fans. Standby filters should be installed outside the cell and sealed in an
acceptable enclosure for direct maintenance. Note: Air leakage through
isolation valves/dampers should be evaluated to avoid the bypassing of
filtration devices; the reduction of exhaust flow from recirculation through
the standby filters; the exposure of personnel changing the isolated filter
elements; and the premature loading of the standby filters.
Exhaust systems should have monitors that provide an alarm if the
concentration of radioactive material in the exhaust exceeds specified
If radioiodine may be present, consideration should be given to the
installation of radioiodine-absorber units.
In facilities where plutonium or enriched uranium is processed, the following are
Wherever possible, the designer should provide enclosures for confining
process work on plutonium and enriched uranium. When these
confinement enclosures are specified and designed, consideration
should be given to whether room ventilation air for either a secondary or
tertiary confinement can be recirculated. If a recirculation ventilation
system is provided, the design should provide a suitable means for
switching from recirculation to once-through ventilation.
If advantageous to operations, maintenance, or emergency personnel,
the ventilation system should provide for independent shutdown. Such a
shutdown should be considered in light of its effect on the airflow in other
interfacing ventilation systems. When a system is shut down, positive
means of controlling backflow of air to uncontaminated spaces should be
provided by positive shutoff dampers, blind flanges, or other devices.
Equipment to continuously monitor oxygen levels should be provided for
occupied working areas of facilities equipped with significant quantities