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CN-122016684-A - Method for measuring hexavalent neptunium in organic phase

CN122016684ACN 122016684 ACN122016684 ACN 122016684ACN-122016684-A

Abstract

The invention relates to the technical field of post-treatment analysis of spent fuel, in particular to a method for measuring hexavalent neptunium in an organic phase. A method for measuring hexavalent neptunium in an organic phase includes preparing a series of organic phase standard solutions of hexavalent neptunium in concentration, measuring the absorption spectrum of the standard solutions, carrying out second derivative treatment on the absorption spectrum of the standard solutions to obtain second derivative spectra of the standard solutions, establishing a quantitative correction relation between peak areas of characteristic absorption peaks and the hexavalent neptunium concentration according to the second derivative spectra of the standard solutions, measuring the absorption spectrum of an organic phase solution to be measured, carrying out second derivative treatment on the absorption spectrum of the solution to be measured to obtain second derivative spectra of the solution to be measured, substituting the peak areas of the second derivative spectra of the solution to be measured at the characteristic absorption peaks into the quantitative correction relation, and calculating the hexavalent neptunium concentration in the solution to be measured. The concentration of Np (VI) in the organic phase can be directly measured, the influence of acidity is eliminated or corrected, and the method is rapid and accurate.

Inventors

  • SUN TAOXIANG

Assignees

  • 清华大学

Dates

Publication Date
20260512
Application Date
20260320

Claims (10)

  1. 1. A method for determining hexavalent neptunium in an organic phase, comprising: Preparing a series of organic phase standard solutions of hexavalent neptunium concentration, and measuring the absorption spectrum of the standard solutions; performing second derivative treatment on the absorption spectrum of the standard solution to obtain a second derivative spectrum of the standard solution; Establishing a quantitative correction relation between the peak area of a characteristic absorption peak and the concentration of hexavalent neptunium according to the second derivative spectrum of the standard solution; Measuring the absorption spectrum of the solution to be measured of the organic phase; performing second derivative treatment on the absorption spectrum of the solution to be detected to obtain a second derivative spectrum of the solution to be detected; substituting the peak area of the second derivative spectrum of the solution to be detected at the characteristic absorption peak into the quantitative correction relation, and calculating to obtain the concentration of hexavalent neptunium in the solution to be detected.
  2. 2. The method according to claim 1, wherein the peak position of the characteristic absorption peak is at least one of 1200 to 1220 nm or 615 to 625nm, preferably 615 to 625nm.
  3. 3. The assay of claim 2, wherein the organic phase comprises 30vt% tributyl phosphate-n-dodecane; optionally, the organic phase is any one of a blank organic phase and a pre-equilibrium organic phase; Optionally, the preparation method of the pre-equilibrium organic phase comprises the steps of adding an aqueous phase into the organic phase, oscillating, standing for layering, taking out the aqueous phase, and repeating for three times to obtain the pre-equilibrium organic phase.
  4. 4. A method according to claim 3, wherein the aqueous phase comprises a nitric acid solution having a nitric acid concentration of 0.1 to 8.0 mol/L, preferably 1.0 to 8.0 mol/L.
  5. 5. The method according to any one of claims 1 to 4, wherein the concentration of the series of concentrations is in a concentration range of 1.0 to 12.0 mmol/L.
  6. 6. The measurement method according to any one of claims 1 to 4, wherein an absorption spectrum of the standard solution or the solution to be measured is measured by a spectrometry method that satisfies at least one of the following conditions: the wavelength range is 200-1400 nm; The spectral wavelength interval is 0.1-1.0 nm; the scanning speed is 60-600 nm/min.
  7. 7. The measurement method according to any one of claims 1 to 4, wherein the second derivative processing includes performing a second derivative on absorbance of the absorption spectrum, and the formula of the second derivative is: Wherein, the Absorbance as the second derivative spectrum; a is absorbance of the absorption spectrum; Lambda is the wavelength of the absorption spectrum.
  8. 8. A method according to any one of claims 2 to 4, wherein the quantitative correction relationship between the peak area and neptunium concentration is S=0.25 c, R 2 =0.99, and RSD=4.0% for the absorption peak at 615 to 625nm, where S is the peak area of the absorption peak and c is neptunium concentration/mol/L.
  9. 9. A method for measuring neptunium concentration according to any one of claims 2 to 4, wherein the quantitative correction relationship between the peak area and the neptunium concentration is S=0.63 c, R 2 =0.99, and RSD=1.6% for an absorption peak at 1200 to 1220 nm, where S is the peak area of the absorption peak and c is the neptunium concentration/mol/L, when the nitric acid concentration is 8.0 mol/L.
  10. 10. The method according to any one of claims 2 to 4, wherein the quantitative correction relationship between the peak area and the nitric acid concentration is S=0.015 e (cA/1.39) +0.15,R 2 =0.98, RSD=9.1% for an absorption peak at 1200 to 1220 nm, S being the peak area of the absorption peak and cA being the nitric acid concentration/mol/L.

Description

Method for measuring hexavalent neptunium in organic phase Technical Field The invention relates to the technical field of post-treatment analysis of spent fuel, in particular to a method for measuring hexavalent neptunium (Np (VI)) in an organic phase. Background Tributyl phosphate (TBP) extraction is a key process for separating and recovering uranium, plutonium and minor actinides in a nuclear fuel reprocessing process. Neptunium (Np) is present as an important minor actinide, mainly in three valence states of tetravalent neptunium (Np (IV)), pentavalent neptunium (Np (V)) and Np (VI) during the post-treatment. Wherein, np (VI) can be effectively extracted into the organic phase by TBP, np (V) is not extracted, and the extraction behavior of Np (IV) is between the two. Therefore, the accurate determination of the concentration of Np (VI) in the organic phase has important significance for monitoring the trend of neptunium, optimizing extraction process parameters and the like. In the related art, CN117949400a discloses a method for determining neptunium in nitric acid solution, which uses a second-order spectroscopic technique to quantitatively analyze the concentration and the morphology of neptunium by determining the characteristic absorption peaks of neptunium in different valence states in the aqueous phase at specific wavelengths (such as Np (VI) at 1225 nm). However, this method is applicable only to aqueous systems, and cannot be directly applied to the determination of Np (VI) in the organic phase after TBP extraction. In the water phase determination method, np (VI) in an organic phase is usually required to be back extracted to the water phase for analysis, the operation is tedious and time-consuming, TBP and n-dodecane are easy to volatilize and lose in the process, loss and determination errors are increased possibly due to incomplete phase separation, cross contamination and the like, and the back extraction step can be omitted in the direct determination of the organic phase, so that the sampling and the determination are realized. For example, an optical fiber probe or a flow cell is directly arranged at the outlet of the extraction tank to realize continuous monitoring, the measured data can be timely fed back to a process control system to automatically adjust the flow rate of the extractant or the concentration of nitric acid, and the organic phase is usually positioned in the closed extraction equipment, so that the link of the operator contacting with the radioactive sample can be directly measured, and the radiation injury of the measuring link to the human body can be reduced. Therefore, a method for determining hexavalent neptunium in an organic phase is needed, which not only can remarkably shorten the determination time and directly realize continuous monitoring at the outlet of an extraction tank, but also can reduce determination errors caused by incomplete phase separation, cross contamination and the like, improve the accuracy, and is beneficial to meeting the requirements of on-line monitoring and process control in a post-treatment flow. Disclosure of Invention The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the invention provides a method for measuring hexavalent neptunium in an organic phase. The method can directly measure the concentration of Np (VI) in the organic phase, can eliminate or correct the influence of acidity on a measurement result, has the characteristics of simplicity and convenience in operation, rapidness and accuracy, and is beneficial to realizing real-time monitoring control in a post-treatment process. According to a first aspect of the present invention there is provided a method for the determination of hexavalent neptunium in an organic phase, comprising: Preparing a series of organic phase standard solutions of hexavalent neptunium concentration, and measuring the absorption spectrum of the standard solutions; performing second derivative treatment on the absorption spectrum of the standard solution to obtain a second derivative spectrum of the standard solution; Establishing a quantitative correction relation between the peak area of a characteristic absorption peak and the concentration of hexavalent neptunium according to the second derivative spectrum of the standard solution; Measuring the absorption spectrum of the solution to be measured of the organic phase; performing second derivative treatment on the absorption spectrum of the solution to be detected to obtain a second derivative spectrum of the solution to be detected; substituting the peak area of the second derivative spectrum of the solution to be detected at the characteristic absorption peak into the quantitative correction relation, and calculating to obtain the concentration of hexavalent neptunium in the solution to be detected. By adopting the technical scheme, the concentration of Np (VI) in the organ