Determination of 36Cl in biological shield concrete using pyrohydrolysis and liquid scintillation counting

Abstract

A method for the determination of ³⁶Cl in biological shield concrete of nuclear reactors was developed. Cl in the concrete sample was extracted quantitatively by pyrohydrolysis at 900 °C and recovered in Na₂CO₃ solution for subsequent measurement of ³⁶Cl by liquid scintillation counting. WO₃ was used as an accelerator in the pyrohydrolysis. The Cl extraction procedure was optimized by investigating experimental conditions with the use of ion chromatography and its recovery was evaluated by the analysis of the geochemical reference samples. The detection limit of ³⁶Cl was 0.02 Bq g⁻¹ for a sample weight of 2 g. The relative standard deviation was 3–7% for the samples containing 0.5 Bq g⁻¹ levels of ³⁶Cl. The method was applied to determine ³⁶Cl in biological shield concrete of the Japan Power Demonstration Reactor.