Nuclear Propulsion for Naval Vessels

Abstract

There is currently a resurgence of interest in nuclear propulsion within the maritime sector, which is reflected by the ambition, as mentioned in the Dutch maritime sector report "No Guts, No Hollands Glorie", to develop a standardized, modular nuclear reactor for ship integration within 10 years. Nuclear energy has the potential to reduce the maritime sector’s contribution to climate change, as it does not emit CO2 during operation. Additionally, in contrary to many other renewable energy sources, nuclear energy offers a high-energy-density power source capable of providing sufficient energy for longer periods of operation. Not only would this improve the strategic autonomy of the Royal Netherlands Navy, but it would also be a solution for the increasing energy demands of additional unmanned systems or advanced combat systems, like high power radars and rail guns.

Implementing nuclear propulsion in future (naval) vessels presents challenges, particularly regarding the dynamic power profile of ships during operation. Land-based nuclear reactors typically operate as stable power sources, which contrasts with the fluctuating power demands of ships, especially naval vessels. This research aims to find a solution for these dynamic power requirements, without the use of energy storage capabilities, like batteries, for peak shaving capabilities.

Based on the expected implementation of a small modular reactor (SMR) by 2034, the Future Air Defender and the Amphibious Transport Ship were selected as potential vessel types of interest for the Royal Netherlands Navy to implement an SMR. Additionally, the high-temperature gas-cooled reactor (HTGR) and the supercritical carbon dioxide (sCO2) recompression power conversion cycle were selected for the nuclear power plant. A dynamic model of the selected SMR and its energy conversion system has been developed to compare its ramp rate with those of conventional naval prime movers, such as diesel engines and gas turbines.

The simulation results indicate that the reactor dynamics alone are insufficient to meet common ramp rates of naval vessels, demonstrating that relying solely on reactor control is not a viable control strategy. However, the implementation of the turbine bypass valve, while operating the reactor at a constant load, provides dynamic power behaviour comparable with diesel engines and even gas turbines. Potential drawbacks include reduced cycle efficiency at part load, as well as significant pressure and temperature gradients within the heat exchangers. The unacceptable temperature increase at the reactor’s inlet was addressed by incorporating a dump cooler into the primary circuit. This research therefore concludes that an HTGR, in combination with an sCO2 cycle and a bypass valve, is capable to provide the dynamic power requirements of a naval vessel.