Heaving motion effect on the transient thermodynamic characteristics of helical coil once-through steam generators in mixed ocean conditions.

• A simulation code for the HCOTSG under ocean motion is established and validated. • The impact of the changes in amplitude and period in IRIS reactor were investigated. • The effect of inclining direction and angle on the thermohydraulic parameters of HCOTSG was researched. • The influence of swaying angle, swaying period, and direction of swaying axis was analyzed. Based on the finite difference method, the fixed boundary method, and a staggered grid method, this paper develops a one-dimensional thermal–hydraulic analysis code to simulate the effects of heave motion and more complex oceanic motions, namely heaving coupled with inclination and heaving coupled with swaying, on the thermal–hydraulic parameters of the International Reactor Innovative and Secure (IRIS) reactor's helical coil once-through steam generator (HCOTSG). The oceanic conditions were achieved by modifying the momentum equation. The validity and accuracy of the code were obtained by comparing the results with the design parameters of HCOTSG for two types of marine nuclear reactors, the SMART reactor and the IRIS reactor, and with the calculations of some similar international prediction programs. The simulation results indicate that (1) when only heave motion is considered, increasing the amplitude and reducing the period both result in a greater magnitude and a faster rate of change in the HCOTSG parameters. (2) When the combined motion of inclining and heaving is present, the dynamic performance of the composite motion inclining towards the positive x-axis deteriorates the most severely, while its thermodynamic conditions improve slightly. In this direction, the inclining angle has little influence on the thermal–hydraulic characteristics of HCOTSG. (3) When the combined motion of heaving and swaying is present, the dynamic performance is more severely affected under swaying motion towards the negative y-axis, despite a slight improvement in thermodynamic conditions. In this direction, as the swaying angle increases, the trend of parameter variation under swaying is similar but with a greater magnitude of change. The deterioration in dynamic performance becomes more severe, although there are small improvements in thermodynamic conditions. With the swaying period increasing, the maximum and minimum values of the secondary side pressure drop show little change. Additionally, the average thermodynamic conditions exhibit little variation. [ABSTRACT FROM AUTHOR]