March 17th 2011
Author: Tina Wolf

Harnessing nuclear energy has been around since the 50s, when the first nuclear power plant to generate electricity for commercial use was opened on June 26, 1954 in Obninsk, Russia. As of January 19, 2011, there are 442 nuclear plants in operation in 30 countries throughout the world. There are 65 more plants in development in 16 countries.

How Nuclear Power Works

In order to understand how a nuclear meltdown can occur, it is important to have a basic understanding of how nuclear power is generated. When broken down, the process of creating nuclear power is quite simple. The process works in a similar fashion to other power plants. Water is heated to produce steam. The steam is used to turn turbines. The turbines then convert this into stored energy. The stored energy can then be distributed as electricity wherever needed. The method of heating the water is different in nuclear reactors, and more efficient.

Generally speaking, a controlled nuclear reaction is responsible for heating water to a boiling point in a nuclear reactor. Enriched nuclear material (Uranium or Plutonium) is shaped inside rods and lowered into a mass of water. Neutrons released by the materials are absorbed by an atom’s nucleus, and then split in two. The energy released by this process heats up the surrounding water, and produces the steam necessary to turn the turbines, which convert it to stored energy. In order to control the amount of energy released, control rods made of neutron absorbing material can be lowered into the water, thereby capturing neutrons released by the nuclear material. They can be lowered to reduce the amount of energy released, and raised to increase the amount of energy released. Lowering enough control rods can completely shut down the process of heating the water.

Conversely, when there are no rods controlling the neutrons, the process continues unabated and allows the atoms to split at accelerated rates, which produce too much heat. Even with control rods present, cold water must constantly be pumped in and around the rods in order to keep temperatures at a stable level.

Mechanics of a Nuclear Meltdown

The easiest way to picture a nuclear reactor is to consider how pressure cookers work. Pressure cookers contain boiling water with steam, as the temperature inside the pot rises and the pressure rises as well because there is no way for the steam to escape. When cooling failures occur inside a nuclear reactor, an excess of steam can build up inside the core and cause it to explode. One way to release the steam from the core of a reactor is through a pressure valve. However, doing this causes the release of radioactive material as well.

With lack of coolant inside the core, zirconium metal will begin reacting with the heat and turn into zirconium oxide. This process creates more heat and causes the zirconium coating covering the fuel rod to begin to melt. When the whole system becomes overheated, the fuel rods, control rods, and radioactive by-products of fission become a molten blob that is so hot it can melt through anything. This is considered full meltdown.

Dangers of a Meltdown

The radioactive “blob” that is created by a full meltdown is capable of melting through any type of material, which can lead to contamination of the surrounding land and ground water. Explosions that can occur from meltdowns can release steam and radioactive gas into the atmosphere. Some of the radioactive by-products that are produced by these explosions are Iodine-131 and Caesium-137, which can also be released into the atmosphere. The farther away from the incident of a nuclear meltdown, the more diluted the by-products of the reaction will be.

Since the early 50s when nuclear power started being used, there have only been two large-scale nuclear meltdowns that have occurred, these were at the Chernobyl Nuclear Power Plant and at Three Mile Island. There have been less than 10 partial core meltdowns around the world.

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