PRELIMINARY EVALUATION OF THERMAL-HYDRAULICS BLOCKAGE EVENTS IN AN OPEN SQUARE CORE DESIGN FOR A LFR REACTOR

Several innovative solutions for a liquid metal fast reactor design are being investigated. Among these solutions the open-assembly configuration is one of the possible core options. In order to analyze the behavior of the whole core in the case of a blockage accident a simplified three-dimensional numerical model of an open square lattice reactor core has been developed. The numerical simulation is performed at assembly length level taking into account the local fluctuations of turbulent viscosity and energy exchange coefficients at sub-channel level through transfer operators based on parametric coefficients. In this work we present some results concerning a blockage event occurring in the core where the coolant flow is reduced in the corresponding assembly. This may happen in a reactor core by various reasons, like the failure of some components such as the cladding of fuel rods. A peak temperature in a small portion of the core may cause damages such as cladding ballooning, which may block a substantial portion of the flow area and restricts the coolant flow. In such cases the heat removal process is strongly reduced and a temperature increase of the coolant is expected. We study both the closed and the open assembly cases. In the closed assembly situation, blockage of the core results in reduced velocity along all the considered assembly. In the open assembly case, convection heat transfer is diminished but still takes place in the rest of the assembly and lower peak temperatures are expected with respect to the closed assembly case