atomic pile - Wiktionary, the free dictionary

From the fact that the first nuclear reactor, at the University of Chicago in 1942-1943, was literally constituted by a tall pile (heap) of graphite moderator blocks. Compare also charcoal pile, a traditional improvised kiln used in charcoal making, which uses a similar basic design to contain a volatile process. The fact that English pile also is related to French pile (“battery”) (with senses of a collection of components and a power source, often both coinstantiated) has also been noted as an interesting nexus of word roots and semantic themes.

atomic pile (plural atomic piles)

1. (nuclear physics) An early nuclear reactor fueled by uranium and moderated with graphite.
   • 1948 The second atomic pile at the Government's research establishment at Harwell […] is expected to be brought into use this summer – The Times (London), May 11 1948, pg 2 col A

• nuclear pile

• nuclear stockpile (semantically quite different from a nuclear pile)

• epitomical