Determination of 63 Ni in Vadose Zone of Underlying Stratain Low and Medium Level Radioactive Solid Waste Disposal Site

63Ni is a corrosion activation product generated during the operation of nuclear facilities and is present in large quantities in nuclear waste. Radioactive waste is usually buried underground for disposal. During the long-term burial process, radionuclides may enter the underground aquifer through the vadose zone of the underlying strata of the disposal site, affecting human health and environmental safety. In order to clarify the adsorption capacity and migration pattern of 63Ni in the vadose zone of underlying strata in the low and medium level radioactive solid waste disposal site, and provide a technical basis and safety assessment basis for the site selection, design and construction of radioactive waste disposal sites, a rapid analysis method for 63Ni in the vadose zone soil was established in this paper. The sample was firstly pretreated to ensure the complete release of 63Ni in the sample. After the sample was baked at 100°C to constant weight, 0. 5 g was taken and 3 mg of nickel tracer was added, and then baked at 300 °C for 3 h. The sample was extracted with 9 mol/L hydrochloric acid at 100°C for 3 h, and then filtered, and the supernatant was collected. Then the supernatant was precipitated twice by butanedione oxime to remove stable iron present in the soil and other potentially interfering radionuclides that affect 63Ni measurements by liquid scintillation counter (LSC). A precipitation was first performed. 1 mL of 1 mol/L ammonium citrate solution was added to the supernatant and the solution pH was adjusted to 9-10 with ammonia, and then 1% (m/V) ethanolic solution of butanedione oxime (DMG) was added to form a bright red precipitate butanedione oxime-nickel (DMG-Ni), and after centrifuga-tion, the precipitate was dissolved with hydrochloric acid. After dissolution, a second precipitation was carried out. 0. 2 mL of 1 mol/L ammonium citrate solution was added to the dissolution solution, followed by adjusting the solution pH = 9-10 with ammonia, and then 1% ethanolic solution of DMG was added, and the formed DMG-Ni precipitate was centrifuged and dissolved with hydrochloric acid. Some samples from the dissolution solution were taken to measure the chemistry recovery by UV-Vis spectrophotometer, and the activity was measured by Hidex 300SL TDCR LSC after adding Hisafe scintillation cocktail to the rest of the samples. The results show that the average chemistry recovery of Ni is (97. 6 ± 2. 4) %, the detection limit for 0. 5 g soil sample measured for 1 h is 0. 18 Bq/g, the decontamination factors of interfering nuclides such as 60Co, 65Zn, 54Mn and 55Fe are all more than 103, and the radiochemical separation process can be completed within 2 h. The validation of the analytical method with spiked samples show that the relative deviation of expected and measured values is less than ±3%. © 2022 Atomic Energy Press. All rights reserved.