Process vessels that could contain uranium should be vented to the
process off-gas system, which should route off-gas through
pretreatment, if needed, and HEPA filtration. Typical pretreatment
features include cyclone dust collection systems, different types of filters,
cold traps, liquid condensers, solvent adsorption systems, and aqueous
solution scrubbers. Nuclear criticality safety should be considered during
the design of pretreatment and HEPA filtration systems.
Secondary Confinement System. The secondary confinement system
generally consists of the confinement barriers and associated ventilation
systems that surround or confine the operating areas that house the process
system and its primary confinement. The following considerations should be
addressed in the design of secondary confinement systems for UCRFs:
Operating area compartments should be equipped with sensors to detect
releases of hazardous materials from the primary confinement system
and provide appropriate alarms. Commensurate with the potential
hazard, the use of redundant sensors should be considered.
Penetrations of the operating area confinement barriers should be
minimized. When practical, equipment components not functionally
required to operate directly in the presence of radioactive materials
should be located outside the operating area compartments.
Penetrations of the secondary confinement should have positive seals to
prevent the migration of contamination out of the operating area.
Each secondary confinement compartment should be supplied with
ventilation air from the building ventilation system. Exhaust ventilation
should be handled by a system with sufficient capacity to control
ventilation flow as required in the event of a credible breach in the
operating compartment confinement barrier. Pressure in the
compartments should be negative with respect to the building ventilation
system. The secondary confinement exhaust ventilation system should
be equipped with HEPA filtration.