Latest information: Application of graphite powder in nuclear test

The radiation damage of graphite powder has a decisive effect on the technical and economic performance of the reactor, especially the pebble bed high temperature gas-cooled reactor. The mechanism of neutron moderation is the elastic scattering of neutrons and the atoms of the moderating material, and the energy carried by them is transferred to the atoms of the moderating material. Graphite powder is also a promising candidate for plasma-oriented materials for nuclear fusion reactors. The following editors from Fu Ruite introduce the application of graphite powder in nuclear tests:

With the increase of the neutron fluence, the graphite powder first shrinks, and after reaching a small value, the shrinkage decreases, returns to the original size, and then expands rapidly. In order to effectively utilize the neutrons released by fission, they should be slowed down. The thermal properties of graphite powder are obtained by irradiation test, and the irradiation test conditions should be the same as the actual working conditions of the reactor. Another measure to improve the utilization of neutrons is to use reflective materials to reflect the neutrons leaking out of the nuclear fission reaction zone-core back. The mechanism of neutron reflection is also the elastic scattering of neutrons and atoms of reflective materials. In order to control the loss caused by impurities to the allowable level, the graphite powder used in the reactor should be nuclear pure.

Nuclear graphite powder is a branch of graphite powder materials developed in response to the needs of building nuclear fission reactors in the early 1940s. It is used as moderator, reflection and structural materials in production reactors, gas-cooled reactors and high-temperature gas-cooled reactors. The probability of the neutron reacting with the nucleus is called the cross section, and the thermal neutron (average energy of 0.025eV) fission cross section of U-235 is two grades higher than the fission neutron (average energy of 2eV) fission cross section. The elastic modulus, strength and linear expansion coefficient of graphite powder increase with the increase of neutron fluence, reach a large value, and then decrease rapidly. In the early 1940s, only graphite powder was available at an affordable price close to this purity, which is why every reactor and subsequent production reactors used graphite powder as a moderating material, ushering in the nuclear age.

The key to making isotropic graphite powder is to use coke particles with good isotropy: isotropic coke or macro-isotropic secondary coke made from anisotropic coke, and secondary coke technology is generally used at present. The size of radiation damage is related to the raw materials of graphite powder, manufacturing process, fast neutron fluence and fluence rate, irradiation temperature and other factors. The boron equivalent of nuclear graphite powder is required to be around 10~6.

Post time: May-18-2022