This work presents the thermodynamic model of steam storage in a steam cycle. The innovative steam storage is an integral part of the unit and thus responds quickly to changes in load. This enhances the primary control reserve while maintaining high efficiency of energy conversion. With regard to power plants, it improves the operational safety of generation units, as it prevents boiler and turbines overload in the case of steep reduction in the load. A steam power plant able to swiftly adjust its generation to load changes becomes more competitive on the capacity market thanks to improve its dynamic characteristics. The relative disadvantage of the steam storage is its limited capacity. Therefore, the article includes a comprehensive assessment of the power plant parameters that will allow developing guidelines and recommendations to determine the optimal operation modes of the steam accumulator for the case of the underlying reference process. This will also take into account changing ambient conditions and current operational requirements. Therefore, it is necessary to use zero-dimensional modelling (0D) which relates to the design level strictly focused on thermodynamic parameters at specific points in the thermodynamic cycle. However, the three-dimensional approach, which allows determining temperature fields, displacements and stresses in relevant space is used for more accurate analysis. This paper also presents the relationship between the different approaches in relation to steam storage. The steam accumulator itself will be analysed in detail by means of Thermal-FSI (Fluid Solid Interaction) based on flow models with phase transitions induced both by change of pressure and temperature. Computational Solid Dynamics (CSD) models will be included to obtain the thermal and mechanical stresses. The mathematical modelling of complex physical phenomena in the steam storage is of increasing interest, particularly with regard to energy storage in the steam cycle. However, taking into account zero-dimensional modelling it is possible to show that charging the energy storage leads to a load reduction of up to 6.5%. On the other hand, discharging the energy storage can produce an additional net power of up to 4.1%. However, a new three-dimensional FSI analyses are necessary.