Assessment of Geochemical Containment Properties in the Near-field of a Deep Underground Repository
- PDF / 428,701 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 167 Views
II1.5.1
Assessment of Geochemical Containment Properties in the Near-field of a Deep Underground Repository Delphine Pellegrini and Laurent De Windt1 Safety Evaluation Department, Institute for Radioprotection and Nuclear Safety, BP17, 92262 Fontenay-aux-Roses, France 1 Centre for Geological Computer Sciences, Paris School of Mines, 35 rue Saint-Honoré, 77305 Fontainebleau, France
ABSTRACT For safety evaluation of deep repositories, the evolution of chemical containment properties of clayey barriers in spent fuel disposal tunnels are assessed using reactive transport modelling. The disturbances related to cement components are more particularly studied for relevant time scales (100,000 years) and dimensions. Theoretical distribution coefficients (Kd) and maximum concentrations are derived for Cs, Tc and U and their sensitivity to the system evolution estimated. Mineralogical transformations and ion sorption are shown to be interdependent mechanisms controlling the intensity and spatial expansion of the alkaline plume. Simulations for a normal diffusive scenario and an altered one involving an advective flow lead to limited perturbations of the mineralogy and containment properties of the multi-barriers system, but emphasize the possibility of a migration pathway through the excavation damaged zone.
INTRODUCTION Within the framework of deep repository feasibility studies, IRSN carries out safety evaluation of the design options developed by the National Agency for the Management of Radioactive Wastes (ANDRA) for a repository in an argillaceous formation. An important step of the evaluation process is to ensure that the safety functions of the containment systems are fulfilled for different scenarios of the evolution of a repository, so-called “normal” and “altered” ones. Realistic modelling features and processes identifies the possible causes of component failure, as well as quantifies their effect on the performances of other components. Such processlevel modelling also puts into perspective the remaining uncertainties on the understanding and quantification of the phenomena. The relative importance of the above findings can then be assessed by integrated-level modelling, in terms of activity transfer on a whole disposal scale. This combination of process-level and integrated-level performance assessments should thus provide information on the advantages and drawbacks, with regard to safety functions, of different disposal options associated with various site configurations. Within this evaluation step, one of the subjects of concern is the possible change in the containment properties of the barriers due to chemical interactions with the surroundings. In a first stage, the evaluation of the modifications in time and space of mineralogy, hydrochemistry and porosity, which may have an impact on containment properties and other characteristics (e.g. mechanics), is carried out. Afterwards, the consequences on radionuclide migration have to be assessed in terms of solubility limits (S) and distribution coefficients
Data Loading...
