Graphite has been used as a reactor material for many y […]
Graphite has been used as a reactor material for many years. Chernobyl was a typical graphite reactor at the beginning. History has proved its feasibility, but it also has unavoidable shortcomings. The following editors will show you the advantages and disadvantages of graphite as a reactor material.
1. Graphite has a high scattering cross section and a very low thermal neutron absorption cross section. A higher scattering cross section is used to slow down neutrons. A low absorption cross section prevents neutrons from being absorbed, enabling nuclear reactors to use a small amount of fuel to reach the critical or normal operation.
2. Graphite is a high-temperature-resistant material. Its triple point is 4024 ° C at 15 MPa. Therefore, it cannot be manufactured by thermal processing methods such as melting, casting, and forging, but only by methods similar to powder metallurgy. It does not decrease in strength with temperature like metal, but increases slightly. It does not cause problems when applied below 2000 ° C.
3. Graphite has good thermal conductivity and can effectively reduce the temperature gradient in the reactor without causing too much thermal stress.
4. Graphite has very stable chemical properties. In addition to oxidation at high temperatures and water vapor, it is resistant to corrosion by acids, alkalis, and salts, so it can be used as the core component of molten salt nuclear reactors and uranium and bismuth nuclear reactors.
5. Graphite has excellent anti-irradiation performance and can be used in the reactor for 30 to 40 years.
6. Graphite has good machinability and can be processed into various shapes.
7. graphite is rich in raw materials, cheap, easy to make a variety of nuclear graphite with high purity, high strength, and different density requirements, but graphite also has disadvantages, it is an anisotropic crystal structure, layered distribution, atoms dense in a, b crystal plane, the closest distance of atoms in the same layer is 0.141nm, covalent bonding with each other, has a strong bonding force; while the layer distance is 0.335nm, the interlayer bonding force is Van der Waals force, the bonding force is weak. This anisotropy is strongly manifested in graphite's physical, strength, and irradiation behaviors.