General

4.130. As an application of the defence in depth concept, and in addition to the measures taken to ensure the leaktightness of the containment, measures should be taken to reduce the inventory of radionuclides in the containment atmosphere.

4.131. In general, a single system is not sufficient for reducing the concentra­tions of radionuclides, and multiple systems are usually employed. Methods used for the reduction of airborne radionuclides in water cooled reactors of extant and new designs are:

(a) Deposition on surfaces,

(b) Spray systems,

(c) Pressure suppression pools,

(d) Ventilation systems.

4.132. As long as active systems for the reduction of the concentrations of airborne radionuclides are in the standby mode in normal operation, they should be testable.