Ventilation Systems - doe-std-1136-20040202

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

uranium should be electro-polished before being placed into service. If high-efficiency particulate air

(HEPA) filtration has failed at any time during facility operation, roofs may require decontamination.

Metal roofs are easiest to decontaminate, but even these may contribute to the volume of radioactive waste

unless unusual measures are taken to clean them. Built-up and composition roofs will be difficult to clean

to unrestricted release levels.

Interior surfaces are most easily cleaned if they were completely primed and painted before the

introduction of radioactive materials into the facility. If interior surfaces are repainted durin g operation,

their disposal as clean waste is likely to require removal of the paint. However, if the paint has

deteriorated, cleaning for unrestricted use may be as difficult as if the material had never been painted.

Wood will almost certainly become contaminated, as will plasterboard and other such materials.

Floor surfaces are likely to be a problem. Concrete should be well sealed and covered with a

protective surface. Single sheet, vinyl flooring with heat-sealed seams is preferable to asphalt or vinyl tile

because it is more easily cleaned. If the floor needs resurfacing, it is preferable to overlay new flooring

material rather than remove the old material and expose the underlying floor.

Carpets are not recommended because they are difficult to clean and survey and bulky to dispose of

and they do not adequately protect the underlying surface. In some areas, such as control rooms, their use

may be justified by noise control requirements; however, their contamination control limitations should be

considered. If used, carpets should be surveyed frequently and disposed of as radioactive waste when they

become contaminated.

10.2.2 Ventilation Systems

In addition to decommissioning considerations, the design of the ventilation system will depend on

the operations conducted in the facility. Adequate air flow for all operations and good design practices will

help keep the facility clean during operations and will facilitate decommissioning. Fiberglass duct work

may present a fire hazard and may be more difficult to decontaminate than stainless steel,

especially stainless steel that has been electro-polished. Welded joints are less likely to collect

contamination than bolted ones; however, bolted joints are easier to remove and the most contaminated

areas are readily accessible for cleaning.

Filters should be positioned in ventilation systems to minimize contamination of ductwork (e.g.,

filtration of glove-box exhaust air before it enters a duct leading to a plenum).

10.2.3 Piping Systems

Potentially contaminated piping systems imbedded in concrete are a common and relatively expensive

decommissioning problem. Most often, they must be sealed and removed last, after all other radioactive

material has been removed and the building is being demolished by conventional methods. Often, they

provide the major impetus for demolishing a building rather than converting it to some non-nuclear use.

For this reason, it is best to run pipes in chases or tunnels that have been lined (usually with stainless steel)

to prevent contamination from penetrating building surfaces. To minimize hand jackhammer work

required during decommissioning, floor drains should not be enclosed in concrete.

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