A gamma radiation dose calculation method for use with Lagrangian puff atmosphericdispersion models used in real-time emergency response systems

Abstract

The paper presents the development of a model for the calculation of the gamma radiationdose rate from a cloud or plume of radionuclides. The model has been implemented in theLagrangian puff dispersion model DIPCOT which is used in the framework of the RODOSsystem for nuclear emergency management. The basic characteristics of the model are itsspeed of execution and its ability to calculate the gamma dose rates from clouds or plumesof random shape formed under non-homogeneous meteorological conditions or overcomplicated topography. The three-dimensional integral that would normally have to benumerically calculated in such circumstances has been transformed to a one-dimensionalone through a coordinate transformation for each model puff and by using aseparation of variables technique. The resulting one-dimensional integrals have beenpre-calculated and their values stored for a range of parameters that cover the possibleranges of photon energies, puff dimensions and distances encountered in cases ofatmospheric dispersion. During runtime the model calculates the exact values byinterpolation from stored tables of values. This is a very fast and accurate method, asthe evaluation study has proved. The model performance has been evaluatedthrough simulations of a real-scale experiment involving routine emissions of 41Ar from a reactor and comparisons of model predictions with measured fluence rates. Thecomparisons have revealed a satisfactory level of agreement and the model performancestatistical indices are well above the acceptance criteria that are suggested in theliterature.