Preparation of Zr-91 stable isotope standard solution for determination of Zr-93 by mass spectrometry

Konda, Miki; Asai, Shiho; Hanzawa, Yukiko  ; Magara, Masaaki  

Isotope dilution mass spectrometry (IDMS) with ICP-MS is reliable method for determination of Zr-93, which is one of the long-lived fission products found in spent nuclear fuel and high-level radioactive wastes. In order to use an isotope standard solution of zirconium as the spike for IDMS, dissolving a commercially available solid isotope standard is indispensable. Prior to the dissolution of the Zr-91 isotope standard, solubility of metal zirconium in a mixture of HNO and HF was evaluated using zirconium metal chips. Then, 2 mg of the Zr-91 isotope standard was dissolved with 0.2 mL of 1 M HNO-3 v/v% HF mixed solution, followed by adjusting the concentration of Zr-91 to approximately 1,000 g/g. IDMS, in which a natural isotopic abundance standard solution of zirconium was used as the spike, was employed for the determination of the concentration of Zr-91 in the prepared Zr-91 isotope standard solution. The concentration of Zr-91 in the prepared Zr-91 isotope standard solution was (9.61.0) 10 g/g, which is in good agreement with the predicted concentration. This indicates that the Zr-91 metal isotope standard was completely dissolved with sufficient chemical stability. Additionally, no impurities were detected in the prepared Zr-91 isotope standard solution. These positive results denote that the Zr-91 isotope standard solution with the preferable quality for IDMS of Zr-93 can be obtained by the proposed dissolution procedures.