MONTE CARLO ANALYSIS OF TUNGSTEN-RHENIUM BASED CERMET FAST REACTORS FOR SPACE PROPULSION AND POWER APPLICATIONS

摘要

Monte Carlo models developed with MNCP5 version 1.4 (MCNP5.1.40) are used to compare uranium mononitride (UN) and uranium dioxide (UO_2) fuels for fast spectrum reactors. All fuels compared within this paper are encapsulated within a tungsten-6wt.%rehnium matrix, which is fabricated into prismatic fuel elements with a flat-to-flat distance of 3.556 cm. Each fuel element is modeled with 37 coolant channels, each filled with hydrogen that decreases in density as a function of axial position. A 14 cm axial neutron reflector comprised of beryllium oxide (BeO) is attached to the fuel inlet end of each fuel element. The fuel elements are arranged into a cylindrical core with a radius to length ratio of 0.75. The effective neutron multiplication (k_(eff)) is determined as a function of bare core radius and mass for uranium mononitride and uranium dioxide engrained into the matrix in a 60/40 and 70/30 fuel-to-matrix ratio. The model is then expanded upon with the addition of a 0.635 cm thick inconel-718 inner pressure vessel, a 15 cm thick beryllium neutron reflector, a 0.635 cm thick inconel-718 outer pressure vessel and 8 control drums consisting of beryllium and boron carbide (B_4C). The radius and core mass required to achieve a k_(eff) of 1.025 was determined for reactors fueled with UN and UO_2 in a fuel-to-matrix ratio of 60/40. Furthermore, the control drums are rotated in a complete open and closed position using cross section databases for 300 K and 3000 K to determine the control drum reactivity insertion capability. The reactors were found to range from 219 kg for UN reactors fueled with U~(233) to 805 kg in the case of the UO_2 core fueled with U~(235). The net control drum reactivity insertion was found to vary from -7.02 △k/k to -9.21 △k/k.