Concept development of renewable and nuclear hybrid micro modular reactor system

Abstract

In the case of islands or remote regions, which can be considered as micro-grid, fuel transportation cost increases substantially compared to other regions, and the energy sources requiring refueling have a disadvantage due to high cost. Considering these characteristics, a small modular nuclear reactor is suitable for the base energy source. However, a small modular reactor with a steam generation system becomes bulky and is disadvantageous in terms of transportation because it cannot fully modularize the core and the power conversion system. Therefore, to solve this problem, the KAIST research team developed a KAIST MMR (Micro Modular Reactor) by combining a s$CO_2$ power cycle with a small component unit and a small modular reactor. MMR combines the power system and the core system into a single module and has the advantage of being transportable via a vehicle such as a trailer or a ship. MMR is designed to meet the electricity demand of isolated regions alone. However, if MMR can be combined with other renewable energy sources to meet larger electricity demand, it can solve the intermittency problem of renewable energy while maintaining the high capacity factor of MMR. Renewable energy for combining with MMR was selected as the CSP (concentrated solar power) that can operate in the temperature range of MMR and can use TES (thermal energy storage system) at the same time. Therefore, this study designed a nuclear-solar hybrid system conceptually that combines MMR, CSP, and TES altogether. First, the installation area was selected for the conceptual design of the hybrid system. Based on the micro-grid of islands of several kW-MW, the electricity demand and DNI of the region where the hybrid system will be installed are determined. In addition, considering the temperature range of MMR and the characteristics of the installation area, thermal energy storage type, thermal energy storage medium, and concentrated solar power receiver technology were decided as well. Next, at the design point, several cycle layouts were optimized and selected between the power cycle with the highest efficiency. However, hybrid systems often operate at a lower load than design points, so it is necessary to consider the off-design performance of the hybrid system. Therefore, the quasi-steady state of the hybrid system was analyzed at part-load and core bypass, inventory control was used to achieve higher off-design efficiency. Finally, the performance of the hybrid system was evaluated using the quasi-steady state results of the hybrid system. For the evaluation of the system, the capacity factor and the electricity fulfillment rate were calculated using the installed area's electric demand and DNI, and the performance was compared with the constructed CSP plant. As a result, it was confirmed that the nuclear-solar hybrid system can solve the problems of intermittency and large solar field area of the CSP and reduce the volume of the TES while maintaining the high capacity of MMR.