Design Objectives - doe-std-1128-98

DOE-STD-1128-98

C.5.1.1

Design Objectives

The ventilation system should be designed to confine dispersible

radioactive material within prescribed areas of the facility. It should also

be designed to limit airborne concentrations of radioactive material in

occupied areas of the facility and in effluents to levels that are less than

the applicable concentration guides and ALARA.

The ventilation system, which serves as an engineered safety and control

system, should be designed to remain operational or fail safely under all

operational and credible accident conditions. The failure of any single

component should not compromise the ability of the system to maintain

confinement of radioactive materials or control their release to the

environment. Specific response requirements of the system and its

components should be identified through a safety analysis.

C.5.1.2

Air Flow and Balance

The design of ventilation systems should ensure that, under all normal

conditions, the air flows toward areas of progressively higher radioactive

material inventory. Air-handling equipment should be sized

conservatively enough that minor fluctuations in air flow balance (e.g.,

improper use of an air lock, or occurrence of a credible breach in a

confinement barrier) do not result in air flowing from higher to lower

radioactive material inventory areas. To prevent the movement of

contamination from high radioactive material areas to low radioactive

material areas in case of a flow reversal, HEPA filters should be

provided at ventilation inlets in confinement area barriers.

A minimum of two negative-pressure zones should exist within a process

building. The first, the process confinement system should serve the

spaces within the glove boxes, conveyors, transfer boxes, and other

spaces that may contain plutonium during the course of normal

operations. The second should serve the process areas and other

potentially contaminated areas adjacent to the process-confinement

system. Controlled areas that are contiguous to process areas and

potentially free of contamination constitute a third zone. Some facilities

have a minimum of three zones and frequently four.

A minimum pressure differential of between 0.75-in. and 1.0-in. (1.9-cm

and 2.5-cm) WG, negative with respect to the room, should be

maintained in all process confinement systems. A negative pressure

differential of at least 0.1-in. (0.25-cm) WG should be maintained

between process and controlled areas and between controlled areas and

uncontrolled areas. Air locks between zones should be provided where

necessary to ensure that proper differential pressures are maintained.

Differential pressure between the containment enclosure and the outside

atmospheric pressure may be as great as 3 in. of water [ERDA 76-21,

Nuclear Air Cleaning Handbook (ERDA, 1976)].

C-22