Dr. Greenspan is a Professor of the Graduate School since summer 2014. He has over 50 years of research experience in a wide variety of nuclear reactor physics, methods development and advanced reactor design related activities. In recent years his research interests are conception, design and analysis of advanced (primarily, Generation-IV) nuclear reactors and advanced nuclear fuel cycles. Specific objectives of his research are: Improving the sustainability of nuclear energy by increasing the utilization of the uranium and thorium fuel resources; minimizing the amount and radiotoxicity of the nuclear waste; improving proliferation resistance of nuclear energy along with improving the safety and economics of nuclear reactors. Over the past 15 years he has been the PI of 9 DOE funded (NERI; NEUP) multi-year projects most of which explored the feasibility of innovative core design and fuel cycles. His presently favorite reactor concept is “breed-and-burn” (B&B) fast reactors. A B&B reactor is a breeder reactor that converts into fissile fuel a significant fraction of the fertile feed fuel and then fissions a significant fraction of the bred fissile fuel without fuel reprocessing. B&B reactors can offer uranium utilization that is between 50 to 120 times that of LWRs. The amount of electricity that could be generated in B&B fast reactors using the presently available depleted uranium stockpiles (nuclear “waste”) is the equivalent of between 8 to 20 centuries of the total present US demand of electricity. Unfortunately, in order to achieve a B&B mode of operation the fuel will have to withstand nearly 2.5 times higher fast neutron induced radiation damage that has been proven acceptable. To alleviate this problem we recently proposed “seed-and-blanket” sodium cooled fast reactor (SFR) cores made of a critical seed and a subcritical B&B blanket. Specifically, we are searching for best ways to make beneficial use of the large fraction (up to 30%) of the fission neutrons that leak out from a seed designed to effectively transmute trans-uranium elements (TRU) from LWR used nuclear fuel to drive a B&B thorium fueled blanket to generate as large a fraction of the core power as possible without exceeding the presently acceptable radiation damage level of the fuel cladding material – 200 displacements-per-atom (DPA). Results obtained so far are highly promising – the reactivity increase with burnup of the B&B blanket greatly improves the performance of the TRU transmuting seed while the excess seed neutrons enable to generate close to 50% of the core power from the blanket while fissioning 7% of the thorium without the need for reprocessing the thorium fuel. He has over 500 publications with his students and other collaborating researchers.