Hybrid nuclear-solar power
Creators: name: Al Kindi, Abdullah
Publisher: name: Imperial College London
Year: 2023

description: Nuclear and solar power, in the form of concentrated solar power (CSP), play a significant role in achieving the ambitious global targets of reducing greenhouse emissions and guaranteeing security of energy supply. However, both power generation technologies still require further development to realise their full potential, especially in terms of attaining economic load following operations and higher thermal efficiencies. Therefore, the aim of this research is to investigate and thermo-economically evaluate the available options of upgrading the flexibility and enhancing the thermal efficiency of nuclear and solar power generation technologies (i.e., through the integration with thermal energy storage (TES) and by hybridising both power generation technologies) while providing reasonable economic returns. The thesis starts with describing the development and validation of several thermodynamic and economic computational models and the formulation of the whole-energy system model. The formulated models are utilised to perform several thermo-economic studies in the field of flexible nuclear and solar power, and to quantify the economic benefits that could result from enhancing the flexibility of nuclear power plants from the whole-energy system perspective. The studies conducted in this research are: (i) a thermo-economic assessment of extending the conventional TES system in direct steam generation (DSG) CSP plants; (ii) a thermo-economic evaluation of upgrading the flexibility of nuclear power plants by the integration with TES and secondary power generation systems; (iii) an investigation of the role of added flexibility in future low-carbon electricity systems; and (iv) a design and operation analysis of a hybrid nuclear-solar power plant. The most common TES option in DSC CSP plants is steam accumulation. This conventional option is constrained by temperature and pressure limits, leading to lower efficiency operations during TES discharging mode. Therefore, the option of integrating steam accumulators with sensible-heat storage in concrete to provide higher-temperature superheated steam is thermo-economically investigated in this research, taking an operational DSG CSP plant as a case study. The results show that the integrated concrete-steam TES (extended) option delivers 58% more electricity with a 13% enhancement in thermal efficiency during TES discharging mode, compared to the conventional steam accumulation (existing) configuration. With an estimated additional investment of $4.2M, the projected levelised cost of electricity (LCOE) and the net present value (NPV) for the considered DSG CSP plant with the extended TES option are respectively 6% lower and 73% higher than those of the existing TES option. The option of upgrading the flexibility of nuclear power plants through the integration with TES and secondary power generation systems is investigated for two conventional nuclear reactors, a 670-MWel advanced gas-cooled reactor (AGR) and a 1610-MWel European pressurised reactor (EPR). In both investigated case studies, the reactors are assumed to continuously operate at full rated thermal power, while load following operations are conducted through the integrated TES tanks and secondary power generators. Based on the designed TES and secondary power generation systems, the AGR-based configuration can modulate the power output between 406 MWel and 822 MWel, while the EPR-based configuration can operate flexibly between 806 MWel and 2130 MWel. The economic analysis results demonstrate that the economics of added flexibility are highly dependent on: (i) the size of the TES and the secondary power generation systems; (ii) the number of TES charge/discharge cycles per day; and (iii) the ratio and difference between off-peak and peak electricity prices. Replacing conventional EPR-based nuclear power plants with added flexibility ones is found to generate whole-system cost savings between $30.4M/yr and $111M/yr. At an estimated cost of added flexibility of $53.4M/yr, the proposed flexibility upgrades appear to be economically justified with net system economic benefits ranging from $5.0M/yr and $39.5M/yr for the examined low-carbon scenarios, provided that the number of flexible nuclear plants in the system is small. The concept of hybridising a small modular reactor (SMR) with a solar-tower CSP integrated with two-tank molten salt TES system, with the aim of achieving economically enhanced load following operations and higher thermal efficiency levels, is also thermo-economically investigated in this research. The integration of both technologies is achieved by adding a solar-powered superheater and a reheater to a standalone SMR. The obtained results demonstrate that hybridising nuclear and solar can offer a great amount of flexibility (i.e., between 50% and 100% of nominal load of 131 MWel) with the SMR continuously operated at full rated thermal power output. Furthermore, the designed hybrid power plant is able to operate at higher temperatures due to the addition of the solar superheater, resulting in a 15% increase of thermal efficiency compared to nuclear-only power plant. Moreover, the calculated specific investment cost and the LCOE of the designed hybrid power plant are respectively 5410 $/kWel and 77 $/MWhel, which are 2% and 4% lower than those calculated for the nuclear-only power plant.