METHODOLOGY OF 3D NEUTRON-PHYSICAL CALCULATION OF NUCLEAR REACTORS OF AXIAL-SYMMETRY WITH FINITE STEP ALONG THE AXIS

Poveschenko T.S., Laletin N.I., Sultanov N.V., NRC «Kurchatov institute», Moscow, Russia

24th Symposium of AER on VVER Reactor Physics and Reactor Safety (2014, Sochi, Russia)
Advances in spectral and core calculation methods

Abstract

METHODOLOGY OF 3D NEUTRON-PHYSICAL CALCULATION OF NUCLEAR REACTORS OF AXIAL-SYMMETRY WITH FINITE STEP ALONG THE AXIS
Poveschenko T.S., Laletin N.I., Sultanov N.V. NRC “Kurchatov Institute”, Moscow, Russia
ABSTRACT
In this paper methodology for 3-D calculation analysis of nuclear reactor cell with axial symmetry and finite mesh step is described. This methodology is based on the method of axial leakage calculation that has been developed for nuclear reactor with closed lattice like VVER. Trial functions used at full core level are defined. Analytical solutions of two-group diffusion equation with “symmetrical ” and ”cross” boundary conditions are given. Two-group cell characteristics that are matrixes of the boundary values of these solutions have been calculated. None-diagonal elements of this matrix are just the deductions caused by curvature of neutron flux. These values have been analyzed in dependence on the step mesh along Z (axis) value.
These results show that if mesh step along Z-axis is enough small (in comparison with neutron free path) then diagonal elements are closed to initial diffusion parameters of the cell and none-diagonal elements can be neglected. But in contrary if step mesh is more than diffusion length of heterogeneous medium then these deductions are essential and they should be taken into account at full core level.
This methodology is used in full core level with Surface Value System with finite step mesh along Z-axis in lattice code SVL.

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