In the process some of the mass of the hydrogen is converted into energy. Deuterium is plentifully available in ordinary water. Tritium can be produced by combining the fusion neutron with the abundant light metal lithium. Thus fusion has the potential to be an inexhaustible source of energy.
To make fusion happen, the atoms of hydrogen must be heated to very high temperatures million degrees so they are ionized forming a plasma and have sufficient energy to fuse, and then be held together i. The sun and stars do this by gravity. More practical approaches on earth are magnetic confinement, where a strong magnetic field holds the ionized atoms together while they are heated by microwaves or other energy sources, and inertial confinement, where a tiny pellet of frozen hydrogen is compressed and heated by an intense energy beam, such as a laser, so quickly that fusion occurs before the atoms can fly apart.
Scientific terms can be confusing. DOE Explains offers straightforward explanations of key words and concepts in fundamental science. Nuclear Fusion Reactions. Depiction of the deuterium D and tritium T fusion reaction, which produces a helium nucleus or alpha particle and a high energy neutron.
Resources and Related Terms How does fusion energy work? Outside of its core, roiling layers of superheated plasma give off heat and light which travel through the abyss of space to warm all of the planets and not-quite-planets sorry, Pluto in our solar system. Eventually, about five billion years from now, the sun will exhaust the once-ample supply of hydrogen and helium in its core by fusing it all together into heavier elements. When that happens, the sun will violently shed what remains of its outer layers and leave behind a small gaseous core of carbon and other heavy elements.
No longer massive enough to force these heavy elements to fuse, this remaining white dwarf will rest, inert, in the center of an expanding cloud of gas until it cools to become a black dwarf. In its core, the sun fuses over million tons of hydrogen every second.
It takes such a great deal of energy to produce nuclear fusion that in our modern and mature universe, nuclear fusion will only occur naturally inside stars like our sun. Even hydrogen, the lightest element, requires a high energy input to fuse that simply cannot naturally occur anywhere else. And, of course, us being humans, we learned about that fusion reaction process and asked ourselves if we could do it here on Earth on a much smaller scale, of course.
After we figured out nuclear fission and created the most destructive weapons the human race has ever known, the race for nuclear fusion—as a source not of destructive power but of energy enough to power our civilization without need for polluting fossil fuels like coal or oil—began.
There are two broad categories of nuclear reactors: nuclear fission reactors, which split heavy atoms apart into less-heavy atoms to produce byproducts such as neutron radiation, radioactive waste, and most importantly, an excess amount of energy released that can be converted to electricity to power our homes and industries; and nuclear fusion reactors, which combine light atoms into less-light atoms in a fusion reaction to produce byproducts such as neutron radiation and in theory excess energy production.
Nuclear fusion as a source of energy production—fusion power—is the holy grail of fusion research. A nuclear fission reactor uses uranium as fuel. When a uranium atom becomes excited and destabilized by exposure to neutron radiation, it breaks apart into smaller atoms such as barium and krypton and releases more neutron radiation, which in turn excites and breaks apart more uranium atoms, causing a chain reaction. The energy released causes water in the reactor to boil, turning into steam and turning a turbine, which then produces electricity.
Some of the lighter elements produced in these chain reactions are quite radioactive and take tens of thousands of years or longer to decay, making disposal problematic. Modern reactors in nuclear power plants are designed with incredibly redundant safety and shutoff systems to prevent these sorts of disaster scenarios.
Not every nuclear fission reactor is a nuclear power plant designed to produce electricity. Non-power-generating research reactors are used for their neutron output for applications such as radiation survivability testing, neutron radiography, and medical isotope production. Fusion nuclear reactors are an altogether different beast from fission reactors.
For starters, fusion works with much lighter elements. In the sun, we mainly see hydrogen, the lightest element, fused together to create helium, the second-lightest element. Here on Earth, fusion reactors combine deuterium and tritium as fusion fuel, two heavy hydrogen isotopes. We choose to use deuterium and tritium for nuclear fusion fuel instead of emulating the hydrogen-hydrogen and helium-helium fusion reactions like our sun.
One of the huge benefits of nuclear fusion over fission, and what makes it such an attractive source of energy compared to not only fission but also basically every other energy source, is the waste material it leaves behind.
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.
0コメント