C-14 concentration measurement in aqueous samples using direct absorption method and liquid scintillation counting

Cernavoda Nuclear Power Station is the only nuclear power plant in Romania and the only CANDU reactor operating in Europe. The Cernavoda Unit 1 is a pressurized heavy water reactor (PHWR) fuelled with natural uranium and moderated and cooled by heavy water. The routine operation of this type reactor and its auxiliary process systems results in the production of a variety of solid, liquid and gaseous radioactive wastes. Carbon-14 is produced mainly via a neutron capture reaction of oxygen-17 in the CANDU reactor. CANDU production and emission rates of C-14 are higher than those of other types of commercial reactors such as light water reactors and gas-cooled reactors. In order to fulfill the exigency of the monitoring program, we propose several studies to optimize C-14 determination in water samples. A complete C-14 measurement procedure adequate for natural level water samples has been developed. The characteristics and specificity of this new measurement technique are discussed and several comparisons with concurrent methods are investigated. Special emphases have been done for sample preparation technique and the direct absorption method has been used with few home-made improvements in order to increase the reproducibility and accuracy of this simple and less-time consumer method. The results confirmed the validity of the sample preparation and measurement procedures, providing an increased reproducibility compared to traditional techniques. A validation test using CaCO3 resulted from oyster shell and marble provided a mean value of 0.2137±0.0039 Bq/gC for an efficiency value of about 64% and a background value of 2.22cpm. The routine procedure was applied on different type of water. (author)