Oak Ridge National Laboratory is developing a new capability to detect diversion of fuel pins from spent nuclear fuel assemblies based on passive fast neutron emission tomography for international safeguards applications. This method has the potential to be the most sensitive partial defect test possible on spent fuel assemblies, detecting individual vacancies or substitutions prior to transfer to storage areas that are difficult to access. This high level of sensitivity is possible by combining the use of fast neutrons (which can penetrate the entire fuel assembly) and computed tomography. Emission tomography uses collimation to isolate activity along “lines of response” through an object. By combining a number of collimated views through the object, the neutron emission from each fuel pin can be mathematically extracted, and an image of the fuel assembly can be constructed. The International Atomic Energy Agency (IAEA) is presently investigating the use of passive gamma emission tomography for the same application. This new fast neutron emission tomography method could be used in conjunction with current gamma emission tomography techniques to compliment and assist with the measurement of larger fuel assemblies. Fast-neutron emission tomography methods can be applied to either irradiated fuel or fresh plutonium mixed oxide (MOX) fuel. If applied to MOX fuel, this technique is expected to have the resolution required to empirically measure the effective 240Pu concentration on a pin-by-pin basis. If applied to irradiated fuel, the exposure of each pin can be measured via the ingrowth of 244Cm. Because curium is primarily produced at the end of the exposure cycle, the technique may even be sensitive to replacement fuel pins that were subsequently irradiated. This paper will report on the progress made toward a physics design of the collimator and envisioned concept of operations of the imaging system.