The pebble bed reactor is randomly filled with thousands of spheres with fuel and moderator elements known as pebbles. Each fuel pebble contains thousands of coated TRISO particles stochastically embedded in the graphite matrix. Compared to PWR reactors with a regular lattice of fuel pellets in the regularly placed fuel assemblies, the fuel lattice is not easily modelled in the calculation codes. This study shows the fuel pebble models and basic optimization from the neutronics point of view. It analyzes the influence of all possible spherical crystalline structure arrangements during burnup. It also analyses the basic influences such as moderator, fuel power, enrichment and overcoat effect
