistic model tools for interpretation of the behavior of bentonite in highly alkaline environments.
Model codes: PHREEQC, Mathematica
Project SAFE: Gas related process in SFR (2001). SKB R-01-11
Coupled transport models (Tough) and semi-analytical probabilistic models were used to examine radionuclide release from SFR vaults (Silo, 1BMA and BTF) as a result of gas generation. The different scenarios included gas escaping as planned, the presence of cracks, 1BMA being backfilled and the Silo not containing evacuation pipes. The expulsion of contaminated water as a result of gas build up was calculated to increase the release of some radionuclides by several orders of magnitude. However the impact on total doses received by the public was found to be limited.
Model code: TOUGH