REBUS is a general purpose fuel cycle analysis code built around DIF3D with features specific to a commercial fast reactor industry. The code can solve problems with 1) the infinite-time, or equilibrium, conditions of a reactor operating under a fixed fuel management scheme or 2) the explicit cycle-by-cycle, or non-equilibrium operation of a reactor under a specified periodic or non-periodic fuel management program. Fast spectrum systems typically require using recycled used fuel as the initial enrichment. The addition of breeding blankets within fast spectrum reactors allows them to progressively eliminate the need for external enrichment feeds as fast spectrum reactors can generate a larger amount of fissile material than they destroy to create power. To model these aspects of the fuel cycle analysis, REBUS contains a fuel fabrication system that can handle multiple feed materials and multiple sources. The fuel fabrication process allows for spent fuel cooling and allows the user to select how effective the reprocessing plant is at separating out the minor actinides and fission products.
More information can be found at https://www.ne.anl.gov/codes/rebus