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The first artificial nuclear reactor, the Chicago Pile-1, used nuclear graphite as a moderator. Graphite-moderated reactors were involved in two of the best-known nuclear disasters: an untested graphite annealing process contributed to the Windscale fire (but the graphite itself did not catch fire), while a graphite fire during the Chernobyl ...
There have been two major accidents in graphite-moderated reactors, the Windscale fire and the Chernobyl disaster. In the Windscale fire, an untested annealing process for the graphite was used, causing overheating in unmonitored areas of the core and leading directly to the ignition of the fire. The material that ignited was the canisters of ...
The fire was in Unit 1 of the two-pile Windscale site on the north-west coast of England in Cumberland (now Sellafield, Cumbria). The two graphite-moderated reactors, referred to at the time as "piles", had been built as part of the British post-war atomic bomb project. Windscale Pile No. 1 was operational in October 1950, followed by Pile No ...
No air-cooled reactors have been built since. The final removal of fuel from the damaged reactor was scheduled to begin in 2008 and to continue for a further four years. Inspections showed that there had not been a graphite fire, and the damage to the graphite was localised, caused by severely overheated uranium fuel assemblies nearby. [89]
Water (sometimes called "light water" in this context) is the most commonly used moderator (roughly 75% of the world's reactors). Solid graphite (20% of reactors) and heavy water (5% of reactors) are the main alternatives. [1] Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.
Graphite moderator blocks in the RBMK can be repaired and replaced in situ, unlike in the other current large graphite moderated reactor, the advanced gas-cooled reactor. [48] Longitudinal cutting in some of the graphite columns during lifetime extension refurbishment work can return the graphite stack to its initial design geometry. [49]
The X-10 Graphite Reactor was the world's second artificial nuclear reactor after Chicago Pile-1 and was the first reactor designed and built for continuous operation. [47] It consisted of a huge block, 24 feet (7.3 m) long on each side, of nuclear graphite cubes, weighing around 1,500 short tons (1,400 t), that acted as a moderator.
Peach Bottom Unit 1 was an experimental helium-cooled, graphite-moderated reactor. It operated from 1966 to 1974. Peach Bottom 2 and 3, General Electric boiling water reactors, went on-line in 1974, and are still in operation on the 620-acre (2.5 km 2) site today.