9. Lattice Physics Computations

This chapter presents a detailed description of the elements that comprise a lattice physics code. Lattice physics codes are used to generate cross section data for nodal codes, where the nodal codes are used to model the coupled neutronics and thermal-hydraulics behavior of the entire reactor core during steady state and transient operation. Lattice physics codes analyze axial segments of fuel assemblies, referred to as lattices, to determine the detailed spatial and spectral distribution of neutrons and photons across the segment. Once the flux distribution is known, the cross sections can be condensed and homogenized into the structure needed by the nodal code. The nodal code then pieces the various lattices together to construct the various fuel assemblies in the reactor core. This chapter is split into individual sections representing the major pieces of a lattice physics code. Section 1 presents a general overview of the computational scheme used for a typical lattice physics code (Knott). The remaining sections of this chapter are used to describe the major pieces in detail. Section 2 describes the contents of the cross section library that accompanies a lattice physics code (Yamamoto). Section 3 discusses the various resonance treatments used in lattice physics calculations (Yamamoto). Section 4 describes a method for removing cross section energy detail without sacrificing too much accuracy (Knott). Section 5 describes the fine-mesh transport calculation on the heterogeneous lattice geometry (Knott). Section 6 discusses the burnup calculation (Yamamoto). Section 7 describes some of the details of a typical case matrix (Knott), and Sect. 8 discusses some of the edits that are provided by the lattice physics code (Knott). This chapter provides the interested reader with a broad understanding of a typical lattice physics code.