In-situ boric acid substractive process in the determinations of some transition metals in reactor coolant water by electrothermal atomic absorption spectrometry

Abstract

Boric acid has a strong influence on the determination of corrosion products in reactor coolant water. Boric acid concentration can be as high as 13 g l^–1. In this study we investigated the removal of boric acid from the sample matrix and the matrix effect of corrosion products. An out-of-core radiation field builds up in a pressurised water reactor because activated species (e.g., corrosion products such as Fe, Ni, Mn, Cr and Co) can re-deposit on out-of-core surfaces. Boric acid could be removed from the sample matrix in situ with a graphite furnace atomic absorption spectrometer. The subtraction process takes place in the graphite tube. Under such conditions concentrated hydrofluoric acid was used to exhaust boron from the graphite tube. The formation of low boiling boron halides, mainly boron trifluoride, constitutes fast chemical reactions. The calculated limit of quantification (p= 0.05) is 0.5 µg l^–1 in all investigated elements. Cobalt, Cr, Fe, Mn and Ni could be determined within that limit. It is also possible to improve the limits of quantification of the soluble species in all the investigated elements and remove the boric acid with use of the described preconcentration method. The powerful tool multiple linear regression, in conjunction with good experimental design, can be used to determine the dependence on the sample matrix being analysed, examine the interfering elements and verify the results. The method is applied routinely to analyse the coolant at the Loviisa Nuclear Power Plant.