The fast neutron reactor uses plutonium -239 as fuel instead of uranium -235, but uranium -238 is placed in the peripheral regeneration area of the core fuel plutonium -239. The fast neutrons released during the fission reaction of plutonium -239 are absorbed by uranium -238 in the peripheral regeneration zone, and uranium -238 will soon become plutonium -239. In this way, plutonium -239 fission, while generating energy, constantly turns uranium -238 into usable fuel plutonium -239, and the regeneration rate is higher than the consumption rate, and the nuclear fuel is burned more and more, which is rapidly proliferating, so this kind of reactor is also called fast breeder reactor. According to calculation, if the fast neutron reactor is popularized and applied, the utilization rate of uranium resources will be increased by 5-6 times, and the problems of a large amount of uranium -238 accumulation and waste and environmental pollution will be solved.
thermal neutron reactor is an economical energy source that meets the requirements of safety and cleanliness, and it will be the main reactor type for developing nuclear power at present and in the future. However, the fuel uranium 235 used in thermal neutron reactors only accounts for .7% of uranium existing in nature, while another isotope uranium 238, which accounts for 99.3% of natural uranium, cannot be fission under the action of thermal neutrons and cannot be used by thermal neutron reactors. Uranium reserves in nature are limited. If only uranium 235 can be used, there will be a danger of shortage of uranium 235 in another 3 years. Therefore, people's long-term hope of obtaining rich nuclear energy is pinned on the ability to use fissile fuel other than uranium 235. As a result, fast breeder reactors came into being.
if the fast neutron produced in nuclear fission is not decelerated as in light water reactor, when it bombards uranium 238, uranium 238 will absorb this fast neutron in a certain proportion and become plutonium 239. Uranium 235 is fissionable by absorbing a slow thermal neutron, while plutonium 239 can be fissionable by absorbing a fast neutron. Plutonium 239 is a better nuclear fuel than uranium 235. From uranium 238 to plutonium first, and then to plutonium fission, the energy released by fission becomes heat, which is transported to the outside and used. This is the working process of fast neutron breeder reactor.
in the fast breeder reactor, the fast neutrons produced by nuclear fission of each uranium-239 can turn 12 to 16 uranium-238 into plutonium-239. Although it is consuming nuclear fuel ring 239, it is also producing nuclear fuel plutonium 239, which is more than consumed and has the proliferation effect of nuclear fuel, so this kind of reactor is also called fast neutron breeder reactor, referred to as fast reactor. In the fast neutron reactor, water can't be used to transfer the heat in the core, because it will slow down the speed of fast neutrons. The alloy of sodium and potassium can be used as a heat exchanger in the fast neutron reactor.
The fast reactor uses a nuclear fuel core with a diameter of about 1m, and uranium 238 surrounds the core to form a proliferation layer, and the process of transforming uranium 238 into plutonium 239 mainly takes place in the proliferation layer. Both the core and the proliferation layer are immersed in liquid sodium metal. Because the nuclear fission reaction in the fast reactor is very intense, it is necessary to use a liquid with strong thermal conductivity to take away a lot of tropical energy generated by the core, and this heat is also used as the energy source for power generation. Sodium has good thermal conductivity, is not easy to slow down the neutron velocity, and will not hinder the chain reaction in the fast reactor, so it is an ideal cooling liquid. The control rod with strong neutron absorption ability is used in the reactor, and the number of neutrons in the reactor is changed by the degree of its insertion into the core to adjust the power of the reactor. In order to isolate the radioactive core from the power generation part, the sodium cooling system is also divided into primary loop and secondary loop. The primary loop is in direct contact with the core, and the heat is transferred to the secondary loop through the heat exchanger. The sodium in the secondary loop is used to heat the boiler and generate steam at about 483℃, which is used to drive the steam turbine to generate electricity. Fast neutron breeder reactor can use uranium resources almost 1%, so all countries are actively developing it. Now there are dozens of small and medium-sized fast reactors in operation all over the world.