Turbulence measurements in an air model of a partly blocked reactor fuel subassembly

The Eulerian integral time-scale and the kinetic energy of the turbulence have been measured at various points in the recirculating regions behind blockages of up to 13 subchannels in a large-scale model of part of a fast reactor fuel subassembly using air to represent the coolant. It is found that roughly the time-scale is directly proportional and the kinetic energy is inversely proportional to the diameter of the blockage. From these measurements approximate values of the eddy diffusivity can be deduced, and are found to be independent of the blockage size. In a fast reactor, the eddy diffusivity behind a blockage would be far greater than the conductive thermal diffusivity. (author)