In general, primary confinement is the irradiated fissile material (IFM) cladding or
canning. Secondary confinement is established by the facility buildings that
enclose the dry storage area and/or the storage pool and auxiliary systems.
Primary Confinement System. The IFM cladding or cans, as appropriate,
provide primary confinement during normal and anticipated operational
occurrences. The IFM cladding or canning are used to provide a corrosion-
resistant confinement for the IFM material and to prevent an uncontrolled
release of radioactive material.
Secondary Confinement System. The facility building and ventilation system
make up the secondary confinement system.
Penetrations of the secondary confinement barrier should have positive seals to
prevent the migration of contamination. The use of positive seals should be
considered for penetration of enclosures within the facility building to provide
proper ventilation flow paths and to prevent the uncontrolled migration of
Ventilation systems should include inlet air filtration (roughing filters) for the
main storage building to prevent dust accumulation, thus reducing the load on
other filters in the facility. Recirculated air in the main storage building should
be filtered through a HEPA filter to reduce the build-up of radioactive material in
the air. Areas with higher potential airborne radioactive contamination (e.g.,
pool water purification and waste treatment system areas) should use only
once-through airflow. Supply air to these facilities should be drawn from the
main storage building if such design is feasible. Exhaust air should be HEPA-
filtered prior to release.
Radioiodine adsorber units, such as activated charcoal or silver zeolite, should
be considered for installation in the exhaust ventilation system when radioiodine
releases are possible.