Simulation of fission products from nuclear weapons explosions

The simulation method MARS, mathematical Radiac Simulation, is primarily intended for preparedness exercises in nuclear fallout areas and simulates the ionizing radiiation dose rates from fission products deposited on the ground, i.e. fallout from a nuclear weapons explosion or from a release of radioactive materia from a nuclear reactor. MARS gives at any time after the fictitious explosion or reactor release the dose rates at any position in the fallout area. A special method, in this report called FOSIM, Fallout Simulation, based on MARS values, has also been developed. This is a technique to produce a standardized solution containing fission products of about the same composition as that caused by a nuclear weapons explosion. The MARS method and the FOSIM technique were both applied in a preparedness group exercise in a nuclear weapons scenario, LOTTA, in a northern region of Sweden in march 1998. This report gives a short description of the FOSIM method and a fairly detailed evaluation of the application results. From these, it is obvious that the technique produces a set of fission products that, from a couple of hours after the explosion and further, is quite similar to that expected in the fallout from a nuclear weapons explosion. The samples, taken in the fallout area, and prepared by addition of certain amounts of the FOSIM solution, offers unique opportunities for the preparedness laboratory to check and further develop its analysing methods. Some steps of the FOSIM technique need to be further developed, but already in this exercise it gave very realistic sample conditions for the benefit of the laboratory analyses.