[en] PERMAK is one of the modules of code package for WWER core analyses developed in I.V. Kurchatov Institute. This code is used for two-dimensional fine-mesh (mesh step is equal to pins lattice step) few-group (from 1 to 6) calculations. The code provides the following possibilities: single state core calculation. Such calculations are used for codes verification on a base of a comparison of calculated and measured data obtained at zero power critical assemblies; calculations of pin by pin fluxes and power release distributions in core layer under burnup taking into account feedback and reloading patterns. Needed for such type calculations values of axial bucklings, full power of layer, water temperature and boron acid concentration are taken from preliminary three-dimensional coarse-mesh calculations. Preliminary prepared elementary cells macro cross sections library is used for such calculations. This library contains information about dependence of macro cross sections on burnup, integral neutron spectrum and other parameters. Two types of balance equations are realized in PERMAK -finite difference diffusion equation and described in Part I of this paper, nodal balance equation. Comparison of calculated and measured data obtained at ZR-6 zero power assembly shows that using nodal type balance equation provides high accuracy of calculations of pin power release distribution and critical parameters for different nonuniform lattices (the full paper contain the results of such comparison). Nodal approach similar to that described above is used in three-dimensional coarse-mesh simulator BIPR-8 code. 11 refs, figs, 2 tabs

[en] The use of tight pitch lattice and MOX fuel is one of the ways to improve fuel utilization in WWERs. The presented report is devoted to an analysis of main neutron-physical and thermohydraulic problems connected with such core design. In order to achieve the needed accuracy of tight pitch lattices burnup calculations it is necessary to provide a high accuracy of reaction rates calculations in the resonance energy range and therefore the cross sections of the used Pu, Am, Cm isotopes and fission products should be reliable. For such calculations the UNIRASOS-2 and SAPFIR codes are used at the Kurchatov Institute. The ''second'' equivalence theorem with specially selected parameters and generalized subgroup approach are used for resonance treatment in these codes. MCU code package calculations have been used for their validation. This code package is based on the Monte-Carlo method with a detailed description of cross section energy dependence in the energy range of resolved resonances. A comparison of MCU, UNIRASOS and SAPFIR calculations with the results of precision calculations, results of benchmark problems on tight lattices burnup solutions and measured data obtained at the PROTEUS critical assembly, has shown that the obtained accuracy of these codes is satisfactory for practical purposes. However, in order to estimate the reliability of void reactivity coefficient calculations under low moderator density, it is necessary to perform special investigations. For two dimensional pin power distribution calculations, the 4-group code PERMAK, in which both diffusion and nodal type balance equations are realized, has been used. (author). 30 refs, 4 figs, 6 tabs