ExtremeTech explains: How does nuclear energy work?

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Nuclear power is ultimately not all that unlike from coal power: Dig upwardly a finite resource and apply free energy in a very specific fashion to unleash a much greater amount of free energy stored within that fuel. For coal, nosotros apply a small amount of heat to coal to release energy held in its chemical bonds. For uranium, we apply a specific sort of radiation to release the free energy stored in its nuclear bonds — and that's a far more than lucrative target, if you tin go at information technology.

To become a lifetime'south supply of ability from coal, the average American will require the creation of tens of tons of solid and airborne waste. The aforementioned figure for nuclear reactors sits effectually five kilograms of spent nuclear fuel. To understand how nosotros go at that sort of energy density, we'll have to become back to the very outset of the planet.

In the World'south early history, when it was billions of years younger and thus the elements that etch information technology were billions of years closer to their dates of birth in various supernovae, the planet had a very different assortment of radioactive isotopes. Radiation is only energy that atoms spontaneously throw off due to instability — they get rid of whatever is making them unstable until they lose enough and become stable. This procedure is known as radioactivity, and as the Earth aged, less stable isotopes threw out energy more than chop-chop and thus decayed more quickly, too. Since its nativity, the overall ratio of isotopes on Earth has shifted toward lower-energy versions of our heaviest elements.

Nuclear centrifuges

A nuclear centrifuge.

That'due south a problem if you're looking to break those nuclear bonds in a process called fission, because nuclear bonds are stiff. In order to pause atoms and release some of the precious free energy they contain, nosotros need elements that are already highly energetic and near to breaking. When nosotros dig upwards a sample of uranium, it'southward going to exist a mixture of fissile and not-fissile versions. That's where the concept of enrichment comes in.

Enrichment is just the process of concentrating one isotope out of a mixture of isotopes, usually by weight thanks to loftier-speed nuclear centrifuges. These centrifuges subject uranium to enormous centrifugal force, separating materials according to the mass difference caused past the presence or absenteeism of just a few extra neutrons per atom. For an overall sample of uranium to become fissile, we accept to enrich it to the bespeak that the fissile isotopes make upwards 3-5% of the overall sample. In the World'south early history, natural samples would have had a high enough fissile portion while sitting in the basis.

nuclear power 2 Once you lot have a sample that's theoretically capable of sustaining fission, you so have to become that fission started — which is actually the like shooting fish in a barrel function. Decaying uranium is constantly throwing out radiation of various kinds, and about importantly for our purposes that includes high-energy neutrons. These neutrons are quite heavy by atomic standards, and when they impact an unstable atom they tin can partially blast that atom apart, releasing more neutrons that so hit more atoms, and so on. To get fissile samples to spit neutrons at one another, all you lot take to do is bring two such samples within neutron-spitting distance of one another.

Hither, nosotros come against the distinction between two types of nuclear reactor: calorie-free versus heavy water. It'southward a scrap counterintuitive, simply it turns out that if a neutron is going besides fast, information technology can't properly impact atoms and begin a fission reaction. So the final step in creation that reaction is filling the space between the two fissile samples with a neutron "moderator." In "light water" reactors we utilise normal h2o, which slows neutrons to the point that fission can brainstorm in samples at our 3-5% enrichment threshold.

nuclear power 3

In "heavy water" reactors, we use a super-expensive version of water that contains the heavy hydrogen isotope deuterium (D_twoO instead of H₂O), which slows the neutrons downward even more. By using a heavy h2o moderator, we can load the reactor with far less enriched nuclear samples — a nice trick, though the incredible expense of filling the tank with heavy h2o in the get-go place potentially washes out any cost gains.

In either instance, we use a moderator to capture heat from the reactor and transfer that heat to a split reservoir of water, which boils into steam and turns a turbine, creating electricity.

Nuclear Cooling Towers Near other reactor designs are evolutionary, within this space. Molten table salt reactors use, well, molten salt as its coolant, assuasive higher operating temperatures without greatly increasing the force per unit area of the system. Many meet potential in the use of thorium every bit a nuclear fuel, as opposed to uranium or plutonium, as it creates less dangerous waste and doesn't present as lucrative a target to terrorist.

All sorts of condom measures have been added over the years, most encouragingly "passive" measures that don't require Fukushima-style diesel generators that could hypothetically fail. Many modern reactors, for instance, have what's called a "freeze plug" at the lesser of the reactor that is kept solid only through the input of free energy; in the example of a power failure, this plug melts, and the nuclear fuel falls down into a physical storage surface area for safety retrieval at a afterward date.

Stored nuclear fuel rods glow an eery, distinctive blue.

Well-nigh new spent fuel rods ("waste") is currently stored on-site at the reactors that created it.

Of class, lurking behind whatever statement about nuclear power is the prospect of a nuclear disaster. The big danger of nuclear power comes from something nosotros already discussed: Once you have two fissionable samples with a suitable neutron moderator in between, the samples will undergo fission on their own, due to their natural backdrop. In fact, in one case the conditions for fission accept all been met, it'south hard to stop a nuclear reaction. And not stopping a nuclear reaction inside a closed pressure vessel leads to higher and higher temperatures, and eventually meltdown.

Nuclear meltdown is when the rut inside the reactor is allowed to get and so slap-up that the nuclear fabric creating that heat melts itself, and molten, still-fissioning uranium is a serious pain in the ass. To this day, researchers aren't totally sure where Fukushima's melted down nuclear samples have concluded up inside the reactor, or what damage they've caused. It'southward ultimately non the worst thing that can happen at a reactor — the worst is what happened at Chernobyl, with a huge conventional explosion that let all the stuff happeningwithin the reactor out to affect the surrounding environment. The meltdown at Fukushima, unbelievably energetic though it was, stayed more often than not contained within the reactor and thus did far, far less damage.

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