Development of metal radioactive liquid reference material for proficiency test

This study developed liquid reference materials containing various metals, to be used for quality assurance of radiation measurements of the most common metallic wastes generated during the operation or decommissioning of nuclear power plants. The liquid reference materials were prepared by assuming the dissolution of stainless-steel using acid and melting of the major metals present in the stainless steel, namely Fe, Ni, Cr, and Mn, along with the standard sources (¹³⁴Cs, ¹³⁷Cs, ⁶⁰Co, ⁹⁰Sr). The theoretical massic activity of the standard sources added to the samples and the measured reference values of the gamma and beta emitters in the samples were compared, and they showed good agreement within a one-sigma confidence interval (k = 1). Using the developed reference materials, a proficiency test was conducted on three domestic labs, and the results were evaluated using Z-score. While the evaluation results showed good agreement between the reference values and the reported values for ¹³⁷Cs and ⁶⁰Co, all participating labs reported lower values than the reference value for ¹³⁴Cs. For ⁹⁰Sr, two out of the three labs reported significantly higher values than the reference value. Based on the results of this study, the developed metal radioactive liquid reference material is expected to be registered as certified reference material (CRM) in the future. They will be used as the CRM for measuring and ensuring the quality of radioactive metal waste.