Explanation

The materials used in thermal neutron reactor to reduce fission fast (neutron) energy. Hydrogen materials such as light water, heavy water, graphite, beryllium and helium are usually used. light water has great moderating capacity and low price, but its absorption cross section is large, which can corrosion metals? It is prone to mdidysis. The absorption cross section of heavy water is small and can occur（ γ. n) Reactions provide neutrons for chain reactions; The disadvantage is that goblets are expensive and need to be careful to prevent leakage losses, pollution, and isotope exchange with hydrides. graphite has a lower absorption cross section than heavy water, is cheap, and is a high-temperature resistant materials, which can be used in high-temperature reactor in non oxidizing atmosphere. As a moderator materials, beryllium has a better moderating ability than graphite, which can reduce the core size. However, beryllium is highly toxic, expensive, and prone to irradiation swelling, so its use is limited.

Classification