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DOE-HDBK-3010-94
2.0 Materials in the Gaseous State
2.2 V A P O R S (C O N D E N S I B LE G A S E S )
2.2.1
S u m m ary of A n alysis of D ata
For generation of vapors plus release from physical containment, the
recommended ARF is 1.0. All materials in the gaseous state can be
transported and inhaled; therefore, an RF of 1.0 is assumed for the purposes
of these analyses.
2.2.2
D iscu ssion
Vapors (materials in gaseous form due to local conditions) may result from two phenomena:
chemical reaction and heating. Some vapors result from chemical reactions that generate a
volatile compound (e.g., halogens in an oxidizing, acidic environment). Other vapors can be
generated when the local temperature exceeds the boiling point of the element or compound
(e.g., evaporation of water). Under most conditions, the ARF (the fraction of vapor formed
initially airborne) assumed for vapors is 1.0. If the local conditions are not adequate for
quantitative vaporization of all the material (e.g., inadequate chemical reactants, inadequate
temperature), the ARF is the fraction of the material converted to vapor form. Release of
vapors generated during inadvertent nuclear criticalities is covered in Chapter 6.
Loss for chemically reactive materials is difficult to quantify due to the uncertainty of the
materials encountered along the pathway, the kinetics of these reactions, and the transport of
the vapors to the surfaces. A conservative value is to assume all the material released is
transported to the facility/environment interface without loss unless engineered emission
control devices (e.g., for radioiodine - impregnated charcoal filters, silver substituted zeolite
filters, silver nitrate coated ceramic saddles; HEPA or other filtration devices for condensed
vapors or vapors adsorbed onto pre-existing particles) are present for removal of the specific
material. In many cases, an assumption of complete transport of the airborne material
without significant loss is very conservative but transport losses must be substantiated for the
specific configurations associated with an event.
Many chemically volatile compounds are reactive and can be lost in transit by reaction with
materials encountered along their path to the facility/environment interface or adsorption on
pre-existing airborne particles. Temperature sensitive materials can condense homogeneously
(particles formed directly from the vapor have been observed to be in the sub-micron range)
or on pre-existing particles. Aerosols form rapidly since entrainment of cooler air invariably
accompanies the formation process. Various natural processes act to attenuate transport of
particles (e.g., agglomeration, gravitational settling, turbulent diffusion) and filtration or
other engineered devices such as water sprays have varying removal efficiencies for particles.
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