The Pebble Bed Modular Reactor (PBMR) is a high-temperature gas-cooled reactor using fuel spheres (pebbles) that circulate through the reactor core. The fuel is of a proven design, able to resist very high temperatures without damage. The plant design requirement is that there be no conceivable situation in which the fuel sustains such damage that a concern for the safety of the public at the boundary of the exclusion zone can be postulated. Under these circumstances a building having the functionality of a conventional Light Water Reactor (LWR) type containment is inappropriate and can be counterproductive in terms of safety.
Instead, a containment system (or confinement) is envisaged whereby the overpressure resulting from a pipe break is vented to the environment and the vent system is closed after the pressure pulse has passed. This enables filtered ventilation to be re-established within a short time after a depressurization event and prevents the build-up of pressure that could conceivably act as a driving force to disperse delayed releases into the environment.

  The PBMR Containment System.pdf