AbstractPurposeThe purpose of this work is to describe the spectrometric analysis of gaseous cloud formation over reactor mixed uranium-and-plutonium (UP) fuel (U0.8Pu0.2)O2 samples heated to a temperature > 2,000°С, and thus forecast and evaluate radiation hazards threatening humans who cope with the consequences of any accident at a fission reactor loaded by UP mixed oxide (U0.8Pu0.2)O2, such as a mixture of 80% U and 20% Pu in weight.Materials and methodsThe UP nuclear fuel samples were heated up to a temperature of over 2,000°С in a suitable assembly (apparatus) at out-of-pile experiments' implementation, the experimental in-depth study of metabolism of active materials in living organisms by means of artificial irradiation of pigs by plutonium. Spectrometric measurements were carried out on the different exposed organs and tissues of pigs for the further estimation of human internal exposure by nuclear materials released from the core of a fission reactor fueled with UP mixed oxide.ResultsThe main results of the research described are the following: (1) following the research on the influence of mixed fuel fission products (radioactive isotopes being formed during reactor operation as a result of nuclear decay of elements included into the fuel composition) on living organisms, the authors determined the quantities of plutonium dioxide (РuO2) that penetrated into blood and lay in the pulmonary region, liver, skeleton and other tissues; and (2) experiments confirmed that the output speed of plutonium out of the basic precipitation locations is very small. On the strength of the experimental evidence, the authors suggest that the biological output of plutonium can be disregarded in the process of evaluation of the internal irradiation doses.ConclusionThe main results of the research are useful for further evaluation of human accidental irradiation in the case of breakdown at fission reactors working on mixed nuclear fuel, and designing medical protection measures for persons irradiated by plutonium isotopes.