Mixed oxide fuel, commonly referred to as MOX fuel, is
nuclear fuel
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...
that contains more than one
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 E ...
of
fissile material
In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be ty ...
, usually consisting 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 ...
blended with
natural uranium
Natural uranium (NU or Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes fr ...
,
reprocessed uranium
Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material s ...
, or
depleted uranium
Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope than natural uranium.: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, hav ...
. MOX fuel is an alternative to the
low-enriched uranium
Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (23 ...
(LEU) fuel used in the
light-water reactor
The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron react ...
s that predominate
nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
generation.
For example, a mixture of 7% plutonium and 93% natural uranium reacts similarly, although not identically, to LEU fuel (3 to 5% uranium-235). MOX usually consists of two phases, UO
2 and PuO
2, and/or a single phase solid solution (U,Pu)O
2. The content of PuO
2 may vary from 1.5 wt.% to 25–30 wt.% depending on the type of nuclear reactor.
One attraction of MOX fuel is that it is a way of utilizing surplus
weapons-grade
Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nucle ...
plutonium, an alternative to storage of surplus plutonium, which would need to be secured against the risk of theft for use in
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
s. On the other hand, some studies warned that normalising the global commercial use of MOX fuel and the associated expansion of
nuclear reprocessing
Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...
will increase, rather than reduce, the risk of
nuclear proliferation
Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as " Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Wea ...
, by encouraging increased separation of plutonium from spent fuel in the civil nuclear fuel cycle.
Overview
In every uranium-based
nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place and the heat is generated. Typically, the fuel will be low-enriched uranium contained in thousands of indi ...
there is both
fission of uranium isotopes such as
uranium-235
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exis ...
, and the formation of new, heavier isotopes due to
neutron capture
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, ...
, primarily by
uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it ...
. Most of the fuel mass in a reactor is uranium-238. By neutron capture and two successive
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 ...
s, uranium-238 becomes
plutonium-239
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main ...
, which, by successive neutron capture, becomes
plutonium-240
Plutonium-240 ( or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron. The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project.
240 ...
,
plutonium-241
Plutonium-241 (241Pu or Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes (especially 239Pu), 241Pu is fissile, with a neutron absorption cross section about one-third greater t ...
,
plutonium-242
Plutonium-242 (242Pu or Pu-242) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years.
The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the la ...
, and (after further beta decays) other
transuranic
The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other elements. ...
or
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...
nuclides. Plutonium-239 and plutonium-241 are
fissile
In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...
, like uranium-235. Small quantities of
uranium-236
Uranium-236 (236U) is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in the re ...
,
neptunium-237
Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be s ...
and
plutonium-238
Plutonium-238 (238Pu or Pu-238) is a fissile, radioactive isotope of plutonium that has a half-life of 87.7 years.
Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 isotope suitab ...
are formed similarly from uranium-235.
Normally, with LEU fuel being changed every five years or so, most of the plutonium-239 is "burned" in the reactor. It behaves like uranium-235, with a slightly higher
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
for fission, and its fission releases a similar amount of
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
. Typically, about one percent of the
spent fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor a ...
discharged from a reactor is plutonium, and some two-thirds of the plutonium is plutonium-239. Worldwide, almost 100 tonnes of plutonium in spent fuel arises each year.
Reprocessing the plutonium into usable fuel increases the energy derived from the original uranium by some 12%, and if the uranium-235 is also recycled by re-enrichment, this becomes about 20%.
Currently plutonium is only reprocessed and used once as MOX fuel; spent MOX fuel, with a high proportion of
minor actinide
The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkeliu ...
s and plutonium isotopes, is stored as waste.
Existing
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 nu ...
s must be re-licensed before MOX fuel can be introduced because using it changes the operating characteristics of a reactor, and the plant must be designed or adapted slightly to take it; for example, more
control rod
Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing ...
s are needed. Often only a third to half of the fuel load is switched to MOX, but for more than 50% MOX loading, significant changes are necessary and a reactor needs to be designed accordingly. The
System 80
System 80 is a pressurized water reactor design by Combustion Engineering (which was subsequently bought by Asea Brown Boveri and eventually merged into the Westinghouse Electric Company). Three System 80 reactors were built at Palo Verde Nuclear ...
reactor design, notably deployed at the U.S.
Palo Verde Nuclear Generating Station
The Palo Verde Generating Station is a nuclear power plant located near Tonopah, Arizona, in western Arizona. It is located about due west of downtown Phoenix, Arizona, and it is located near the Gila River, which is dry save for the rainy seaso ...
near
Phoenix, Arizona
Phoenix ( ; nv, Hoozdo; es, Fénix or , yuf-x-wal, Banyà:nyuwá) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona, with 1 ...
, was designed for 100% MOX core compatibility, but so far has always operated on fresh low enriched uranium. In theory, the three Palo Verde reactors could use the MOX arising from seven conventionally fueled reactors each year and would no longer require fresh uranium fuel.
Fast neutron
BN-600
The BN-600 reactor is a Liquid metal cooled reactor, sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. Designed to generate electrical power of 600 Watt (unit), MW in t ...
and
BN-800 reactor
The BN-800 reactor (Russian: реактор БН–800) is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia.
The reactor is designed to generate 880 MW of electrical po ...
s are designed for 100% MOX loading. In 2022, the BN-800 was fully loaded with MOX fuel for the first time.
According to
Atomic Energy of Canada Limited
Atomic Energy of Canada Limited (AECL) is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed thi ...
(AECL),
CANDU reactor
The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...
s could use 100% MOX cores without physical modification. AECL reported to the
United States National Academy of Sciences
The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...
committee on plutonium disposition that it has extensive experience in testing the use of MOX fuel containing from 0.5 to 3% plutonium.
Spent MOX fuel
The content of
un-burnt plutonium in spent MOX fuel from thermal reactors is significant – greater than 50% of the initial plutonium loading. However, during the burning of MOX the ratio of fissile (odd numbered) isotopes to non-fissile (even) drops from around 65% to 20%, depending on burn up. This makes any attempt to recover the fissile isotopes difficult and any bulk Pu recovered would require such a high fraction of Pu in any second generation MOX that it would be impractical. This means that such a spent fuel would be difficult to reprocess for further reuse (burning) of plutonium. Regular reprocessing of
biphasic
Biphasic, meaning having two phases, may refer to:
* Phase (matter)
In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples ...
spent MOX is difficult because of the low solubility of PuO
2 in nitric acid.
As of 2015, the only demonstration of twice-recycled, high-burnup fuel occurred in the
Phénix
Phénix (French for phoenix) was a small-scale (gross 264/net 233 MWe) prototype fast breeder reactor, located at the Marcoule nuclear site, near Orange, France. It was a pool-type liquid-metal fast breeder reactor cooled with liquid sodium. I ...
fast reactor.
Current applications
Reprocessing of commercial nuclear fuel to make MOX is performed in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
and to a lesser extent in
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
,
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
and
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. In the UK
THORP
''Thorp'' is a Middle English word for a hamlet or small village.
Etymology
The name can either come from Old Norse ''þorp'' (also ''thorp''), or from Old English (Anglo-Saxon) ''þrop''. There are many place names in England with the suffi ...
operated from 1994 to 2018.
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
plans to develop
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 mate ...
s and reprocessing. Reprocessing of spent commercial-reactor nuclear fuel is not permitted in the United States due to nonproliferation considerations. Germany had plans for a reprocessing plant at
Wackersdorf
Wackersdorf is a municipality in the district of Schwandorf in Bavaria, Germany. It is famous for playing host to rounds of the CIK-FIA Karting European Championship.
See also
* Wackersdorf nuclear reprocessing plant
*Anti-nuclear movement in Germ ...
but as this failed to materialize, it instead relied on French nuclear reprocessing capabilities until legally outlawing the transport of German spent fuel for reprocessing in 2005.
The United States was building a MOX fuel plant at the
Savannah River Site
The Savannah River Site (SRS) is a U.S. Department of Energy (DOE) reservation in the United States in the state of South Carolina, located on land in Aiken, Allendale, and Barnwell counties adjacent to the Savannah River, southeast of August ...
in South Carolina. Although the
Tennessee Valley Authority
The Tennessee Valley Authority (TVA) is a federally owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, and small areas of Georgia, North Carolina ...
(TVA) and
Duke Energy
Duke Energy Corporation is an American electric power and natural gas holding company headquartered in Charlotte, North Carolina.
Overview
Based in Charlotte, North Carolina, Duke Energy owns 58,200 megawatts of base-load and peak generation in ...
expressed interest in using MOX reactor fuel from the conversion of weapons-grade plutonium, TVA (currently the most likely customer) said in April 2011 that it would delay a decision until it could see how MOX fuel performed in the nuclear accident at
Fukushima Daiichi
The is a disabled nuclear power plant located on a site in the towns of Ōkuma and Futaba in Fukushima Prefecture, Japan. The plant suffered major damage from the magnitude 9.0 earthquake and tsunami that hit Japan on March 11, 2011. Th ...
. In May 2018, the Department of Energy reported that the plant would require another $48 billion to complete, on top of the $7.6 billion already spent. Construction was cancelled.
Thermal reactors
Most modern thermal reactors using high burn up uranium oxide fuel produce a quite significant proportion of their output towards the end of core life from fission of plutonium produced by neutron capture in uranium 238 earlier in the life of the core, so adding some plutonium oxide to the fuel at manufacture is not in principle a very radical step. About 30 thermal reactors in Europe (Belgium, the Netherlands, Switzerland, Germany and France) are using MOX
and an additional 20 have been licensed to do so. Most reactors use it as about one third of their core, but some will accept up to 50% MOX assemblies. In France, EDF aims to have all its 900 MWe series of reactors running with at least one-third MOX. Japan aimed to have one third of its reactors using MOX by 2010, and has approved construction of a new reactor with a complete fuel loading of MOX. Of the total nuclear fuel used today, MOX provides 2%.
Licensing and safety issues of using MOX fuel include:
* Plutonium oxide is substantially more toxic than uranium oxide, making fuel manufacture more difficult and expensive.
* As plutonium isotopes absorb more neutrons than uranium fuels, reactor control systems may need modification.
* MOX fuel tends to run hotter because of lower thermal conductivity, which may be an issue in some reactor designs.
* Fission gas release in MOX fuel assemblies may limit the maximum burn-up time of MOX fuel.
About 30% of the plutonium originally loaded into MOX fuel is consumed by use in a thermal reactor. In theory, if one third of the core fuel load is MOX and two-thirds uranium fuel, there is zero net change in the mass of plutonium in the
spent fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor a ...
and the cycle could be repeated; however, there remains multiple difficulties in reprocessing spent MOX fuel. As of 2010, plutonium is only recycled once in thermal reactors, and spent MOX fuel is separated from the rest of the spent fuel to be stored as waste.
All plutonium isotopes are either fissile or fertile, although
plutonium-242
Plutonium-242 (242Pu or Pu-242) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years.
The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the la ...
needs to absorb 3 neutrons before becoming fissile
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
-245; in thermal reactors isotopic degradation limits the plutonium recycle potential. About 1% of
spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor an ...
from current
LWR
The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reac ...
s is plutonium, with approximate isotopic composition 52% , 24% , 15% , 6% and 2% when the fuel is first removed from the reactor.
Fast reactors
Because the fission-to-capture ratio of high energy or
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 ...
s changes to favour
fission for almost all of the
actinides
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...
, including , fast reactors could use all of them for fuel. All actinides can undergo neutron induced fission with unmoderated or fast neutrons. A
fast 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 t ...
is therefore more efficient than a thermal reactor for using plutonium and higher actinides as fuel.
These fast reactors are better suited for the
transmutation of other actinides than thermal reactors. Because thermal reactors use slow or moderated neutrons, the actinides that are not fissionable with thermal neutrons tend to absorb the neutrons instead of fissioning. This leads to buildup of heavier actinides and lowers the number of thermal neutrons available to continue the chain reaction. A
subcritical reactor
A subcritical reactor is a nuclear fission reactor concept that produces fission without achieving criticality. Instead of sustaining a chain reaction, a subcritical reactor uses additional neutrons from an outside source. There are two general c ...
with an external
neutron source
A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutron sources are used in physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, and nuclear p ...
could either be run in the fast neutron spectrum (without the need for highly enriched fuels as otherwise common in fast reactors) or use
thermal 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 ...
s to breed fissile materials, compensating the loss of neutrons by increasing the flux from the neutron source.
Fabrication
Plutonium separation
The first step is separating the plutonium from the remaining uranium (about 96% of the spent fuel) and the fission products with other wastes (together about 3%) using the
PUREX
PUREX (plutonium uranium reduction extraction) is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. PUREX is the ''de facto'' standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium fr ...
process.
Dry mixing
MOX fuel can be made by grinding together uranium oxide (UO
2) and plutonium oxide (PuO
2) before the mixed oxide is pressed into pellets, but this process has the disadvantage of forming much radioactive dust.
Coprecipitation
A mixture of
uranyl nitrate
Uranyl nitrate is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels.
Uranyl nitrate can be prepa ...
and plutonium nitrate in
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
is converted by treatment with a base such as ammonia to form a mixture of
ammonium diuranate and plutonium hydroxide. After heating in a mixture of 5%
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-toxic, an ...
and 95%
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
will form a mixture of
uranium dioxide
Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear rea ...
and
plutonium dioxide
Plutonium(IV) oxide or (plutonia) is the chemical compound with the formula Pu O2. This high melting-point solid is a principal compound of plutonium. It can vary in color from yellow to olive green, depending on the particle size, temperature a ...
. Using a
base, the resulting powder can be run through a
press
Press may refer to:
Media
* Print media or news media, commonly called "the press"
* Printing press, commonly called "the press"
* Press (newspaper), a list of newspapers
* Press TV, an Iranian television network
People
* Press (surname), a fam ...
and converted into pellets. The pellets can then be
sintered into mixed uranium and plutonium oxide.
Americium content
Plutonium from reprocessed fuel is usually fabricated into MOX within less than five years of its production to avoid problems resulting from impurities produced by the
decay
Decay may refer to:
Science and technology
* Bit decay, in computing
* Software decay, in computing
* Distance decay, in geography
* Decay time (fall time), in electronics
Biology
* Decomposition of organic matter
* Tooth decay (dental caries ...
of short-lived
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s of plutonium. In particular, plutonium-241 decays to
americium-241
Americium-241 (, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is com ...
with a 14-year half-life. Because americium-241 is a
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 ...
emitter, its presence is a potential
occupational health
Occupational safety and health (OSH), also commonly referred to as occupational health and safety (OHS), occupational health, or occupational safety, is a multidisciplinary field concerned with the safety, health, and welfare of people at wor ...
hazard. It is possible, however, to remove the
americium
Americium is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was na ...
from the plutonium by a chemical separation process. Even under the worst conditions, the americium/plutonium mixture is less radioactive than a spent-fuel dissolution liquor, so it should be relatively straightforward to recover the plutonium by
PUREX
PUREX (plutonium uranium reduction extraction) is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. PUREX is the ''de facto'' standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium fr ...
or another aqueous reprocessing method.
Curium content
It is possible that both
americium
Americium is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was na ...
and
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
could be added to a U/Pu MOX fuel before it is loaded into a fast reactor or a
subcritical reactor
A subcritical reactor is a nuclear fission reactor concept that produces fission without achieving criticality. Instead of sustaining a chain reaction, a subcritical reactor uses additional neutrons from an outside source. There are two general c ...
run in "Actinide burner mode". This is one means of transmutation. Work with curium is much harder than americium because curium is a neutron emitter, the MOX production line would need to be shielded with both
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 cu ...
and
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
to protect the workers.
Also, the neutron irradiation of curium generates the higher
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...
s, such as
californium
Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding ...
, which increase the
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 beh ...
dose associated with the
used nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor an ...
; this has the potential to pollute the fuel cycle with strong neutron emitters. As a result, it is likely that curium will be excluded from most MOX fuels. A subcritical reactor such as the
Accelerator Driven System could "burn" such fuels if the problems associated with their handling and transportation are solved. However, to avoid
power excursions due to unintended criticality, the
neutronics
Neutron transport (also known as neutronics) is the study of the motions and interactions of neutrons with materials. Nuclear scientists and engineers often need to know where neutrons are in an apparatus, what direction they are going, and how qu ...
must be known precisely at any given point in time, including the effect of build-up or consumption of neutron emitting nuclides as well as neutron poisons.
Thorium MOX
MOX fuel containing
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
and plutonium oxides is also being tested.
According to a Norwegian study, "the
coolant void reactivity of the thorium-plutonium fuel is negative for plutonium contents up to 21%, whereas the transition lies at 16% for MOX fuel."
The authors concluded, "Thorium-plutonium fuel seems to offer some advantages over MOX fuel with regards to
control rod
Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing ...
and
boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
worths, CVR and plutonium consumption."
See also
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Nuclear fuel cycle
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the ''front end'', which are the preparation of the fuel, steps in the ''service period'' in w ...
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Nuclear breeder reactor
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Spent nuclear fuel shipping cask
A nuclear flask is a shipping container that is used to transport active nuclear materials between nuclear power station and spent fuel reprocessing facilities.
Each shipping container is designed to maintain its integrity under normal transport ...
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Nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
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Nuclear fission
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radio ...
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Nuclear power plant
A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a electric generator, generato ...
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Hanford Site
The Hanford Site is a decommissioned nuclear production complex operated by the United States federal government on the Columbia River in Benton County in the U.S. state of Washington. The site has been known by many names, including SiteW a ...
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Remix Fuel Remix Fuel was developed in Russia to make use of Mixed Recycled Uranium and Plutonium from spent nuclear fuel to manufacture fresh fuel suitable for widespread use in Russian reactor designs. Compared to "conventional" MOX-fuel
MOX or Mixed Oxid ...
References
External links
Technical Aspects of the Use of Weapons Plutonium as Reactor FuelSynergistic Nuclear Fuel Cycles of the Future
{{Authority control
Nuclear fuels
Nuclear reprocessing
Plutonium compounds
Uranium compounds