Simultaneous determination of radionuclides in seawater by hydroxide precipitation

A method was established for determining simultaneously 51Cr, 54Mn, 59Fe, 58Co, 60Co, 65Zn, 95Zr, 95Nb and 140La present in seawater in concentrations corresponding to 5 mrem/yr for whole-body dose, the level set as guideline by the Japan AEC for light-water-cooled power reactor. Prior to concentration of the sample by precipitation of hydroxides at pH 10.5, chromate ion was reduced to trivalent form by treatment with sulfurous acid and 1 v/o of hydrochloric acid. After the concentration, the sample was found to retain 85% of Zr and Nb, and 95% of the other elements of interest in the original sample. The determination of 59Fe, 65Zn and 95Zr called for removal of Mg, which was obtained by re-precipitation of the nuclides at pH 7.5. The method thus established by the basic study was applied to trial treatment of 400 l of natural seawater, which yielded percentage of recovery practically equal to those obtained in the basic study for Cr, Mn and Co. The proposed method proved to permit determination of concentrations below those specified previously by the authors as needed for effective assessment of the environment to accord with the AEC guideline. The time required for the chemical procedures and the γ-spectrometry to determine the nine radionuclides in 400 l of natural seawater is about 34 h. The proposed method is practical in terms also of the time required for the determination. (author)