Today in class, we discussed the properties of Uranium, as well as how it is used in nuclear power plants.
Of all the naturally occurring atoms on Earth, Uranium is the largest in size. Because of its large size, Uranium is very unstable, and very reactive. In order to stabilize itself, Uranium (and any other large, unstable atoms) must release matter and/or energy. There are two types of matter an atom can release: alpha and beta. Alpha Decay occurs when an atom releases a proton or neutron to stabilize itself, and Beta Decay occurs it releases electrons. An atom can also release energy, or Gamma Rays. Unstable atoms naturally release one, two, or all of these three, causing the atom to decay over time. Given time, Uranium will naturally decay until it becomes the stable lead atom. An atom is considered radioactive when it constantly releases matter or energy.
A Half Life of an atom is the time period that it takes for half a sample of that atom to decay into a nonradioactive, or stable state. Uranium 235 has a half life is 710 million years.
Because Uranium is the largest atom, and therefore the most likely to decay, it is also the most radioactive of all the atoms. This comes in handy with nuclear power plants, which use Nuclear Reactors to create energy from Uranium.
When finding the Uranium to use in nuclear reactors, the only isotope of Uranium that can be used is Uranium-235. An Isotope is an atom that has the same number of protons, but a different number of neutrons. The number that follows the atom name (235) is the number of neutrons that the particular isotope has. Although Uranium-235 is the main source of fuel used, it is also one of the smallest Uranium amounts found in nature (less than 1%).
Nuclear Fission is the atomic process that powers nuclear reactors. Nuclear fission occurs when the nuclei of a large atom is hit by a neutron, and therefore split, producing a split atom and another free neutron. A Nuclear Fission Chain Reaction occurs when the neutron that was produced by the original nuclear fission hits another atom’s nucleus, producing more free neutrons, and therefore the chain continues.
The Chain Reaction produces a LOT of heat, which is used to power the nuclear reactors. In nuclear reactors, Fuel Rods (Uranium) and Control Rods (neutron control) are placed in a containment building. The fuel rods are placed in a huge vat of water, and when the chain reaction occurs (the speed of which can be controlled by the control rods, which absorb or release neutrons) the water is heated. The water in the vat then boils, turning into steam. The steam is sent through Steam Pipes/Heat Exchangers, which use the steam to spin a Turbine, creating energy. All the steam then travels to the cooling tower, where excess heat is vented through steam stacks. There are no pollutants released from nuclear Power plants. Here is a cite explaining nuclear reactors in more detail: http://www.howstuffworks.com/nuclear-power.htm
After fuel rods are used, they are still very radioactive, and must be placed securely in storage for hundreds of years. If not placed in storage, radioactivity can be very harmful to human health. Released alpha particles are not strong enough to get past the outer layer of human skin, but can cause skin cancer. Beta particles are a little stronger, and can pass to the epidermal, or inner layer of skin. Gamma Rays are nasty, and can pass through any type of tissue, bone included. This is useful for treating diseases like cancer, but harmful in any other way.
I hope this helps!