European supercritical water-cooled small modular reactor: Design and analysis

This paper presents the design concept and in-depth analysis of a European Super-Critical-Water-cooled Small Modular Reactor (SCW-SMR), developed within the framework of the Joint European-Canadian-Chinese (ECC-SMART) project, aimed at advancing next-generation nuclear reactor technologies. The reactor features an innovative horizontal fuel assembly configuration with seven heat-up stages and intermediate mixing zones, specifically designed to enable passive residual heat removal through natural circulation. The horizontal core configuration generates unique natural circulation patterns in the vessel that improve heat removal efficiency during accident conditions. Key innovations include the elimination of high-pressure injection requirements through the use of subcooled water inventory, the reliance on the large volume of feedwater at 280 °C as a thermal buffer, and the successful demonstration of passive decay heat removal for extended periods that exceed 72 h. Based on extensive material testing within the ECC-SMART, the design specifies 310S stainless steel and Alloy 800H as alternative candidates for fuel cladding. Comprehensive safety analyses demonstrate the reactor’s capability to manage design basis accidents, including long-term station blackout (LTSBO) and large-break loss-of-coolant accidents (LBLOCA) using primarily passive safety systems. Detailed thermal-hydraulic analyses confirm acceptable peak cladding temperatures below 625 °C during normal operation and below 780 °C during design-based accidents. Neutronic analyses and coupled neutronic-thermal-hydraulic simulations confirmed strongly negative reactivity coefficients and demonstrated feasibility of a two-year burnup cycle without fuel shuffling. The European SCW-SMR design is a 290 MW t h reactor operating at 25 MPa with core outlet temperatures of 500 °C, achieving thermal efficiency approaching 44%. The design represents a significant advancement in Generation IV reactor technology, combining the inherent simplicity of supercritical water cooling with enhanced passive safety features suitable for small modular reactors deployment.