Use of Radioactive Tracers for Measuring the Density of the Emulsion (Water-Steam) Flowing in the Water-Wall Tubes of Industrial Boilers

Introduction of a radioactive nuclide into the water offers a rapid procedure for diagnosing the functioning and properties of industrial boilers without altering the phenomena to be measured. The choice of radionuclide must satisfy strict criteria; after a large number of trials, a mixture of 186Re and 188Re obtained by neutron irradiation of natural rhenium was chosen. The background noise is measured at the time of the trials with the help of a system of three tubes placed in front of the boiler, or of one tube placed in an inspection chamber. The density of the emuision (water- steam) can be measured with an accuracy of between 10% and 15%. Trials were carried out on a boiler with a capacity of 3 tons of water operating under a pressure of 10kg/cm2 at 180°C. The emulsion density in several water-wall tubes was compared for different vapour flows, the density being measured along the whole length of the tube, which gives information on the thermal exchanges between the furnace and this tube. Trials will very soon be carried out on a power boiler belonging to Electricité de France (Creil Power Station). The personnel working around the boiler run no risk of irradiation since the quantities of radionuclide (10 to 25 μCi/litre of water) are small. The complete calculation of the isodose curves, verified by dosimetric measurements, shows that the dose 20 cm outside the boiler is below 90 mrads after 210 h, which is 6 or 7 times lower than the maximum tolerable dose. The dose is even smaller in the case of a large boiler. (author)