A series of calculations is presented assessing the criticality aspects of specific configurations of FTR fuel. Results for regularly spaced arrangements of fuel pins or fuel assemblies as a function of spacing in each of four media (water, Mobiltherm, sodium, or air) are given. This information is intended to be of a broad general nature conservatively applicable both to normal fuel configurations likely to be encountered in the operation of the FFTF and to accident condition configurations postulated for criticality review purposes.