DETERMINATION OF PLUTONIUM IN HIGH ACTIVE LIQUID WASTE OF REPROCESSING PLANT BY SPECTROPHOTOMETRY USING NEODYMIUM AS AN INTERNAL STANDARD

A rapid verification technique with conventional spectrophotometer has been developed to achieve onsite safeguards measurements in which neodymium as an internal standard was chosen to determine the plutonium concentration in high radioactive liquid waste. An actual sample with a known amount of neodymium(III) standard was heated with a mixture of nitric acid and hydrofluoric acid to dissolve plutonium in solid state. Subsequently plutonium was quantitatively oxidized to plutonium(VI) in 3M nitric acid using a cerium(IV) nitrate solution prior to spectrophotometric measurement. The absorbance of the plutonium(VI) was measured at 830 nm as well as that of neodymium(III) at 795 nm. The plutonium concentration in the sample was calculated using the molar extinction coefficient ratio of neodymium(III) to plutonium(VI), and the absorbance ratio of neodymium(III) to plutonium (VI) in the sample that a known quantity of neodymium was being added. The amount of neodymium initially existing in the sample was corrected with the absorbance ratio of neodymium(III) to plutonium(VI) in it without neodymium standard. As a result, it was found that the measurement result obtained with the proposed method was in good agreement with that of isotope dilution mass spectrometry, which has been so far used in application for safeguards verification to determine the plutonium concentration in the high radioactive liquid waste. In this method, neodymium standard is intended to be independently provided by the International Atomic Energy Agency so that an inspector can independently control it not only as an internal standard but also as an authentication purpose. The plutonium measurement will be performed in “common mode” by national/international inspectors. They calculate the coefficients of the regressed calibration curve from the results obtained from standards and evaluate the plutonium concentration of the samples accordingly, using authenticated software to evaluate the spectra of all measurements. This method will provide the on-site analytical capabilities as it allows rapid and simple analyses at Tokai Reprocessing Plant.