Nuclear fission works by by bombarding an unstable atom (most commonly a heavy Uranium or Plutonim atom) with a free neutron, causing it to briefly add a neutron to its nucleus. However, this bombardment renders the new nucleus unstable, and the nucleus splits into both lighter elements and releases free neutrons and massive amounts of energy. This starts a chain reaction, as these free neutrons then bombard other atoms and release even more energy.
The below diagram shows what happens when you bombard a uranium-235 nucleus with a free neutron. It turns into a uranium-236 nucleus but soon splits into krypton and barium while releasing three free neutrons, which go on to bombard other uranium-235 nuclei. Massive amounts of energy are released by these free neutrons, and the reaction produces photons (the explosions create fireballs that light up the entire sky) that release energy in the form of gamma rays. In a bomb, all of this happens at once in a manner similar to the example below. In a fission reactor, this reaction is controlled so that for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus.
Simple diagram of nuclear fission. Credit: Wikipedia User Fastfission
Fission Power
Reactors and Cooling Towers at the Susquehanna Steam Electric Station. Credit: US Government
The general premise behind nuclear power is to control a nuclear reaction so that it heats water into steam and drives a turbine, producing electricity. To do this, enriched uranium is generally formed into 2.5 cm long pellets with a dime-size diameter. These pellets are lined up into long rods, which are then collected together into bundles. These bundles are submerged in water inside a pressure vessel to prevent them from overheating. A nuclear meltdown is when these rods overheat, melt, and create a steam explosion. It is NOT a massively uncontrolled reaction that causes runaway fission to occur and and fry the city.
Control Rods. Credit: Nic Ransby
In addition to the water, control rods are used to prevent a meltdown. These rods are made of elements that are non-fissionable and can absorb neutrons. Boron, silver, indium, and cadmium are a few examples. These rods are inserted into the bundles using a mechanism that can raise or lower them, and raising or lowering the rods allows the operators to control the rate of the reaction. The control rods are raised out of the uranium bundle to increase the rate of reaction by allowing fewer neutrons to be absorbed and vise versa.
Finally, the water is heated to steam and then spins a turbine. This turbine is connected to a generator, and when the turbine spins, it also spins the generator, producing power. You can’t hold on to that steam forever, so you gotta send it through these huge cooling towers sooner or later.
If fission and nuclear waste storage is executed in a safe and secure manner, it has the potential to bring clean power to us for generations to come. However, a malfunctioning nuclear plant can be disastrous to people and the environment, so every precaution must be taken to ensure that we are using nuclear power in the safest way possible.
Written by Charlie Phillips – charlie.weathertogether.net. Last updated 12/1/2017