[en] A nearly equilibrium five-year cycle has been achieved at Dukovany NPP over the last years. This means that working fuel assemblies (WFA) with an average enrichment of 4.25 w% (control assemblies (CA) with an average enrichment of 3.82 w%) are normally loaded and reloaded for five years. Operation at uprated thermal power (105% of the original one, increase from 1375 MW_t to 1444 MW_t) is being prepared by use of WFA with an average enrichment of 4.38 w% (CA with an average enrichment of 4.25 w%). With the aim of fuel cycle economy improvement, the fuel residence time in the core has to be prolonged up to six years with one cycle duration time up to 18 months and preserving loadings with very low leakage. In order to achieve this goal, at least neutron-physical characteristics of FA must be improved and such changes should be evaluated from other viewpoints. Some particular changes have already been analyzed earlier. Designs of new fuel assemblies with higher (and in the central part of a FA the highest possible, i.e. 4.95 w%) enrichment with preserving low pin power non-uniformity are described in the presented paper. An FA with an average enrichment of 4.66 w% (lower than originally evaluated) containing six fuel pins with 3.35 w% Gd₂O₃ content was selected in the end. Fuel pins have bigger pellet diameter, bigger pin pitch and thinner FA shroud. A newly designed FA was evaluated from the viewpoint of physics (pin power non-uniformity, criticality of fuel at transport and storage and determination of basic quantities for spent fuel storage purposes by ORIGEN code), thermo-hydraulics (comparison of subchannel output temperatures and the departure from nucleate boiling ratio - DNBR) and mechanical properties. The purpose of this study was to simulate an FA subject to the loads during its six- year lifetime whereas normal working conditions were taken into account. There are presented two models with different shroud thickness undergoing these analyses. Both models also undergo buckling shroud analyses. Next the maximum inner excessive pressure limits (as a consequence of accident conditions) were determined. Furthermore, the low shroud thickness limit for loads representing normal working conditions was assessed. The model, whose shroud thickness was reduced down to 1.0 mm, was subjected to a low cycle fatigue analysis. Possibilities of fuel cycles are evaluated on model loadings with the newly designed FA, where the base are loadings for 27^th - 34^th cycles of the third unit of Dukovany NPP for uprated power. These cycles were prolonged (from approx 330 FPD to 370 FPD) using FA with higher enrichment. Moreover, newly optimized loadings of a length of up to 500 FPD (18 months) were considered. The transient process started from the last of the set of loadings (27^th - 34^th) for uprated power. Newly designed fuel assemblies were loaded regularly in 18-month cycles. Average enrichment of CA was 4.38 w%. Transient loadings are formed by cycles 35-37 and the equilibrium cycle is created by cycles 38 and 39. Each cycle was optimized individually and fuel assemblies intended for unloading were determined for each cycle separately. The 'equilibrium' cycle is realized by three consecutive loadings with 16 fresh WFA and 2 fresh CA. Basic characteristics of a reference cycle and an 18-month cycle were compared. Optimization was performed by the OPAL_-B code on the basis of 3D n-ph calculations of the MOBY-DICK code with the target function F_dh < 1.51. Consecutive thermo-hydraulic calculations were executed following the core neutron-physical analysis that had been carried out by the MOBY-DICK code in the 1/6 core symmetry. These thermo-hydraulic calculations were executed for loadings of both existing and newly designed fuel assemblies. Fast neutron fluences (calculated by TORT transport code based on neutron sources calculated by MOBY-DICK code) onto the reactor pressure vessel for proposed the 12-month and 18-month cycles were also calculated and compared. The analyses performed confirmed that fuel cycles using newly designed FA and fulfilling basic safety criteria can be designed together with fuel cycle economy improvement. (authors)