Deuterium–tritium fusion (DTF) is a type of

nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...

in which one

deuterium Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more c ...

(H) nucleus (deuteron) fuses with one

tritium Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...

(H) nucleus (triton), giving one

helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consi ...

nucleus, one free

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

, and 17.6 MeV of total energy coming from both the neutron and helium. It is the best known fusion reaction for

fusion power Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices d ...

and

thermonuclear weapon A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...

s. Tritium, one of the reactants for DTF, is

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 conside ...

. In

fusion reactor Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices ...

s, a ' breeding blanket' made of lithium orthosilicate or other lithium-bearing ceramics, is placed on the walls of the reactor, as lithium, when exposed to energetic neutrons, will produce tritium.

Concept

In DTF, one deuteron fuses with one tritium, yielding one

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

nucleus, a free

, and 17.6 MeV, which is derived from about 0.02 AMU. The amount of energy obtained is described by the

mass–energy equivalence In physics, mass–energy equivalence is the relationship between mass and energy in a system's rest frame. The two differ only by a multiplicative constant and the units of measurement. The principle is described by the physicist Albert Einstei ...

: E = mc. 80% of the energy (14.1 MeV) becomes kinetic energy of the neutron traveling at 1/6 the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

. The mass difference between H+H and neutron+He is described by the

semi-empirical mass formula In nuclear physics, the semi-empirical mass formula (SEMF; sometimes also called the Weizsäcker formula, Bethe–Weizsäcker formula, or Bethe–Weizsäcker mass formula to distinguish it from the Bethe–Weizsäcker process) is used to approxim ...

that describes the relation between mass defects and binding energy in a nucleus.

Discovery

Evidence of DTF was first detected at the

University of Michigan The University of Michigan (U-M, U of M, or Michigan) is a public university, public research university in Ann Arbor, Michigan, United States. Founded in 1817, it is the oldest institution of higher education in the state. The University of Mi ...

in 1938 by Arthur J. Ruhlig. His experiment detected the signature of neutrons with energy greater than 15 MeV in secondary reactions of H created in H(d,p)H reactions of a 0.5 MeV incident deuteron beam on a heavy

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...

target, HPO. This discovery was largely unrecognized until recently.

Reactant sourcing

About 1 in every 6700

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

atoms in seawater is

, making it easy to acquire.

Tritium Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...

, however, is a

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

with a short half-life and no natural sources. This can be circumvented by exposing

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

to energetic neutrons, which produces tritons. Also, DTF itself emits a free neutron, which can be used to bombard lithium. A ' breeding blanket', made of lithium orthosilicate, is often placed along the walls of

s so that free neutrons created by DTF react with it to produce more H. This process is called ''tritium breeding''.

Fusion reactors

DTF is planned to be used in

ITER ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy through a fusion process s ...

, and many other proposed fusion reactors. It has many advantages over other types of fusion, as it has a relatively low minimum temperature, 10 kelvin.

Spin polarization

Spin-polarized D-T fuel can increase tritium burn efficiency (TBE) by an order of magnitude or more without compromising output. TBE increases nonlinearly with decreasing tritium fraction, while power density increases roughly linearly with D-T cross section. In a 481 MW ARC-like

tokamak A tokamak (; ) is a device which uses a powerful magnetic field generated by external magnets to confine plasma (physics), plasma in the shape of an axially symmetrical torus. The tokamak is one of several types of magnetic confinement fusi ...

with unpolarized 53:47 D-T fuel, the minimum tritium inventory was 0.69 kg. Spin-polarizing the fuel with a 63:37 D-T mix reduces the required tritium to 0.03 kg. With advancements in helium divertor pumping efficiency, TBE values of approximately 10%–40% could be achieved using low-tritium-fraction spin-polarized fuel with minimal power loss. This lowers tritium startup inventory requirements.

References