Vapors (Condensible Gases)

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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