The paper details the computational fluid dynamic and system-level modeling, including a mechanistic representation of a Terry turbine/pump, for Fukushima Daiichi Unit 2. Until this recent effort, mechanistic modeling had been confined to an otherwise coarse model of Fukushima Daiichi Unit 2 laden with manipulations of boundary conditions that substituted for detailed representations of the reactor, drywell, and wetwell. This work has provided insights in modeling uncertainties and provides confirmation for experimental efforts for the Terry turbopump. Analytical efforts ongoing at Sandia National Laboratories to understand the design and off-design operation of Terry turbines are introduced in this paper. The efforts are described mostly in the context of RCIC systems.