Model for the Formation of Iodine Oxide Nanoparticles within the Reactor Containment

Abstract

A description is given of the model of formation of iodine oxide nanoparticles in the volume of the containment of a nuclear reactor during radiation-chemical reactions and clustering with subsequent formation of nanoparticles. The results of test calculations are presented. Nanoparticles of radioactive iodine oxides pose a potential hazard as a source of long-term radiation exposure to NPP personnel. They also penetrate outside the power plant through the air-ventilation system even if the enclosure remains sealed. In addition, calculations have shown that the formation of radioactive iodine oxide nanoparticles is closely related to the formation of volatile iodine compounds in the gas phase. Moreover, the intensity of formation of the latter depends significantly on air humidity. The main feature of the proposed model is the consideration of the kinetics of phenomena for processes in both the gas and aerosol phases when exposed to ionizing radiation on oxygen and water vapor in the air. The main result of the calculations is confirmation of the fundamental possibility of the formation of aerosol nanoparticles consisting of iodine oxides in a humid atmosphere even with a relatively low dose rate of radiation energy absorbed by the air. At the same time, radiolysis of water vapor has a weak effect on the size and concentration of iodine oxide nanoparticles. However, taking into account the chemical interaction of radiolysis products, in particular hydrogen radicals, induced by water vapor radiolysis, significantly affects the formation of volatile iodine compounds with hydrogen: HI and HOI. The obtained results, despite their preliminary nature, are important since they indicate the inevitability of the formation of suspended nanoparticles of iodine oxides and hydrogen iodide in the atmosphere of the reactor premises in the event of emergency situations with the release of radionuclides beyond the first circuit of the reactor. Therefore, this mechanism must be taken into account when developing models of the formation and behavior of fission product aerosols at NPPs.