Nuclear Energy Overview

Topics: Nuclear power, Uranium, Nuclear fission Pages: 21 (2590 words) Published: September 4, 2014


Nuclear Energy Overview:

The Basics of Nuclear Energy — An Overview
Nuclear power uses the energy created by controlled nuclear reactions to produce electricity.

Fission

Nuclear Fission
Source: Atomicarchive.com at: http://www.atomicarchive.com/Fission/Fission1.shtml

The most commonly used nuclear reaction for power generation is nuclear fission. Nuclear fission is the splitting of an atom's nucleus into parts (lighter nuclei that are different from the parent and neutrons) by capturing a neutron. Nuclear fission produces heat (also called an exothermic reaction), because if you add all the masses together of the products of reaction you do not get the starting mass. That loss of mass is the heat and electromagnetic radiation produced during fission, and it produces large amounts of energy that can be utilized for power. Fission produces neutrons which can then be captured by other atoms to continue the reaction (chain reaction) with more neutrons being produce at each step. When a reaction reaches critical mass, the reaction becomes self sustaining. If too many neutrons are generated, the reaction can get out of control and an explosion can occur. To prevent this from occurring, control rods that absorb the extra neutrons are interspersed with the fuel rods. Uranium-235 is the most commonly used fuel for fission. Nuclear fission can produce 200 MeV of energy.

An Example of a Chain Reaction
Source: Atomicarchive.com at: http://www.atomicarchive.com/Fission/Fission1.shtml

Fusion

Nuclear Fusion
Source: Atomicarchive.com at: http://www.atomicarchive.com/Fusion/Fusion1.shtml

Nuclear fusion is another method to produce nuclear energy. Two light elements, like tritium and deuterium, are forced to fuse and form helium and a neutron. This is the same reaction that fuels the sun and produces the light and heat. Unlike fission, fusion produces less energy (~18 MeV), but the components are more abundant and cheaper than uranium.

Radioactive Decay
Radioactive Decay occurs when an unstable nucleus losses a particle and electromagnetic radiation. This decay produces a daughter atom that may also be unstable and occurs at an average rate, which is called the half-life (the amount of time it takes for one half of the parent material decay to the daughter). While radioactive decay has been utilized for deep-space probes (using plutonium-238 pellets), it does not create the amount of energy that fission or fusion does and therefore it has limited potential for large power-producing facilities.

Radioactive Decay
Source: NRC at http://www.nrc.gov/reading-rm/basic-ref/glossary/full-text.html

How Uranium is Enriched

Uranium Enrichment

Yellowcake Uranium
Source: Photo courtesy of Cogema, Inc

When the uranium leaves the ISL facility or a uranium mill, it is in the form of uranium oxide (U3O8) or what is commonly called yellowcake. This uranium oxide is not the form of uranium that is used by nuclear reactors (UO2), therefore it has to be refined or enriched for civilian use. The uranium for power plants is processed to enrich U-235 (about U Isotopes) with respect to the other isotopes of uranium. For reactor grade this is approximately 3-5% U-235. Weapons grade uranium has greater than 90% U-235, is the metallic form of uranium and is referred to as highly enriched uranium (HEU). The enrichment process involves:

converting the uranium oxide (solid) to uranium hexafluoride (UF6), a gas, the UF6 is then enriched with respect U-235 and converted to UO2, and this process creates depleted uranium (DU) which has more U-238 and enriched uranium which has more U-235 than natural uranium. How is uranium enriched?

To separate the isotopes of uranium, you have to expend a lot of energy to create nuclear fuel. Because the two isotopes are almost the same size and weight, those slight differences have to be exploited in the separation process using similar techniques over and over, finally...
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