Nuclear physical properties of carbon graphite materials:
Nuclear reactors are devices in which nuclear fuel undergoes controlled fission. Nuclear fission materials produce fast neutrons during fission and are not easily captured by nuclear fuel, so nuclear fission cannot continue. It must be reduced to a slow neutron with a decelerating material, and a slow neutron is used to bombard the nucleus of the nuclear fission material in order for it to continue to produce nuclear fission.
As a decelerating material, it must have the following characteristics: in each collision, the neutron loses more energy, absorbs less neutrons, and improves the utilization of neutrons; it can withstand the bombardment of fast neutrons and other high-energy particles for a long time. Chemically stable, does not chemically react with substances in the fission zone.
As a reflective material for nuclear reactors, nuclear graphite materials have large scattering cross sections and small absorption cross sections. Generally, graphite contains impurities, and some impurities such as cadmium, boron, and rare earth metals have very large absorption cross sections, so nuclear graphite must be high purity graphite. .
The reduction ratio of graphite material is much smaller than that of water, but higher than other materials. Heavy water is the most ideal deceleration material, but the production cost is very high. Graphite production costs are much lower than water, so graphite has been used as a retarding material since the world’s first nuclear reactor.
