Although nuclear power is considered a low carbon power generation source, its legal inclusion with renewable energy power sources has been a subject of debate and classification. Statutory definitions of renewable energy usually exclude many present nuclear energy technologies, with notable exceptions in the states of Utah, and Arizona in the United States, where only a particular implementation of nuclear fission with "waste"/fuel recycling meets the state's criteria. Dictionary sourced definitions of renewable energy technologies often omit or explicitly exclude mention to every nuclear energy source, with an exception made for the natural nuclear decay heat generated within the Earth/geothermal energy.