Graphite Plates as Neutron Moderators in Nuclear Reactors

Graphite plates are used as one of the primary neutron moderators and reflectors in the construction of nuclear reactors. Early nuclear reactors primarily utilized graphite plates, and currently, many production reactors (a type of nuclear reactor primarily used to convert uranium-238 into plutonium-239 for nuclear weapons) still use graphite plates as a moderating material.

Graphite plates have a very high melting point and maintain high strength at elevated temperatures, allowing them to be used for extended periods around 1000°C. This gives graphite plates an advantage over water and heavy water (both of which can also serve as neutron moderators). Graphite has a low probability of absorbing thermal neutrons but is less effective at slowing down thermal neutrons compared to heavy water. Therefore, nuclear reactors using graphite plates as the core structural material tend to be larger.

Types of reactors using graphite plates as core structural materials include:

1. Graphite-Water Cooled Reactors: These use graphite as the neutron moderator and water as the coolant.
2. Graphite-Gas Cooled Reactors: In these reactors, graphite serves as the neutron moderator, and carbon dioxide or helium is used as the coolant.
3. High-Temperature Gas-Cooled Reactors: Generally, helium is used as the coolant, with the outlet helium temperature reaching up to 1000°C.
4. Graphite-Sodium Reactors: These reactors use sodium as the coolant.
5. Graphite Slow Neutron Breeder Reactors: These reactors convert uranium-thorium into fissile material.

Currently, the primary power reactors for electricity generation are light water reactors and heavy water reactors. However, overseas predictions suggest that after the 1990s, high-temperature gas-cooled reactors using graphite plates will see significant development. By the end of the century, graphite slow neutron breeder reactors (uranium-thorium conversion) are expected to mature and develop further. Consequently, graphite materials will receive increasing attention in future nuclear reactor engineering projects.