Development of a Method for Neutronics Treatment of Nonmultiplying Zones in Pebble Bed Reactors

In this paper, a diffusion-transport hybrid nodal method is presented that can effectively treat non-multiplying zones in pebble bed reactors. The new method seamlessly combines the analytic coarse-mesh finite difference (CMFD) diffusion formulation and a transport theory-based response matrix formulation while retaining the properties and structure of the CMFD diffusion solver. The resulting combined formulation is utilized in selected non-multiplying nodes in order to avoid using poorly homogenized data. Numerical results demonstrate the accuracy of the new methodology. (author)