Application of RADTRAN to Estimation of Doses to Persons in Enclosed Spaces*

The RADTRAN computer code for transportation risk analysis (Neuhauser and Kanipe, 1992) can be used to estimate doses to persons in enclosed volumes. This application was developed in response to a need to examine consequences of a hypothetical container leak during accident-free transportation by cargo air. The original problem addressed tritium containers, but the method can be applied to any gaseous or suspended particulate material potentially released in an airplane or other enclosed area (e.g., warehouse) under accident-free conditions. Such leakage can occur during shipment of any radioactive gas or material with a gaseous phase. Atmospheric dispersion is normally modeled in RADTRAN as a series of downwind isopleths each of which is assigned a dilution factor (also known as time-integrated concentration or X/Q value). These values are located in look-up tables in RADTRAN and are normally taken from externally performed Gaussian dispersion calculations. The dilution factors are used to estimate inhalation dose to persons in the specified downwind areas. The basic equation for inhalation dose in RADTRAN is: Dinb = Ci • PPS • RF • AER • RESP • RPC • DF • BR • PD • A (1) Where Dinh = inhalation dose (person-rem) Ci = curies in package (Ci) PPS = number of packages in shipment RF = fraction of material released from a package AER = fraction of released material in aerosol form RESP = fraction of aerosol material that is respirable RPC = dose conversion factor (rem/Ci) DF = dilution factor (Ci-sec/m3 /Ci released) BR = breathing rate (m3 /sec) PD = population density (persons/m2) A = isopleth area (m2). Equation 1 is located in the accident module of RADTRAN; it is usually applied iteratively. That is, a separate calculation is performed for each potentially released isotope in each downwind area for each accident severity specified by the user, and the results of these intermediate calculations are then summed. The following sections outline the procedure by which terms in Equation 1 can be replaced to yield a single calculation for an enclosed-volume dose for a fixed time of exposure.