Interchannel Mixing in Wire Wrapped Liquid Metal Fast Reactor Fuel Assemblies

The available experimental data applicable to mixing rates between subchannels in wire wrapped liquid metal fast breeder reactor fuel assemblies are reviewed. A rate of mass mixing between interior subchannels of 0.03 in terms of the dimensionless ratio β (i.e., the ratio of the mixing flow rate per unit length per unit of spacing between pins to the axial mass flux) is recommended as conservative for the typical geometries of present U.S. fuel bundles. The quantitative dependence of mass mixing rates with key variables of subchannel geometry, wire lead, and pin pitch to diameter ratio is presented and discussed.