Fine mesh calculations for core monitoring

A new fine axial mesh calculation method has been developed and implemented in the Westinghouse nuclear reactor core simulator code ANC. This new method will be used by the BEACON core monitoring system for continuous evaluation of the most limiting values of the core power distribution. The new fine mesh method is physically based as opposed to the current method used in the BEACON system which employs spline fitting along with spacer grid adjustment factors. The newly developed fine mesh method uses 1-Dimensional diffusion theory calculations for each vertical neutronic channel in the core. This calculation is done using radially smeared cross-sections for each of the axial material layers in a given neutronic channel. Radial leakage effects derived from the 3D nodal solution are accounted for in these channel-wise calculations. This paper presents the theory behind the new methodology. Fine mesh results obtained with this methodology are compared against reference 3D fine mesh results for proof of principle. The method was shown to be capable of predicting axial fine mesh power distributions with acceptable accuracy. This methodology is also appropriate for prediction of detector signals