Keywords: thermal simulation, spent nuclear fuel, prototype repository, finite element method.

The unique opportunity for model verification and validation is the prototype repository experiment. This is the physical model of the small part of the repository. The experimental data can be used for comparison with the computed data. The main goal of this paper is a comparison between the results achieved in the prototype repository experiment and the results obtained from the model. The temperatures are compared at sample points where the sensors in the experiment are placed. The accuracy of the model and its capabality to predict the behaviour of the real design of the deep geological spent nuclear fuel repository are shown. The main temperature profiles in the vicinity of the boreholes are shown in this paper.

The mathematical models of the thermal dimensioning must be evaluated with the physical experiments. One of the most complex experiments relating to the deep geological spent nuclear fuel repository was realised in Sweden, in the SKB Aspo Hard Rock Laboratory (HRL) [1]. This prototype repository simulates part of a KBS-3 nuclear waste repository. The aim of the prototype repository is to demonstrate the integrated function of the repository components and to provide a full-scale reference for comparison with models and assumptions.

The problem is solved using the ANSYS software package. It includes two different environments: ANSYS "native" and ANSYS Workbench [2]. ANSYS Workbench is a relatively new product characterised by a user friendly graphical user interface. But it does not include all ANSYS features accesible in batch mode or when using the old "native" interface. But the Workbench is a sufficient tool for our first simple case study. All tasks are performed using ANSYS Workbench including geometry creation in the Design Modeler, finite element mesh creation, setting of the boundary and initial conditions, executing the solve and result processing. The more sophisticated procedures of ANSYS usage are shown in [3].

The temperature profiles at the centre of the height of the first container, 2 meters from the axis of the container are shown. The temperatures at the left side and right side from the borehole are shown in the figure. It can be concluded, that the computed temperatures are similar to the experimental results achieved. The difference is about 8 percent.

The finite element models focus on the thermal dimensioning of the deep geological spent nuclear fuel repository to solve the crucial problems for the repository construction. The comparison with the experimental results provides the opportunity for model verification and validation. The prototype repository experiment provides a good opportunity for evaluation of these results.

The next step is to use the model for the prediction of temperature conditions for the planned concepts of the deep geological spent nuclear fuel repository. The concepts are expected to be similar to the prototype repository.

1

SKB Aspo Hard Rock Laboratory, 2011. http://www.skb.se/Templates/Standard____25506.aspx

2

ANSYS, Inc., "Release 13.0 Documentation for ANSYS", ANSYS Incorporated, 2010.

3

J. Novak, M. Hokr, "Finite Element Simulations of the Thermal Conditions in a High-Level Waste Repository", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 130, 2009. doi:10.4203/ccp.91.130

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