Quantitative method to measure void fraction of two-phase flow using electronic imaging with neutrons

A quantitative method of image processing coupled with the neutron radiography technique is proposed to accurately measure the void fraction of a two-phase flow in a metallic duct. The spatial distribution of the dark current component is experimentally shown to be smooth, and the temporal variation cannot be ignored. Since the neutrons scattered in an object can be smoothed and reduced by setting the test section at a large distance from the converter, it is clarified that the corrections for the dark current and scattered neutrons can be represented by an offset. The offset value can be determined by using the total macroscopic cross section of the object (Σ-scaling method). By comparing the calculated void fractions with the measured ones obtained by simulating the known void profile using a standard test section, the void fraction can be measured by this method within 2% error. The measurement error is estimated to be up to ∼10% when no correction for scattered neutrons is made or arbitrary offset values are used.