Rotational Symmetry Boundary Condition in Current Coupled Whole Core Pin by Pin Transport Theory Code

The advances in computer processing power have made it possible to perform a detailed pin by pin calculation of the whole core. The methods based on response matrix are being used to perform whole core transport calculations. This includes the current coupled methods based on 2D collision probability (CP) and method of characteristic (MOC). The basic approach in the whole core transport theory methods is not to homogenize the lattice cells and subdivide each cell location in the fuel assembly (FA) into finer regions. The coupling of lattice cells within the assembly and assembly to assembly coupling can be achieved using interface currents. Due to very fine discretisation of the lattice structure and large core size, the physical memory requirements for the whole core simulations are huge. This requirement is compounded if ultra-fine discretisation of energy domain is also considered. When there is an inherent symmetry one can solve for the symmetric portion of the core, thereby save both memory and computational time. Rotational symmetry boundary condition in the whole core is normally considered. Application of this boundary condition gets very complicated when the whole core is modeled by a pin by pin approach. The present paper describes the methodology to apply the rotational symmetry boundary condition in the core discretized with complex microstructures of various heterogeneous cells of the problem.