3. Reactor Physics

Introduction by M. A. Jessee and F. Bostelmann

SCALE supports a wide range of reactor physics analysis capabilities. SCALE reactor physics calculations couple neutron transport calculations with ORIGEN to simulate the time-dependent transmutation of various materials of interest. The two reactor physics analysis tools within SCALE are TRITON and Polaris. TRITON is SCALE’s modular reactor physics sequence for a wide variety of system types; Polaris is SCALE’s light water reactor (LWR) lattice physics sequence.

The primary function of TRITON is to simulate the time-dependent evolution of nuclide inventories of a reactor system through a series of multigroup transport calculations and depletion/decay calculations. Before each multigroup transport calculation, TRITON executes the XSProc module to calculate multigroup cross sections for each user-designated depletion material. The XSProc calculation is performed based on the time-dependent material compositions and the user-defined cross section processing definitions. TRITON provides maximum modeling flexibility, supporting the full range of cross section processing options in XSProc along with support for four different multigroup transport modules available in SCALE. These transport modules include the following:

  • XSDRN: one-dimensional discrete ordinates (SN) transport module for modeling simple slab, cylindrical, and spherical geometries,

  • NEWT: two-dimensional (2D) SN polygon-mesh deterministic transport module with arbitrary geometry model definitions, and

  • KENO-V.a and KENO-VI and Shift: three-dimensional Monte Carlo transport modules with arbitrary geometry model definitions.

In addition to the multigroup-based calculation sequences, TRITON supports continuous-energy (CE) transport calculations with KENO-V.a and KENO-VI and Shift. For each depletion material, the CE Monte Carlo calculation tallies energy-integrated nuclide-dependent reaction rates to couple the transport solution to the ORIGEN depletion calculation. Both the multigroup- and CE-based depletion calculations are parallelizable and can run on an arbitrary number of processors.

TRITON provides easy-to-use input options to define the time-dependent reactor condition, including power history, material temperatures, and material compositions. TRITON also provides the option to perform lattice physics calculations, with input options to define branch calculations, homogenization edits, few-group energy structures, and assembly discontinuity factors. The homogenized few-group cross sections are archived onto auxiliary data files for subsequent in-reactor core calculations.

TRITON generates several data files for follow-on SCALE analysis. It creates the ORIGEN binary concentration file (.f71 extension) that stores all of the material inventories at each depletion/decay step. This file can be used as input to ORIGEN, ORIGAMI, and MAVRIC to support spent fuel characterization and shielding analysis. TRITON also creates the ORIGEN binary library file (.f33 extension) that stores the ORIGEN transition matrix for each depletion material at each depletion/decay step. The ORIGEN library files can be used as input to ORIGEN or ORIGAMI for rapid assessment of spent fuel inventories. Finally, TRITON also generates the aforementioned lattice physics few-group cross section archive (xfile016) for reactor core calculations.

In addition to the TRITON reactor physics sequence, SCALE supports an alternative easy-to-use LWR depletion sequence for generating lattice physics data for full-core reactor calculations. The Polaris lattice physics sequence couples 2D multigroup transport calculations with ORIGEN depletion to simulate LWR fuel assemblies. Polaris provides easy-to-use input definitions for defining the primary inputs necessary for lattice physics analysis, namely the pin and lattice geometry, the material compositions, and specifications for the power history and branch calculations. Polaris supports systematic input defaults for analysis of both fuel and reflector models for both pressurized water reactor (PWR) and boiling water reactor (BWR) geometries. It uses a novel approach for cross section processing called the Embedded Self Shielding Method (ESSM). The hallmark feature of ESSM is that the self-shielding calculation is performed on the 2D fuel assembly geometry, eliminating the need for user-defined cross section processing definitions. The ESSM calculation and the keff calculation are performed with a deterministic transport module based on the Method of Characteristics (MOC) approach. The Polaris sequence generates the lattice physics archive file (.t16 and .x16 extension), the ORIGEN binary concentration file (.f71 extension), the ORIGEN binary library file (.f33 extension), and a geometry plot file (.png extension).