Reactor Types

1.Pressurized Water Reactors (PWR)

PWRs use nuclear-fission to heat water under pressure within the reactor. This water is then circulated through a heat exchanger (called a "steam generator") where steam is produced to drive an electric generator. The water used as a coolant in the reactor and the water used to provide steam to the electric turbines exists in separate closed loops that involve no substantial discharges to the environment. Of the 104 fully licensed reactors in the United States, 69 are PWRs.

 www.eia.doe.gov/cneaf/nuclear/page/nuc_reactors

/pwr.html

 

2.Boiling Water Reactors (BWR)

The remaining 35 operable reactors in the United States are BWRs.  BWRs allow fission-based heat from the reactor core to boil the reactor’s coolant water into the steam that is used to generate electricity. General Electric built all boiling water reactors now operational in the United States. Areva NP and Westinghouse BNFL have each designed BWRs.www.eia.doe.gov/cneaf/nuclear/page/nuc_

reactors/bwr.html

 

3.Pressurized Heavy Water Reactors (PHWR)

PHWRs have been promoted primarily in Canada and India, with additional commercial reactors operating in South Korea, China, Romania, Pakistan, and Argentina. Canadian-designed PHWRs are often called "CANDU" reactors. Siemens, ABB (now part of Westinghouse), and Indian firms have also built commercial PHWR reactors. Heavy water reactors now in commercial operation use heavy water as moderators and coolants.  The Canadian firm, Atomic Energy of Canada Limited (AECL), has also recently proposed a modified PHWR (the ACR series) which would only use heavy water as a moderator.  Light water would cool these reactors. No successful effort has been made to license commercial PHWRs in the United States. PHWRs have been popular in several countries because they use less expensive natural (not enriched) uranium fuels and can be built and operated at competitive costs. The continuous refueling process used in PHWRs has raised some proliferation concerns because it is difficult for international inspectors to monitor.  Additionally, the relatively high Pu-239 content of PHWR spent fuel has also raised proliferation concerns.  The importance of these claims is challenged by their manufacturers.  PHWRs, like most reactors, can use fuels other than uranium and the ACR series of reactors is intended to use slightly enriched fuels.  Particular interest has been shown in India in thorium-based fuel cycles.

 http://www.eia.doe.gov/cneaf/nuclear/page/nuc_

reactors/china/candu.html

 

4.High Temperature Gas-cooled Reactors (HTGR):

HTGRs are distinguished from other gas-cooled reactors by the higher temperatures attained within the reactor. Such higher temperatures might permit the reactor to be used as an industrial heat source in addition to generating electricity.  Among the future uses for which HTGRs are being considered is the commercial generation of hydrogen from water.  In some cases, HTGR turbines run directly by the gas that is used as a coolant.  In other cases, steam or alternative hot gases such as nitrogen are produced in a heat exchanger to run the power generators.  Recent proposals have favored helium as the gas used as an HTGR coolant.  The most famous U.S. HTGR example was the Fort Saint Vrain reactor that operated between 1974 and 1989. Other HTGRs have operated elsewhere, notably in Germany. Small research HTGR prototypes presently exist in Japan and China. Commercial HTGR designs are now promoted in China, South Africa, the United States, the Netherlands, and France though none of these is yet commercially marketed.  The proposed Next Generation Nuclear Plant (NGNP) in the U.S. will most likely be a helium-based HTGR, if it is funded to completion.

http://www.nuc.berkeley.edu/designs/mhtgr/mhtgr.

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5.Sodium-cooled reactors reactors

Sodium-cooled reactors are included on this list primarily because of proposals to build a Toshiba 4S reactor in Alaska. Sodium-cooled reactors use the molten (liquid) metal sodium as a coolant to transfer reactor generated heat to an electricity generation unit.  Sodium-cooled reactors are often associated with “fast breeder reactors (FBRs)” though this is technically not the case in the 4S design.