Thermal Reactor

Also found in: Dictionary, Thesaurus, Wikipedia.

thermal reactor

[′thər·məl rē′ak·tər]
(chemical engineering)
A device, system, or vessel in which chemical reactions take place because of heat (no catalysis); for example, thermal cracking, thermal reforming, or thermal polymerization.
A nuclear reactor in which fission is induced primarily by neutrons of such low energy that they are in substantial thermal equilibrium with the material of the core.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Thermal Reactor


a nuclear reactor in which the overwhelming majority of fissions of nuclei of the fissionable substance occur upon interaction with thermal neutrons.

A moderator—a substance that contains light nuclei and is a weak absorber of neutrons—is placed in the reactor core to slow neutrons to thermal energies. (The mean energy of fission neutrons is about 2 mega electron volts, or MeV.) Hydrogen (protium and deuterium), beryllium, carbon, and compounds thereof, such as ordinary and heavy water, hydrocarbons, or beryllium oxide, may be used as moderators. The most common moderators are water and graphite.

Such fissionable isotopes of uranium and plutonium as 233U 235U, 239Pu and 241 Pu, which have large capture cross sections for low-energy neutrons, are used as the fuel in a thermal reactor. This makes possible the construction of thermal reactors with relatively low critical mass and, consequently, with a relatively small charge of fissionable substance. The main type of nuclear fuel used in a thermal reactor is natural uranium or uranium slightly enriched with the isotope 235U. The fission of 235U releases ~2.5 neutrons per nucleus; when this occurs, an average of one neutron goes to sustain the nuclear reaction, and part of the remainder neutrons (up to 0.9 neutron) interacts with the 238U present in the fuel, sometimes called the fertile material, forming a secondary nuclear fuel, 239Pu. The fraction of neutrons interacting with the fertile material is determined by the choice of moderator and by the amount of fertile material actually in the core. In a thermal reactor with a uranium-thorium cycle, in which 233U is the nuclear fuel and 232Th is the fertile material, the number of such neutrons may exceed the number of split nuclei by a factor of 1.05–1.1. This makes possible the breeding of nuclear fuel.

The operation of a thermal reactor is usually regulated—that is, the rate of fission is slowed or stepped up when necessary—by a regulator rod: substances that intensively absorb neutrons are inserted into or withdrawn from the core. Cadmium, boron, and the rare-earth elements are good absorbers. Compounds of boron (such as boron carbide) or boron steel are most often used; in water-moderated water-cooled reactors, partial control is accomplished by changing the concentration of boron-containing substances, such as boric acid, in the coolant water. The operating state of a thermal reactor is characterized by the effective multiplication factor Keff, which is the ratio of the number of neutrons of one generation absorbed in the reactor to the number of absorbed neutrons of the previous generation. When Keff = 1 the reactor is in a critical steady state, when Keff > 1 the reactor power is increasing, and when Keff < 1 the power is decreasing.

Liquids and gases that are weak absorbers of neutrons and are capable of providing effective heat exchange—for example, ordinary and heavy water, organic liquids, carbon dioxide, and helium—are used as coolants to remove the heat of the fission process from the reactor. In some cases, liquid metals and salts are used. Water and organic liquids usually act simultaneously as moderator and coolant in a thermal reactor.

Structural materials for the core of a thermal reactor include Al for temperatures of 200°–250°C, Zr for 250°–400°C, and steel for temperatures above 400°C. Al and Zr have comparatively little effect on the rate of absorption of neutrons in the reactor; steel has a large neutron absorption cross section, and therefore enriched fuel must be used in thermal reactors with a steel core.

In modern nuclear engineering (mid-1970’s), thermal reactors are the most important and most widely used type of reactors. They are used for the generation of electric power, desalination of water, and production of artificial fissionable substances and radioactive isotopes. They are also used in technological tests of materials and structures, in the study of physical processes and phenomena, and in other applications.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The neutron energy boundaries of the JHR range between 1-10-11 and 20 MeV (thermal reactor) with the part from 1-10-9 to 10 MeV being of greater importance.
Compared to the previous catalyst manufactured from polymers susceptible to radiation in general, which was used for heavy water refinement at the Advanced Thermal Reactor "Fugen Nuclear Power Station", the performance of this newly developed catalyst is not affected even by a radiation dose of 530 kGy.
The 165,000-kilowatt reactor, an original Japanese prototype of the advanced thermal reactor, generated a total of some 22 billion kw-hours and generated revenues worth some 206.5 billion yen, according to the institute.
Antinuclear activists and others are furious that the Fugen advanced thermal reactor (ATR) in western Japan, which was shut down last May following a radioactive leak and is to be dismantled, is to resume operations for 10 months.
The dismantling of the Fugen advanced thermal reactor in Tsuruga, Fukui Prefecture, will cost some 84 billion yen, sources at the government-operated Japan Nuclear Cycle Development Institute said Monday.
The tritium leak was detected in a facility housing the Fugen advanced thermal reactor. It occurred between the exterior of the reactor container and a concrete wall surrounding the facility.
The tritium leak was detected at the facility housing the Fugen advanced thermal reactor between the outside of the reactor container and the concrete wall surrounding the facility, the local government said.
The pluthermal process uses MOX fuel to power a thermal reactor. The fuel is made by mixing uranium with plutonium chemically extracted from spent nuclear fuel.
The process entails using MOX fuel, which is made by mixing uranium with plutonium chemically extracted from spent nuclear fuel, to power a thermal reactor. The plebiscite will be the first of its kind in Japan.
The process entails using MOX fuel -- made by mixing uranium with plutonium chemically extracted from spent nuclear fuel -- to power a thermal reactor.
(TEPCO) will put off plans to use plutonium-uranium mixed oxide (MOX) fuel in a thermal reactor at its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture due to opposition from locals, company sources said Wednesday.
Growing usage of ceramic fibers in power plants for insulation, turbines, thermal reactors, boilers, and metal industries is expected to drive the global fireproof ceramics market demand over the projected period.