Air Supply - STD-1128-98master0328

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Building penetrations for ventilation ducts should be kept to a minimum and should

be designed to protect the critical systems against postulated accidents. No

penetrations should be permitted if the barrier around the process area is the outside

wall of the building.

Room air in controlled and process areas may be recirculated if the recirculating air

system is provided with two HEPA filter banks in series. One of the filter banks

should be in the exhaust duct leading from the rooms where airborne activity might

be introduced. An air monitor should be located between the two filters and set to

alarm when the air concentration reaches a preset point. Airflow should then be

diverted either manually or automatically to a once-through system using the air-

monitor alarm indication to trip the system. Recirculation from a zone of higher

contamination to a zone of lower contamination should be prohibited.

C.5.1.3 Air Supply

Supply air should be appropriately filtered and conditioned in accordance with

operational requirements and with the levels recommended for comfort.

The ventilation rate in process areas where uncontained radioactive materials are

handled should be from 12 to 60 air changes per hour (ORNL, 1970) depending on

whether the area is normally occupied by workers, the need for removal of process

or decay heat, and the need for removal of decay fumes. A minimum of eight air

changes per hour should be provided in support facilities within the process area.

Adequate air filters should be used at the intake of the ventilation supply system to

minimize dust in the process area and to reduce the dust loading on HEPA filters.

A downward air-flow pattern should be provided at worker locations to direct air

from any potential leak point down and away from the worker's face.

Consideration should be given to the distribution of inlet air through a number of

small ports or by slot-type distributors to decrease the possible occurrence of "dead

spots" with little air circulation.

Glove boxes, conveyors, and other systems that require a controlled atmosphere

may be equipped with a recirculating air system. All parts of the system should

operate at air pressures that are negative with respect to the room. Process

enclosures that use normal air may receive their air supply from the room through

dust-stop and HEPA filters mounted on the glove box.

Consideration should be given to isolating process rooms from each other during

accidents. The principle of compartmentation and separation should be extended to

systems handling ventilation in working areas by the most practicable use of

individual ventilation systems. Emergency back-up should be provided through

combinations of manifolds and damper cutovers between adjacent individual

ventilation systems. Redundancy can be minimized by the provision of a back-up

unit for each two individual systems.

C-22