material processing, the functional requirements for secondary confinement
refer to the operating area boundary and the ventilation system serving the
Design features incorporated into the secondary confinement system should
have been proven effective by extensive experience in similar applications or by
formal prototype testing. Such design features include the following:
Continuous monitoring capability should be provided to detect loss of
proper differential pressure with respect to the process area. Operating
areas should also be continuously monitored. Commensurate with the
potential hazards, consideration should be given to the use of redundant
sensors and alarms.
Permanent penetrations of the secondary confinement (e.g., pipes,
ducts) should have positive seals or isolation valves or double closure
with controlled secondary to primary leakage on pass-through
penetrations (e.g., personnel air locks and enclosed vestibules).
Ventilation systems associated with secondary confinement should be
designed with adequate capacity to provide proper direction and velocity
of airflow in the event of the largest credible breach in the barrier.
Secondary and tertiary barriers may exist in common such as a single
structural envelope (e.g., walls, roof slab, floor slab), provided the barrier
can withstand the effects of external events, and does not contain
access ways that allow the routine transfer of personnel, equipment, or
materials directly to the exterior of the facility. Access ways into the
interior of the single structural envelope should be designed so that the
access way is entered from another level of confinement.
Special features (e.g., air locks, enclosed vestibules) should be
considered for access through confinement barriers to minimize the
impact of facility access requirements on the ventilation system and to
prevent the release of radioactive airborne materials.