1. Coating Material
The application of nano materials to coating can improve the abrasion resistance, corrosion resistance and oxidative stability. A large amount of researches have proved that the application of silicon carbide nanopowders, Zirconium carbide nanoparticles, Titanium carbide nanopowders, Titanium nitride nanoparticles, Boron carbide nanopowders to the compound coating of metal can give super abrasion resistance and self-lubrication. Its abrasion resistance is 100 times higher than bearing steel, friction coefficient being 0.06~0.1, and meanwhile it is also equipped with high-temperature stability and abrasion resistance. The application of nano technology to the key parts of engineer of liquid rocket can largely lengthen the service life of these parts.
2. Application of Nano Boron carbide in Nuclear Reactor
Theory of Using Boron carbide nanoparticles in Nuclear Reactor
Boron and boron carbide are mostly used for neutron absorption in nuclear reactor. Natural boron contains two isotopes, namely 10B and 11B. Absorption of neutron mainly relies on 10B whose thermal neutron section can be up to 347×10—24cm2. Abundance of 10B in boron carbide for reactor should be larger than 19% and the reaction equation with neutron is 10B+1n→7Li+4He. If the products of above reaction, lithium and helium remain in control rob, it results in swelling of material or release of helium in great amount, indicating a serious disadvantage of boron-included materials. As B4C is much lower cost than Ag, In and Cd alloys as well as hafnium, B4C pellet is usually encapsulated in 304 stainless steel sheath and applied more and more widely in light-water reactor.
NaBond’s boron carbide nanoparticles is featured by higher neutron absorption capacity, larger neutron capture section, wider energy spectrum for absorption and absence of secondly radiation pollution. Comparing to other neutron absorption materials, boron carbide nanoparticles doesn’t emit harmful gamma ray while absorbing neutrons, and its wider neutron energy range can effectively absorb neutrons. It represents better proportional environment in absorption materials and corruption resistance in liquid sodium. Meanwhile, an optimized design of micro-structure of material can reduce swelling rate of material.
Application of boron carbide in high-temperature water in nuclear reactor:
A boron-carbon brick can be prepared by compounding boron carbide and graphite and is used in the surrounding of reactor to prevent leakage of radioactive substances and as reactor screening material in second-layer protection of reactor;
Applied to reactor control bar as the absorber of radioactive substances and controller of reaction rate of reactor with control bar as the first shutdown system, absorptive balls of boron carbide as the second shutdown system, and isolation block in spent fuel handling to prevent a critical accident.
For current reactors in operation, about 50% of them are with boron carbide as the material of control and screening. Type of reactors includes: pressurized water reactor, boiling water reactor, graphite reactor, heavy water reactor, high-temperature gas cooled reactor, fast breeder and low-temperature nuclear heat reactor.
To prevent a critical accident of spent fuel in storage, it is necessary to add an isolation block of strong neutron absorption capacity to the spacing between spent fuel elements or components of intense storage. Boron carbide serves as a good material for isolation block. In the internationally advanced spent fuel storage system, adoption of boron carbide as isolation block can make a storage pond of 15-year storage period achieve the recommended temporary storage period of spent fuel by International Atomic Energy Agency (IAEA), being at least 50 years.
Prospect of boron carbide for nuclear reactor
With sustained development of nuclear energy around the world, especially for the acceleration of China’s nuclear energy strategy, China will invest to set up 30 nuclear power plants of megawatt magnitude from 2005 to 2015. Boron carbide nanoparticles, as a screening and control material, will have a promising application in nuclear reactors and open up a great market of huge potential economic and social benefits.