A containment vessel, as in a nuclear reactor: a large container or containment building intended to isolate its contents from the outside.

container

strong, sturdy, indestructible; hardy

sturdiness, indestructibility

store, lock up / contain (nuclear materials) / (computing) put into memory

containment (of nuclear materials) / storage of equipment / (computing) putting into computer memory

extraordinary, unusual

emergency

very; extremely / exceedingly; tremendously

stairs used in emergencies