Spectral zones selection methodology for pebble bed reactors

A methodology is developed for determining spectral zones for Pebble Bed Reactors. The spectral zones are selected in such a manner that the error between the reference transport solution and the diffusion code solution takes a minimum value. This is achieved by choosing spectral zones through optimally minimizing the error between the diffusion code solution and the reference transport solution. The objective function for the optimization algorithm is the total reaction rate error, which is defined as the sum of the leakage, absorption and fission reaction rates errors in each zone. The selection of these spectral zones is such that the core calculation results based on diffusion theory are within an acceptable tolerance as compared to a proper transport reference solution. Through this work, a consistent approach for identifying spectral zones that yield more accurate diffusion results is introduced.