The lead-cooled fast reactor is a

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 from n ...

design that features a

fast neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

spectrum and molten

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...

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. I ...

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 corrosio ...

. Molten lead or lead-bismuth eutectic can be used as the primary coolant because especially lead, and to a lesser degree bismuth have low

neutron absorption Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...

and relatively low

melting point The melting point (or, rarely, liquefaction point) of a substance 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 ...

Neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

s are slowed less by interaction with these heavy nuclei (thus not being

neutron moderator In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely mor ...

s) and therefore, help make this type of reactor a

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 ...

. In simple terms, if a neutron hits a particle with a similar mass (such as hydrogen in a Pressurized Water Reactor PWR), it tends to lose

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accel ...

. In contrast, if it hits a much heavier atom such as lead, the neutron will "bounce off" without losing this energy. The coolant does, however, serve as a

neutron reflector A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, tungsten carbide, gold, or other materials. A neutron reflector ...

, returning some escaping neutrons to the core. Fuel designs being explored for this reactor scheme include fertile uranium as a metal, metal

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the ...

or metal

nitride In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...

. Smaller capacity lead-cooled fast reactors (such as SSTAR) can be cooled by natural

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convecti ...

, while larger designs (such as ELSY) use forced circulation in normal power operation, but will employ natural circulation emergency cooling. No operator interference is required, nor pumping of any kind to cool the residual heat of the reactor after shutdown. The reactor outlet coolant temperature is typically in the range of 500 to 600 °C, possibly ranging over 800 °C with advanced materials for later designs. Temperatures higher than 800 °C are theoretically high enough to support thermochemical production of hydrogen through the sulfur-iodine cycle, although this has not been demonstrated. The concept is generally very similar to

sodium-cooled fast reactor 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 ...

, and most liquid-metal fast reactors have used sodium instead of lead. Few lead-cooled reactors have been constructed, except for some Soviet

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, ...

reactors in the 1970s, but a number of proposed new nuclear reactor designs are lead-cooled. The lead-cooled reactor design has been proposed as a

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 ...

. Plans for future implementation of this type of reactor include modular arrangements rated at 300 to 400 MWe, and a large monolithic plant rated at 1,200 MWe.

Modular nuclear reactors

Reactors that use lead or lead-bismuth eutectic can be designed in a large range of power ratings. The Soviet union successfully operated the Alfa class submarines with a lead-bismuth cooled fast reactor in the sixties and seventies, which had approximately 30 MW of mechanical output for 155 MW thermal power (see below). Other options include units featuring long-life, pre-manufactured cores, that do not require refueling for many years. The lead-cooled fast reactor battery is a small turnkey-type power plant using cassette cores running on a closed fuel cycle with 15 to 20 years' refuelling interval, or entirely replaceable reactor modules. It is designed for generation of electricity on small grids (and other resources, including

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxi ...

and

potable water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ag ...

Advantages of lead in fast reactors

The use of lead as a coolant has several advantages if compared to other methods for reactor cooling. * Molten lead does not significantly

moderate Moderate is an ideological category which designates a rejection of radical or extreme views, especially in regard to politics and religion. A moderate is considered someone occupying any mainstream position avoiding extreme views. In American ...

neutrons. Moderation occurs when neutrons are slowed down by repeated collisions with a medium. When the neutron collides with atoms that are much heavier than itself, almost no energy is lost in the process. Thus, the neutrons are not slowed down by lead, which ensures that the neutrons keep their high energy. This is similar to other fast reactor concepts, including the molten liquid sodium designs. * Molten lead acts as a reflector for neutrons. Neutrons escaping the core of the reactor are to some extent directed back into the core, which allows a better

neutron economy Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production. The distribution of neutron energies in a nuclear reactor differs from the f ...

. This in turn enables more spacing between the fuel elements in the reactor, allowing better heat removal by the lead coolant. * Lead undergoes almost no activation by neutrons. Thus, virtually no radioactive elements are created by absorption of neutrons by the lead. This is in contrast to the

which was used in other fast designs, including in Russian submarines. The bismuth in this mixture (which has a lower melting point, 123.5 °C, than that of pure lead) is activated to some degree to ²¹⁰Po, Polonium-210, which is an alpha emitter. * Although virtually no neutrons are absorbed by the lead, lead is very effective at absorbing

gamma rays 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 sh ...

and other ionizing radiation. This ensures that radiation fields outside the reactor are extremely low. * In contrast to molten sodium metal, another relatively popular coolant that is used in fast reactors, lead does not have issues with flammability (although the combustion of sodium in air is a mild reaction, not to be confused with the violent reaction between sodium and water), and will solidify from a leak. * The very wide temperature range at which lead remains liquid (more than 1400 K or °C) implies that any thermal excursions are absorbed without any pressure increase. In practice, the operational temperature will be kept at around -, mainly because of other material properties. * As with all fast reactor designs, because of the high temperature and the high thermal inertia,

passive cooling Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption. This approach works either by preventing heat from ...

is possible in emergency situations. Thus, no electrical pumping is required, natural air convection is sufficient to remove residual heat after shutdown. To achieve this, reactor designs include dedicated passive heat removal systems, that requires no electrical power and no operator action. * All fast reactor designs operate at substantial higher temperatures in the core than water cooled (and moderated) reactors. This allows a significantly higher thermodynamic efficiency in the steam generators. Thus, a larger portion of the nuclear energy is converted into electricity. More than 40% efficiency is achievable in real life, compared to around 30% in water cooled reactors. * Similarly, as with all fast spectrum reactors, the coolant is not pressurized. This means that no pressure vessel is required, and the piping and ducts can be constructed with non-pressure resistant steel and alloys. Any leak in the primary coolant circuit will not be ejected at very high pressures. * Lead has a high thermal conductivity (35 W/m.K) compared to that of water (0.58), which means that heat transport from the fuel elements to the coolant is effective. *Instead of refueling, the whole core can be replaced after many years of operation. Such a reactor is suitable for countries that do not plan to build their own nuclear infrastructure. * Lead's nuclear properties allow it to prevent a positive

void coefficient In nuclear engineering, the void coefficient (more properly called void coefficient of reactivity) is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids (typically steam bubbles) form in the reactor ...

, which is difficult to prevent in large

sodium fast reactor 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 ...

cores. * Lead does not react significantly with water or air, unlike sodium which burns readily in air and can explode in contact with water. This allows easier, cheaper and safer containment and heat exchanger/steam generator design.

Disadvantages

* Lead and lead-bismuth are very dense, increasing the weight of the system therefore requiring more structural support and possibly seismic protection which increases building cost, although a more compact structure may be beneficial as well. * While lead is cheap and abundant, bismuth is expensive and quite rare. A grid connected lead-bismuth reactor requires hundreds of tonnes of lead-bismuth depending on reactor size. * Solidification of lead-bismuth solution renders the reactor inoperable. However,

has a comparatively low melting temperature of , making melting a relatively easily accomplished task. Lead has a higher melting point of 327.5 °С, but is often used as a pool type reactor where the large bulk of lead does not easily freeze. * By leaking and solidifying, the coolant may damage equipment (see Soviet submarine K-64), if measures to contain such leaks are not taken. * Lead-bismuth produces a considerable amount of

polonium Polonium is a chemical element with the symbol Po and atomic number 84. Polonium is a chalcogen. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character ...

from neutron activation of bismuth. This radioactive element will dissolve in the lead-bismuth, and is an alpha emitter with a half-life of 138 days. This can complicate maintenance and pose a plant contamination problem. The alpha particle emitted has a high energy, and is therefore hazardous. Pure lead produces orders of magnitudes less polonium, and so has an advantage over lead-bismuth in this regard. * The most challenging problem of lead is the potential for corrosion of the reactor internals. New specialized materials such as alumina forming austenitic steels, which maintain a protective oxide layer on the reactor components, are candidates under investigation.

Implementation

Russia/USSR

Two types of lead-cooled fast reactor were used in

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 nationa ...

Alfa class submarine The Alfa class, Soviet designation Project 705 Lira (russian: Лира, meaning "Lyre", NATO reporting name Alfa), was a class of nuclear-powered attack submarines in service with the Soviet Navy from 1971 into the early 1990s, with one serving ...

s of the 1970s. The OK-550 and BM-40A designs were both capable of producing 155MWt. They were significantly lighter than typical water-cooled reactors and had an advantage of being capable to quickly switch between maximum power and minimum noise operation modes. A joint venture calle
AKME Engineering
was announced in 2010 to develop a commercial lead-bismuth reactor. The SVBR-100 ('Svintsovo-Vismutovyi Bystryi Reaktor' - lead-bismuth fast reactor) is based on the Alfa designs and will produce 100MWe electricity from gross thermal power of 280MWt, about twice that of the submarine reactors. They can also be used in groups of up to 16 if more power is required. The coolant increases from to as it goes through the core. Uranium oxide enriched to 16.5% U-235 could be used as fuel, and refuelling would be required every 7–8 years. A prototype is planned for 2017. Another two lead cooled reactors are developed by Russians: BREST-300 and BREST-1200. The BREST-300 design was completed in September 2014. WNA mentions Russia role on boosting other countries interest in this field:

Proposals and in-development

Belgium

The

MYRRHA Myrrha (Greek: , ''Mýrra''), also known as Smyrna (Greek: , ''Smýrna''), is the mother of Adonis in Greek mythology. She was transformed into a myrrh tree after having had intercourse with her father, and gave birth to Adonis in tree form. A ...

project (for Multi-purpose hYbrid Research Reactor for High-tech Applications) is a first-of-a-kind design of a nuclear reactor coupled to a proton accelerator (so-called Accelerator-driven system (ADS)). This will be a 'Lead-bismuth-cooled fast reactor' with two possible configurations: sub-critical or critical. The project is managed by

SCK•CEN SCK CEN (the Belgian Nuclear Research Centre), until 2020 shortened as SCK•CEN, is the Belgian nuclear research centre located in Mol, Belgium, more specifically near the township of Donk. SCK CEN is a global leader in the field of nuclear r ...

, the Belgian center for nuclear energy. It will be built based on a first successful demonstrator
GUINEVERE
The project entered a new phase of development in 2013 when a contract for the front-end engineering design was awarded to a consortium led by Areva. MYRRHA enjoys international recognition and was listed in December 2010 by the European Commission as one of 50 projects for maintaining European leadership in high-tech research in the next 20 years.

United States

The initial design of the

Hyperion Power Module Gen4 Energy, Inc (formerly Hyperion Power Generation, Inc.uranium nitride Uranium nitrides is any of a family of several ceramic materials: uranium mononitride (UN), uranium sesquinitride (U2N3) and uranium dinitride (UN2). The word nitride refers to the −3 oxidation state of the nitrogen bound to the uranium. Uraniu ...

fuel encased in HT-9 tubes, using a quartz reflector, and lead-bismuth eutectic as coolant. The firm went out of business in 2018. The

Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...

developed SSTAR was a lead-cooled design.

Germany

The '' dual fluid reactor'' (DFR) is a German project combining the advantages of the

molten salt reactor A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. Only two MSRs have ever operated, both research reactors in the United States. The 1950's A ...

with the ones of the

liquid metal cooled reactor A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use and have been s ...

. As a breeder reactor the DFR can burn both natural uranium and thorium, as well as recycle nuclear waste. Due to the high thermal conductivity of the molten metal, the DFR is an inherently safe reactor (the decay heat can be removed passively).

Russia

Insofar as serious development is involved, Russia seems to be on the forefront of developing the lead cooled fast reactor. The BREST reactor is currently under construction. This reactor will employ pure lead as coolant, a plutonium/uranium nitride fuel, generate 300 MWe (electric) from 750 MWth, and is a pool type reactor. The foundation has been completed in November 2021. The reactor sits as the Siberian Chemical Combine's (SCC's) Seversk site.

Sweden

The company LeadCold is in collaboration with

KTH Royal Institute of Technology The KTH Royal Institute of Technology ( sv, Kungliga Tekniska högskolan, lit=Royal Institute of Technology), abbreviated KTH, is a public research university in Stockholm, Sweden. KTH conducts research and education in engineering and technolo ...

and

Uniper Uniper SE �juːnipɚis an energy company based in Düsseldorf, Germany. The name of the company is a portmanteau of "unique" and "performance" given by long-term employee Gregor Recke. Uniper was formed by the separation of E.ON's fossil fuel ...

developing the SEALER (Swedish Advanced Lead Reactor) reactor, a lead-cooled reactor using uranium nitride as fuel.

References

Advanced reactor, fuel cycle, and energy products workshop for universities

External links

Idaho National Laboratory Lead-Cooled Fast Reactor (lead-cooled fast reactor) Fact Sheet

Heavy-Metal Aerosol Transport in a Lead-Bismuth Cooled Fast Reactor with In-Vessel Direct-Contact Steam Generation

Comparison of sodium and lead-cooled fast reactors regarding reactor physics aspects, severe safety and economical issuesRBEC-M Lead-Bismuth Cooled Fast Reactor Benchmarking Calculations
* * {{Nuclear fission reactors Liquid metal fast reactors Lead