chain reactor vs atomic pile

chain reactor and atomic pile both are nouns.

Word	Noun	Adjective	Verb	Adverb
chain reactor	Yes	No	No	No
atomic pile	Yes	No	No	No

As nouns, chain reactor and atomic pile are synonyms defined as:

chain reactor and atomic pile: a nuclear reactor that uses controlled nuclear fission to generate energy

Other synonyms of chain reactor include atomic reactor, pile.

chain reactor (noun)	atomic pile (noun)
a nuclear reactor that uses controlled nuclear fission to generate energy	a nuclear reactor that uses controlled nuclear fission to generate energy