Studsvik’s in-core fuel management code package CMS5- VVER, which includes the CASMO5-VVER lattice physics code and SIMULATE5-VVER three-dimensional nodal code, is currently in use for VVER-1000/1200 reactor analysis. Recently, a new commercially available CASMO5 nuclear data library has been generated based on the ENDF/B-VIII.0 evaluation. The ENDF/B-VIII.0 evaluation represents the state-ofthe- art in nuclear data and features new incident-neutron cross section evaluations from the CIELO project for 1 H, 16 O, 56 Fe, 235 U, 238 U and 239 Pu. A summary of the main features and validation of the new ENDF/B-VIII.0-based data library, referred to as E8R0 library, is presented in this work. Comparisons of predicted criticality and fission rate distributions to measurements from various hexagonal-lattice critical experiments, such as the ZR-6 (TIC) and P-Facility, show excellent agreement between the E8R0-based calculations and measurements. In addition, validation results are presented for CMS5-VVER using the new E8R0 library and the X2 VVER-1000 benchmark problem. These results indicate that the E8R0 library provides comparable accuracy to E7R1 results for the various reactor physics parameters such as critical boron concentration, temperature reactivity coefficients, and control rod worth.