Development of a neutron device to measure steam quality at a high pressure

Abstract

Steam quality, measured as the void fraction in a two-phase, steam-water flow in an autoclave, was investigated by the fast neutron scattering technique. This technique based on the slowing-down of neutrons, resulting from the thermalization of fast neutrons, is proportional to the number of hydrogen nuclei in the liquid. A Monte Carlo simulation demonstrated that linearity between void fraction and neutorn count rate (detector response) could be achieved using the instrument geometry; viz. 252Cf as isotropic neutron source, helium detector and half-inch stainless steel pipe. Before the steam-water system was studied, a static experiment usingLucite rods and a nitrogen-water experiment in which nitrogen was bubbled through water in a plexiglas tube were performed to confirm the Monte Carlo results. A simplified calibration method was used to estimate the void fraction obtained from experiment; the estimated value varied linearly with the actual value of the void fraction. At high pressure and temperature, the density of water was found to be proportional to neutron count rate. The measurement of steam quality calculated from the parameters of the autoclave operation was detected by a neutron scatterometer. It was found that the neutron count rate decreased as steam quality increased as predicted.