Investigation of causes of the accidents, leading to explosions and fires at nuclear facilities, is an important component in ensuring nuclear and radiation safety because of the significant impact of such accidents on the personnel, population and environment. Among a large num-ber of nuclear facilities, the most dangerous are SNF reprocessing plants, which are currently using processes such as PUREX, UNEX, which consist in the extraction/back-extraction of target components by organic solutions from nitric acid media. This combination of organic reductant and nitric oxidant poses a potential danger of uncontrolled exothermic chemical re-actions, that more than once led to explosions at the radiochemical enterprises both in Russia and abroad.
The aim of this work was to study the explosiveness and radiation stability of extraction mix-tures: di(N-ethyl-4-fluoroanilide)-2,6-pyridinedicarboxylic acid (Et(pFPh)DPA), di(N-ethyl-4-ethylanilide)-2,2'-bipyridine-6,6'-dicarboxylic acid (DYP-9) and di(N-ethyl-4-hexylanilide)-2,2'-bipyridine-6,6'-dicarboxylic acid (DYP-7) in the diluent F3. Ionizing radiation of radio-nuclides was simulated by irradiating samples on a linear electron accelerator UELV-10-10 S70 with a vertical scanning electron beam with an energy of 8 MeV. The average dose of 4.68 kGy was absorbed by the sample, passing through an electron beam with a fixed velocity of 1.65 cm/s at a current of 500 μA. The number of passes provided the required total ab-sorbed dose: 0.1, 0.5 and 1 MGy. The thermolysis of the irradiated samples in contact with aqueous nitric acid solutions was carried out in an apparatus for studying the parameters of a thermal explosion at an elevated pressure. This apparatus contains a thermostat where auto-clave with volume of 300 cm3 was placed with a sample. The volume of the samples was 30 ml. The error in the pressure measurements was less than 0.5%. The thermolysis duration in all the experiments was 5 hours. The temperature of the autoclave during these experiments was 170 and 200 °C.
Following results have been obtained when the irradiated samples were heated in the closed autoclave containing extraction mixtures irradiated to doses from 0 to 1 MGy and 14 mol/L nitric acid solution:
pressure values were from 18 to 23 atm.;
the highest pressure values were close for all the studied extraction systems with the diluent F-3;
the rate of pressure increase, as in the case of the diluent FS-13, varied almost in the same interval: from 0.014 to 0.019 atm./s;
the rate of pressure increase was almost independent on the absorbed dose;
insignificant exothermic effects were detected;
the maximum increase in temperature (self-heating) of the samples as a result of exothermic processes was from 4 to 10 °C.