[en] One part of the LMFBR safety assurance program has been the testing to failure of prototypic fuel in a sodium environment. Effort has recently been applied toward development of a new Safety Test Facility (STF) which would provide improved testing capability. Alternative test reactor design work has been done on the Phoebus/Uhtrex design and the High Fluence Fast Pulse Reactor (HFFPR). As part of the HFFPR design effort, a criterion has been developed to allow rapid and inexpensive scoping analyses of different core designs, using zero-dimensional neutronics calculations. This paper derives this criterion and describes several promising core designs which were explored with this method