CRUD, boron, and burnable absorber layer 2-D modeling requirements using MOC neutron transport

Abstract

The method of characteristics (MOC) neutron transport modeling requirements of very thin CRUD and burnable absorber layers on pressurized water reactor (PWR) fuel rods are investigated. Ray tracing parameters, including spacing size and number of angles, and mesh refinement studies are performed for two-dimensional assembly simulations using the DeCART code. It is found that the presence of a 10μm thick Integral Fuel Burnable Absorber (IFBA) layer within the lattice model requires a ray spacing that is approximately five times smaller than modeling a lattice without IFBA. The modeling of a CRUD layer necessitates less stringent requirements, due to the fact that the boron-10 concentration in a CRUD layer is at least one order of magnitude lower than what is typically found in IFBA layers. Three dimensional CRUD distributions and compositions computed by the CRUD chemistry code MAMBA are extracted and utilized. The reactivity effects of radial and azimuthal mesh refinement, including homogenization strategies of the CRUD layer with the coolant, are investigated. Additionally, the reactivity effect of including the CRUD structure porosity is discussed. A fresh fuel lattice with 1300ppm is also compared with a reduced boron concentration of 0ppm to assess the reactivity response of the system to changes in the reactor environment.