First-Collided Source Treatment for Discrete-Ordinate Radiation Transport Solutions in Rattlesnake

Abstract

Deterministic neutron transport plays a fundamental role in reactor core modeling and simulation. With the growth of computing, higher fidelity simulation is desired and the most common neutron transport scheme that produces these enhanced solutions is that of the method of discrete ordinates. However, the discrete ordinates approximation suffers from large angular discretization errors in problems with localized, small sources embedded in regions of low density or with low scattering materials. It has long been recognized that a semi-analytical treatment of the uncollided flux using ray-tracing techniques, coupled with a standard discrete ordinate treatment of the collided flux, can be a remedy for ray effects. However, current ray-tracing techniques do not support non block geometries, let alone FEM grids, and are not developed to be scalable. In this thesis, a ray-tracing approach for obtaining the uncollided flux is considered that (1) can perform in arbitrary grids, (2) supports arbitrary sources, and (3) is scalable. An implementation is then provided for the use of this uncollided flux solution as a first-collision scattering source for the purpose of ray effect treatment in the deterministic transport code Rattlesnake, a MOOSE (Multiphysics Object Oriented Simulation Environment) application.