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In the event of a loss-of-coolant accident in a PWR, the moderator is also lost and the reaction will stop. This negative void coefficient is an important safety feature of these reactors. In CANDU the moderator is located in a separate heavy-water circuit, surrounding the pressurized heavy-water coolant channels.
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan, India and Canada). In a PWR, water is used both as a neutron moderator and as coolant fluid for the reactor core.
A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10 −21 J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the energy corresponding to the most probable speed at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature, E peak = k T.
The mechanical arrangement of the PHWR, which places most of the moderator at lower temperatures, is particularly efficient because the resulting thermal neutrons have lower energies (neutron temperature after successive passes through a moderator roughly equals the temperature of the moderator) than in traditional designs, where the moderator ...
A neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235. A good neutron moderator is a material full of atoms with light nuclei which do not easily absorb neutrons. The neutrons strike the nuclei and bounce off.
The speed of this neutron affects its probability of causing additional fission, as does the presence of neutron-absorbing material. On the one hand, thermal neutrons are more easily absorbed by fissile nuclei than fast neutrons, so a neutron moderator that slows neutrons will increase the reactivity of a nuclear reactor. On the other hand, a ...
The most common moderator is ordinary water, which acts by elastic scattering until the neutrons reach thermal equilibrium with the water (hence the term "thermal neutron"), at which point the neutrons become highly reactive with the 235 U. Other moderators include heavy water, beryllium and graphite. The elastic scattering of the neutrons can ...
Print/export Download as PDF; Printable version; In other projects ... Pages in category "Neutron moderators" The following 9 pages are in this category, out of 9 ...