γ Radiation Stability And Radiolysis Products Of Di-(1-methyl-heptyl) Methyl Phosphonate And Tri-isoamyl Phosphate

Nuclear power is a clean, efficient and relatively secure energy resource. It is the only high-quality energy that is of the ability to replace fossil fuels in large-scale. With the development of nuclear energy, the spent fuel generated in nuclear power plant is getting more and more. So the reprocessing of spent fuel has become an urgent affair. Purex process is the only matured process for spent nuclear fuel recovery. It uses tributyl phosphate(TBP) as extractant, n-dodecylamine or kerosene as diluent and nitric acid as salting-out agent, separates and purifies U and Pu by utilizing differences among U, Pu and the fission products in the behavior of being extracted. However, the solubility of TBP in water is a little higher and its degradation products can combine with highly-charged metal ions to give poorly soluble complex. Then the third phrase can be formed and this will affect the normal operation of the system. Di-(1-methyl-heptyl) methyl phosphonate(P350) and tri-isoamyl phosphate(TiAP) are of very low water-solubility. There is no the third phrase when they are used to extract higher concentration Pu and U. Therefore, P350 and TiAP are expected to replace TBP as extractant in future spent fuel reprocessing. The effects of preequilibrated nitric acid concentration and dose on the γ-radiation stability and radiolysis products of P350 and TiAP were studied. These results will give reference to the application of P350 and TiAP in the reprocessing of spent fuel. The main results are as follows. 1) P350 was analyzed by acidometric titration. TiAP was analyzed by high performance liquid chromatography. The analysis of hydrogen, methane, ethane, ethylene, propane, propylene, n-butane, n-pentane, i-pentane and 3-methyl-1-butene was performed by gas chromatography. Hexane, n-heptane, n-octane, n-decane, n-undecane were analyzed by gas chromatography with headspace sampling. Di-iso-amyl-phosphate, methylenephosphonic acid and phosphoric acid were analyzed by ion chromatography. 2) For 1.098 mol/L P350-dodecane solution preequilibrated by nitric acid with different concentrations irradiated to 200 kGy, the radiation stability of P350 increases with the concentration of preequilibrated nitric acid. For 1.098 mol/L P350-dodecane solution preequilibrated by 3.0 mol/L nitric acid, at the dose beween 30 and 200 kGy,the radiation stability of P350 decreases with the increasing dose. The main radiolysis products are hydrogen, methane, ethane, ethylene, propane, propylene, n-butane, n-pentane, hexane, n-heptane, n-octane, n-decane, n-undecane, methylenephosphonic acid and phosphoric acid. The volume fraction of hydrogen, methane, ethane, ethylene, propane, propylene, n-butane and n-pentane increases with increasing dose, but decreases with increasing concentration of preequilibrated nitric acid. The concentration of hexane, n-heptane, n-octane, n-decane, n-undecane, methylenephosphonic acid and phosphoric acid increases with increasing dose and decreases with increasing concentration of preequilibrated nitric acid. 3) For 1.098 mol/L TiAP-dodecane solution preequilibrated by nitric acid with diffent concentrations irradiated to 200 kGy, the radiation stability of TiAP increases with the concentration of preequilibrated nitric acid. For 1.098 mol/L TiAP-dodecane solution preequilibrated by 3.0 mol/L nitric acid, at the dose beween 30 and 200 kGy, the radiation stability of TiAP decreases with the increasing dose. The main radiolysis products are hydrogen, methane, ethane, ethylene, propane, propylene, n-butane, n-pentane, i-pentane, 3-methyl-1-butene, n-hexane, n-heptane, di-iso-amyl-phosphate and phosphoric acid. The volume fraction of hydrogen, methane, ethane, propane, n-butane, n-pentane, i-pentane and 3-methyl-1-butene increases with increasing dose, but decreases with increasing concentration of preequilibrated nitric acid. The volume fraction of ethylene and propylene increases with increasing concentration of preequilibrated nitric acid then takes a maximum value at 1.0 mol/L and decreases at the higher concentration. The volume fraction of hydrocarbon gas increases with increasing dose. The concentration of i-pentane and n-heptane decreases with increasing concentration of preequilibrated nitric acid, but that of n-octane increases with increasing concentration of preequilibrated nitric acid. The concentration of phosphoric acid increases with increasing concentration of preequilibrated nitric acid then takes a maximum value at 2.0 mol/L and decreases at the higher concentration. The concentration of di-iso-amyl-phosphate decreases with increasing concentration of preequilibrated nitric acid then takes a minimum value at 2.0 mol/L and increases at the higher concentration. The concentration of i-pentane, n-heptane, di-iso-amyl-phosphate and phosphoric acid increases with increasing dose.