Sodium Fast Reactor Design: Fuels, Neutronics, Thermal-Hydraulics, Structural Mechanics and Safety

Motivations for Fast Neutron Systems

Basic Principles and Consequences

In any nuclear reactor, there is both fissile material destroyed (FD)

$${ }^{233}{\mathrm{U\ or}\ }^{235}{\mathrm{U\ or}\ }^{239}\mathrm{Pu}$$

and produced by conversion of the fertile material (FP):

$${ }^{238}\mathrm{U} {\Rightarrow }^{239}\mathrm{U} {\Rightarrow }^{239}\mathrm{Np} {\Rightarrow }^{239}{\mathrm{Pu\ or}\ }^{232}\mathrm{Th} {\Rightarrow }^{233}\mathrm{Th} {\Rightarrow }^{233}\mathrm{Pa} {\Rightarrow }^{233}\mathrm{U}$$

The degree of conversion that occurs in a reactor is denoted by the general term of conversion ratio, CR, which is defined as CR = FP/FD. If this conversion ratio is greater than 1, it is called breeding ratio, BR.

Conditions for Breeding

A nuclear reactor can be a breeder in broad neutron energy spectrum, but adequate breeding ratios can be achieved only by selecting the appropriate fertile and fissile isotopes for that spectrum.

Starting from the fission process, if

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