The filtration system should be designed to allow for reliable in-place
testing of the HEPA filters and ease of filter replacement to the extent
The exhaust system for a glove box or hood should be separate from the
exhaust system for room air. The hood exhaust system need not be
separate from room exhaust ventilation if ventilation is once-through.
Exhaust air should be drawn through a HEPA filter at the glove-box or
hood-exhaust point to maintain primary control at that point and
minimize contamination of ductwork. This filter should not be counted
as a confinement barrier unless it is testable in place. Additional HEPA
filters in series should be separated at a sufficient distance to permit in-
place testing of each stage of the filters.
Dampers should be installed in the glove-box, hood, and room-exhaust
ducts so that required air-pressure differentials can be maintained.
Automatic backflow dampers should be installed in series with the
exhaust dampers. Manual controls, or automatic controls with manual
override, should be provided as needed for ventilation systems or their
components for flexibility of operation.
Integral fire-suppression equipment should be provided as needed within
each ventilation system to ensure that a safety-basis fire could not
degrade the integrity of the high-efficiency air cleaning system. Where
appropriate, a cool-down chamber with water sprinklers, a pre-filter
demister, and a spark arrestor screen should precede the first stage of the
final HEPA filtration system. The water spray from a cool-down
chamber should be automatically actuated by appropriate temperature-
and smoke-sensing devices as determined by the accident analysis.
All potentially contaminated air should be exhausted through a common
stack. Continuous monitoring and a representative, redundant sampling
capability should be provided on exhaust stacks that may contain
radioactive or toxic materials. The ventilation exhaust stack should be
located as far away from any air intake as is reasonably possible. Design
criteria for effluent monitoring and sampling and elements for
consideration in effluent radioactivity measurement are described in
DOE/EH-0173T, Environmental Regulatory Guide for Radiological
Effluent Monitoring and Environmental Surveillance (DOE, 1983).
ANSI N42.18 provides specifications and performance of onsite
System Testing and Control
The ventilation system is considered an essential safety and control
system and should be designed in accordance with ANSI/ASME N509-
1989, Nuclear Power Plant Air Cleaning Units and Components (ANSI,
1989b). The minimum acceptable response requirements for the
ventilation system, its components, instruments, and controls, should be
established based on results of safety analyses for normal, abnormal, and