Analyses and Development of Effective Compensation Shields in a Multilegged Duct Streaming System

The 14-MeV neutron streaming experiment with three straight ducts is analyzed with the cell flagging technique of the MCNP code. The contributions of neutrons passing through the flagging cell located at the duct inlet and entering the detectors located in the duct are identified quantitatively. Furthermore, the streaming paths of neutrons entering in the duct inlet are cleared by the analysis. As an application of the cell flagging technique, a neutron streaming system with two-bend cylindrical duct in a thick concrete shield is prepared, and the flagging cells are located around the duct. The contributions of neutrons passing the flagging cells to the detector located at the duct outlet are cleared, and effective compensation shields to reduce the neutron dose-equivalent rate at the duct outlet are obtained by replacing some of the flagging cells with the NS-4-FR shield. Moreover, it is expected that the equilibrating contribution from each flagging cell to the dose-equivalent rate at the duct outlet is the essential function to make an effective compensation shielding system with neutron streaming.