VERIFICATION OF NEUTRON RADIOSCOPIC MEASUREMENT OF VOID FRACTION BY MONTE-CARLO SIMULATION

Neutron radioscopic images have been simulated using the Monte Carlo m ethod to verify the Sigma-scaling method used in void fraction measure ment of two-phase flow. Continuous energy Monte Carlo code MCNP was us ed for the accurate treatment of the test section with complex geometr y. Radioscopic images of water-layer thickness distribution in a conce ntric triple-tube test section were successfully reproduced by the Mon te Carlo simulation. The simulated images at various distances between the test section and the converter were obtained using an ideal monod irectional (parallel) beam and realistic beam with unparallelness defi ned by the L/D ratio, thus enabling the separate treatment of the unsh arpness of the image caused by the scattered neutrons and the unparall elness of the incident neutron beam. The treatment of the scattered co mponent and the unparallelness of incident beam employed in the Sigma- scaling method was verified to be appropriate through the simulation, which shows that the Sigma-scaling method could be successfully adopte d for the quantitative measurement of void fraction of two-phase flow. (C) 1998 Elsevier Science B.V. All rights reserved.