Abstract
The objective of this project was to provide a robust fallout analysis and planning tool for the National Technical Nuclear Forensics interagency ground sample collection team. Their application called for a fast-running, portable mission-planning tool for use in response to emerging improvised nuclear device (IND) post-detonation situations. The project met those goals by research and development of models to predict the physical, chemical, and radiological properties of fallout debris. ORNL has developed new graphical user interfaces for two existing codes, the Oak Ridge Isotope Generation (ORIGEN) code and the Defense Land Fallout Interpretive Code (DELFIC). ORIGEN is a validated, radionuclide production and decay code that has been implemented into the Fallout Analysis Tool to predict the fallout source term nuclide inventory after the detonation of an IND. DELFIC is a validated, physics-based, research reference fallout prediction software package. It has been implemented into the Fallout Planning Tool and is used to predict the fractionated isotope concentrations in fallout, particle sizes, fractionation ratios, dose rate, and integrated dose over the planned collection routes - information vital to ensure quality samples for nuclear forensic analysis while predicting dose to the sample collectors. DELFIC contains a particle activity module, which models the radiochemical fractionation of the elements in a cooling fireball as they condense into and onto particles to predict the fractionated activity size distribution for a given scenario. This provides the most detailed physics-based characterization of the fallout source term phenomenology available in an operational fallout model.
