Models for estimating radiation dose and LAR from radioactive fallout: extended dose algorithms for the computational tool LARCalc

Abstract: Today, emergency preparedness is needed against both nuclear reactor accidents and nuclear weapons fallout. Both scenarios can lead to exposure of ionizing radiation. Upon exposure, radionuclides will incur a radiation dose both internally and externally. Based on a known organ absorbed dose, an estimate of the risk of developing cancer during a lifetime can be obtained. This estimate is referred to as the ”lifetime attributable risk” (LAR), and is defined as age- and sex-dependent coefficients for the increased number of cancer cases per absorbed organ dose for 10,000 individuals. A Matlab program, LARCalc, has previous been developed to easily visualize radiation dose and LAR estimates to an individual or population, based on a known soil deposition. The current version can estimate external radiation dose from ground as well as internal dose from 137Cs and 134Cs. Immediately at the beginning of a fallout, radionuclides will be present in high concentrations in the airborne release plumes. These radionuclides will lead to both internal doses in the form of inhalation and external radiation from the plume. In connection with nuclear reactors and nuclear weapons detonations, radioactive strontium isotopes are generated. Strontium is an analogue of calcium and will therefore accumulate in the skeleton. As both 90Sr and its daughter 90Y are beta emitters, they will only give radiation doses locally. Another radionuclide that contributed to large radiation doses after the Chornobyl accident in 1986 was 131I, where intake via milk was the major route of exposure. The aim of this study was to expand the capacity of LARCalc for radiological consequence assessments by developing and incorporating additional models for estimating dose and LAR from inhalation of initial release plumes, ingestion of 90Sr, and ingestion of dairy milk containing 131I. Using already published data, organ and nuclide specific exposure models were developed to estimate dose and LAR based on ground deposition density of the considered isotope (kBq m−2). This was done for 131I by milk consumption, inhalation of nuclides from the plume, external radiation from the plume, and ingestion of 90Sr. To the extent possible, attempts have been made to verify the models with other data. In the cases where it was possible, the estimates were correct and were then in the order of magnitude expected.