Dynamic modelling and optimisation of a Small Modular Reactor for electricity production and district heating in the Helsinki region

The decarbonisation of the heat sector represents one of the main challenges to be tackled for the energy transition. In this context, nuclear reactors could play a key role by providing dispatchable and low-carbon heat and power. This paper investigates the potential of integrating a light-water cooled Small Modular Reactor (SMR) into a nuclear hybrid energy system (NHES), in which the thermal power produced by the reactor is dynamically allocated for power production or to drive non-electric applications, in particular for supplying heat to the district heating network (DHN) in the metropolitan area of Helsinki, Finland. The aim of this work is to propose a NHES architecture tailored for this purpose, encompassing the SMR, the balance of plant, and the DHN. The proposed balance of plant, obtained with the CYCLOP tool, has been modified by including an intermediate heat exchanger to transfer thermal power to the DHN. These subsystems were modelled in the object-oriented modelling language Modelica to test the dynamic response of the global architecture in different case studies based on the Backbone optimisation model output. The ultimate goal of this work is to evaluate the opportunities of deploying a NHES to supply heat to the DHN in the Helsinki area, focusing on dynamic operation to meet different heat requirements. In general, the simulation outcomes indicate that the NHES could meet variable heat demands while operating the reactor at nominal conditions. However, a notable mismatch between the power flows obtained with the dynamic model and those generated by the optimiser is observed. This discrepancy can be partially attributed to the DHN’s high thermal inertia, pointing out the importance of considering the system’s dynamics when estimating its optimal operation