Trans. of KNS Autumn meeting , CD-ROM, 2009.
The triangle-based polynomial expansion nodal (TPEN) method involving a two-dimensional polynomial expansion within a triangle is an advanced nodal method to solve neutron diffusion problems in hexagonal-z geometry. The TPEN method combines the higher order polynomial expansion nodal (HOPEN) method and the nodal expansion method (NEM) by decoupling the three-dimensional neutron equation into a radial and an axial one. This method had already been implemented in the PARCS code and its high accuracy was verified with various hexagonal benchmark problems for thermal reactors. In this work, the TPEN method is employed in a multi-group spatial kinetics code FREK for the fast reactor core analysis and its performance is examined for real fast reactor cores such as KALIMER-150/600. Since FREK can also be applied to thermal reactors, the VVER benchmark problems are also analyzed
