Technology of Fast Breeder Reactors

Abstract

Unlike light-water reactors (LWR’s), heavy-water reactors (HWR’s) and high-temperature gas cooled reactors (HTGR’s), breeder reactors with a fast neutron spectrum (fast breeder reactors, FBR’s) have compositions of materials in their reactor cores and breeding blankets which do not greatly slow down neutrons after collisions with atomic nuclei. In FBR’s, neutrons generated by nuclear fission with an average kinetic energy of approximately 2 MeV are slowed down only to an average kinetic energy of about 100 keV by elastic and inelastic collisions with the atomic nuclei of the fissile and fertile materials (uranium-plutonium mixed oxide), the structural material (steel), and the coolant (sodium or helium gas). Most of the nuclear reactions of neutrons and atomic nuclei take place somewhat below this energy range. Besides nuclear fission and elastic or inelastic collisions mainly capture reactions in the U-238 fertile material are of interest. Due to these capture reactions, fissile plutonium is produced through subsequent nuclear reactions (Fig.1). If a mixture of plutonium-239 (fissile material) and uranium-238 (fertile material) is used as a fuel in the reactor core, nuclear fission and capture continuously destroy Pu-23 9 fissile nuclei; at the same time, however, neutrons are continuously captured by atomic nuclei of U-238 (fertile material) so that new artificial fissile nuclei of Pu-239 are generated.