EXPERIMENTS AND CALCULATIONS ON NEUTRON STREAMING THROUGH BENT DUCTS

Neutron spectra in a cylindrical straight duct and in bent ducts with angles of 30-degrees, 60-degrees and 90-degrees have been measured by the multiple foil activation and thermoluminescence dosimetry methods. Two-dimensional discrete ordinates and three-dimensional Monte Carlo calculations are executed, and the results are compared with the measu rements. The flow rate at the duct entrance calculated by the DOT3.5 c ode is underestimated by approximately 30%, due to a conversion of the core and reflector geometry from XY to RZ geometry. The fast neutron flux in the ducts is underestimated by 20% by the MORSE-SGC/S code due to a too coarse angular mesh of the source, which does not properly r epresent the actual angular distribution of the fast flux, which is hi ghly peaked forwardly into the ducts. The thermal neutron flux was ove restimated by the Monte Carlo calculation. A method is proposed to cal culate the angular distribution of the flow rate at the duct entrance and to calculate the source strength and the angular distribution of t he flow rate at the entrance of the second leg of the duct. The result s are compared with those of the transport calculations. Generally, th e agreement is quite satisfactory.