Monte Carlo simulation of additional safety control rod for commercial MNSR to enhance safety

A Monte Carlo simulation of additional safety rods for NIRR-1 HEU and LEU cores was carried out using the MCNP5 version 1.6 code. Two additional safety control rods having the same material composition as the main central control rod except for the surface area were studied. The following reactor core physics parameters were determined; neutron flux distribution within the core with safety rods withdrawn, control rod (CR) worth for each rod, core excess reactivity, shutdown margin and some kinetic parameters. Results obtained indicate that it would be feasible to include two additional safety control rods to improve safety level of the MNSR with little or no modification to the existing core configuration.

► We modeled the NIRR-1 HEU and LEU core with two additional control rods.
► The worth of the rods is adequate to shut down the reactor.
► The inclusion of the rods does not affect the neutron flux in withdrawn position.