At present, all nuclear power plants use nuclear fission; thorium and nuclear fusion are not yet available for electricity generation.

Nuclear energy includes both nuclear fission and nuclear fusion. Uranium is used as a nuclear fission material in operational nuclear power stations. Other elements could also be used, such as thorium. With nuclear fusion, light elements combine into heavier ones, but this technique is still in a research phase and its availability is not to be expected in the coming decades. Existing nuclear power plants use the heat from fission to make steam that drives a generator which in turn generates electricity. There are around 450 nuclear power plants in operation worldwide (source: IAEA). At present, the most commonly used reactor types are the pressurized water reactor (PWR) and the boiling water reactor (BWR). In Western Europe, development is ongoing on the European Pressurized Reactor (EPR). This third-generation reactor type is due to become the standard for future nuclear reactors with improved safety and efficiency. EPR plants are being constructed in Finland (Olkiluoto), France (Flamanville) and the UK (Hinkley Point). Research is currently being carried out on the use of thorium in future power stations. Thorium can be used in a conventional nuclear power plant or in a reactor where thorium is dissolved in molten salt, however, a commercial plant that works with molten salt is not expected for some time yet.

Despite the negligible greenhouse gas emissions from nuclear fission energy, the process is not considered sustainable.

In the Netherlands there is a closed nuclear plant in Dodewaard and an operational plant in Borssele. The Borssele plant generates around 3% of the electricity produced in the Netherlands (source: CBS). Even though CO2 is not released during the nuclear fission process, nuclear waste from the process remains radioactive for thousands of years. The nuclear waste coupled with the finite nature of nuclear fission material are two important factors that render nuclear energy unsustainable.

Nuclear energy can contribute to a climate-neutral energy supply.

The extraction of nuclear fission material and the construction of nuclear power plants currently requires the use of fossil fuels (as is the case for the construction of renewable energy installations). All the same, nuclear energy results in very low CO2 emissions per quantity of electricity produced. Another advantage is that the electricity production is not dependent on the weather, unlike electricity from sun and wind. Depending on the extent to which production can be scaled up and down, it could be a good supplement as much needed CO2-free  dispatchable electricity generation capacity. Another way to vary the amount of electricity supplied to the grid is to use a varying part of the electricity produced for hydrogen production. This means that nuclear energy can make a useful contribution to a climate-neutral energy supply. Most Intergovernmental Panel on Climate Change (IPCC) scenarios for a global climate-neutral energy supply include a role for nuclear energy.

The advantages and disadvantages of nuclear energy, however, require careful consideration.

In addition to the advantages of an almost CO2-free and non-weather dependent form of electricity generation requiring a small amount of space, there are also important disadvantages to nuclear energy. There is no generally accepted method of long-term storage of nuclear waste. This disadvantage would be less with a thorium reactor because less nuclear waste is released, and the nuclear waste from thorium has a shorter half-life. Other disadvantages are that fission products can be used in nuclear weapons and in dirty bombs (conventional explosives combined with radioactive material). Furthermore, accidents with nuclear power plants make large areas uninhabitable. Additionally, the construction costs and the duration of construction of new nuclear power plants in Europe and in the US have risen sharply. The construction costs in China and the rest of South East Asia are lower. The higher costs in Europe and in the US are mainly due to increased safety requirements, new and more complex reactor designs and materials, high labour costs and the need to regain experience with the construction of nuclear power plants. 

As mentioned above, in most global IPCC scenarios there is a role for nuclear energy. Regional differences can lead to different combinations of CO2-free energy technologies in order to arrive at a locally optimal approach, and to a choice whether or not to use nuclear energy.