3D Nodal Expansion Method HEXNEM for Solution of the Neutron Diffusion Equation in Hexagonal Geometry
3D Nodal Expansion Method HEXNEM for Solution of the Neutron Diffusion Equation in Hexagonal Geometry
Grundmann, U.
The nodal expansion method (NEM) used in the hexagonal version of the code DYN3D is based on the node averaged values of fluxes in the node volume and averaged values of fluxes and currents at the interfaces of the nodes [1]. The 3dimensional neutron diffusion equation for two energy groups is split into a 2dimensional equation in the hexagonal plane solved with the help of Bessel functions and a 1dimensional equation in axial direction solved by polynomial expansion. The two equation systems are coupled by the transversal bucklings. The accuracy of this method is sufficient for the VVER440 where the assembly pitch is 14.7 cm. The assemblies of the VVER1000 have a larger pitch of 24.1 cm. Comparing with mathematical benchmarks for the VVER1000 the maximal deviation of powers is in the order of 5%. The new nodal expansion method HEXNEM presented here uses a different flux expansion in the nodes. In addition to the average values at the interfaces of the hexagon the values at the corner points are included, too. It is shown that the accuracy is improved for the VVER1000 problems.
Keywords: neutron diffusion theory; nodal method; hexagonal geometry; two energy groups

Lecture (Conference)
Jahrestagung Kerntechnik '99, 18.  20. Mai, 1999, Karlsruhe, S. 15  18 
Contribution to proceedings
Jahrestagung Kerntechnik '99, 18.  20. Mai, 1999, Karlsruhe, S. 15  18
Permalink: https://www.hzdr.de/publications/Publ1577
Publ.Id: 1577