DIF3D solves the steady state, multi-group diffusion and transport equations using the finite difference approximation (one-dimensional slab, sphere, and cylinder, two-dimensional Cartesian, hexagonal, and r-z, and three-dimensional Cartesian, hexagonal prism, and r-θ-φ), the transverse integrated nodal method (two-dimensional Cartesian and hexagonal and three-dimensional Cartesian and hexagonal prism), and a hybrid finite element method (two-dimensional Cartesian and hexagonal and three-dimensional Cartesian and hexagonal prism). It also has a spherical harmonics transport capability built on the hybrid finite element method which provides solutions to the even-parity transport equation. The GAMSOR processing code enables a sequence of DIF3D calculations that allows users to run a coupled neutron-gamma calculation needed for neutronics calculations.
More information can be found at https://www.ne.anl.gov/codes/dif3d