Physics calculations have been made for various combinations of the four types of fuel assemblies to be used in the EBWR core. Two thicknesses of plates, 0.205 in. and 0.274 in., including the two 0.020-in. cladding layers, are to be made of both natural U and U containing 1.44% U235. A total of 148 assemblies, 74 natural and 74 enriched, are to be fabricated with six identical plates each. Various configurations of these fuel assemblies will be used to (1) change the critical size of the core, (2) change the power distribution in the core, and (3) change the amount of reactivity corresponding to a given stream volume in the core. The physics calculations show that uncertainties in critical mass are adequately covered by the number and variety of fuel assemblies and that the possible changes in core characteristics with the different fuel assemblies should provide valuable information about the factors affecting maximum power density and stability in a boiling water reactor.