so nuclear reactors generate power by splitting atoms but what actually splits these atoms?
In: 6
An atom randomly releases a neutron. That neutron hits another atom and makes it unstable. It splits releasing energy and more neutrons. Those neutrons carry on the chain reaction
Some atoms are unstable and so naturally want to fall apart. An example of such an atom is Uranium. When an unstable atom like Uranium falls apart, it releases energy/neutrons. This natural release of energy is what we call “radioactivity”.
So if you pile up a whole bunch of Uranium together, some atoms will randomly decay releasing neutrons. These neutrons can then strike other uranium atoms, causing THOSE to split apart, releasing more neutrons and thus perpetuating the cycle of splitting atoms.
Now, it is a little bit more complicated than that. It’s a misconception that the neutrons “shatter” the atoms upon impact. What actually happens is that the neutron is absorbed by a Uranium atom, making it even MORE unstable and thus more likely to naturally decay. This is why (if you’ve ever seen the TV show “Chernobyl” they kept referring to the graphite as a “neutron flux moderator”. The graphite *slows down* (moderates) the neutrons released from decayed Uranium nuclei, making them *more likely* to be absorbed by other Uranium atoms.
Watch uranium chasing the dragons tale it’s a good show and explains how uranium is unstable meaning it is in a constant state of decay changing into new elements each time these atoms decay or loose protons and neutrons cesium is one of the daughter’s of uranium and cesium 137 is very unstable by adding a single proton to it you cause it to split apart into two different elements loosing part of the original mass in the process by shooting off extra protons. This also creates heat. Someone had the diabolical idea to put a bunch of it together and then it causes a chain reaction splitting other atoms untill you get a nuclear detonation. Someone figured out that different elemental daughter’s of uranium could be harnessed and controlled in a fission process and the much more controlled and slower reaction moderated by things like graphite we can create steam and turn turbines to make power. Instead of blowing up.
Short answer is idk but adding a proton makes them split and shoot off extra protons that cause chain reactions 1 hits two two hits 4. 4 hits well you get it we can controll this reaction in fission process with reactors
Radioactive fuel can be arranged in such away that it reacts with itself and releases more radiation than under normal circumstances. The radiation heats water which turns into steam which is used to spin turbines which generate electricity
Atomic nuclei consist of roughly the same number of neutrons (no electrical charge) and protons (one positive charge) glued together by the strong force – which has to overcome the repulsion between protons as identical charges repel each other and want to fly away.
If there are lots of protons as in heavy elements like uranium, plutonium, thorium, &c., that “gluing” can become strained and the nucleus unstable. This is radioactivity, the kernel splits and the element decays into two lighter kernels (to simplify; there are other possible processes), i. e. different elements. Uranium, for example, can split into Krypton and Barium.
So the splitting, radioactivity, is a natural property of matter.
In a nuclear reactor things are arranged in such a way that these spontaneous splits get amplified (but not too much or you’d have an A-bomb!): the fission also emits neutrons which, being neutral, can go hit other nuclei and trigger another split in a nearby unstable nucleus. And you have a chain reaction.
Take an atom of uranium-235 — a nearly-stable isotope. Hit it with a slow-moving neutron, which it absorbs, becoming an atom of U-236, in an excited state. One time in seven, it releases some energy, and settles down to becoming another nearly-stable atom. But the other six times….
The positively-charged protons in an atomic nuclei want to escape from each other, driven by their mutual electrical repulsion. However, the protons and neutrons are held together by the strong nuclear force. Large nuclei can be in such an excited state that, instead of spherical, they become oval-shaped. From there, they can loose energy by splitting — fissioning — into two smaller nuclei. The lost energy shows up as the two halves speeding away from each other, plus a few neutrons doing the same. These two new atoms interact with other atoms, raising the temperature of the general environment.
Radioactive atoms have a nucleus which is unstable. The nucleus can rearrange itself spontaneously and this rearrangement will release energy, and often a particle as radiation.
The common types of radioactive decay are alpha (a cluster of 2 protons and 2 neutrons gets kicked out of the nucleus), beta (a neutron turns into a proton and electron, and the electron gets kicked out) and gamma (the protons and neutrons in the nucleus rearrange into a more compact shape releasing energy as “light”).
However, those are not the only ways. There is a very rare way called fission, where the nucleus splits into two large chunks which then recoil away from eqhx other with massive energy. This does happen very occasionally in some atoms like uranium, but it is not usually significant.
However, you can make new atoms by firing neutrons at existing nuclei. If a neutron hits a nucleus, there is a chance that the neutron will get sucked in and become a new part of the nucleus. In some cases, the new atom is radioactive, potentially extremely radioactive and the new nucleus decays very quickly.
It turns out that if you hit a natural uranium 235 atom there is a high chance that the neutron will get captured, and the new energised and wonky uranium nucleus will almost instantly decay by fission. This strange and rare property means that it is possible to trigger fission by neutrons, and therefore fission is controllable.
The other interesting thing is that although the main product of fission is two big chunks of nucleus, there are also a number of little shrapnel pieces, which are almost always neutrons.
So, not only is fission controllable, fission can trigger more fission, in other words, a chain reaction.
By changing how many neutrons are available to continue the chain reaction (by moving uranium atoms apart so that the neutrons miss, or by adding other atoms which capture neutrons but don’t fission) the rate of the chain reaction can be controlled.
This means that all you need to get a chain reaction going is to put enough concentrated uranium together in one block, that when one atom fissions, more than 1 neutron from the fission triggers another fission. This is called a critical mass. Below a critical mass, too many neutrons escape out of the block into the air and the chain reaction doesn’t chain. Keep adding uranium and the chain reaction will start once a spontaneous fission occurs.
Practical control is a bit more difficult. Nuclear reactors use other atoms to control the speed of neutrons (slow neutrons are better for triggering fission) and to absorb neutrons. Essentially, they have a combination of uranium and neutron absorbers packed into metal cans. The core is built with more than a critical mass of uranium, but with more absorbers than needed to stop the chain reaction. Then to start, the cans with the absorbers in are very carefully pulled out of the core. Once enough absorbers are removed, then the chain reaction starts. Put the absorbers back and the chain reaction stops.
Latest Answers