Vladimir Domanov

Abstract:

Experimental evidence for the existence of volatile oxides and hydroxides of nat.U, 238,239Pu and 244,243,244Cm is obtained. They were produced under thermal oxidation of trace quantities of these actinides in a slow stream of the dry He and O2 mixture. The volatile compounds were separated by the thermochromatographic (TC) method. The initial sample was a purified quartz powder with actinides in question adsorbed on its surface. It was placed into the starting zone of an empty quartz TC column. The results of the experiments showed that the uranium compounds were transported along the column and adsorbed at 45025C, 25025C and 12025C. The deposition zones were found with an α-spectrometer. The location of the plutonium deposition zones resembled the distribution of the uranium adsorption zones, and one more very volatile compound deposited at a negative temperature about 100C was registered. In similar conditions, curium formed three adsorption zones located at 55025C, 39025C and at negative temperature equal to 8050C. An increase in the efficiency of uranium and plutonium transport into the third zone (12025C) with the enhancement of the gas humidity can be connected with formation of volatile hydroxides. For completeness of the interpretation of the results obtained, model experiments with trace quantities of 249Cf and carrier-free 185Os, 183Re, 97Ru and 96Tc radioisotopes were performed. It was shown that 249Cf formed volatile dioxide adsorbed at 45025C. It was also found that other model radioisotopes in a stream of helium with a negligible touch of oxygen were adsorbed at 450-500C and 250-300C in the forms of dioxides and trioxides, respectively. Based on these data, it is assumed that the first adsorption zone appears due to formation of actinides dioxides, and the second one appears due to formation of trioxides. There is some similarity when we compared 185OsO4 and 97RuO4 adsorption zones to last adsorption zones of plutonium and curium. We can draw a conclusion that octavalent plutonium and curium were produced, which were in a form of very volatile PuO4 and CmO4 deposited at a negative temperature. The results obtained point to the possibility of migration of oxidation products of uranium, plutonium, and curium in the atmosphere after nuclear tests and accidents at nuclear power plants. It was concluded that dioxides and trioxides of actinides can migrate in the atmosphere by an aerosol mechanism, the volatile tetraoxides PuO4 and CmO4 can be transferred by airflow, and the transfer of volatile U and Pu hydroxides can be affected by a mixed mechanism.