抄録
Systems analysis codes, such as RELAP5-3D^[○!C], are generally aimed at modeling the behavior of an entire system such as a pressurized water reactor plant. While such codes generally have the capability to model multi-dimensional effects, their capacity to produce widely accepted analyses of multi-dimensional behavior is limited by the assumptions and capabilities that stem from their field equation formulations. Historically RELAP5-3D^[○!C]was developed first to analyze the behavior of two-phase systems that could be modeled in one-dimension. Because of the need to analyze two-phase flow, the assumptions used to define the field equations resulted in a simplification of the viscous stress terms and the use of many empirical relationships that cannot be traced to first-principles, e.g., flow regime transitions and the models describing the interactions between phases. The RELAP5-3D^[○!C]field equation set was later extended to analyze two- and three-dimensions. However, the assumptions inherent to the one-dimensional equation set were retained. The starting point and the needs that led to the development of codes such as Fluent and RELAP5-3D^[○!C]led to different products with different capabilities, limitations, strengths, and weaknesses. In summary, the fundamental strengths and weaknesses of the Fluent and RELAP5-3D^[○!C]codes, from an analysis perspective, are given in Table 1. The CFD codes are without peer when analyzing the complex flow behavior of single-phase systems in two- or three-dimensions, for either steady-state or transient behavior. The systems analysis codes, such as RELAP5-3D^[○!C], are without peer for analysis of two-phase systems in one-, two-, or three- dimensions.
