Scenario-based assessment of the role of nuclear units’ flexibility in an electricity grid with high intermittent renewable penetration

As a result of national and world-wide clean energy targets (laid down in the COP21 Paris Agreement and the National Energy and Climate Plan), the Hungarian electricity system has undergone a significant expansion of solar photovoltaic (PV) capacity in recent years, while nuclear power remains the primary generating source. The growing share of intermittent renewable sources necessitates a corresponding increase in flexible, dispatchable generation to ensure system stability. Consequently, within these emerging nuclear-renewable hybrid energy systems, an observable trend is that Transmission System Operators (TSOs) and electricity market participants are increasingly instructing nuclear power plant units to enhance their participation in load-following maneuvers to support grid balancing. To capture the effects of these changes for future strategies, this paper investigates the role of nuclear power in the planned power plant portfolios and projected consumption for the 2030s, based on the National Energy and Climate Plans of seven European countries. While our primary focus is on Hungary, we also consider its interconnections with neighboring countries. The analysis is based on full-year hourly dispatch simulations, providing insights into the system's dynamics. Unlike previous studies that often limit their analysis to a few scenarios, this paper provides a comprehensive examination of individual flexibility attributes of the nuclear units and their combinations. Key characteristics of generating units include maximal permitted ramp rate, minimal stable load, and minimum downtime. Different scenarios were defined by adjusting constraints for Hungary's existing four 500 MWe Gen2 and two new 1200 MWe Gen3+ nuclear power plant units. The simulations reveal that in the interconnected system, electricity prices are resilient to nuclear operational patterns, with the annual average price varying by only 0.26% depending on flexibility. Notably, despite higher curtailment, Gen3+ units in the most flexible scenarios achieve a more favorable contribution margin due to better adaptation to price fluctuations. This finding suggests that enhancing flexibility can even increase investment attractiveness in the electricity market, potentially supplemented by additional revenue from ancillary services in reserve markets. • Nuclear-renewable hybrid systems are the pathway towards zero-emission powergrids. • Flexible nuclear units enhance security of suppy alongside intermittent renewables. • Key properties like ramp rate, minimum load, minimum down time define the units' flexibility. • Enhanced flexibility of nuclear units allows them to adapt to price fluctuations. • Nuclear operational rigidity risks driving prices down through overproduction, ultimately threatening the plants' profitability.