Method of isolating a nuclear reactor or other large structures

A method of entombing a nuclear reactor where the reactor with its bio-shield remains intact. An access shaft, several lateral adits, and several chambers below the reactor location are excavated to provide access at underground locations below the reactor. A main cavern is excavated and lined with a lower base, surrounding sidewall, and a roof structure which has thermal plate at its lower surface. Freeze/thaw pipes are erected vertically in the cavern, and these extend through the earth strata below the cavern into a lower operating chamber. The cavern is filled with water which is then frozen, and the earth strata immediately below the reactor and are isolated from the surrounding earth strata and structure. The upper surface of the ice block is melted by the thermal plate in a controlled manner to lower the reactor, after which concrete and other material is used to fill all of the man made cavities and thus entomb the reactor.