In advanced ceramic materials, toxicity is the inherent “label” of beryllium oxide, and in many applications, beryllium oxide is the first to be excluded. But this ceramic material that talks about color change can conquer a “difficult” industry – the nuclear industry.
Since the first nuclear reactor was established in the United States in 1942, the nuclear industry has been developing for nearly eighty years. During this period, the development center of the nuclear industry shifted from nuclear weapons to nuclear energy applications, and the materials used in the nuclear industry were constantly being updated. Among them, ceramic materials for nuclear reactors are one of the important materials used in reactors. In reactors and fusion reactors, ceramic materials receive high-energy particles and γ Radiation from radiation, therefore, in addition to high temperature and corrosion resistance, ceramic materials also need to have good structural stability. The fission reaction in a nuclear fission reactor is caused by neutron bombardment of 235U. In light water reactors, heavy water reactors, and high-temperature gas cooled reactors, slow neutrons are more likely to cause 235U fission compared to fast neutrons produced by neutron fission. Therefore, materials that can slow down neutron velocity are needed in these reactors, which are called moderators. At present, the commonly used moderators internationally include water, graphite, beryllium, beryllium oxide, etc. Among them, beryllium oxide as a ceramic material is considered as a future moderator.
Beryllium oxide is a refractory material that is very stable and dense. Its high temperature vapor pressure and low evaporation rate can be used for a long time in an inert atmosphere, even if the temperature reaches 2000 ℃. However, due to the reaction between beryllium oxide and water vapor to generate beryllium hydroxide, it evaporates significantly when the temperature reaches 1800 ℃ in an oxidizing atmosphere, and a large amount of volatilization occurs when the temperature reaches 1500 ℃ in water vapor. The main performance of BeO ceramic pellets differs from theory. It is worth noting that as the temperature increases, the specific heat capacity of BeO increases sharply, the thermal conductivity decreases sharply, and the coefficient of thermal expansion slightly increases.
In terms of mechanical strength, BeO is about 1/4 of Al2O3, but it has good high-temperature strength. In addition, BeO has good nuclear performance, strong neutron deceleration ability, and high penetration ability for X-rays. At high temperatures, BeO only reacts weakly with carbon, silicon, and boron.
In addition, ceramic particles formed by beryllium oxide and uranium oxide can be combined to form a new type of nuclear fuel. In nuclear fuel neutron source assemblies, both initial and restart of the reactor require a neutron source to “ignite”. Polonium (PO) beryllium source is commonly used in primary neutron source rods, while antimony beryllium source is commonly used in secondary neutron source rods. Currently, the Korean Nuclear Research Institute uses beryllium oxide ceramics to act on the startup control rods of primary neutron source reactors, which is very rare.
In addition, compared with graphite materials, beryllium oxide ceramics have excellent comprehensive properties such as oxidation resistance, corrosion resistance, high thermal conductivity, better neutron slowing and breeding ability, and are expected to play important roles as structural materials, moderators, and matrix materials in small nuclear reactors for deep-sea deep space exploration, land-based mobile nuclear power, and thermonuclear propulsion in the future.
