Fission reactor fission reactor To achieve controlled fission chain reaction device. Also known as nuclear reactors, referred to as the reactor, reactor. 1942 e. scientific team led by Fermi built the world's first artificial fission reactors, the first time a controlled nuclear fission chain reaction. Beginning of the reactor main service for military purposes, since the mid-1950s a large number of construction for a variety of the world's research reactors, and start building nuclear power plants for electricity generation. Reactor mainly consists of the following components: ① fuel. Also known as fissile material. Generally enriched uranium, which increases 235u composition of uranium, natural uranium can also be used, made of rod-like, arranged in the core, exceeding the size of the critical volume. ② moderator. As the thermal neutron fission cross section of 235u large and fast neutron fission release, need a moderator to neutron moderation, common moderator is graphite or heavy water, fast for the elastic collision with them, can quickly deceleration into thermal neutrons. ③ rod. Absorbs neutrons into the core to enable the reaction is slowed down or stopped; the contrary, the proposed core, the reaction can be accelerated. The control rod is commonly used cadmium or boron steel bar rods, cadmium or boron for slow neutron capture cross section is very. ④ coolant. Circulation flow through the reactor core, core removed from the reaction of large quantities of heat, and then through the secondary heat exchanger to transfer heat to the reactor for power generation or other external energy use, have used pressurized coolant water or heavy water, helium or carbon dioxide, or liquid metal sodium, which has a high thermal conductivity. ⑤ reflective layer. Under normal circumstances, the core is surrounded by reflective layer, the reflection of neutrons to escape back to the core, in order to reduce neutron losses. Reflective layer is a heap outside the shell, the outside shell to prevent radiation injury to the body of concrete protection wall; reactor is also equipped with other control systems to ensure safety and to adjust power. Reactor has many uses, can provide a lot of nuclear energy for power generation or promotion of nuclear submarines; available neutron flux of energy, nuclear physics, or other experimental studies; can produce a variety of radionuclides; also used to produce 239pu, 233u and other nuclear fuel, the relative content of the natural world more 238u and 232th neutron irradiation on the reactor used to produce the compound nucleus 239u and 233th, and then after two β-decay of fissile material well and 239pu 233u, and so on.
Translated by Google
百科 Daquan
liebian fanyingdui Fission reactor fission reactor An implementation of controlled nuclear fission chain reaction device. In the nuclear energy in it one of the most important device. Usually referred to as the reactor or reactors. History 1938 O. Hahn and F. Strassmann sent a nuclear fission of uranium, the scientists then began exploring the use of nuclear fission by a huge release of energy. When a uranium nuclear fission energy release of about 200MeV, a carbon atom than the energy released during oxidation (4.1eV) Big 5 × 10 □ times. To make sense of the practical application of fission energy has to be a large number of uranium fission. Nuclear fission of uranium caused mainly neutrons, so the question comes down to how to obtain a large number of neutrons. As the nuclear fission of uranium will emit several neutrons, people thought the use of the material in the piece itself of nuclear fission neutrons to trigger a new nuclear fission, the fission reaction going to form a nuclear chain reaction. December 1942, E. Fermi led a team of scientists built the world's first artificial fission reactors (see color pictures of the world's first atomic reactor core was built in 1942, Chicago, USA), the first time control nuclear fission chain reaction. Then use the first U.S. reactor to uranium-238 into plutonium-239, the charge as the atomic bomb, made of a plutonium bomb, and later with the reactor as a power source built nuclear submarines. 1940s and 1950s, the main reactor for military purposes. From the mid-1950s, the world's large construction work for a variety of research reactors, and reactors for power generation to start building nuclear power plants. Nuclear fuel is rich in resources, the economy is good, fuel consumption is very small, has many advantages. Since the mid-1960s, many countries have to develop nuclear power, or the development of nuclear power. After that ten years, nuclear power has developed rapidly. As of mid 1984, the world has 281 nuclear power plants in operation, the total power of up to 1.8 × 10 □ kW. Working principle of a self-sustaining fission chain reaction fission reaction is called fission chain reaction. For example, uranium-235 nuclear fission after absorbing a neutron, and neutron release twenty-three, except consumption, at least one neutron causes another fission of uranium-235 nuclei, the self-sustaining fission to proceed. Nuclear fission chain reaction for the process is basically a medium of neutrons, fission nuclide mass into energy part of the process. Produced in a nuclear chain reaction within the reactor material as fuel, also known as fissile material. Only in large numbers to obtain, and easy to absorb thermal neutrons and cause fission nuclides can serve as nuclear fuel. This isotope uranium-235, uranium 233 and plutonium-239 three. Only the uranium-235 present in natural uranium, and uranium-233 and plutonium-239 have to rely reactors. Reactors produce nuclear energy, need to address the following questions: ① chain reaction of nuclear fission to provide the necessary conditions for the chain reaction going, and the energy generated by the reaction can take out of the application; ② able to control the chain reaction, to work to be done by; ③ avoid nuclear fission chain reaction or radioactive neutron produced by the staff and material harm the health of nearby residents. In the reactor, the neutrons are only three destination: cause fission, is absorbed or escapes heap outside. To achieve a nuclear chain reaction, it is important to reduce the loss of the latter two. □ U-235 is an odd nucleus, binding energy is small, the compound formed after neutron capture nuclear fission barrier is low, it can be any fission energy neutrons, and the thermal neutron fission cross section has great; uranium -238 is the even-even nuclei, the larger binding energy, nuclear fission barrier composite high, only high-energy neutron energy greater than 1MeV to make fission and fission cross-section is not. High-energy neutrons with uranium-238 in the main role of the non-nuclear elastic scattering, most of the fission neutrons through inelastic scattering of lower energy, then in a number of uranium-238 nucleus collision was absorbed, can not achieve a nuclear chain reaction. The main component of natural uranium is uranium-238, while only 0.71% uranium-235, to the use of natural uranium nuclear chain reaction in two ways: ① the method used to increase the separation of natural uranium isotope uranium-235 concentration, that concentration of enriched uranium or uranium. Such treatment, even with relatively small device can achieve a nuclear chain reaction, which caused the reactor neutron fission reaction energy can be higher, so they can build fast neutron reactors; ② the _set_ of natural uranium or low enriched uranium made of smaller rods, _insert_ed in the moderator (usually a smaller cross-section of neutron absorption, such as water, heavy water and graphite and other light material), so that nuclear fission energy neutrons released soon slow down to thermal energy area, and uranium -235 thermal fission