Nuclear energy: a novel clean energy system for carbon neutral society

It is essential to have a carbon-free and reliable energy system to achieve Net Zero. A Clean Energy System has been developed as a solution. It is composed of a Molten Salt Fast Reactor and Liquid Air Energy Storage to provide consistent and clean energy with flexibility.

Article | Spring 2023

As the climate crisis is rapidly approaching, countries around the world have agreed to reach net zero emissions by 2050. To achieve this goal, nations are looking for ways to create an energy mix that does not rely on fossil fuels. While renewable energy sources are often considered, it is important to note that they are not always available and a significant amount of energy storage systems would be required to solely rely on them. As an alternative, Small Modular Reactors (SMRs) are becoming an increasingly attractive solution. The Center for Advance Reactor Research in the Department of Nuclear & Quantum Engineering (NQe), led by Professor Yong Hoon Jeong, is at the forefront of this trend by developing a Clean Energy System as shown in Figure 1. This system is composed of a Molten Salt Reactor (MSR) and Liquid Air Energy Storage (LAES), which work together to provide consistent and clean energy with flexibility.

MSR is a type of Small Modular Reactor (SMR) that is considered to be an ultimate reactor due to its use of liquid fuel, unlike other SMRs that use solid fuel. The main advantage of using liquid fuel is that it fundamentally cannot experience core melting and thus does not pose the risk of a Fukushima-like incident, as the fuel is already in a melted state. In case of an accident, the fuel temperature will naturally decrease and the fuel solidifies, making it easier to handle in post-accident scenarios. MSR also produces minimal spent fuel and can even be used to reduce the existing spent fuel.

LAES is a promising technology for storing large amounts of energy, which uses liquidized ambient air as a storage medium. When electricity supply exceeds demand, the air is compressed to -196℃ (an energy-dense liquid state) and stored in a tank. When energy is needed again, the liquefied air is converted back to high-pressure gaseous air and used to rotate a turbine and generate electricity. LAES is highly scalable, as capacity and system size can be increased by simply adding more storage tanks. Additionally, it captures fine dust and CO2 during liquefaction, contributing to cleaner air in surrounding areas.

 

The research focuses on reactor core design, safety evaluation, and energy storage system design. The key characteristic of the reactor core is its ability to operate for an extended period without refueling. The research team has proposed an innovative core design as shown in Figure 2, fast spectrum with a moderator and burnable absorber, which was shown to enable a minimum of 30 years of operation without refueling. Safety is ensured through the use of a passive safety system, called the Reactor Vessel Auxiliary Cooling System (RVACS). The passive safety means any electrically-worked devices are not involved and cooling proceeds only with natural phenomena such as natural convection by gravity. This means that reactor would cool down automatically even if the operator was to leave, making the reactor ‘walk-away safe’. The feasibility of this passive safety system was demonstrated with RVACS and the characteristics of liquid fuel. The team has also conducted research on the coupling layout of MSR and LAES. The high temperature of the molten salt can be used to increase the overall efficiency of the system, and it was found that connecting the MSR to the LAES during the discharge process can increase the round-trip efficiency by about 13%. More information about the research can be found at the following YouTube link, https://www.youtube.com/watch?v=ZYBm40SBJMg.