The integration of nuclear propulsion into civilian maritime vessels offers a promising pathway towards low‑emission, long‑endurance operations, particularly for energy‑intensive offshore applications. High‑Temperature Gas‑Cooled Reactors (HTGRs) are well suited for such use due to their inherent safety characteristics and high thermal efficiency, but their limited load‑following capability restricts their ability to directly meet the highly dynamic power demands of ships. This thesis investigates how a hybrid energy storage system (ESS), combining thermal and electrical storage, can be sized, configured, and integrated to enable safe and efficient HTGR‑based maritime propulsion.

A dynamic, system‑level model is developed in Python to represent the interaction between an HTGR, an intermediate molten‑salt loop, a steam Rankine power cycle, auxiliary diesel generators, and hybrid energy storage. Reactor ramp‑rate constraints, thermal inertia, turbine efficiency limits, and storage charge–discharge constraints are modelled. A 14‑day operational load profile of the deep‑sea mining vessel Hidden Gem is used as a case study to quantify power mismatches and storage requirements. A comprehensive sizing study is performed for a range of thermal and electrical storage capacities, evaluating feasibility based on unmet load, dumped energy, diesel fuel consumption, and operational stability.

The results demonstrate that a hybrid ESS substantially improves operational flexibility, eliminates unmet load across feasible configurations, and reduces diesel fuel consumption compared to a non‑storage baseline. Thermal storage primarily buffers medium‑timescale reactor ramp limitations, while electrical storage absorbs fast transients and residual mismatches. The findings highlight that optimal ESS sizing strongly depends on the temporal structure of the ship’s load profile, rather than peak demand alone, and provide a structured methodology for hybrid ESS integration in future nuclear‑powered vessels. ... Read more