A semi-analytic multigroup nodal method

This paper describes a hybrid of the analytic nodal method and the polynomial nodal expansion method where the out-group source of the equivalent one-dimensional diffusion equation is approximated by a 4th-order polynomial. Then the higher-order source terms are updated in a weighted residual manner. The resulting equations are very similar to those of the nodal expansion method and are of a general multigroup form. The method has been demonstrated on several LWR benchmark problems, and the results show that the method gives the accuracy comparable to the analytic nodal method and is especially suitable for situations where steep flux gradients occur at assembly interfaces.