Determination of low-level 90Sr in large volumes of seawater

Abstract

The release of radioactive substances into the environment, particularly the discharge of contaminated water from the Fukushima Daiichi Nuclear Power Plant, has raised public concern. ⁹⁰Sr, a highly hazardous radionuclide, remains a significant challenge for accurate determination in environmental seawater due to its low concentration. In this work, an effective co-precipitation of ⁹⁰Sr with SrCO₃ and CaCO₃ was established for pre-concentration of ⁹⁰Sr from a large volume of seawater up to 45 L by using an appropriate concentration of (NH₄)₂CO₃ instead of Na₂CO₃ followed by removal of calcium by hydroxide precipitation. A chemical yield of (88 ± 2)% was achieved for strontium from 45 L of seawater, and the decontamination factors for most radionuclides were higher than 10⁴. The ⁹⁰Y ingrown from ⁹⁰Sr decay was used for the determination of ⁹⁰Sr, and sulfate precipitation was employed to remove radionuclides of Sr, Ba, Ra, and Pb, and the Y was further purified by hydroxide precipitation. The chemical yield of Y was higher than 90% in this step, and the counting efficiency of ⁹⁰Y by liquid scintillation counting reached 100%. The detection limit for ⁹⁰Sr was estimated at 0.11 mBq/L for 45 L seawater, an order of magnitude lower than surface seawater levels without direct human nuclear contamination. The method was validated by the standard addition method and successfully applied to determine ⁹⁰Sr in seawater collected from China seas. The developed method is simple and cost-effective compared to the reported methods and robust for routine analysis of seawater for ⁹⁰Sr.