Laser-induced breakdown spectroscopy for contamination analysis of Sr and Cs on 316L stainless steels in alkaline environment for spent nuclear fuel storage

Highlights: • LIBS satisfactorily measured the accumulation of Sr and Cs on the surface of 316L stainless steel. • The concentration of Sr and Cs on the surface reached the maximum values at 21 days. • Strontium had two forms on the steel surface: SrCrO₄ in the oxide layer and SrCO₃ in the matrix. • The contamination of Cs was more inclined to the surface than Sr. • The contamination mechanism of Sr and Cs on the surface of 316L stainless steel was analyzed. The contamination of fission products (⁹⁰Sr and ¹³⁷Cs) on the metallic material (316L stainless steel) of alkaline spent fuel storage pond threatens to decommission nuclear facilities. Compared with previous studies unable to detect Cs on the surface of contaminated steel by laser-induced breakdown spectroscopy (LIBS), this study selected the emission lines of Sr II 407.74 nm and Cs I 455.77 nm as the analytical spectral lines of LIBS, and for the first time satisfactorily measured and analyzed the accumulation of Sr and Cs on the surface of 316L stainless steel for 7, 14, 21, 30 and 60 days, respectively. It was found during the accumulation, the concentration of Sr and Cs on the surface reached their maximum after 21 days, and relatively stabilized 30 days later. In addition, combined with the physicochemical characterizations, the contamination mechanism of Sr and Cs on 316L stainless steel was proposed, with the contaminants gradually diffusing from the oxide layer dissolved and damaged in the alkaline corrosive environment to the matrix. Strontium had two forms on the steel surface: SrCrO₄ in the oxide layer and SrCO₃ in the matrix, but the contamination of Cs was more inclined to the surface than Sr.