Whether nuclear power should be considered a form of renewable energy is an ongoing subject of debate. Legal definitions of renewable energy usually exclude nuclear energy technologies, with the notable exception of the U.S. state of Utah. Dictionary-sourced definitions of renewable energy technologies often omit or explicitly exclude mention of nuclear energy sources, with an exception made for the natural nuclear decay heat generated within the Earth. The most common fuel used in conventional nuclear fission power stations, uranium-235 is "non-renewable" according to the United States' Energy Information Administration, the organization, however, is silent on the recycled MOX fuel. The National Renewable Energy Laboratory does not mention nuclear power in its "energy basics" definition. In 1987, the Brundtland Commission (WCED) classified fission reactors that produce more fissile nuclear fuel than they consume (breeder reactors, and if developed, fusion power) among conventional renewable energy sources, such as solar power and hydropower. The monitoring and storage of radioactive waste products is also required upon the use of other renewable energy sources, such as geothermal energy.
Definitions of renewable energy
Renewable energy flows involve natural phenomena, which with the exception of tidal power, ultimately derive their energy from the sun (a natural fusion reactor) or from geothermal energy, which is heat derived in greatest part from that which is generated in the earth from the decay of radioactive isotopes. Renewable energy resources exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries.
Fission fuel supply In 1987, the World Commission on Environment and Development (WCED), an organization independent from, but created by, the United Nations, published Our Common Future, in which a particular subset of presently operating nuclear fission technologies, and nuclear fusion were both classified as renewable. That is, fission reactors that produce more fissile fuel than they consume - breeder reactors, and when it is developed, fusion power, are both classified within the same category as conventional renewable energy sources, such as solar and falling water. To fulfill the conditions required for a nuclear renewable energy concept, one has to explore a combination of processes going from the front end of the nuclear fuel cycle to the fuel production and the energy conversion using specific fluid fuels and reactors, as reported by Degueldre et al. (2019). Extraction of uranium from a diluted fluid ore such as seawater has been studied in various countries worldwide. This extraction should be carried out parsimoniously, as suggested by Degueldre (2017). An extraction rate of kilotons of U per year over centuries would not modify significantly the equilibrium concentration of uranium in the oceans (3.3 ppb). This equilibrium results from the input of 10 kilotons of U per year by river waters and its scavenging on the sea floor from the 1.37 exatons of water in the oceans. For a renewable uranium extraction, the use of a specific biomass material is suggested to adsorb uranium and subsequently other transition metals. The uranium loading on the biomass would be around 100 mg per kg. After contact time, the loaded material would be dried and burned (CO2 neutral) with heat conversion into electricity, e.g. The uranium ‘burning’ in a molten salt fast reactor helps to optimize the energy conversion by burning all actinide isotopes with an excellent yield for producing a maximum amount of thermal energy from fission and converting it into electricity. This optimisation can be reached by reducing the moderation and the fission product concentration in the liquid fuel/coolant. These effects can be achieved by using a maximum amount of actinides and a minimum amount of alkaline/earth alkaline elements, yielding a harder neutron spectrum. Under these optimal conditions, the consumption of natural uranium would be 7 tons per year and per gigawatt (GW) of produced electricity.e.g. The coupling of uranium extraction from the sea and its optimal utilisation in a molten salt fast reactor should allow nuclear energy to gain the label renewable. In addition, the amount of seawater used by a nuclear power plant to cool the last coolant fluid and the turbine would be ~2.1 gigatons per year for a fast molten salt reactor, corresponding to 7 tons of natural uranium extractable per year. This practice justifies the label renewable.
Conventional fission
Nuclear fission reactors are a natural energy phenomenon, having naturally formed on Earth in the past. For example, a natural nuclear fission reactor in present-day Oklo, Gabon was discovered in the 1970s. It ran for a few hundred thousand years, averaging 100 kW of thermal power during that time. Conventional manmade nuclear fission power stations largely use uranium, a common metal found in seawater and rocks around the world, as its primary fuel source. Uranium-235 "burnt" in conventional reactors, without fuel recycling, is a non-renewable resource, and if used at present rates would eventually be exhausted. This is similar to geothermal energy derived from the natural nuclear decay of the large but finite supply of uranium, thorium, and potassium-40 present within the Earth's crust. Due to nuclear decay, this renewable energy source will eventually run out of fuel. The Sun's energy will too be exhausted.
Breeder reactors
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![Nuclear power proposed as renewable energy: Proportions of the isotopes, U-238 (blue) and U-235 (red) found in natural uranium, versus grades that are enriched. light water reactors and the natural uranium capable CANDU reactors, are primarily powered only by the U-235 component, failing to extract much energy from U-238. While by contrast uranium breeder reactors mostly use U-238/the primary constituent of natural uranium as their fuel.[12]](https://upload.wikimedia.org/wikipedia/commons/thumb/2/25/Uranium_enrichment_proportions.svg/500px-Uranium_enrichment_proportions.svg.png?utm_source=en.wikipedia.org&utm_campaign=parser&utm_content=thumbnail)

