Estimation of the Fast Neutron Fluence at Control Rod Tips using a 3-D Diffusion/2-D Transport Calculation Scheme

This paper presents the development and application of a methodology to estimate, using state-of-the-art deterministic lattice/core analysis methods, the fast neutron fluence at the tips of control rods inserted during operation in PWR reactors. The developed methodology is based on a 3-D Nodal Diffusion/2-D Lattice Transport hybrid calculation scheme where the operating history of the nuclear environment around the tip is tracked in 3-D core follow analyses and used thereafter as boundary conditions in 2-D transport calculations to compute the fast neutron flux. Three correction factors are thereafter applied to the computed fast flux before performing the time-integration to estimate the fluence. The developed methodology has been applied to estimate the fluence for a total of 15 control rods over several operating cycles of a Swiss nuclear power plant. (authors)