Confinement Ventilation Systems cont'd

DOE-HDBK-1132-99

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

limits.

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

additional considerations:

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

I-20