Appendix A. Nuclear Filtration and Air Cleaning Systems

DOE-STD-1066-99

Appendix A. Nuclear Filtration and Air Cleaning Systems

Other types of nuclear filtration systems and air cleaning systems mentioned in this document:

High Efficiency Metal Fiber Filter Systems

This type of filtering has only been commercially available in the United States since the mid-1980s.

High Efficiency Metal Fiber (HEMF) filters are made of sintered stainless steel fibers that are welded

into steel housings and steel frames. HEMF filters are generally not disposed of when they become

plugged or "loaded" like HEPA filters because they can be cleaned by following a manufacturer's

cleaning procedure. After cleaning a dirty, used HEMF filter, there is little or no effect in the filter's

efficiency and structural integrity when compared to that filter's original efficiency and structure.

In contrast to HEPA filters, metal fiber filters are not weakened by moisture impingement. Also,

HEMF filters can operate for longer and hotter time periods than HEPA filters because the metal filters

contain no flammable components and they are inherently resistant to high temperatures (although

the finely divided filter media in a metal filter will not resist a direct flame impingement). The

resistance of it to moisture and heat make this filter attractive for fire protection purposes. Since the

use of HEMF filters is relatively new to the DOE community, little fire protection design data based on

actual fire testing are currently available.

Radioiodine Adsorber Air Cleaning Systems

Although much discussion in the nuclear community has been generated for the past 40 years as to

fire protection of adsorbers, little consensus and few conclusions as to the proper method of

extinguishment of adsorber fires involving combustible materials has been achieved. Some methods

include utilizing a combination of manual and automatic water spray systems, limiting air flow to the

adsorbers, and the utilization of alternative non-combustible adsorber medias such as silver zeolite.

Adsorber air cleaning systems are often utilized in nuclear reactor emergency ventilation confinement

systems where they are often referred to as charcoal or carbon type filters (but other inorganic

adsorber materials are available for adsorber media such as silver oxide, silver nitrate, aluminum

silicate, and silver zeolite). Although the nuclear industry has experienced less than six known

adsorber fires in its history, it is generally accepted that as a minimum, adsorbers should be provided

with fire detection equipment.

For carbon type filters an insurance carrier2 for nuclear power plants recommends the following fire

protection:

A hydraulically designed automatic water spray system, utilizing directional solid-cone spray

nozzles controlled by an approved deluge valve, with remote suitably located manual

actuation stations, should be provided for charcoal filters.

J. J. Carney, ANI's Recommendations for Carbon Filters, American Nuclear Insurers, C.3.1, September 1977.

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