Athermal-neutron reactoris anuclear reactorthat uses slow orthermal neutrons.( "Thermal" does not mean hot in an absolute sense, but means inthermal equilibriumwith the medium it is interacting with, the reactor's fuel, moderator and structure, which is much lower energy than thefast neutronsinitially produced by fission.)
Afast-neutron reactor,on the other hand, operates using high-energy neutrons that are not slowed by a moderator. These reactors can efficiently use a broader range of fuels, including plutonium and other heavy atoms, and have the capability to breed more fissile material, such as uranium-238 into plutonium-239, which is not possible in thermal reactor. In contrast to thermal-neutron reactors,integral fast reactors(IFRs) operate using fast neutrons and are designed for increased fuel efficiency. These reactors are capable of recycling nuclear waste and breeding new fuel, which enhances sustainability. Additionally, IFRs incorporate passive safety features that allow them to safely shut down without external power or human intervention
Mostnuclear power plantreactors are thermal reactors and use aneutron moderatorto slowneutronsuntil they approach the averagekinetic energyof the surrounding particles, that is, to reduce the speed of the neutrons to low-velocity, thermal neutrons. Neutrons are uncharged, this allows them to penetrate deep in the target and close to the nuclei, thus scattering neutrons by nuclear forces, some nuclides are scattered large.[1]
Thenuclear cross sectionofuranium-235for slow thermal neutrons is about 1000barns,while for fast neutrons it is in the order of 1 barn.[2]Therefore, thermal neutrons are more likely to cause uranium-235 tonuclear fissionthan to be captured byuranium-238.If at least one neutron from the U-235 fission strikes another nucleus and causes it to fission, then thechain reactionwill continue. If the reaction will sustain itself, it is said to becritical,and the mass of U-235 required to produce the critical condition is said to be acritical mass.
Thermal reactors consist of the following:
- Neutron moderatorto slow down theneutrons.Inlight water reactorsandheavy water reactorsit doubles as thenuclear reactor coolant.
- Nuclear fuel,which is afissile material,usuallyuranium.
- Reactor vesselthat is apressure vesselcontaining thecoolantandreactor core.
- Radiation shieldingto protect people and the environment from the harmful effects ofionizing radiation.
- Containment buildingswhich are designed to contain the escape ofradiationin an emergency.
- Instrumentation to monitor and control the reactor's systems.
See also
editReferences
edit- ^Squires, G. L. (2012-03-29).Introduction to the Theory of Thermal Neutron Scattering.Cambridge University Press.ISBN978-1-107-64406-9.
- ^"Some Physics of Uranium".Archived fromthe originalon March 3, 2008.Retrieved2009-01-18.