A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
where the primary
coolant
A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosi ...
is a
liquid metal
A liquid metal is a metal or a metal alloy which is liquid at or near room temperature.
The only stable liquid elemental metal at room temperature is Mercury (element), mercury (Hg), which is molten above −38.8 °C (234.3 K, −37.9&nbs ...
. Liquid metal cooled reactors were first adapted for
nuclear submarine
A nuclear submarine is a submarine powered by a nuclear reactor, but not necessarily nuclear-armed. Nuclear submarines have considerable performance advantages over "conventional" (typically diesel-electric) submarines. Nuclear propulsion, ...
use and have been studied for power generation applications.
Metal coolants remove heat more rapidly and allow much higher
power density
Power density is the amount of power (time rate of energy transfer) per unit volume.
In energy transformers including batteries, fuel cells, motors, power supply units etc., power density refers to a volume, where it is often called volum ...
. This makes them attractive in situations where size and weight are at a premium, like on ships and submarines. To improve cooling with water, most reactor designs are highly pressurized to raise the
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
, which presents safety and maintenance issues that liquid metal designs lack. Additionally, the high temperature of the liquid metal can be used to produce vapour at higher temperature than in a water cooled reactor, leading to a higher thermodynamic efficiency. This makes them attractive for improving power output in conventional nuclear power plants.
Liquid metals, being electrically highly conductive, can be moved by
electromagnetic pump
An electromagnetic pump is a pump that moves liquid metal, molten salt, brine, or other electrically conductive liquid using electromagnetism.
A magnetic field is set at right angles to the direction the liquid moves in, and a current is passed ...
s.
Disadvantages include difficulties associated with inspection and repair of a reactor immersed in opaque molten metal, and depending on the choice of metal, fire hazard risk (for
alkali metal
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
s), corrosion and/or production of radioactive activation products may be an issue.
Design
In practice, all liquid metal cooled reactors are
fast-neutron reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as oppose ...
s, and to date most fast neutron reactors have been liquid metal cooled fast breeder reactors (
LMFBR
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mater ...
s), or naval propulsion units. The liquid metals used typically need good heat transfer characteristics. Fast neutron reactor cores tend to generate a lot of heat in a small space when compared to reactors of other classes. A low neutron absorption is desirable in any reactor coolant, but especially important for a fast reactor, as the good neutron economy of a fast reactor is one of its main advantages. Since slower neutrons are more easily absorbed, the coolant should ideally have a low
moderation
Moderation is the process of eliminating or lessening extremes. It is used to ensure normality throughout the medium on which it is being conducted. Common uses of moderation include:
*Ensuring consistency and accuracy in the marking of stud ...
of neutrons. It is also important that the coolant does not cause excessive corrosion of the structural materials, and that its melting and boiling points are suitable for the reactor's
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
.
Ideally the coolant should never boil as that would make it more likely to leak out of the system, resulting in a
loss-of-coolant accident
A loss-of-coolant accident (LOCA) is a mode of failure for a nuclear reactor; if not managed effectively, the results of a LOCA could result in reactor core damage. Each nuclear plant's emergency core cooling system (ECCS) exists specifically t ...
. Conversely, if the coolant can be prevented from boiling this allows the pressure in the cooling system to remain at neutral levels, and this dramatically reduces the probability of an accident. Some designs immerse the entire reactor and heat exchangers into a pool of coolant, virtually eliminating the risk that inner-loop cooling will be lost.
Coolant properties
While pressurised water could theoretically be used for a fast reactor, it tends to slow down neutrons and absorb them. This limits the amount of water that can be allowed to flow through the reactor core, and since fast reactors have a high
power density
Power density is the amount of power (time rate of energy transfer) per unit volume.
In energy transformers including batteries, fuel cells, motors, power supply units etc., power density refers to a volume, where it is often called volum ...
most designs use molten metals instead. Water's boiling point is also much lower than most metals demanding that the cooling system be kept at high pressure to effectively cool the core.
Mercury
Clementine
A clementine (''Citrus × clementina'') is a tangor, a citrus fruit hybrid between a willowleaf mandarin orange ( ''C.'' × ''deliciosa'') and a sweet orange (''C. × sinensis''), named in honor of Clément Rodier, a French missionary who fir ...
was the first liquid metal cooled nuclear reactor and used mercury coolant, thought to be the obvious choice since it is liquid at room temperature. However, because of disadvantages including high toxicity, high vapor pressure even at room temperature, low boiling point producing noxious fumes when heated, relatively low thermal conductivity, and a high
neutron cross-section
In nuclear physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. The neutron cross section σ can be defined as the area in cm2 for which the number of ...
, it has fallen out of favor.
Sodium and NaK
Sodium and NaK (a
eutectic sodium-potassium alloy) do not corrode steel to any significant degree and are compatible with many nuclear fuels, allowing for a wide choice of structural materials. They do, however, ignite spontaneously on contact with air and react violently with water, producing hydrogen gas. This was the case at the
Monju Nuclear Power Plant
was a Japanese sodium-cooled fast reactor, located near the Tsuruga Nuclear Power Plant, Fukui Prefecture. Its name is a reference to Manjusri. Construction started in 1986 and the reactor achieved criticality for the first time in April 1994. ...
in a 1995 accident and fire. Sodium is also the coolant used in the Russian BN reactor series and the Chinese CFR series in commercial operation today. Neutron activation of sodium also causes these liquids to become intensely radioactive during operation, though the half-life is short and therefore their radioactivity does not pose an additional disposal concern.
There are two proposals for a sodium cooled
Gen IV LMFR
A sodium-cooled fast reactor is a fast neutron reactor cooled by liquid sodium.
The initials SFR in particular refer to two Generation IV reactor proposals, one based on existing liquid metal cooled reactor (LMFR) technology using mixed oxide fue ...
, one based on oxide fuel, the other on the metal-fueled
integral fast reactor
The integral fast reactor (IFR, originally Liquid metal cooled reactor, advanced liquid-metal reactor) is a design for a nuclear reactor using fast neutrons and no neutron moderator (a Fast-neutron reactor, "fast" reactor). IFR would breed more f ...
.
Lead
Lead has excellent neutron properties (reflection, low absorption) and is a very potent radiation shield against
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
s. The higher boiling point of lead provides safety advantages as it can cool the reactor efficiently even if it reaches several hundred
degrees Celsius
The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...
above normal operating conditions. However, because lead has a high melting point and a high vapor pressure, it is tricky to refuel and service a lead cooled reactor. The melting point can be lowered by alloying the lead with
bismuth
Bismuth is a chemical element with the Symbol (chemistry), symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental ...
, but
lead-bismuth eutectic
Lead-Bismuth Eutectic or LBE is a eutectic alloy of lead (44.5 at%) and bismuth (55.5 at%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative.
It h ...
is highly corrosive to most metals
used for structural materials.
Lead-bismuth eutectic
Lead-bismuth eutectic
Lead-Bismuth Eutectic or LBE is a eutectic alloy of lead (44.5 at%) and bismuth (55.5 at%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative.
It h ...
allows to operate at a lower temperature while preventing the freezing of the metal coolant in a lower temperature range (
eutectic point
A eutectic system or eutectic mixture ( ) is a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutectic tempe ...
: .
Beside its highly corrosive character,
its main disadvantage is the formation by
neutron activation
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emit ...
of
(and subsequent
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
) of
(
T = 138.38 day), a volatile
alpha-emitter highly
radiotoxic
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
(the highest known
radiotoxicity
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
, above that of
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
).
Tin
Although
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
today is not used as a coolant for working reactors because it builds a crust, it can be a useful additional or replacement coolant at
nuclear disasters or
loss-of-coolant accident
A loss-of-coolant accident (LOCA) is a mode of failure for a nuclear reactor; if not managed effectively, the results of a LOCA could result in reactor core damage. Each nuclear plant's emergency core cooling system (ECCS) exists specifically t ...
s.
Further advantages of tin are the high boiling point and the ability to build a crust even over liquid tin helps to cover poisonous leaks and keeps the coolant in and at the reactor. Tin causes any
reactor type to be unusable for normal operation. It has been tested by
Ukrainian
Ukrainian may refer to:
* Something of, from, or related to Ukraine
* Something relating to Ukrainians, an East Slavic people from Eastern Europe
* Something relating to demographics of Ukraine in terms of demography and population of Ukraine
* So ...
researchers and was proposed to convert the
boiling water reactor
A boiling water reactor (BWR) is a type of light water nuclear reactor used for the generation of electrical power. It is a design different from a Soviet graphite-moderated RBMK. It is the second most common type of electricity-generating nu ...
s at the
Fukushima Daiichi nuclear disaster into liquid tin cooled reactors.
Propulsion
Submarines
The
Soviet
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nation ...
and all seven s used reactors cooled by a lead-bismuth alloy (
VT-1 reactor
The VT-1 reactor was the nuclear fission reactor used in a pair to power the as part of the Soviet Navy's Project 645 Кит-ЖМТ. It is a liquid metal cooled reactor (LMR), using highly enriched uranium-235 fuel to produce 73 MW of power.
...
s in ''K-27'';
BM-40A and
OK-550 reactor The OK-550 reactor is the nuclear fission reactor used to power three of the seven boats of the Soviet Navy's Project 705 Лира (Lira or Alfa in NATO designation) fourth generation submarines. It is a liquid metal cooled reactor (LMR), using ...
s in others). Both the Soviet and US navies had earlier constructed prototype attack submarines using LMFR power units.
The second nuclear submarine, was the only U.S. submarine to have a sodium-cooled nuclear power plant. It was commissioned in 1957, but it had leaks in its
superheaters, which were bypassed. In order to standardize the reactors in the fleet, the submarine's sodium-cooled reactor was removed starting in 1958 and replaced with a
pressurized water reactor
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 and Canada). In a PWR, the primary coolant (water) i ...
.
Nuclear aircraft
Liquid metal cooled reactors were studied by
Pratt & Whitney for use in
nuclear aircraft
A nuclear-powered aircraft is a concept for an aircraft intended to be powered by nuclear energy. The intention was to produce a jet engine that would heat compressed air with heat from fission, instead of heat from burning fuel. During the Col ...
as part of the
Aircraft Nuclear Propulsion program.
Power generation
The
Sodium Reactor Experiment
The Sodium Reactor Experiment was a pioneering nuclear power plant built by Atomics International at the Santa Susana Field Laboratory near Simi Valley, California. The reactor operated from 1957 to 1964. On December 20, 1951, the first Experimen ...
was an experimental sodium-cooled nuclear reactor sited in a section of the
Santa Susana Field Laboratory
The Santa Susana Field Laboratory (SSFL), formerly known as Rocketdyne, is a complex of industrial research and development facilities located on a portion of Southern California in an unincorporated area of Ventura County in the Simi Hills betw ...
then operated by the Atomics International division of
North American Aviation
North American Aviation (NAA) was a major American aerospace manufacturer that designed and built several notable aircraft and spacecraft. Its products included: the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F ...
. In July 1959, the Sodium Reactor Experiment suffered a serious incident involving the partial melting of 13 of 43 fuel elements and a significant release of
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
gases.
The reactor was repaired and returned to service in September 1960 and ended operation in 1964. The reactor produced a total of 37 GW-h of electricity.
Fermi 1
Fermi 1 was the United States' only demonstration-scale breeder reactor, built during the 1950s at the Enrico Fermi Nuclear Generating Station on the western shore of Lake Erie south of Detroit, Michigan. It used the sodium-cooled fast reactor cyc ...
in
Monroe County, Michigan
Monroe County is a county in the U.S. state of Michigan. As of the 2020 Census, the population was 154,809. The largest city and county seat is Monroe. The county was established as the second county (after Wayne County) in the Michigan Ter ...
was an experimental, liquid sodium-cooled
fast breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mater ...
that operated from 1963 to 1972. It
suffered a partial nuclear meltdown in 1963 and was decommissioned in 1975.
At
Dounreay
Dounreay (; gd, Dùnrath) is a small settlement and the site of two large nuclear establishments on the north coast of Caithness in the Highland area of Scotland. It is on the A836 road west of Thurso.
The nuclear establishments were create ...
in
Caithness
Caithness ( gd, Gallaibh ; sco, Caitnes; non, Katanes) is a historic county, registration county and lieutenancy area of Scotland.
Caithness has a land boundary with the historic county of Sutherland to the west and is otherwise bounded by ...
, in the far north of
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
, the
United Kingdom Atomic Energy Authority
The United Kingdom Atomic Energy Authority is a UK government research organisation responsible for the development of fusion energy. It is an executive non-departmental public body of the Department for Business, Energy and Industrial Strategy ...
(UKAEA) operated the
Dounreay Fast Reactor
Dounreay (; gd, Dùnrath) is a small settlement and the site of two large nuclear establishments on the north coast of Caithness in the Highland area of Scotland. It is on the A836 road west of Thurso.
The nuclear establishments were creat ...
(DFR), using NaK as a coolant, from 1959 to 1977, exporting 600 GW-h of electricity to the grid over that period. It was succeeded at the same site by PFR, the
Prototype Fast Reactor
Dounreay (; gd, Dùnrath) is a small settlement and the site of two large nuclear establishments on the north coast of Caithness in the Highland area of Scotland. It is on the A836 road west of Thurso.
The nuclear establishments were create ...
, which operated from 1974 to 1994 and used liquid sodium as its coolant.
The Soviet
BN-600
The BN-600 reactor is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. Designed to generate electrical power of 600 MW in total, the plant dispatches 560 MW ...
is sodium cooled. The
BN-350
The BN-350 is a Liquid metal cooled reactor, sodium-cooled, fast reactor located at the ''Mangyshlak Nuclear Power Plant'', located in Aktau (formerly known as Taras Shevchenko, Shevchenko under the control of the USSR in 1964–1992), Kazakhsta ...
and U.S.
EBR-II
Experimental Breeder Reactor-II (EBR-II) is a sodium-cooled fast reactor designed, built and operated by Argonne National Laboratory at the National Reactor Testing Station in Idaho. nuclear power plants were sodium cooled.
EBR-I
Experimental Breeder Reactor I (EBR-I) is a decommissioned research reactor and U.S. National Historic Landmark located in the desert about southeast of Arco, Idaho. It was the world's first breeder reactor. At 1:50 p.m. on December 20, ...
used a liquid metal alloy,
NaK
In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communicatio ...
, for cooling. NaK is liquid at room temperature. Liquid metal cooling is also used in most
fast neutron reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as opposed ...
s including
fast breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mater ...
s such as the
Integral Fast Reactor
The integral fast reactor (IFR, originally Liquid metal cooled reactor, advanced liquid-metal reactor) is a design for a nuclear reactor using fast neutrons and no neutron moderator (a Fast-neutron reactor, "fast" reactor). IFR would breed more f ...
.
Many
Generation IV reactor
Generation IV reactors (Gen IV) are six nuclear reactor designs recognized by the Generation IV International Forum. The designs target improved safety, sustainability, efficiency, and cost.
The most developed Gen IV reactor design is the sodium ...
s studied are liquid metal cooled:
*
Sodium-cooled fast reactor (SFR)
*
Lead-cooled fast reactor
The lead-cooled fast reactor is a nuclear reactor design that features a fast neutron spectrum and molten lead or lead-bismuth eutectic coolant.
Molten lead or lead-bismuth eutectic can be used as the primary coolant because especially lead, and ...
References
{{DEFAULTSORT:Liquid Metal Cooled Reactor
Nuclear physics