The optimisation of the nuclear fuel cycle is a key issue for the sustainability of nuclear energy. This book presents the papers from a workshop which investigated alternative nuclear energy futures, with emphasis on back-end of the fuel cycle options that could enhance the sustainability of nuclear energy in the long term, to 2050 and beyond. The papers lay out the conditions that need to be fulfilled for nuclear energy to remain a viable option and highlight the technological and strategic developments underway to address those issues. Subjects covered include natural resource management, radioactive waste minimisation, cost reduction and proliferation resistance aspects of alternative reactor and fuel cycle technologies.