operating temperature of the reactor. Thermodynamics states that the maximum possible thermal efficiency of any heat engine equals

(To-Ta)/Ta where To is the operating temperature and Ta is the ambient temperature.

The operating temperature in a nuclear power cycle is determined largely by the materials and working fluid used. So long as water is used as a medium, existing heat exchanger & turbine technology limits operating temperature so that a maximum efficiency is about 40%. If a bottoming cycle using isobutane is added, the efficiency goes up to perhaps 50% at most.

This depends in no way upon the source of the heat. The same efficiencies (40% for steam, 50% for combined cycles) are possible for coal burning power plants as well.

Recycling fuel is very costly and opens up the potential for environmental release of radioisotopes from the moment that the spent fuel elements are dissolved in acid. That is why it has not been done until now.

Even with all of the stops being pulled out, a single-neutron fuel cycle would use up all of the available uranium-235 within a few decades if China were to build its electric power system around nuclear power as France has. Nuclear power is STILL not a long-term solution.

To use uranium-238 as fuel, a very tight neutron economy is required in the reactor. This, in turn, means that highly concentrated fuel (bomb-grade) must be used in a rather small reactor surrounded by a blanket of U-238. Then the Pu that results must be extracted and reprocessed into fuel elements after removal of neutron absorbing isotopes result from fission. The production of bomb-grade fuel in quantity is an open invitation to terrorists, making the "breeder" a risky proposition.