Exploratory Study on Nuclear-powered Trailing Suction Hopper Dredgers

Abstract

Dredging is an energy-intensive operation and, due to the nature of the process, there are large and rapid fluctuations in the power requirement. With the signing of the Paris Agreement, implementation of IMO 2020 and expansion of ECAs, the external pressures for the reduction of different emissions(CO2, SO_x, PM, and/or NO_x) in dredging are rising. Additional motivating factors are the rise in the fuel expenses which form a major component of dredging project costs and the incentives from regulatory authorities to reduce the carbon intensity in dredging operations. Often, the achievement of one objective leads to deterioration of another, for example, the use of IMO-compliant fuel can increase the overall carbon emissions. In recent years, alternative fuels like LNG and biofuels have been explored. However, they suffer from their own set of issues and with the predicted trends, the usage of these alternative fuels would imply lower production and earnings, especially in large dredging projects. In this work, a marine power plant concept that has been rarely discussed in the context of dredging is explored and forwarded: a nuclear-based system. Fundamentally, such a power plant addresses the issues related to the emissions and essentially eliminates bunkering stops. This was the first study focused on nuclear-powered Trailing Suction Hopper Dredgers (TSHD), the most common type of dredging vessel. In this work, a system-level study was carried out to ascertain the retrofittability of a nuclear-based system on four existing TSHDs. The feasibility of retrofitting the nuclear-based system has been studied by comparison of mass and volume requirements of the nuclear power plant, with the mass and volume of the engine and fuel storage system of current dredging vessels. No re-design of the vessel was considered here.The ”inherently safe” High Temperature Gas-cooled Reactor (HTGR) with Nuclear Air-Brayton Cycle (NABC) was determined as the nuclear power system of choice. It appeared that for such a system,the TSHD sizes that are interesting for the deployment starts around 12000 m³ hopper capacities.The bigger the hopper capacities than this baseline, the better the nuclear system performed. It was found that despite the satisfaction of the mass and volume constraints, a redesign of the TSHD is required for the placement of the reactor and for the compliance with the nuclear related regulations.In addition to the nuclear power plant, the retrofitting of the TSHDs with Proton Exchange Membrane Fuel Cell (PEMFC) in combination with solid, compressed and liquid H₂ storage and batteries was considered. With the current commercially available offerings, PEMFC with liquid or 500 bar compressed H₂ storage were found to be suitable for maintenance dredging or capital dredging for a short duration(couple of days). However, it was established that the realisation of endurance level of current dredgers is not possible without a reduction of hopper capacities or factorial increase in energy density of storage. Further, the smaller TSHDs were found to be better suited to use PEMFC or battery-based systems.A part of this work also tried to answer the pertinent question of the third party liability insurance premiums for a nuclear-powered vessel and the regulations such a ship would be subjected to. Further, a preliminary business case was developed and the sustainability of the concept was evaluated. It was realised that the technological forces and trends like the development of Small Modular Reactors, deep-sea mining and autonomous ships, could favour the development of a fleet of nuclear-powered dredging vessels in the future. However, the regulations and the support for these vessels would be highly dependent on the flag country and operational location.