Thermo-neutronic analysis of natural circulation in the ABV small modular reactor under ocean-induced motions

Abstract

Floating deployment of Small Modular Reactors (SMRs) requires reliable passive cooling performance under dynamic ocean-induced motions. In this work, a comprehensive thermo-neutronic analysis of the ABV reactor was performed to assess the capability of its natural circulation system under inclination, heaving, and rolling conditions. A steady-state coupling between ANSYS CFX and PARCS was implemented, and transient CFD simulations were conducted for dynamic scenarios. Results show that at 30° inclination, the core mass flow decreases by about 9.7 % with a temperature rise of 3.3 K, while at 45° the reduction reaches 19.2 % and 6.9 K, accompanied by a slight decrease in $k_{\mathrm{eff}}$ and a shortened cycle length. Under heaving motion, coolant and power oscillations vary between ± 5 % and ± 18 % depending on amplitude and period. Rolling motion produces peripheral flow oscillations with amplitudes below ± 1.5 %, with limited effect on DNBR. These findings demonstrate that ocean-induced motions can significantly affect natural circulation, reactivity feedback, and safety margins, highlighting the necessity of coupled multi-physics modeling and the adoption of power derating and adaptive control strategies for floating nuclear power plants.