Quantitative CT-reconstruction of void fraction distributions in two-phase flow by neutron radiography

A quantitative void fraction measurement method based on the umbra method using a neutron absorber grid was applied to the void fraction measurement of two-phase flow in a rod bundle. The grid 3 mm in width and 3 mm in interval was made from B4C. The two-phase flow direction was vertical and the grid was placed vertically between the rod bundle and the neutron source. A cooled-CCD camera in the JRR-3 M thermal neutron radiography system was used. CT reconstruction was carried out for 60 horizontal slices with a vertical interval of 3 mm. Subchannel void fraction distributions were also calculated. The quantitative measurement with spatial resolution 0.1 mm, size of the image element, horizontally and 3 mm vertically was carried out.