Secondary Confinement System

DOE-HDBK-1132-99

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.

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