The Study Of Water Radiolysis Under γ Irradiation Condition

The groundwater around a radioactive waste repository will dissociates into highly reactive radicals such as ·OH, ·H,aqe, ·HO2 and ·O2-and molecular species such as H2, O2,and H2O2 due to γ ionizing radiation from the radioactive substances. These decomposition products are highly reactive, can induce and enhance metal corrosion in the environment, and oxidize and dissolve the solidified wastes in the metal container, so the radionuclides can migrate long distances with the flow of the groundwater. Yields of these dissociation products are largely dependent on factors including the additives, pH, type of radiation, temperature,and oxides.A series of experiments were carried out for the study of the degree of water radiolysis under different γ radiation dose, the main research contents and achievements are:1.Extrapolate the activity of an unknow60 Co standard source by combine the results with actual measurement and MCNP simulation, the activity is about 0.8mCi.2.Irradiate distilled water in reagent bottles with the standard source, as there is a thermoluminescent dosemeter(TLD) on each bottle and the TLDs are directly toward the source, so use the dose recived by TLDs to represent the dose recived by water. When the irradiation is completed, use a TL reader to read the dose received by the TLDs, use a laboratory pH/potential value meter to measure the pH and redox potential values of the water samples.3.The results demonstrate that the pH value of the water will decline slowly and the redox potential value of the water will rise slowly with increasing dose. That’s because during radiolysis, water breaks down to oxidizing agents(·OH, ·HO2 and H2O2)and reducing agents(·H,aqe and H2), on the one hand, the oxidizers are strong oxidizing agents, can oxidize the N2 which dissolved in water to HNO3, and HNO3 is a strong acid and strong oxidant; on the other hand, H2 will disappear from the water very soon, but the oxidants will stay in thesystem, this makes the oxidation of the system increased.4.The radioactivity in geological disposal repository is much higher than the radioactivity in the laboratory, so we can infer that with the radiolysis of groundwater occurs,the acidity and oxidizing properties of the environment around the repository will significantly enhanced, this will produce bad effects on the longterm security of the repository.