2. The beginnings of nuclear power

The early days of nuclear power saw the emergence of a large number of projects combining different materials:

• fissile materials: uranium ( ²³⁵ U) and plutonium ( ²³⁵ Pu) ;

• moderators: ordinary water (H ₂ O), heavy water (D ₂ O) and graphite (C) ;

• fertile materials: uranium ( ²³⁸ U) and thorium (Th) ;

• Heat carriers: ordinary water, heavy water, organic liquids, carbon dioxide (CO ₂ ), helium (He), sodium (Na), lead (Pb), mercury (Hg) ;

• structural...