Comparison of various spectrophotometric methods for oil traces determination in WWER type reactor primary circuit

Three methods are compared of detecting crude oil substances in the coolant of the primary circuit of nuclear power plants: spectrophotometry in the IR, UV and visible (VIS) regions of the spectrum. A detailed analysis is made of the preconcentration of oil by extraction into n-hexane organic solvent for the UV and VIS methods and into CCl4 for the IR method. From the practical point of view (sample volume, cuvette volume and extract processing losses) the most suitable was the extraction ratio 1:67 for the IR method and 1:100 for the UV method. It was also experimentally verified that extraction proceeds with higher yield at pH≤4, i.e., when the effect of admixtures of boric acid, ammonia and potassium hydroxide is negligible. Statistical processing of results of the analyses with a view to the specificities of the methods showed that spectrophotometry in the IR region is the best method for determining the presence of crude oil products in the primary circuit. The VIS spectroscopy was found unsuitable. (author)