The three-dimensional plant simulator TRAC/BF1-ENTRÉE was validated based on a one-pump trip test. Trends in major plant process parameters and three-dimensional power distributions were studied with regard to in-core flow reduction, insertion of control blades, and neutron spectrum mismatch. An improved moderator direct heating model was proposed by separately modeling the neutron slowing down and the gamma-ray absorption mechanism. The delayed heat conduction caused by the gamma heating in metallic regions was implemented. Sensitivities of water level and three-dimensional power were studied by varying the core power history, the dryer loss coefficient, and the neutron kinetics solution approach.