As of April 2009, there are 441 nuclear power plants worldwide, according to the World Nuclear Association (WNA). The U.S. Environmental Protection Agency reports roughly 20 percent of U.S. energy originates from the more than 100 U.S. nuclear power plants. The U.S. currently uses two reactor types: pressurized water reactors and boiling water reactors. A new design currently used in Japan, France and Russia is expected to become the primary worldwide plant design in the next two decades, according to the WNA.
Pressurized Water Reactors
Pressurized water reactors are the most common reactor in use today, according to the WNA. Pressurized reactors contain enriched uranium fuel sources that are used to heat highly pressurized water that generates steam. This steam is used to turn a turbine that generates electricity collected and used in the power grid. Pressurized water reactors also use water as a cooling device. Secondary cooling measures to prevent overheating (meltdown) include adding boron to the system.
Boiling Water Reactors
Boiling water reactors are similar to pressurized water reactors. Boiling water reactors are simpler in design and less expensive but the required maintenance makes up for this initial cost savings, reports the WNA. The steam in boiling water reactors is irradiated, thus radiological protection is needed for the electric turbine and any maintenance within the reactor. Luckily, the water radioactivity is short lived. Boiling water reactors utilize enriched uranium fuel.
Fast Neutron Reactors
Fast neutron reactors use plutonium and uranium as fuel. Natural fuels in place of enriched fuels lower nuclear power plant fuel costs; however, fast neutron reactors are fairly expensive to construct, according to the WNA. Fast neutron reactors get as much as 60 times the energy from natural fuels as other reactors. Of the 441 nuclear plants worldwide, four are fast neutron plants. The WNA expects a rise in fast neutron power plant design and implementation around the globe.