Time Dependent Radio-toxicology of Fission Products

Ionizing radiation, emitted by radiological materials, is known to cause damage to biological tissue. Prolonged exposure to radiation may cause a vast array of harmful medical effects, from enhancing future probability of cancer, up to Acute Radiation Syndrome resulting in multi-system failure. In complex radiologic release events involving fission products (nuclear fallout, reactor failures), the products' physical decay chains dictate a time dependent product inventory. As the ratios between different products vary, so does the toxicology of the radioactive inventory as a whole. The temporally varying toxicological factors should be taken into account when producing radiological risk assessments for populations. In this paper we study the time varying toxicology of fission products, using a specialized model named Koala, developed in Soreq NRC. A significant and monotonous rise in the aggregate toxicity of ingested fission products was noted. This result carries important implications for risk assessment, as it partially cancels out the fission product physical decay. A similar, albeit less pronounced rise was found for external exposure. Factoring activity and toxicity together allows computation of effective source terms for simple events involving fission products. We demonstrate one such source term, based on fallout from a nuclear explosion. This source term may be easily introduced into suitable atmospheric dispersion models