ABSTRACT
Analysis of a single or multiple fuel assemblies including up to full cores simultaneously inspired the development of the subchannel analysis approach. This subchannel approach was introduced in Chapter 5 by standardizing the porous body control volume equations to a specific nodal layout. Subchannel properties, like axial velocity and density, are represented by single, averaged values. Constitutive equations are presented for input parameters like friction factors and lateral momentum and energy exchange rates between adjacent subchannels. The subchannel approach introduces a major simplification in the treatment of these lateral exchanges since it is assumed that any lateral flow in the gap region between subchannels loses its sense of direction after leaving the gap region. This leads to simplifications in the lateral convective terms which makes the method most appropriate for predominantly axial flow. The constraint in subchannel analysis of treating the subchannel itself as a lumped parameter region has motivated the more local analysis capability afforded by computational fluid dynamics. However, analysis of operating core efficiency and safety performance is still principally the province of subchannel analysis investigation. This chapter closes with identification and presentation of the major developments in moving from the initial simple rod bundle geometry to whole core analysis.
