Evaluation of Background Cross Section for Heterogeneous and Complicated Geometry by the Enhanced Neutron Current Method

Abstract

A new approach for evaluating the background cross section for heterogeneous and complicated geometry (the enhanced neutron current method) is presented. The present method utilizes the result of a onegroup fixed source transport calculation in heterogeneous geometry, which can be carried out in short computation time. The background cross section can be evaluated from the total reaction rate in a resonance region. Since the present method can be applied to complicated geometry, it will be useful not only for lattice physics calculation with production codes but also for general purpose neutronics code calculation for advanced reactors. The validity of the present method is confirmed by comparison with that of the conventional method by rational approximation for first-flight collision probability and the Dancoff factor. Calculation results indicate that the background cross sections obtained by both methods are identical.

Resonance treatment using pin-based pointwise energy slowing-down method

“…7. The enhanced neutron current method [12] solves a fixed source transport equation in Eq. 18without the resonance scattering XS.…”

“…The Dancoff factor is calculated using the enhanced neutron current method [12] by solving the following MOC fixed source problem for a whole problem.…”

Cross Section Generation Capability in Griffin

“…A Dancoff factor for each fuel pin is calculated using the enhanced neutron current method (ENCM) [49] by solving the following FSP once using the DFEM-SN solver in Griffin.…”

Griffin Software Development Plan

“…Each axial segment of every fuel pin in a lattice (or each pebble) is decoupled to 1D cylindrical (or spherical cell), which preserves the Dancoff factor at the black fuel limit. The Dancoff factor for an axial segment of a fuel pin (a pebble) is calculated using the enhanced neutron current method (ENCM) [32] that only requires a one-time fixed source calculation. Then, an equivalent 1D cell for an axial segment of a fuel pin (a pebble) is determined by the binary search, which seeks the outer radius of the cell giving the same Dancoff-factor from the 1D collision probability method (CPM).…”

“…Diffusion is used as the main solver for quick core calculations; however, improved accuracy with diffusion relies on the use of homogenization equivalence to preserve the reaction rates in the core. The calculation of discontinuity factors (DFs) [32] is available with the discontinuous transport solvers given surface fluxes/currents, whereas the calculation of superhomogenization (SPH) [36] factors is available for CFEM solvers given volume-integrated fluxes. Furthermore, Griffin includes a hybrid DF-SPH method for DFEM solvers.…”