Confinement cont'd - doe-std-1128-98

DOE-STD-1128-98

should be designed to prevent accidental flooding. All primary confinement piping

joints should be tested for leak tightness. Penetrations in the primary confinement

barrier, such as conduit, ports, ducts, pipes, and windows, should be protected

against the release of radioactive material.

Where necessary, recycle ventilation systems may be used in process enclosures,

hot cells, and canyons. Inert gas systems should be designed as recycle systems,

unless it is impracticable to do so. Recycled inert gas systems should be maintained

completely within the primary barrier system. Extreme caution should be exercised

in the use of recycle systems for contaminated or potentially contaminated air. A

recirculation system should not direct air to an area where the actual or potential

contamination is less than the area from which the air originated. The decision to

use a recirculation system in a contaminated area should be based on a documented

safety evaluation that compares the risks versus the benefits. Filtration should be

provided to limit the concentrations of radioactive material in recirculated air to

ALARA levels. The design should allow for in-place testing of HEPA filters or

filter banks.

Continuous sampling and monitoring of recirculated air for airborne radioactive

material should be provided downstream of fans and filters. Monitoring should be

provided for the differential pressure across the filter stages and for airborne

radioactive material behind the first HEPA filter or filter stage. The means for

automatic or manual diversion of airflow to a once-through system or stage should

be provided. The monitoring system alarm should result in the automatic diversion

of airflow to a once-through system or a parallel set of filters if an automatic

system is used.

The secondary confinement barrier encloses the room or compartment in which the

primary confinement barrier is located, and provides contamination protection for

plant personnel who are outside of the secondary confinement area. High-

efficiency particulate air filtration should be required for air supplied to and

exhausted from a secondary confinement barrier. Secondary confinement rooms,

compartments, or cells should be separated from each other by fire doors or stops.

Both the barrier walls and the fire doors should be constructed of materials that are

capable of withstanding a design-basis accident. The secondary confinement should

be designed for pressures that are consistent with the criteria for the ventilation

system. The secondary confinement area should be at a positive air pressure with

respect to the primary confinement areas and at negative pressure with respect to

the outside environment and adjacent building areas that are not primary or

secondary barriers.

The building is the structure that encloses both the primary and secondary

confinement barriers, as well as the offices, change rooms, and other support areas

that are not expected to become contaminated. It is the final barrier between the

potential contamination and the outside environment. The building structure or any

portion thereof may serve as the secondary confinement barrier if the requirements

for both structure and confinement are met. The portion of the structure that houses

activities involving radioactive material in a dispersible form should be able to

withstand design basis accidents, site-related natural phenomena, and missiles

without a breach of integrity that would result in releases of radioactive material

from the structure in excess of DOE guidelines.

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