The use of a new Monte Carlo Ser pent code for the cal cu la tion of wa ter-cooled re ac tors is presented and a cal cu la tion scheme of the fuel as sem bly for VVER-1000 re ac tors de vel oped. The cal cu la tion of neu tron-phys i cal char ac ter is tics for the fuel as sem bly of VVER-1000 is car ried out for dif fer ent states and the re sults ob tained by the Ser pent model com pared with the results of other re ac tor codes. The anal y ses of these re sults are pre sented in the pa per sub mit ted here. Based on this ar ti cle, the Monte Carlo Ser pent code could be used for neu tron-phys i cal cal cu la tions of VVER-1000 re ac tors.