Sodium cooled Fast Reactors (SFRs) have been part of the international nuclear enterprise since the 1960s. They are valued especially because they offer the potential of improved nuclear fuel use. However, they have not achieved widespread use, primarily because of high costs, the inconvenience of using sodium as a reactor coolant and the potential for reactor criticality accidents. In a multiuniversity 4-year study an investigation sought ways to improve safety at low cost building upon previously proposed SFR concepts. This was done within the context of the NRC’s Technology Neutral (regulatory) Framework (TNF), a risk-informed treatment of safety regulation that was also extended to the potential problem of regulation of proliferation threats. We concluded that the costs of SFRs and their electricity output could not easily be reduced below the levels of competing LWRs, primarily because of the problems of using sodium as a coolant. The TNF was found to be a practical method for guiding safety improvements and evaluating their effectiveness. Also, past emphases of safety concerns to criticality accidents and sodium fires were found to be less important than seismic risks limit that limit the degree of feasible safety improvements. The same framework was extended to treatment of proliferation risks, where we showed how they could be treated in a manner similar to those of safety. However, no government has yet undertaken such regulation using any method of nuclear system evaluation.