ИСТИНА

Objects of the fuel cycle are the sources of radioactive pollution of the World Ocean, representing a serious danger. Direct entry into the World Ocean of technogenic radionuclides, as well as their movement through rivers into the sea from radiochemical plants for the reprocessing of spent nuclear fuel, including the consequences of the accidents, represents a serious potential danger. The causes of such serious accidents can be natural and technogenic factors that were not considered during the design of a hazardous facility. A typical example of a technogenic catastrophe that occurred due to the complex impact of external factors is the accident at the Fukushima nuclear power plant. The external impacts on an object which uses atomic energy, such as loss of energy supply, fire, air shock wave and others, can cause disruptions in the operation and maintenance of the object and lead to the creation of favorable conditions for the occurrence of uncontrolled exothermic processes in nitric acid solutions, containing reducing agents or contacting with reducing agents, representing a potential danger. Objective of the study: to evaluate the fire and explosion hazard of systems containing nitric acid and water-soluble organic compound (monoethanolamine). Monoethanolamine (MEA), used in nuclear power industry as a corrective additive to maintain the pH of the secondary coolant in the range that ensures minimal corrosion of equipment in the system, is a reducing agent in the pair "MEA - nitric acid". Studies were conducted by thermal analysis methods using a differential scanning calorimeter DSC-500 and sealed crucibles, as well as a device for assessing thermal stability under high pressure conditions [1]. It is shown, that nitrate solutions with MEA are thermally highly unstable, and at the temperatures close to boiling points of 105-110 °C decompose with gas evolution, the maximum rate of which increases with increasing concentrations of reagents. When the pressure is above atmospheric, the process is accompanied by heat evolution and proceeds in the mode of uncontrolled exothermic reaction - thermal explosion. The intensity of the thermal explosion depends on the concentration of HNO3, it is quite high at concentrations from 18 to 26.5% of HNO3. The maximum intensity of thermal explosions is achieved by rapidly heating the solution to the start temperature of exothermic process TSE, in particular, at a thermostat temperature of 150 °C, which is confirmed by the data of experiments in an autoclave. Thus, in the presence of even small amounts of MEA in the solution, during their exothermic interaction with the oxidizing agent, it is possible to create pressures which are sufficient to cause emergency situations. To ensure safety, we can recommend to exclude the presence of MEA in solutions entering high-temperature operations. This work was financially supported by Russian Science Foundation (project 16-19-00191). References: 1. Rodin A.V., Nazin E.R., Zachinyaev G.M., Belova E.V., Tkhorzhnitsky G.P., Danilin D.I., Tananaev I.G. Radiation-thermal interaction of TBP with nitric acid at atmospheric pressure. Voprosy radiatsionnoy bezopasnosti, 2011, 3, 45-50