Solution of multigroup diffusion equations of fast reactor using new version of nodal method

The nodal expansion method of solving multigroup diffusion equations for fast reactors is modified for two-dimensional r,z geometry. For describing the spatial distribution of neutron flux inside each node, polynomial expansion is used. The possibility of separating the variables inside each node is assumed. The course of the neutron flux is then determined by solving one-dimensional problems in the individual directions. This variant of the nodal expansion method contributes two fundamental improvements, namely the calculation of spatial correlation coefficients is made more accurate and the spatial distribution of the neutron flux inside the node is determined. (O.K.)