Abstract: The passive system is suitable for prefabrication and installation as a variable volume unit enclosing industrial components, systems, buildings and structures at operating light water reactors without interference with the design basis operations and performance of the buildings, structures, systems and components enclosed. This invention removes the energy from residual heat and hydrogen generation accumulated inside the containment buildings and spent fuel pool buildings challenged by over temperature and over pressure during severe accidents, while encapsulating the radioactive atmospheric fallout, condensing steam by heat exchange with the atmosphere and retaining the resulting water coolant. This invention also encapsulates design basis accidents releases such as the release of radioactive steam through hardened venting systems to the atmosphere, and the release of radioactive steam through containment bypass systems to the atmosphere.