Nexus between geometry and thermal-hydraulic scaling of horizontal steam generator

Mature technology of large-scale nuclear power plants is a strong basis for the development of small modular and medium size reactors. Therefore, it is important to study the nexus between geometry and thermal–hydraulic scaling with the aim to take advantage of large-scale plants to develop safe and reliable scaled-down plants. The present study investigates the thermal-hydraulics of a large-scale Horizontal Steam Generator (HSG) built in the WWER 1000 type nuclear power plant, and a thermal-hydraulics of its replica with the 50 % scaled-down geometry. Unlike most previous studies, which primarily relied on the similitude concept for scaling analysis, this work employs numerical simulations with an in-house computational code based on a three-dimensional two-fluid model approach and closure laws for the prediction of interfacial transport phenomena. Obtained results show that a uniform linear reduction of HSG dimensions in three-dimensional space leads to strong non-linear changes of thermal–hydraulic parameters. Nearly the same ranges of void fraction and two-phase flow velocity changes along vertical and horizontal directions of tube bundles are obtained in the full-size HSG and in the HSG with 50% scaled-down geometry if the tube bundle volumetric heat flux in the 50% scaled-down HSG geometry is two times greater than the full-size HSG value. It is shown that a significant increase of the volumetric heat flux is achievable with a reduced diameter of tubes in the bundle and a corresponding increase of the primary side reactor coolant flow rate, although the HSG primary and secondary fluid inlet and outlet temperatures and pressure levels are kept constant. Therefore, the scaled-down HSG geometry enables significant increase of heat power per unit of tube bundle volumes, while the preserved similarity of the thermal–hydraulic conditions ensures that the scaled-down HSG operates within safe and reliable limits comparable to the full-size HSG. The findings contribute to an understanding of HSG scaling effects and support the development of small modular and medium size reactors.