During the current project phase of the disposal of category A waste ONDRAF/NIRAS must, following the governmental decision of 23 June 2006, develop a near surface disposal facility in Dessel. The disposal facility needs to provide safe disposal of waste and the demonstration of the long term safety is required by means of safety and performance assessment.
The objectives of the present report are to provide insight into the behaviour of the disposal system under expected long-term conditions. The report builds on the developed phenomenological view on the “expected evolution” which serves as a basis for the development of a conceptual near field model. Modelling requires an abstraction and mathematical representation and simplification of processes. A number of hypotheses, detailed in section 2.2, describe and substantiate the choices taken for the development of the expected evolution scenario near field model (EES model).
Chapter 3 gives a description of conceptual and mathematical EES model. First the description of the processes is given, followed by a geometrical features of the model. The processes are then described by a mathematical models, separately for flow and for species transport. Both include the description of flow and transport in fractured systems as well. Any model requires initial and boundary conditions which are given in sections 3.5 and 3.6, respectively.
Sensitivity analysis is an important element of assessment and gives the insight into system behavior as well as the importance of different features and processes for the evolution of fluxes from the system. They also support the decisions regarding the conceptual models taken forward in building the EES model.
In Chapter 4 the modelling results are analysed in terms of water flow and mass transport. These results are used for the analysis of the modelling assumptions, such as the use of different monoliths, effect of gradual degradation, effect of boundary conditions in terms of upward diffusion, inter-monolith space transmissivity effect and the effect of transport properties of different components.
Chapter 5 provides the description of the hypotheses for dose calculations and dose analysis for the EES model. From the sensitivity and uncertainty analysis of the EES model, one bounding model is selected for the so-called “reference scenario” which is used to determine radiological waste acceptance (site capacity).
The reference scenario is then applied to calculate several indicators, such as effective dose rate for different receptors and age groups, for compliance with drinking water standards, for skin and eye dose, ingestion dose, inhalation dose and in terms of spatial distribution of contamination in geosphere.
Finally some details are on the calculations are given in the Appendices.
|Number of pages||342|
|State||Published - 4 May 2023|
|Name||SCK CEN Reports|