Performance comparison of rectangular and toroidal natural circulation loops under steady and transient conditions

► Disparity in modelling strategies makes it difficult to compare different NCL geometries. ► A unified model has been proposed, with proper definition of characterizing groups. ► Developed model aids the comparison between different geometrical configurations. ► Rectangular loop shows higher flow rate and wider power range than toroidal loop. ► Toroidal loop is more stable than rectangular loop due to weaker buoyancy force.