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The HASCAL 2.0 code provides dose estimates for nuclear, chemical, and biological facility accident and terrorist weapon strike scenarios. In the analysis of accidents involving radioactive material, an approximate method is used to account for decay during transport. Rather than perform the nuclide decay during the atmospheric transport calculation, the decay is performed a priori and a table look up method is used during the transport of a depositing tracer particle and non depositing (gaseous) tracer particle. In order to investigate the accuracy of this decay methodology two decay models were created using the ORIGEN2 computer program. The first is a HASCAL like model that treats decay and growth of all nuclide explicitly over the time interval specified for atmospheric transport, but does not change the relative mix of depositing and non-depositing nuclides due to deposition to the ground, nor does it treat resuspension. The second model explicitly includes resuspension as well as separate decay of the nuclides in the atmosphere and on the ground at each deposition time step. For simplicity, both of these models uses a one-dimensional layer model for the atmospheric transport. An additional investigation was performed to determine the accuracy of the HASCAL like model inmore » separately following Cs-137 and I-131. The results from this study show that the HASCAL decay model compares closely with the more rigorous model with the computed doses are generally within one percent (maximum error of 7 percent) over 48 hours following the release. The models showed no difference for Cs-137 and a maximum error of 2.5 percent for I-131 over the 96 hours following release.« less |
