Graphite-moderated reactor

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"Graphite reactor" directs here. for the graphite reactor at Oak Ridge National Laboratory, see X-10 Graphite Reactor.

A graphite reactor is a nuclear reactor that uses carbon as a neutron moderator, which allows un-enriched uranium to be used as nuclear fuel.

The very first artificial nuclear reactor, the Chicago Pile-1, used graphite as moderator. Two graphite moderated reactors were involved in major accidents: An untested graphite annealing process contributed to the Windscale fire (but the graphite itself did not caught fire), and a graphite fire during the Chernobyl disaster contributed to the spread of radioactive material (but was not a cause of the accident itself).

Types

There are several types of graphite-moderated nuclear reactors that have been used in commercial electricity generation:

History

The first artificial nuclear reactor, Chicago Pile-1, a graphite-moderated device that produced a microscopic amount of heat, was constructed by a team led by Enrico Fermi in 1942. The construction and testing of this reactor (an "atomic pile") was part of the Manhattan Project. This work led to the construction of the X-10 Graphite Reactor at Oak Ridge National Laboratory, which was the first nuclear reactor designed and built for continuous operation, and began operation in 1943.

Accidents

There have been several major accidents in graphite moderated reactors, with the Windscale fire and the Chernobyl disaster probably the best known.

In the Windscale fire, an untested annealing process for the graphite was used, and that contributed to the accident – however it was the uranium fuel rather than the graphite in the reactor that caught fire. The only graphite moderator damage was found to be localized around burning fuel elements.12

In the Chernobyl disaster the graphite was not a contributing factor to the cause of the accident, however a graphite fire after the main event contributed to the spread of radioactive material. A massive power excursion in Chernobyl during a mishandled test had led to the rupture of the reactor vessel and a series of steam explosions, which destroyed the reactor building. Now exposed to both air and the heat from the reactor core, the graphite moderator in the reactor core caught fire, and this fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area.3

In addition, the French Saint-Laurent Nuclear Power Plant and the Spanish Vandellòs Nuclear Power Plant – both UNGG graphite-moderated natural uranium reactors – suffered major accidents. Particularly noteworthy are an partial core meltdown on 17. October 1969 and an heat excursion during graphite annealing on 13. March 1980 in Saint-Laurent, which were both classified as INES 4. The Vandellòs NPP was damaged on 19. October 1989, and an repair was considered not economic.

References

  1. ^ "Meeting of RG2 with Windscale Pile 1 Decommissioning Project Team" (PDF). Nuclear Safety Advisory Committee. 2005-09-29. NuSAC(2005)P 18. Retrieved 2008-11-26. 
  2. ^ Marsden, B.J.; Preston, S.D.; Wickham, A.J. (8–10 September 1997). "Evaluation of graphite safety issues for the British production piles at Windscale]". AEA Technology (IAEA). IAEA-TECDOC—1043. Retrieved 13 November 2010. 
  3. ^ "Frequently Asked Chernobyl Questions". International Atomic Energy Agency – Division of Public Information. May 2005. Retrieved 23 March 2011. 







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