Nuclear Power Reactors - The Diigo Meta page

• 20 May 08
  

  Erik Dreisbach

  science 8th environment

• 17 Jul 07
  

  Mrs. H

  nuclear power environmental science

• 16 Aug 06
  

  Hayley

  nuclear power reactors

  • In a BWR, water boils inside the reactor itself, and the steam goes directly to the turbine-generator to produce electricity. Here, too, the steam is condensed and reused.
  • In a PWR, the heat is removed from the reactor by water flowing in a closed pressurized loop. The heat is transferred to a second water loop through a heat exchanger. The second loop is kept at a lower pressure, allowing the water to boil and create steam, which is used to turn the turbine-generator and produce electricity. Afterward, the steam is condensed into water and returned to the heat exchanger. 
  • Heat is produced in a nuclear reactor when neutrons strike Uranium atoms causing them to fission in a continuous chain reaction. Control elements, which are made of materials that absorb neutrons, are placed among the fuel assemblies. When the control elements, or control rods as they are often called, are pulled out of the core, more neutrons are available and the chain reaction speeds up, producing more heat. When they are inserted into the core, more neutrons are absorbed, and the chain reaction slows or stops, reducing the heat. 
      Most commercial nuclear reactors use ordinary water to remove the heat created by the fission process. These are called light water reactors. The water also serves to slow down, or "moderate" the neutrons. In this type of reactor, the chain reaction will not occur without the water to serve as a moderator. In the United States, two different light-water reactor designs are currently in use, the Pressurized Water Reactor (PWR) and the Boiling Water Reactor (BWR). 
     
  • heavy steel pressure vessel surrounding a reactor core. The reactor core contains the Uranium fuel. The fuel is formed into cylindrical ceramic pellets about one-half inch in diameter, which are sealed in long metal tubes called fuel tubes. The pins are arranged in groups to make a fuel assembly. A group of fuel assemblies forms the core of the reactor.
  • the fission of Uranium atoms in the reactor provides the heat to produce steam for generating electricity.

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