Comparisons between experimental results and numerical simulations for the Sonaco sodium natural convection experiments

The SONACO experiments are conducted on an electrically heated 37-pin rod bundle, immersed in liquid sodium and contained within a hexagonal wrapper. The rig was designed to investigate natural convection cooling for a geometry representative of fast reactor fuel assemblies. Heat can be removed from the test section in several ways, but in this paper only the axial cooling mode is examined. Above the heated bundle is a plenum, at the top of which is a cooling coil containing a separate, forced sodium flow. Heat transfer from the bundle to this cooling coil is effected by means of buoyancy driven circulatory flow in the sodium, and in the axial cooling mode almost all the heat is removed by the coil. This mode is intended to simulate the natural convection cooling of a blocked fuel assembly by way of thermosyphon coupling to the inner pool. In this paper experimental results are presented, for the temperatures measured under such conditions, and these are compared with results from a numerical simulation using the general purpose, three dimensional thermalhydraulic code ASTEC