They are expected to be deployable within the next three decades. Comparative advantages include reduced capital cost, enhanced nuclear safety, minimal generation of nuclear waste, and further reduction of the risk of weapons materials proliferation. Work has started on four of the selected systems. The goals set for Generation IV nuclear energy systems are:
GIF studies have defined four classes of nuclear fuel cycle including once through, with partial recycle of plutonium, with full plutonium recycle, and with full recycle of transuranic elements. These were modelled over a century based on nuclear energy demand projections developed by the World Energy Council and the International Institute for Applied Systems Analysis.
The once-through cycle was shown to be the most uranium resource-intensive generating the most waste in the form of spent fuel, but the wastes produced are still small compared with other energy technologies. Uranium resources are sufficient to support a once-through cycle at least until mid-century. However, the limiting factor is the availability of repository space. This becomes an important issue, requiring new repository development in a few decades. In the longer term, beyond 50 years, uranium resource availability also becomes a limiting factor.
Systems that employ a fully closed fuel cycle can reduce repository space and performance requirements, although costs must be held to acceptable levels. Closed fuel cycles permit partitioning of nuclear waste and management of each fraction with the best strategy. Advanced waste management strategies include transmutation of selected nuclides, cost effective decay-heat management, flexible interim storage, and customised waste for specific geologic repository environments. They also promise to reduce the long-lived radiotoxicity of waste destined for geological repositories by at least an order of magnitude by recovering most of the heavy long-lived radioactive elements.
Various reactors could also be combined in symbiotic fuel cycles including combinations of thermal and fast reactors. Actinides from the thermal systems can be recycled into fast systems, reducing actinide inventories worldwide. Improvements in the burn-up capability of gas- or water-cooled thermal reactors may also contribute to actinide management in a symbiotic system. Thermal systems may also develop features, such as hydrogen production in high-temperature gas reactors or highly economical light water reactors as part of an overall system offering a more sustainable future.
GIF studies also found that nuclear energy is unique in the market since its fuel cycle contributes only about 20% of its production cost. They further suggested that adopting a fuel cycle that is advanced beyond the once through cycle may be achievable at reasonable cost.