INFLUENCE OF SCATTERED NEUTRONS ON VOID FRACTION MEASUREMENT OF 2-PHASE FLOW USING THERMAL-NEUTRON RADIOSCOPY

The purpose of this study was to study the influence of scattered neut rons on void fraction measurement of two-phase flow using thermal neut ron radioscopy and to develop a practical correction method for scatte red neutrons. Experimental and analytical studies resulted in the foll owings. (1) It was confirmed that neutrons scattered in the object cou ld be smoothed out by taking an appropriate distance between the objec t and the converter. The distance was roughly estimated to be greater than the object width and was independent of the object thickness. The maximum distance was estimated to be the product of the spatial-resol ution and L/D ratio of the neutron radiography facility in view of the image unsharpness due to unparallelness of an incident neutron beam. (2) The previously proposed method for correcting scattered neutrons ( Sigma-scaling method) was verified experimentally. (3) In such a syste m that neutrons scattered in surrounding shields cannot be ignored, it was pointed out analytically that void fraction measured without no c orrections of scattered neutrons might include a large measurement err or. This measurement error depended on the void fraction, the object m aterial, and the flux of scattered neutrons.