Airborne Release Fraction (ARF)

DOE-HDBK-3010-94

1.0 Introduction

As an example, assume 600 g from a total of 1000 g of material X are in a form that would

not be affected by an explosion. Of the remaining 400 g, 200 g have a high release fraction

and 200 g have a low release fraction. If the 600 g is included in the MAR, specific DRs

for the MAR of 1000 g are 0 for the unaffected material, 0.2 for the high release fraction

material, and 0.2 for the low release fraction material. If the 600 g is not included, specific

DRs for the MAR of 400 grams are 0.5 for the high release fraction material and 0.5 for the

low release fraction material. The basic distinction is whether or not DRs of 0 are officially

designated. Neither convention cited in the example is necessarily correct. What is

important is that one convention is used consistently to avoid an obvious potential for

assigning incorrect DR values.

The DR is estimated based upon engineering analysis of the response of structural materials

and materials-of-construction for containment to the type and level of stress/force generated

by the event. Standard engineering approximations are typically used. These approximations

often include a degree of conservatism due to simplification of phenomena to obtain a useable

model, but the purpose of the approximation is to obtain, to the degree possible, a realistic

understanding of potential effects.

Airborne Release Fraction (ARF)

The ARF is the coefficient used to estimate the amount of a radioactive material suspended in

air as an aerosol and thus available for transport due to a physical stresses from a specific

accident. For discrete events, the ARF is a fraction of the material affected. For

mechanisms that continuously act to suspend radionuclides (e.g., aerodynamic

entrainment/resuspension), a release rate is required to estimate the potential airborne release

from postulated accident conditions. Generally, accident release rates (ARRs) are based

upon measurements over some extended period to encompass most release situations for a

particular mechanism. The rates are average rates for the broad spectrum of situations and,

as such, the most typically meaningful time unit to reflect average conditions is 1 hour.

There is evidence (discussed later in the subsection on the aerodynamic entrainment of

surface contamination) that in some situations (e.g., aerodynamic entrainment of sparse

powder deposits on a heterogeneous surface), the rate of release is not uniform with time.

Even in the situations where the rates are relatively uniform, the source is depleted by the

removal of particles from the surface by aerodynamic forces, and the amount of material

airborne decreases with time unless the source is continuously replenished.

This handbook specifically deals with ARFs and ARRs, although ARF will connote both

concepts in generic discussions for the sake of simplicity. The ARFs are based primarily

upon experimentally measured values for the specific material (e.g., plutonium, uranium,

mixed fission products) or surrogates subjected to the particular type of stress under

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