3. DESCRIPTION OF PROGRAM OR FUNCTION
REBUS-3 is a system of codes designed for the analysis of fast reactor fuel cycles. Two basic types of analysis problems are solved: 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 nonequilibrium operation of a reactor under a specified periodic or non-periodic fuel management program. For the equilibrium type problems, the code uses specified external fuel supplies to load the reactor. Optionally, reprocessing may be included in the specification of the external fuel cycle and discharged fuel may be recycled back into the reactor. For non-equilibrium cases, the initial composition of the reactor core may be explicitly specified or the core may be loaded from external feeds and discharged fuel may be recycled back into the reactor as in equilibrium problems.
Four types of search procedures may be carried out in order to satisfy user-supplied constraints: 1) adjustment of the reactor burn cycle time to achieve a specified discharge burnup, 2) adjustment of the fresh fuel enrichment to achieve a specified multiplication constant at a specified point during the burn cycle, 3) adjustment of the control poison density to maintain a specified value of the multiplication constant throughout the reactor burn cycle, and 4) adjustment of the reactor burn cycle time to achieve a specified value of the multiplication constant at the end of the burn step.
REBUS will handle both equilibrium and non-equilibrium problems using a number of different core geometries including triangular and hexagonal mesh. The neutronics solution may be obtained using finite difference, nodal diffusion-theory and variational nodal transport methods. Fixed source depletion may be done with the three solution methods. Other features include: fully automatic restart capability, no restrictions on number of neutron energy groups, and general external cycle with no restrictions on number of external feeds, reprocessing plants, etc. Fuel management is completely general for nonequilibrium problems. Microscopic cross sections are permitted to vary as a function of the atom density of various reference isotopes in the problem as appropriate for soft spectrum systems. The user may specify control rod positions at each time node in the problem. A number of relational database datasets containing various types of summary results are available for use in tailoring reports.
This is a standalone and expanded version of the modular REBUS-3 code system described in Ref. 1 and 2. REBUS-3 is fully compatible with the CCCC coding standards and interface data sets. It utilizes the DIF3D nodal option of DIF3D and VARIANT 8.0 (CCC-649) codes to obtain the neutronics solution. However, this CCC-653 distribution does not include the DIF3D main program which is in the CCC-649 DIF3D package.