containment building

A containment building, in its most common usage, is a steel or concrete structure enclosing a nuclear reactor. It is designed to, in any emergency, contain the escape of radiation despite pressures in the range of 60 to 200 psi ( 410 to 1400 kPa). The containment is the final barrier to radioactive release, the first being the fuel ceramic itself, the second being the metal fuel cladding tubes, the third being the reactor vessel and coolant system.
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A structure designed to prevent the accidental release of radioactive materials.