A Parametric Study of a Repository Tunnel for Decommissioning Waste

Abstract

The development of a radionuclide transport model for a tunnel of a repository for short-lived low and intermediate level waste is presented in this work. The model is two-dimensional and uses the finite element method to describe a cross-section perpendicular to the tunnel's main axis. It is shown that the use of a realistic geometry of the system, albeit in 2D, results in a transparent model that can handle the equations in a flexible way. The geometry can easily be changed and also extended to a 3D representation without affecting the numerical code. The disadvantage is the computational requirement. It is expected however that radionuclide transport modelling will evolve to 2D or 3D representations that are more realistic and transparent than today's 1D analytical models which involve many simplifications whose impact on the output is difficult to evaluate.,1752'8&7,21An important fraction of the low and intermediate level waste from the decommissioning of nuclear power plants is short-lived. In Sweden it is envisaged that this short-lived low and intermediate level waste (LILW) will be isolated in underground tunnels at a depth of approximately 300 meters in a crystalline rock formation. Safety studies related to the final disposal of this type of waste are not at the same advanced stage as for high-level nuclear waste or spent nuclear fuel. Nevertheless, the disposal of LILW poses some major technological challenges that require a substantial effort to be put on performance studies of a repository for this kind of waste in the years to come.In this work a model for the estimation of radionuclide migration in the near-field of a repository tunnel has been developed. The investigation has been conducted for regulatory purposes. In the next section we briefly describe the Swedish Nuclear Fuel and Waste Management CO (SKB) concept of the SFL-5 repository. In Section Three we introduce the 2Dmodel and the input data. The discussion of the results is given in Section Four. Section Five presents the conclusions and the summary.$ 5(326,725< )25 6+257/,9(' /,/:A convenient way to isolate the low-level waste is to enclose it in tunnels. The Swedish Nuclear Waste and Management Company, SKB, has performed one preliminary analysis study of a repository 'concept' for this type of waste [1]. According to SKB, the short-lived waste will be placed in a system of tunnels which form the SFL 3-5 repository. A schematic view of this Mat. Res. Soc. Symp. Proc. Vol. 807