The shielding effect of iron louvers for neutrons and gamma rays

The shielding effect for neutrons and gamma rays provided by a louver-type steel structure inserted into the second leg of a concrete duct was measured and analyzed. The louver is an assembly of steel plates that are stacked at the same interval to reduce the radiation streaming while keeping air flowing through the duct. The experiment was carried out at the Japan Research Reactor-4 (JRR4) using a large concrete duct that was temporarily installed for this experiment. Experimental data for the shielding effect of the louver were obtained through the use of thermoluminescent dosimeters (CaSO4 and BeO) and an ionization chamber for the gamma dose. A rem counter was used to obtain neutron dose, while a solid-state track detector was used for fast neutron dose. Finally, indium activation foil was used to obtain the thermal neutron flux. A NaI(Tl) scintillation spectrometer was used for the measurement of gamma rays from activated foil. The measured data were compared to that derived from numerical analyses. Numerical analyses included the use of the conventional S-n transport code DOT3.5, the Monte Carlo code MCNP4A, and calculations with empirical formulas. MCNP4A provided satisfactory estimates for all cases. If proper calculations were carried out, then DOT3.5 provided acceptable estimates except for the thermal neutrons in spite of the limitations of the code's two-dimensional geometrical modeling. Calculations by hand using simple empirical formulas with modifications, like that for the angular flux correction, also could provide fairly accurate estimates.