The paper presents the dynamic multivariable model of Nuclear Power Plant steam turbine. Nature of the processes occurring in a steam turbine causes a task of modeling it very difficult, especially when this model is intended to be used for on-line optimal process control (model based) over wide range of operating conditions caused by changing power demand. Particular property of developed model is that it enables calculations evaluated directly from the input to the output, including pressure drop at the stages. As the input, model takes opening degree of valve and steam properties: mass flow and pressure. Moreover, it allows access to many internal variables (besides input and output) describing processes within the turbine. The model is compared with the static steam turbine model and then verified by using archive data gained from researches within previous Polish Nuclear Power Programme. Presented case study concerns the WWER-440 steam turbine that was supposed to be used in Żarnowiec. Simulation carried out shows compliance of the static and dynamic models with the benchmark data, in a steady state conditions. Dynamic model also shows good behavior over the transient conditions.
 J. Bassas: Development and implementation of a Nuclear Power Plant steam turbine model in the system code ATHLET. Master Thesis. Technische Universität München, 2011.
 A. Chaibakhsh, A. Ghaffari: Steam turbine model. Simulation Modelling Practice and Theory,16 (2008), 1145-1162.
 M. Czapliński, P. Sokólski, K. Duzinkiewicz, R. Piotrowski and T. Rutkowski: Comparison of state feedback and PID control of pressurizer water level in nuclear power plant. Archives of Control Sciences,23(4), (2013).
 J. Dobosz, K. Duzinkiewicz, S. Perycz and W. Próchnicki: Steam turbine simulation model of transient states for nuclear power unit with WWER-440 reactor with omega=const. The Institute of Electrical Power and Control Engineering, Gdansk University of Technology, Gdansk, Poland, 1989, (in Polish).
 A. Duczkowska-Kadziel: Analysis of combined 370 MW power unit with gas turbine. Department of Mechanical Engineering, Opole University of Technology, Opole, Poland, 2011, (in Polish).
 D. Flynn: Thermal Power Plant Simulation and Control. The Institution of Electrical Engineers, London, 2003.
 W. Grote: Ein Beitrag zur modellbasierten Regelung von Entnahmedampturbinen. Fakultät für Maschinenbau der Ruhr-Universität Bochum, Bochum, Germany, 2009. (in German).
 B. Grunwald, J. Lewandowski, A. Miller and J. Plewa: Mathematical steam turbine model for saturated steam, allowing to study dynamics of nuclear power plant unit. Institute of Heat Engineering, Warsaw University of Technology, warsaw, Poland, 1972, (in Polish).
 R. Janiczek: Exploitation of steam power plants. Wydawnictwa Naukowo-Techniczne, Warsaw, 2008, (in Polish).
 Z. Jankowski, Ł. Kurpisz, L. Laskowski, J. Łajkowski, A. Miller, J. Portacha, W. Sikora and M. Zgorzelski: Mathematic model of turbine in various conditions e.g. 200 MW power unit. Warsaw University of Technology, Technical Report, Warsaw, 1972, (in Plish).
 A. Kobylarz, K. Kulkowski, K. Duzinkiewicz and M. Grochowski: Modelling of Nuclear Power Plant Steam Turbine. XVIII Nat. Conf. on Control, Wrocław, Poland, (2014).
 A. S. Leyzerovich: Wet-steam Turbines for Nuclear Power Plants. PennWell Corp., Tulsa, USA, 2005.
 T.K. Nowak, K. Duzinkiewicz and R. Piotrowski: Fractional neutron point kinetics equations for nuclear reactor dynamics - Numerical solution investigations. Annals of Nuclear Energy, Annals of Nuclear Energy, 73 (2014), 317-329.
 T.K. Nowak, K. Duzinkiewicz and R. Piotrowski: ORF approximation in numerical analysis of fractional point kinetics and heat exchange model of nuclear reactor. XVIII Nat. Conf. on Control, Wrocław, Poland, (2014).
 T. Nowak, K. Duzinkiewicz and R. Piotrowski: Numerical solution of fractional neutron point kinetics model in nuclear reactor. Archives of Control Sciences,24(2), (2014).
 S. Perycz and W. Próchnicki: Steam turbine mathematical model of nuclear power unit with WWER reactor, allowing to analyze transient states with omega=var. Institute of Electrical Power Engineering and Control Engineering, Gdansk University of Technology, Poland, Technical Report, 1989, (in Polish).
 J. Portacha: Enegetic reasearch on thermal systems of power plants and heating. Oficyna Wydawnicza Politechniki Warszawskiej, Warszawa, Poland, 2002, (in Polish).
 B. Puchalski, K. Duzinkiewicz and T. Rutkowski: Multi-regional fuzzy control PIλDμ of nuclear reactor power. XVIII Nat. Conf. on Control, Wrocław, Poland, (2014).