For the past 18 months, Oak Ridge National Laboratory has been developing a passive fast-neutron emission tomography capability. The goal of this development is a new passive capability to detect diversion of single fuel pins (rods) from spent or used nuclear fuel assemblies by performing neutron emission tomography. At present, a laboratory prototype imager is under construction. The purpose of the prototype imager is to demonstrate imaging capability sufficient to resolve individual fuel pins in a spent nuclear fuel assembly. This report documents the results of simulation studies to optimize the design of the prototype imager.