Lead-bismuth eutectic
Encyclopedia
Lead-Bismuth Eutectic or LBE is a eutectic alloy
of lead
(44.5%) and bismuth
(55.5%) used as a coolant
in some nuclear reactor
s, and is a proposed coolant for the lead-cooled fast reactor
, part of the Generation IV reactor
initiative.
It has a melting point
of 123.5 °C (pure lead melts at 327 °C) and a boiling point
of 1670 °C.
Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C.
Alloys with between 48% and 63% bismuth have melting points below 150 °C.
While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting.
s used LBE as a coolant for their nuclear reactors throughout the Cold War
.
The Russians are the acknowledged experts in lead-bismuth cooled reactors, with EDO "Gidropress" (the Russian developers of the VVER-type LWRs) having special expertise in their development. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian expertise with this technology.
Recently, however, Hyperion Power Generation
, a United States firm connected with Los Alamos National Laboratory
, announced plans to design and deploy a uranium nitride
fueled small modular reactor cooled by lead-bismuth eutectic for commercial power generation, district heating, and desalinization. The proposed reactor, called the Hyperion Power Module, will be a 70 MWth reactor of the integral, modular type, factory assembled, and transported to site for installation, and transported back to factory for refueling.
, lead-based coolants have significantly higher boiling points, meaning a reactor can be operated without risk of coolant boiling at much higher temperatures. This improves thermal efficiency and could potentially allow hydrogen production
through thermochemical processes.
Lead and LBE also do not react readily with water or air, in contrast to sodium
and NaK
which ignite spontaneously in air and react explosively with water. This means that lead- or LBE-cooled reactors, unlike sodium-cooled designs, would not need an intermediate coolant loop, which reduces the capital investment required for a plant.
Both lead and bismuth are also an excellent radiation shield, blocking gamma radiation while simultaneously being virtually transparent to neutron
s. In contrast, sodium will form the potent gamma emitter sodium-24
(half-life
15 hours) following intense neutron radiation
, requiring a large radiation shield for the primary cooling loop.
As heavy nuclei, lead and bismuth can be used as spallation
targets for non-fission neutron production, as in Accelerator Transmutation of Waste (see energy amplifier
).
Both lead-based and sodium-based coolants have the advantage of relatively high boiling points as compared to water, meaning it is not necessary to pressurise the reactor even at high temperatures. This improves safety as it reduces the probability of a loss of coolant accident dramatically, and allows for passively safe designs.
to steel
than sodium, and this puts an upper limit on the velocity of coolant flow through the reactor due to safety considerations. Furthermore, the higher melting points of lead and LBE (327 °C and 123.5 °C respectively) may mean that solidification of the coolant may be a greater problem when the reactor is operated at lower temperatures.
Finally, upon neutron radiation
bismuth-209
, the main stable isotopes of bismuth present in LBE coolant, undergo neutron capture
and subsequent beta decay
, forming polonium-210, a potent alpha emitter
. The presence of radioactive polonium in the coolant would require special precautions to control alpha contamination
during refueling of the reactor and handling components in contact with LBE.
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
(44.5%) and bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
(55.5%) used as a coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
in some nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s, and is a proposed coolant for the lead-cooled fast reactor
Lead cooled fast reactor
The lead-cooled fast reactor is a nuclear power Generation IV reactor that features a fast neutron spectrum, molten lead or lead-bismuth eutectic coolant. Options include a range of plant ratings, including a number of 50 to 150 MWe units featuring long-life, pre-manufactured cores...
, part of the Generation IV reactor
Generation IV reactor
Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Most of these designs are generally not expected to be available for commercial construction before 2030...
initiative.
It has a melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of 123.5 °C (pure lead melts at 327 °C) and a boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
of 1670 °C.
Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C.
Alloys with between 48% and 63% bismuth have melting points below 150 °C.
While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting.
History
The Soviet Alfa-class submarineAlfa class submarine
The Soviet Union/Russian Navy Project 705 was a class of hunter/killer nuclear powered submarines. The class is also known by the NATO reporting name of Alfa...
s used LBE as a coolant for their nuclear reactors throughout the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
.
The Russians are the acknowledged experts in lead-bismuth cooled reactors, with EDO "Gidropress" (the Russian developers of the VVER-type LWRs) having special expertise in their development. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian expertise with this technology.
Recently, however, Hyperion Power Generation
Hyperion Power Generation
Hyperion Power Generation, Inc. is a privately held corporation formed to construct and sell several designs of relatively small nuclear reactors, which they claim will be modular, inexpensive, inherently safe, and proliferation-resistant...
, a United States firm connected with Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
, announced plans to design and deploy a uranium nitride
Uranium nitride
Uranium nitride refers to a family of several ceramic compounds: uranium mononitride , uranium sesquinitride , which exists in either an alpha or beta phase, and uranium dinitride ....
fueled small modular reactor cooled by lead-bismuth eutectic for commercial power generation, district heating, and desalinization. The proposed reactor, called the Hyperion Power Module, will be a 70 MWth reactor of the integral, modular type, factory assembled, and transported to site for installation, and transported back to factory for refueling.
Advantages
As compared to sodium-based liquid metal coolants such as liquid sodium or NaKNaK
NaK, or sodium-potassium alloy, an alloy, of potassium , and sodium , is usually liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions...
, lead-based coolants have significantly higher boiling points, meaning a reactor can be operated without risk of coolant boiling at much higher temperatures. This improves thermal efficiency and could potentially allow hydrogen production
Hydrogen production
Hydrogen production is the family of industrial methods for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Many other methods are known including electrolysis and thermolysis...
through thermochemical processes.
Lead and LBE also do not react readily with water or air, in contrast to sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and NaK
NaK
NaK, or sodium-potassium alloy, an alloy, of potassium , and sodium , is usually liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions...
which ignite spontaneously in air and react explosively with water. This means that lead- or LBE-cooled reactors, unlike sodium-cooled designs, would not need an intermediate coolant loop, which reduces the capital investment required for a plant.
Both lead and bismuth are also an excellent radiation shield, blocking gamma radiation while simultaneously being virtually transparent to neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s. In contrast, sodium will form the potent gamma emitter sodium-24
Sodium-24
Sodium-24 is one of the more important isotopes of sodium. It is radioactive and created from common sodium-23 by neutron bombardment. With a 15-hour half-life, 24Na decays to 24Mg by emission of an electron and two gamma rays. Exposure of the human body to intense neutron flux creates 24Na in...
(half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
15 hours) following intense neutron radiation
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...
, requiring a large radiation shield for the primary cooling loop.
As heavy nuclei, lead and bismuth can be used as spallation
Spallation
In general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection or vaporization of material from a target during impact by a projectile...
targets for non-fission neutron production, as in Accelerator Transmutation of Waste (see energy amplifier
Energy amplifier
In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation...
).
Both lead-based and sodium-based coolants have the advantage of relatively high boiling points as compared to water, meaning it is not necessary to pressurise the reactor even at high temperatures. This improves safety as it reduces the probability of a loss of coolant accident dramatically, and allows for passively safe designs.
Limitations
Lead and LBE coolant are more corrosiveCorrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
to steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
than sodium, and this puts an upper limit on the velocity of coolant flow through the reactor due to safety considerations. Furthermore, the higher melting points of lead and LBE (327 °C and 123.5 °C respectively) may mean that solidification of the coolant may be a greater problem when the reactor is operated at lower temperatures.
Finally, upon neutron radiation
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...
bismuth-209
Bismuth-209
Bismuth-209 is the isotope of bismuth with the longest half-life. It has 83 protons and 126 neutrons, and an atomic mass of 208.9803987 u. All primordial bismuth is of this isotope...
, the main stable isotopes of bismuth present in LBE coolant, undergo neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
and subsequent beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, forming polonium-210, a potent alpha emitter
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
. The presence of radioactive polonium in the coolant would require special precautions to control alpha contamination
Radioactive contamination
Radioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases , where their presence is unintended or undesirable, or the process giving rise to their presence in such places...
during refueling of the reactor and handling components in contact with LBE.