There is no universal definition of fissile material, but it is usually taken to mean high enriched uranium (HEU – uranium enriched to 20% or more in U-235) and separated plutonium (plutonium separated from irradiated fuel by reprocessing). Production of nuclear weapons requires either HEU or separated plutonium. Having fissile material or the means to produce them (i.e. enrichment and/or reprocessing) can present a proliferation risk. Fissile material can also present the risk of acquisition and use by terrorists.

The terrorist risk has been recognized by the international program to minimize HEU in civilian programs, and now by the Nuclear Security Summit process launched by President Obama in 2009 (the second Nuclear Security Summit will be held in Seoul in 2012). A question is whether sufficient is being done to minimize risks involved with separated plutonium. E.g. the fast breeder reactor presents serious proliferation and terrorism risks if very high-fissile plutonium produced in breeding blankets is separated. Technical measures are needed to build proliferation-resistance into plutonium recycling technologies.

In addition, institutional measures are needed to address enrichment and plutonium recycling issues. These capabilities present a proliferation risk, so alternatives to national fissile material production programs are required for aspirant states. These capabilities also present risks to disarmament ? the proposed fissile material cut-off treaty will be an important step, but in the longer term the need to replace national enrichment and reprocessing programs applies also to nuclear-weapon states. Multilateral approaches should be developed, to provide energy security without the need for national fissile material production programs.