Airborne release fractions

The potential source term for each of the selected DBAs was conservatively derived based on the maximum potential radiological inventory and assuming that the entire inventory was available for release (i.e. the airborne release fraction was assumed to be 1.0). 

ARF = Airborne Release Fraction (or fraction of MAR x DR that becomes airborne),... 

The source term associated with six targets was analyzed previously in Section 3.4.2.1 (Process Spill). A small fraction of the nonvolatile liquid contents of the acid cocktail would normally be expected to be airborne and available for release from the bottle or target to the ventilation system based on DOE-HDBK-3010-94. This handbook suggests an airborne release fraction of 0.001 as the mean release fraction for boiling liquids and 0.002 as the bounding... 

DOE-HDBK-3010 Airborne Release Fractions (ARFs)/Rates and Respirable Fractions (RFs) for Nonreactor Nuclear Facilities... 

DOE-HDBK-3010, Airborne release fractions/rates and respirable fractions for nonreactor nuclear facilities. Document is available from Department of Energy, AD-631 /FORS, Washington, DC. 

US DOE. Airborne Release Fractions/Rates and Respirable Fractions for Nonrcac-tor Nuclear Faeilities. DOE-HDBK-3010-94. Prepared by Mishima J, Pinkston D. Washington, DC, US Department of Energy, 1994. 

Mishima, J., 1993, Recommended Values and Tedmical Bases for Airborne Relea.se Fractions (ARFs), Airborne Release Rates (ARRs), and Respirable Fractions (RFs) for Materials from Accidents in DOE Fuel Cycle, Ex-Reactor Facilities, Revision 2, Draft DOE report, April. 

The generic approach to airborne release development was that approach used by DOE in developing the HC2 threshold quantity for each isotope as described in Attachment 1 of DOE-STD-1027-92, Change 1 (DOE, 1992). DOE developed a set of final release fraction values (FRFVs) for the various physical forms of materials that could be present in a facility. These FRFVs were used to reduce the quantity of radioisotope materials at risk for airborne release from the facility in an accident situation. The FRFVs were intended to address all of the uncertainties noted above on a facility wide basis. DOE noted that it was possible to calculate higher values for FRFVs for some physical forms and processes but that those processes were likely to be present on only a local and not a facility wide basis. Thus, DOE concluded the FRFVs were an adequate average for hazard categorization purposes. DOE used the FRFVs... 

In conventional treating systems using cold-gas cleanup, the small fraction of metals released to the gas phase is captured effectively in the gas cooling and gas treating steps. The combination of gas cooling and multistage gas—Hquid contacting reduces very substantially the potential for airborne emissions of volatile metals such as lead, beryUium, mercury, or arsenic. 

For a given release scenario, estimate the state of the released contaminant after it has depressurized and become airborne (including any initial dilution). The initial mole fraction of hazardous components will be applied to the final reported concentrations and hazardous endpoint concentrations throughout the process. If source momentum is important (as in a jet release or for plume rise), other models are available that can address these considerations. Disregarding the dilution due to source momentum will likely result in higher concentrations downwind, but not always. 

Females begin to emit pheromone 9 or more days after the adult molt (Bodenstein, 1970 Takahashi et al., 1976 Hawkins and Rust, 1977), but clearly, this is variable and temperature dependent. The attractancy of gut extracts made on the first day after the imaginal molt corresponds to that of 0.1 ng ( )-periplanone-B (Sass, 1983). During the next 20 days, the effectiveness of both fractions of the sex pheromone (periplanone-A and periplanone-B) in behavioral assays increases 100-fold and remains high for at least the next 45 days. Collection of airborne pheromone with Tenax followed by behavioral assays showed that periplanone-A and periplanone-B were released by 10-25-day-old females in equal amounts, equivalent to 0.6 ng periplanone-B per female per day (Sass, 1983). Yang et al. (1998) confirmed an increase in pheromone activity in the early adult but showed a decline in pheromone between days 20 and 30. 

The interaction of atmospheric HTO with vegetation and soil has several time scales. After a short release, airborne HTO is deposited to land or sea by vapour diffusion with a vg of about 10 mm s-1 (Garland, 1980). From land, about 75% of the HTO returns to the atmosphere within days or weeks depending on climate. At sea, HTO mixes downwards and only a small fraction re-enters the atmosphere within the radioactive life of tritium. 

The method by Wells and Alexander uses lower air velocities (the extraction rate is only 50 litres/minute) and does not, therefore, require a deflector plate. The method does not necessarily release all of the potentially airborne particles in the sample in fact, the dust release may be constant in many repeated pourings of the same sample. Either total airborne dust samples may be collected on a filter (i.e. all particles that are still airborne on leaving the box, i.e. smaller than about 10 microns) or only the respirable fraction may be collected by extraction through the Hexhlet sampler. 

In the above case, the source term means how much airborne Pu02 particulates are released to the atmosphere due to the drop of a container, what is the respirable fraction of the airborne Pu02 particulates. 

RF = Respirable Fraction (or the fraction of airborne particles that are small enough to enter the respiratory system of the body), and LPF Leakpath Factor (release reduction from facility features such as plate out, filtering, etc.). 

Low dispersible radioactive material has properties such that it will not give rise to significant potential releases or exposures. Even when subjected to high velocity impact and thermal environments, only a limited fraction of the material will become airborne. Potential radiation exposure from inhalation of airborne material by persons in the vicinity of an accident would be very limited. 

When low dispersible material is subjected to the high velocity impact test, particulate matter can be generated, but of aU airborne particulates up to 100 pm only a small (less than 10%) fraction will be expected to be in the respirable size range below 10 pm if the 100 limit is met. In other words, an equivalent quantity of low dispersible material less than 10 A2 could be released airborne in a respirable size range. It has been shown that for a reference distance of around 100 m and for a large fraction of atmospheric dispersion conditions this would lead to an effective dose below 50 mSv. 

This derivation assumes that all of the released material becomes airborne and is available for inhalation, which may be a gross overestimate for many materials. Also, equilibrium conditions are assumed to pertain at all times. These factors, together with the principle that leakage from Type B packages should be minimized, indicated that the exposure of transport workers would be only a small fraction of the ICRP limits for radiation workers [1.5]. In addition, this level of conservatism was considered adequate to cover the unlikely situation of several leaking packages contained in the same vehicle. 

Following a loss-of-coolant accident, a fraction of the radionuclides released from the primary circuit remains airborne in the containment atmosphere, as was discussed in the preceding sections. In order to reduce the airborne activity concentrations, standby filters are installed in the annulus of the German PWR plants, consisting of aerosol filters and iodine filters. In the German RSK Guidelines a retention efficiency of 99.9% for particulate iodine, of >99.99% for h and of >99% for organoiodides is required under accident conditions. In certain other countries, the specified iodine species as well as the required retention efficiencies differ somewhat from these values. 

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