Investigation of Particle Size Effects in Inhalation Dose Assessment For Short Term Radiological Events

Abstract

Given the concern over terrorist events involving radioactive materials, developing the modelling capability to analyze the radiological consequences of a terrorist event involving radioactive material is in demand. One of the remaining questions in modelling radiological consequence of a RDD terrorist event is how should the particle size effect be treated.

A FORTRAN code called 'PIDA' was developed in this research to examine the importance of particle size effect in the consequence analysis of a short-term terrorist event involving RDD. Given the focus of this study on the particle size effect, only the human inhalation dose exposure was modeled in the code. The code is established by coupling the conceptual Gaussian puff model with the inclusion of particle size dependent, dry deposition velocity and resuspension modelling capability and ICRP inhalation dose model through its database software. An uncertainty analysis version of PIDA was also developed in order to perform uncertainty analysis for the particle size effect and other key parameters.

The PIDA code was successfully developed and implemented (under certain assumptions) to analyze the effect of particle size distribution in the consequence analysis of radiological terrorist event. For the benchmarking of the code, each submodels of PIDA code were compared with the state-of-the-art modelling tool for each specific area for the calculation results. It was found that PIDA code in general is conservative in estimation the radiological consequence of the event. Sensitivity and uncertainty analysis for the particle size effect were performed using PIDA code. Results indicated that particle size is one of the key parameters that contributes to the uncertainty of an inhalation dose evaluation due to this terrorist event. Ignoring particle size distribution is expected to result in overestimation of inhalation dose in a radiological terrorist event. It was also found that the particle size effect is (1) Minor in describing atmospheric transport, (2) Minor in describing deposition, (3) Minor in describing resuspension and, (4) Significant in describing lung deposition and resulting the dose.