ABSTRACT
In Chapter 1, general descriptions were made of power systems. For most of these, there are no major variants on the basic scheme. However, with nuclear power, there are a number of combinations of reactor type and fuel flows, which have markedly different characteristics in uranium requirements, fuel storage, reprocessing and waste arisings. If uranium-235 (natural abundance in uranium, only 0.72%) is the main source of fission in the fuel cycle, the usage efficiency in fissioning the natural isotopes of uranium will clearly be very low. However, if uranium-238, the dominant natural isotope, can be either directly or indirectly fissioned, the usage efficiency can be much higher and natural uranium requirements much lower.
