Using water as a coolant would reduce the neutron abundance, since neutrons are absorbed by water. Therefore liquid sodium is used instead. This immediately raised concerns of safety when initially thought of, since sodium is a highly reactive element. It is important to keep the liquid sodium from contact with air or oxygen to avoid explosions, however they aren't any more dangerous than pressurized water reactors.
This makes the bursting of pipes far less likely than in other water-reactors. Liquid sodium is also a very good choice because of its heat transfer capabilities, due to its high specific heat capacity. Other fast breeder types include supercritical water cooled reactors , molten salt reactors , and gas-cooled reactors. You can read more about fast breeder reactors here.
The possibility to breed fissile material in slow neutron reactors is unique to thorium , as uranium cannot use thermal neutrons to do so. The technology is much simpler than that of the liquid metal fast breeder; light water is used as the coolant to remove the heat produced by the continuous series of fission reactions rather than a liquid metal system. Thorium hasn't been used in large scale reactors, however some reactors have used it successfully in the past.
A light water breeder reactor in Shippingport, Pa. USA operated for 5 years, and by the end of its operation it had 1. An important concept for a breeder reactor is how much fissionable fuel is being produced compared to how much fuel is being used. This is known as the breeding ratio.
For example for the breeding of plutonium, the ratio would be the amount of plutonium produced to the amount of uranium used. The number 1. Only 1 neutron is needed for the fission chain reaction to be stable, so the remaining 1. The amount of time for a breeder to produce enough material to fuel a second reactor is called its doubling time.
Please help us raise funds to update and increase the number of pages. Fossil Fuels. Atomic Energy Commission, Van Nostrand Reinhold Company , describes general terminology used in this specification. The Nuclear Engineering Handbook," edited by H. For clarity and precision, specific terminology used in this specification is defined as follows:.
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Active Core: The central portion of a nuclear reactor which contains fissile and fertile material and in which the fission chain is sustained and most of the energy of fission is released as heat. Blanket Region: An active core region immediately surrounding the seed region containing predominantly fertile material and characterized by conversion of the fertile material into fissile material by neutron capture. Breeder Reactor: A nuclear reactor which produces a fissile material to replace that used to maintain the fission chain.
Further limited herein to nuclear reactors which produce more fissile material than they consume. Breeding Ratio: The ratio of the number of fissile atoms produced to the number of fissile atoms that have been consumed. Conversion Ratio: The ratio of the instantaneous rate of production of fissile atoms to the instantaneous rate of destruction of fissile atoms.
Doubling Time: The time required for a breeder reactor to produce a surplus amount of fissile material equal to that required for the initial charge of inventory of the reactor, after accounting for reprocessing and refabrication losses.
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Epithermal Reactor: A nuclear reactor characterized by a neutron energy spectrum in which more than half of the fissions result from the absorption of neutrons having energies above 0. Fast Reactor: A nuclear reactor characterized by a neutron energy spectrum in which more than half of the fissions result from the absorption of neutrons having energies greater than , electron volts 0. Fertile Material: Material which can be converted into fissile material through neutron capture; for example thorium and uranium fertile materials are converted respectively to uranium and plutonium- fissile material.
Fissile Material: Material which will undergo fissions with neutrons of all energies; including thermal to fast neutrons; for example uranium, uranium and plutonium Module Geometry: The geometrical configuration of a nuclear reactor having modules dependently nuclearly coupled to form an active core. Movable Region: An active core fuel region disposed for longitudinal movement, in reference to a stationary fuel region during normal reactor operation.
Seed Region: An active core region containing substantial fissile material and characterized by neutron leakage to a blanket region. Stationary Region: An active core fuel region which remains fixed during normal reactor operation. In such a reactor, more than half of the fissions result from the absorption of neutrons having neutron energies below 0.
Variable Geometry Control: A means of reactivity control by axially positioning a movable region with re spect to a stationary region and thereby changing the leakage of neutrons from the movable region to the stationary region. To satisfy the nations energy requirements over the long term through efficient utilization of our natural resources requires the development and use of a class of nuclear reactors which have been designated breeder reactors.
Such reactors convert fertile material to fissile material during operation in addition to providing heat for such things as power generation, desalination or chemical processing.
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By effecting such conversion, the reserves of economically available nuclear fuel feed material can be extended almost indefinitely. In developing breeder reactors, although not essential to high fuel utilization, it is desirable to achieve short doubling times. Doubling times may be shortened by reducing parasitic absorption of neutrons in nonfissile and nonfertile material such as core structural material, cladding, moderator, and fission products; by reducing neutron leakage of neutrons from the reactor core; and by providing a fissile fuel and a neutron energy spectrum wherein the maximum number of neutrons is liberated per average fission.
Neutron spectra which are slightly harder or of slightly higher characteristic energy than thermal typically provide a smaller number of neutrons per fissile atom destroyed than thermal spectra, while neutron spectra having very much higher characteristic energy, such as sodium cooled fast reactors, utilize the fast fission of U to provide a greater number of neutrons per fissile atom destroyed. However, sodium cooled reactors need extensive development in materials due to elevated pressures and temperatures inherent in such a system.
Both pressurized light and heavy water moderated and cooled breeder reactors are highly attractive from an engineering standpoint because of the availability of the extensive pressurized water technology which has already been developed in the nuclear power field. As the neutron spectrum is hardened in an uranium fueled lightwater breeder reactor, the conversion ratio steadily increases from a thermal value of 0.
This conversion ratio increase is due to a reduction in parasitic neutron absorption in the moderator and structural material more than compensating for a decrease in eta 17 in the higher energy neutron spectra. However, light water breeders provide only a sufficient breeding margin to permit self-sustained operation with very long doubling times.
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Heavy water is also attractive from a breeding standpoint because of its low parasitic neutron absorption. Heretofore, heavy water moderated converter reactors have been restricted to designs characterized by very thermal neutron spectra. The result is best understood by noting the conversion ratio is approximately equal to ne minus 1. In view of this prior art, heavy water moderated and cooled converters were thus considered useful only in the thermal region.
A pressurized heavy water moderated converter reactor which operates with a thermal neutron spectrum requires a wide lattice spacing to gain sufficient moderation because of the low moderating power of heavy water. This spacing requirement causes the core size to be very large, thereby causing problems in providing suitable pressure vessels and increasing the capital costs associated with maintaining large heavy water inventories.
It is a further object of the invention to provide a pressurized heavy water moderated and cooled reactor having an epithermal to intermediate neutron spectrum with an increased conversion ratio. It is a further object of this invention to provide a breeder reactor characterized by a favorable breeding ratio utilizing pressurized water technology.
Other objects of the invention will become apparent upon examination of the following description in conjunction with the appended drawings.
In accordance with the invention, a pressurized heavy water moderated and cooled nuclear reactor having an active core with fissile and fertile material is provided which operates from an epithermal to intermediate neutron spectrum as defined by the restriction of the moderator-to-fuel atom ratio range from 0. An unexpected favorable breeding ratio occurs in a reactor operating within this moderator-to-fuel atom ratio range heretofore believed to produce a less favorable breeding ratio as evidenced with prior art heavy water moderated converter reactors.
Reactor designs having a particular fuel rod diameter and spacing within the restrictive moderator-to-fuel atom ratio range define representative embodiments of the inventive pressurized heavy water breeder reactor. Hence a conversion ratio of one exists when production of fissile material from fertile material just matches the burning up of fissile material. To ensure criticality and satisfactory breeding performance of the reactor, the atom ratio of fertile to fissile material should be within a range from 5 to As noted above, both light and heavy water moderated reactors are considered to have attractive breeder capabilites.
Our studies on uranium fueled reactors have determined characteristic intermediate neutron spectra E. These studies indicated that the largest fraction of neutron absorptions per energy group in the LWBR occurs between Thus, our studies set forth clear distinctions between the range of fractional neutron absorptions by energy for heavy and light water breeder reactors having an intermediate neutron spectrum.
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To further illustrate features of the present invention, reference is made to FIG. This increased conversion ratio is mainly achieved by the reduction in parasitic absorption in the moderator and core structural material. Applicants, however, have discovered an unexpected increase in the initial conversion ratio of uranium fueled reactors containing thorium for breeding and heavy water moderator and coolant when the dueterium-to-fuel atom ratio is decreased only to the range from 4. This result can best be understood by again noting the effect and parasitic losses have on conversion ratio.
A rod spacing 0. Typically, rod diameters could range from 0. It is noted that although both may be utilized, cylindrical fuel rods permit greater fuel inventory in a given volume than fuel plates. As the selection of a desired moderator-to-fuel atom ratio defines volume of coolant per unit mass of fuel, it is necessary to circulate heavy water moderator by the rods at a flow rate sufficient to provide adequate cooling thereof. A breeder reactor constructed in accordance with the above design limitations has certain advantages over other breeder reactor systems including:. The ability to use the advanced technology associated with pressurized water moderated and cooled reactors including materials well developed to operate at pressures from 1, psia to 2, psia and temperatures from F to F;.
A more compact overall size than is possible with heavy water moderated reactors which operate with thermal neutron spectra;. A lower sensitivity to neutron poisons than reactors which operate with thermal neutron spectra because of the typically lower absorption cross sections of most structural materials at neutron energy levels above thermal;.
An inherent self-shutdown capability due to the moderating coolant and fuel Doppler characteristics;. The basic advantages and design limitations of the invention have been illustrated in FIGS.