About chemical form and binding energy of 14c in irradiated graphite of uranium graphite nuclear reactors
Problems related to the management of irradiated graphite of uranium graphite nuclear reactors were considered. It is shown that the choice of approaches, methods and means for handling irradiated graphite is determined by the form of the finding and binding energy of the long lived radionuclide 14C. The purpose of this work is to determine the possible chemical compounds in which 14C can be found and to assess the strength of its fixation in the structure of irradiated graphite. The domestic and foreign experience in handling graphite radioactive waste was analyzed, calculations and experiments were performed to achieve the goal. Information on the accumulation channels of 14C in the structure of reactor graphite was given and it was shown that the greatest amount of this radionuclide is formed by the nuclear reaction 14N(n, p)14C. At the same time, the majority of radioactive carbon is created on N2, which placed in unirradiated graphite in chemical impurity and in supported gas. Radionuclide 14C generated by nuclear reaction 14N(n, p)14C is localized in surface layer of graphite (including surface of pores) at a depth no more than 50 nm. Assessment of possible chemical compounds in which radioactive carbon can be located was carried out. It is proved that the form of finding is determined by the operational features of a particular graphite element in the reactor. The binding energy of 14C in the structure of irradiated graphite and the calculated depth of its penetration into the structure were estimated. Selective removal of this radionuclide is possible only at elevated temperatures in a weakly oxidative environment, which is due to binding energy up to 800 kJ / mol was established. Radiocarbon, which generated by nuclear reaction 13C(n, γ)14C is placed uniformly in irradiated graphite elements and have binding energy about 477 kJ / mol. The selective removal is possible only during crystal fracture and organization of isotope separation process. The data obtained make it possible to select methods of handling irradiated graphite during decommissioning of uranium graphite reactors.
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