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Confinement - doe-std-1128-98_ch10296
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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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.
C-6


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