Optimizing the flexibility of the steam Rankine cycle of an SMR for load following and cogeneration by combining a double partial arc admission for the turbine

In the context of the energy sector decarbonization, the interactions between variable renewable energies and Nuclear Power Plants (NPPs) productions are becoming increasingly important. In this regard, the main objective of this work is to improve the flexibility performance of the steam Rankine cycle coupled to a small modular reactor (SMR). To this end, partial arc admission (PAA) is employed in the turbine, which is an approach in contrast to the conventional Full Arc Admission (FAA) method in NPPs. The first study maximized efficiency in electrical grid load-following (LF) scenarios. With a dual PAA/PAA applied respectively to high/low-pressure turbine groups, efficiency gains from 1 to 2 points in the 20%–80% load range, are achieved. In a second study, a 24-hour scenario mixing pure electricity production and cogeneration was defined, mimicking possible trends linked to the paradigm shift in the energy sector, for methodological purposes. Based on a same thermodynamic incentive to produce heat and electricity, the results showed that an optimum was established for a cogeneration capacity at 41% of Steam Generator (SG) power, with the remaining thermal power producing electricity. This case conveniently demonstrates the flexibility of the system to supply substantial quantities of heat at 150 °C, with a 1-point gain for electricity efficiency compared to FAA as well as the achievement of SG and cogeneration combined control. Adapting the developed multi-case, multi-objective methodology to other energy conversion cycles is a key direction for next R&D, along with exploring other scenarios assigning different values to heat and electricity production. • A Rankine cycle with Partial Arc Admissions (PAAs) in the turbine is modeled using Modelica. • Dual PAAs are optimized for the combined control of Steam Generation and cogeneration operations. • Efficiency gain from 1. to 2. points is obtained in the 20%–80% load range. • Cogeneration of 41% of SG power shows a 1. point gain in electrical efficiency. • The performance of one of the designs proves to be resilient to flexibility scenarios.