Laser-induced breakdown spectroscopy for the on-line multielement analysis of highly radioactive glass melt. Part 1: Characterization and evaluation of the method

Abstract

Laser-induced breakdown spectroscopy (LIBS) is presented for the on-line multielement analysis of molten radioactive glass at a simulated vitrification process of high level liquid waste (HLLW). A plasma plume is produced by focusing the third harmonic of a Nd: YAG laser (lambda = 355 nm) onto the glass melt surface at 1200 degreesC, and the plasma emission is guided via optical fiber and is characterized by an echelle spectrometer for the spectral range from 200 to 780 nm with a resolution of +/-0.01 nm. Compared to a Czerny-Turner spectrometer, the echelle spectrometer appears distinctively superior for its broad operational spectral range and high resolution. The laser-induced plasma is found as optically thin and locally in thermodynamic equilibrium (LTE) as characterized by measuring the electron density and plasma temperature. The matrix temperature effect on the spectral emission is observed as significant, increasing the emission line intensities with increasing temperature, but differently from element to element. The applicability of LIBS is demonstrated on a laboratory scale with an inactive simulated HLLW glass melt for various analytical characteristics concerned. Index Headings: Laser-induced breakdown spectroscopy (LIBS); Echelle spectrometer; Czerny-Turner spectrometer; Vitrification; Borosilicate glass; High level liquid waste.