Repurposing gas power stations for modular nuclear and hydrogen systems: a techno-economic assessment

In the UK, many fossil-fuel power stations are approaching retirement, yet these sites retain valuable brownfield assets, notably developed industrial land and high-capacity grid connections, and can be repurposed for low-carbon generation. Repurposing such sites for low-carbon generation could therefore offer three linked advantages: lower upfront capital requirements through reuse of grid connections and developed industrial land; shorter project delivery times by reducing permitting needs and avoiding lengthy grid-connection queues; and higher system value through the provision of dispatchable flexibility and improved asset utilisation. This study examines repurposing end-of-life gas power stations into modular nuclear plants and further enabling hydrogen integration via high-temperature electrolysis, where the electricity-heat split is governed by endogenous reactor choice. A repurposing-oriented optimisation framework is proposed to embed inherited brownfield constraints, particularly land availability and grid-export limits, while co-optimising technology selection with hourly unit commitment and economic dispatch. Under the selected representative-week simulations, results show that the repurposed modular nuclear can deliver system-level flexibility comparable to that of gas turbines while meeting brownfield constraints. Nuclear‑hydrogen integration further increases reactor utilisation by using co-located electrolysis as a flexible local demand for nuclear-derived electricity and heat, eliminating renewable curtailment and substantially reducing plant-level levelised cost of electricity (LCOE) relative to power-only repurposing under these simulations. Among the electrolyser options, high-temperature electrolysis coupling gives the lowest plant-level levelised cost of hydrogen (LCOH), while producing the largest hydrogen output with the lowest plant-level upfront investment. This advantage arises from the ability of high-temperature electrolysis to use both electricity and cost-effective nuclear heat, reducing reliance on electricity-priced input energy. Sensitivity analysis identifies nuclear and high-temperature electrolyser capital costs as the main upward cost drivers, while stack lifetime remains the key durability-related lever. Overall, the findings indicate that brownfield nuclear‑hydrogen integration can provide a valuable pathway for converting retiring thermal power station sites into flexible low-carbon power and hydrogen production assets.