Core

• (anthropology, archaeology)

1. a blocky nucleus of stone from which flakes or blades have been removed.
2. a column or lineal sample of materials obtained by "coring" the ground, trees, etc.

• (chemistry) The central portion of a nuclear reactor containing the fuel elements, moderator, neutron poisons, and support structures. Source: U.S. Nuclear Regulatory Commission
• (environment) The uranium-containing heart of a nuclear reactor, where energy is released.
  Source: Terms of the Environment