Nuclear fission reactors leave behind very heavy elements from the splitting of uranium atoms which remain highly radioactive for up to tens or hundreds of thousands of years. For example, uranium, the particular isotope of uranium used as nuclear fuel, has a half-life of over seven hundred million years, while molybdenum, an isotope used to produce contrast agents for medical imaging, has a half-life of roughly two and a half days.
A smorgasbord of radioactive waste byproducts are produced from uranium and plutonium fission, some of which have half-lives of days or hours and some of which have half-lives in excess of two hundred thousand years.
How to store and dispose of long-lived nuclear waste is a major concern regarding fission power, but practically a nonissue in fusion power. Deuterium-deuterium and deuterium-tritium reactions produce helium-3 and helium-4, two stable isotopes of helium.
There are two broad categories of fusion reactor designs: magnetic confinement reactors and inertial confinement reactors. Fusion reactions begin with plasma, the fourth fundamental state of matter.
Plasma is a hot, electrically conductive gas of ions and unbound charged particles that forms the perfect crucible for nuclear fusion, and all of our technology used to instigate fusion involves wrangling and controlling this state of matter in a high-energy, high-intensity environment.
This is what happens in the core of our sun. To replicate that energy-creating fusion process in a fusion reactor here on Earth and harness fusion power for our own use, we need technology that controls the flow of superheated plasma. A magnetic confinement fusion system relies on using powerful magnetic fields to contain and control the movement of superheated plasma.
As particles within the plasma are guided by a strong magnetic field, they collide with each other and fuse into new elements. The concept of magnetic energy confinement for a fusion reactor was first developed in the s, and initial fusion research left scientists optimistic that magnetic confinement would be the most feasible way to produce fusion energy.
The most well-explored and well-known type of magnetic confinement system is the tokamak reactor , first developed by Soviet scientists Igor Tamm and Andrei Sakharov in the s based on Z-pinch machines. A tokamak is a doughnut-shaped fusion reactor that generates a helix-shaped magnetic field using powerful electromagnets placed in the inner ring. A similar fusion reactor design, called a stellarator , uses external magnets to apply a containment field to the superheated plasma within the fustion reaction chamber.
In the s, and with a glut of funding pouring into research institutions from governments with the hope of developing fusion power plants to meet energy needs during the oil crisis, experimental tokamak and stellarator but mostly tokamak fusion reactors began to pop up all over the world.
This was a joint effort between fusion science researchers from the United States, Soviet Union, European Union, and Japan, as fusion energy researchers had quickly discovered that no one nation had the resources to develop a powerful enough tokamak fusion reactor on their own. JET is one of the only facilities in the world that makes more neutrons than us! Currently, while advances in plasma science and materials science are still needed to make fusion reactors that can output more fusion energy than it takes in, tokamak reactors are still regarded as the most promising path in fusion research to one day creating power plants for clean fusion energy production.
Inertial confinement fusion relies on shooting high-energy laser beams at a fuel pellet target containing deuterium and tritium fuel for the reaction. The impact of the high-energy beam causes shockwaves to travel through the fuel pellet target, heating and compressing it to induce fusion reactions.
This method of inducing nuclear fusion reactions was first suggested in the s, and in the s, high-energy ICF inertial confinement fusion research suggested that it could be a more promising path to fusion energy than tokamak and stellarator fusion reactors.
However, over the next two decades, researchers gradually discovered more and more hurdles that needed to be overcome in order to reach ignition within such a fusion reactor, and estimations regarding how much energy the laser beams needed to induce fusion doubled on a yearly basis. Completed in , as of this system has only been able to reach one-third of the conditions needed for ignition. The NIF is currently used mainly for materials science and weapon research rather than fusion power research.
There are also fusion research facilities exploring fusion projects such as colliding beam fusion, which involves accelerating a beam of ions into a stationary target or another beam to induce a nuclear fusion reaction, similar to inertial confinement fusion. Neutron radiation is a byproduct of all nuclear processes, including fission and fusion, and since the s, industrial and research applications such as neutron radiography and medical isotope production have depended on fission reactors for their high neutron yield.
But recent developments in colliding beam fusion, or accelerator fusion, is making fusion a more convenient way to produce neutrons than fission. On the largest scale of colliding beam fusion are enormous particle accelerators such as the Spallation Neutron Source at Oak Ridge National Laboratory, which produce massive neutron yields and are primarily used for neutron scattering research. Scientists use neutron scattering to better understand the molecular composition of materials such as metals, polymers, biological samples, and superconductors.
On the smallest scale of colliding beam fusion are sealed-tube neutron sources, which are very small accelerators—small enough to fit on a table or workbench, and often small enough to be used for fieldwork—that work by shooting a beam of deuterium or tritium ions at a deuterium or tritium target to make fusion start. The smaller the neutron source, the lower its yield, and these tiny sealed-tube sources tend to be used mostly for work which only needs a low neutron yield from a portable source, such as oil well logging, coal analysis, and most applications of neutron activation analysis.
These sealed-tube sources are widely used in the petroleum industry. These high-flux neutron generators work under the same basic principles as sealed-tube sources, except massively scaled up from tabletop-sized neutron emitters so that they can be used in the same high-yield industrial and research niches as fission reactors. If we are successful, we will have an energy source that is inexhaustible. One out of every 6, atoms of hydrogen in ordinary water is deuterium, giving a gallon of water the energy content of gallons of gasoline.
In addition, fusion would be environmentally friendly, producing no combustion products or greenhouse gases. While fusion is a nuclear process, the products of the fusion reaction helium and a neutron are not radioactive, and with proper design a fusion power plant would be passively safe, and would produce no long-lived radioactive waste.
Design studies show that electricity from fusion should be about the same cost as present day sources. While fusion sounds simple, the details are difficult and exacting. Heating, compressing and confining hydrogen plasmas at million degrees is a significant challenge.
Most involve the isotopes of hydrogen called deuterium and tritium:. Conceptually, harnessing nuclear fusion in a reactor is a no-brainer.
But it has been extremely difficult for scientists to come up with a controllable, nondestructive way of doing it. To understand why, we need to look at the necessary conditions for nuclear fusion. Isotopes are atoms of the same element that have the same number of protons and electrons but a different number of neutrons.
Some common isotopes in fusion are:. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe.
Prev NEXT. Physical Science. Nuclear Science. Proton-proton chain - This sequence is the predominant fusion reaction scheme used by stars such as the sun.
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