Improvements and core applications of the migration mode method

The problem to achieve detailed information in energy for the neutron flux with reasonable computational time has always been of great interest. Commonly, this aim is pursued with calculations in multigroup theory using many energy groups, although this disregards the goal of fast computations. Recently, some energy treatments have been developed to overcome this drawback, thus giving good approximation of the neutron spectrum. Among them, the migration mode method shows interesting features. Its derivation as a spectral synthesis method is discussed in the paper. New choices for the test weighting function sets allow the solution reproducing integral properties of the analyzed system. The multigroup method is obtained following the same approach of synthesis too. Applications to 3D full core calculations are studied in stationary conditions solved by an upgraded version of the code SMART. The MMM is compared here with the standard 2 MGM, usually chosen to model neutronically industrial cores. A simple system, for which an analytical solution is possible, is drawn to check consistency and robustness of the implemented code. Then results pertaining to a PWR core follow. (authors)