[en] The whole-core LMFBR thermal-hydraulics codes COBRA-WC, COMMIX, CORE-3D, CORTRAN and SUPERENERGY-2 were evaluated from a design analyst's point of view. The issues considered in this evaluation were the basic algorithms, code capabilities, physical models, user instructions and general code features. The existing codes were classified as either benchmark-type codes (COMMIX, COBRA-WC) or approximate codes (CORE-3D, CORTRAN, SUPERENERGY-2). The CORTRAN code was recommended for whole-core design analysis because it is fast-running, easy to use and has a transient analysis capability. An expanded and improved version of CORTRAN, called CORTRAN-C was developed and applied to the analysis of split inlet plenum designs. Orificing strategies for split inlet plenum designs were investigated as well as the sensitivity of coolant outlet temperature to changes in the number of orificing zones. The transient capability of CORTRAN-C was demonstrated