Fuel particles in consequences of the accident at the ChNPP

Abstract

As a result of the nuclear explosion at the fourth block of the Chornobyl NPP (ChNPP), the radioactive cloud containing an aerodispersed system with aerosols formed at the explosion appeared in air above the ChNPP territory. The accident occurred at the end of the reactor company before the assumed reloading of the active zone. Thus, the cloud composition included the products of fission and activation of uranium that were accumulated in the reactor fuel during the company. On that night, the east wind carried the radioactive cloud to the west, by leaving the aerosol fallouts on Earth’s surface as a radioactive trace. The results of the own studies (1986–1990) of aerosol fallouts on the west trace formed at once after the explosion at the ChNPP are presented. On this basis, the characteristics [physico-chemical forms, radionuclidic composition, activity median aerodynamic diameters (AMADs), etc.] of the aerodispersed system created at once after the explosion of the active zone of the reactor are reconstructed. In the frame of the respiratory model given in ICRP Publication 66, the contributions caused by the inhalation of fuel particles (microscopic particles which are fragments of exploded fuel elements and have conserved mainly their radionuclidic characteristics) to the doses of irradiation of parts of respiratory organs and gastrointestinal tract (GIT) are evaluated. It is shown that the cause for a mass cough in the summers of 1986 and 1987 on territories underwent the action of emergency fallouts was the inhalation of radionuclides of ruthenium in the form of RuO4 that was formed in “hot” particles contacting with air and then evaporated from them. The “hot” particles are compact inclusions formed by fission products. They consist mainly of atoms close to noble metals (molybdenum, ruthenium, rhodium, etc.) formed during a regular operating period in fuel tablets and released from the latter at the explosion of the active zone. The reasons for the disagreement between the clinic consequences and the ascribed values of the dose for the sufferers who were present in premises of the NPP at the emergency time and then died from acute radiation sickness in three-four weeks after the accident are explained.