Accelerator-driven subcritical reactor
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An accelerator-driven subcritical reactor (ADSR) is a nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core with a high-energy proton or electron accelerator. It could use
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 ...
as a fuel, which is more abundant than
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
. The neutrons needed for sustaining the fission process would be provided by a
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
producing neutrons by spallation or photo-neutron production. These neutrons activate the thorium, enabling fission without needing to make the reactor critical. One benefit of such reactors is the relatively short
half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...
of their waste products. For proton accelerators, the high-energy proton beam impacts a 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 cu ...
target inside the core, chipping or "spalling" neutrons from the lead nuclei. These spallation neutrons convert fertile thorium to
protactinium-233 Protactinium (91Pa) has no stable isotopes. The three naturally occurring isotopes allow a standard atomic weight to be given. Thirty radioisotopes of protactinium have been characterized, with the most stable being 231Pa with a half-life of 32, ...
and after 27 days into fissile
uranium-233 Uranium-233 (233U or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a reactor fuel. It has been used successfully in exp ...
and drive the fission reaction in the uranium. Thorium reactors can generate power from the
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 ...
residue left by uranium reactors. Thorium does not require significant refining, unlike uranium, and has a higher
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 ...
yield per neutron absorbed.


Accelerator developments

The "electron model of many applications" ( EMMA) is a new type of particle accelerator that could support an ADSR. The prototype was built at
Daresbury Laboratory Daresbury Laboratory is a scientific research laboratory based at Sci-Tech Daresbury campus near Daresbury in Halton, Cheshire, England. The laboratory began operations in 1962 and was officially opened on 16 June 1967 as the Daresbury Nuclear P ...
in Cheshire, UK. Uniquely, EMMA is a new hybrid of a
cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
and a synchrotron, combining their advantages into a compact, economical form. EMMA is a non-scaling fixed-field alternating-gradient (
FFAG accelerator A Fixed-Field alternating gradient Accelerator (FFA; also abbreviated FFAG) is a circular particle accelerator concept that can be characterized by its time-independent magnetic fields (''fixed-field'', like in a cyclotron) and the use of alternat ...
). The prototype accelerates electrons from 10 to 20 MeV, using the existing ALICE accelerator as the injector. In FFAG accelerators the magnetic field in the bending magnets is constant during acceleration, causing the particle beam to move radially outwards as its momentum increases. A non-scaling FFAG allows a quantity known as the "
betatron A betatron is a type of cyclic particle accelerator. It is essentially a transformer with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electrons in the vacuum around a circular path. Th ...
tune" to vary unchecked. In a conventional synchrotron such a variation results in beam loss as the tune hits various resonance conditions. However, in EMMA the beam crosses these resonances so rapidly that the beam survives. The prototype accelerates electrons instead of protons, but proton generators can be built using the same principles.


Safety

Unlike uranium-235, thorium is not fissile – it essentially does not split on its own, exhibiting a half-life of 14.05 billion years (20 times that of U-235). The fission process stops when the proton beam stops, as when power is lost, as the reactor is subcritical. Microscopic quantities of plutonium are produced, and are then burned in the same reactor.


Rubbia design

The Norwegian group
Aker Solutions Aker Solutions ASA, an engineering company based in Oslo, provides the products, systems and services required to unlock energy from sources such as oil, gas, offshore wind and capture. The company, founded in 1841, was known as Aker Kværner u ...
bought "Energy amplifier for nuclear energy production driven by a particle beam accelerator" held by Nobel Prize-winning physicist
Carlo Rubbia Carlo Rubbia (born 31 March 1934) is an Italian particle physicist and inventor who shared the Nobel Prize in Physics in 1984 with Simon van der Meer for work leading to the discovery of the W and Z particles at CERN. Early life and educa ...
and as of 2013 was working on a thorium reactor. The company proposes a network of small 600 megawatt reactors located underground that can supply small grids and do not require an enormous facility for safety and security. Costs for the first reactor are estimated at £2bn.
Richard Garwin Richard Lawrence Garwin (born April 19, 1928) is an American physicist, best known as the author of the first hydrogen bomb design. In 1978, Garwin was elected a member of the National Academy of Engineering for contributing to the application ...
and
Georges Charpak Georges Charpak (; born Jerzy Charpak, 1 August 1924 – 29 September 2010) was a Polish-born French physicist, who was awarded the Nobel Prize in Physics in 1992. Life Georges Charpak was born Jerzy Charpak to Jewish parents, Anna (Szapiro) and ...
describe the
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 ...
in detail in their book "Megawatts and Megatons: A Turning Point in the Nuclear Age?" (2001) on pages 153 to 163. Earlier, the general concept of the
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 ...
, namely an accelerator-driven subcritical reactor, was covered in "The Second Nuclear Era" (1985), a book by
Alvin M. Weinberg Alvin Martin Weinberg (; April 20, 1915 – October 18, 2006) was an American nuclear physicist who was the administrator at Oak Ridge National Laboratory (ORNL) during and after the Manhattan Project. He came to Oak Ridge, Tennessee, in 1945 ...
and others.


See also

*
Liquid fluoride thorium reactor The liquid fluoride thorium reactor (LFTR; often pronounced ''lifter'') is a type of molten salt reactor. LFTRs use the thorium fuel cycle with a fluoride-based, molten, liquid salt for fuel. In a typical design, the liquid is pumped between a ...
*
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 ...
*
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 ...


References


External links

*: Bowman, C (1992) "Apparatus for nuclear transmutation and power production using an intense accelerator-generated thermal neutron flux" *{{youtube, hspcafUoh6M, Towards an Alternative Nuclear Future by Professor Robert Cywinski Nuclear power reactor types Thorium