An accurate analysis of the thermal-mechanical behaviour of the fuel is particularly important for advanced reactor systems due to their increased safety requirements. The fuel types considered for advanced reactors may differ significantly from traditional designs, and so often the currently available codes cannot model such fuels without significant modifications. Thus, the adaptation and qualification of existing codes becomes an important requirement in the transient analysis of such reactors.
The 2400 MWt helium-cooled (U-Pu)C-fuelled fast reactor is one of the most promising Generation-IV concepts. The design goal of the Gas-cooled Fast Reactor (GFR) is to combine a number of features, including flexible breeding parameters and high coolant temperatures. The high temperatures allow for both high thermodynamic efficiency and hydrogen production. Several new fuel designs are currently being considered within the GFR project. One of them, which is the reference design, is a ceramic plate matrix with a honeycomb inner structure containing small fuel cylinders. The fuel is mixed uranium-plutonium carbide, while the matrix material is silicon carbide.
A two-dimensional approach to the thermal-mechanical simulation of such fuel, taking into account the inner heterogeneity, is being developed at PSI, individual phases of the development involving benchmarking against detailed finite-element calculations. One of the distinctive features of the analytical scheme is taking into account the influence (on the transient temperature distribution in the fuel elements) of the elastic deformation and thermal expansion of the materials, as well of fuel swelling, fission gas release, and closure and reopening of the gas gaps Once integrated into the PSl transient analysis coupled code system "FAST", the resultant model will provide detailed fuel and matrix temperatures to determine neutronic feedbacks and to evaluate fuel integrity in a comprehensive manner.
The paper presents the development of the 2D thermal model for the GFR plate-type fuel, its integration into the transient analysis code system, as also the benchmarking of the model against 3D finite-element solutions obtained using the ANSYS™ code.