Hybrid Energy Systems with Small Modular Reactor Based Nuclear Power Plants and Renewable Energy Sources: Modeling, Operation and Planning Studies
With increasing environmental concerns over greenhouse gas emissions, more emphasis is being given to the generation technologies with a low carbon footprint. Renewable energy sources (RESs), such as wind and photovoltaics (PVs) are the most popular among clean energy alternatives, but the intermittency, uncertainty and lack of inertia associated with them are major concerns. Another major hurdle in this global transition to clean energy is providing economical and reliable energy to the remote and offgrid communities with limited access to the electric grid and natural gas pipelines. Small modular reactors (SMRs), an emerging nuclear power plant (NPP) technology with flexibility in size and improved power maneuvering capability, offer clean energy solutions for electrical grids and isolated communities. This research work investigates the planning and dynamic aspect of SMR and RES, focusing on exploring the issues and realizing the benefits offered by SMR due to its smaller size, flexible operation and cogeneration. The combination of SMR and distributed RES in remote communities is governed by SMR's capability to respond to the demand fluctuations. The flexibility requirements of remote communities increase almost proportionally with the increment in the RES penetration level. Therefore, it is essential to analyze SMR's flexible operation in the context of the flexibility requirements it has to provide in remote communities in the presence of RES penetration. In this research work, SMR's flexible operation is investigated with its operating limits for ramp rate and the net power variation in load following and frequency regulation modes. Electrical energy storage (EES) is used as an energy buffer to absorb the fluctuations and facilitate SMR-RES synergy in remote communities. The benefit of EES in the synergy is quantified in terms of the improvement in SMR's plant load factor. The proposed application of SMRs with RESs in an isolated system requires them to continually operate in flexible mode and respond to large demand variations. The approximated turbine-governor models currently used in power system software cannot correctly represent SMR, resulting in erroneous simulated dynamics. This thesis proposes a detailed dynamic model of SMR and integrates it with the standard turbine-governor model in PSS/E software. The proposed model mimics the source dynamics by including the component models for the reactor core, primary coolant circuit, steam generator and the secondary coolant circuit of the SMR plant. The proposed model improves the accuracy of power system dynamics and facilitates the analysis of internal reactor responses. SMR's cogeneration scheme for district heating will be advantageous for remote communities with limited access to electric grid and gas pipelines. The proper coordination of steam distribution for heat and electricity, on the other hand, could significantly improve the load following capability allowing the system to host distributed RES to form standalone SMR-RES hybrid energy systems in isolated communities. SMR, being the primary source of energy, will be responsible for maintaining the system performance while adhering to its operational limits for flexible operation. The battery energy storage system (BESS) and thermal energy storage (TES) could play a significant role in alleviating the fluctuations in power and heat sides. In this context, this thesis proposes a simulation model of the SMR-RES hybrid energy system with a detailed dynamic model of a cogenerating SMR and a quasi-static model of the DH system. Furthermore, a multi-time scale operational scheme is proposed to operate the hybrid energy in load following and frequency regulation modes. An optimization problem is also proposed to optimally operate the hybrid energy system and evaluate RES hosting capability based on steady-state and dynamic constraints related to the reactor, power system, and district heating system. Another excellent opportunity with SMR is in electrical grids as a new generation plant or as a clean energy replacement to the aging fossil fuel-based thermal plants. Various electrical and non-electrical factors impact the deployment of SMR in electrical grids. In this thesis, the electrical grid considerations of SMR's siting and sizing is investigated focusing on steady-state, dynamic and safety aspects. The steady-state aspect includes the accessibility to the electrical grid, transmission line and voltage limits, generation congestion, load demand and the hosting capacity. The dynamic aspect focuses on analyzing the impact of SMR's siting and sizing on system frequency and voltage dynamics. The safety aspect, on the other hand, assesses the suitability of a site based on the offsite power reliability. The proposed framework of SMR's siting and sizing is implemented in the Saskatchewan provincial electrical grid with no previous nuclear experience. The combination of SMR and RES offers an excellent clean energy solution to the remote communities and electrical grids. In this context, the proposed models, simulations and research findings in this thesis would help deploy the proposed energy solutions to realize sustainable clean energy systems.
Power System Dynamics, Dynamic Modelling, Small Modular Reactors, Nuclear Power Plants, Renewable Energy Sources, Hybrid Energy Systems, District Heating, Flexible Operation, Load Following, Frequency Control, Optimal Operation: Renewable Hosting Capability, Power System Planning.
Doctor of Philosophy (Ph.D.)
Electrical and Computer Engineering