Operational Stability and Safety of LDR Lite Under Extended Load-Following Conditions

LDR lite is a small modular reactor concept for district heat production. Its design features, such as natural circulation and boron-free operation, pose unique challenges for flexible operation. In this study, two extended operational scenarios were calculated to assess the stability and safety of the reactor during load-follow conditions. The first scenario represents periodic power variation between 50 % and 100 %, while the second scenario is based on historical district heat demand and weather data from Helsinki, where both the power and network temperatures vary with outdoor temperature. The cases are calculated using process simulation software Apros coupled with 3D nodal neutronics solver Ants. In the control scheme, the secondary circuit temperatures remain constant while control rods are used to adjust the reactor power. Results show that the reactor tracks the power and temperature setpoints without instabilities in both scenarios. Key safety parameters, including temperatures, peaking factors and axial offset, show only minor increases from initial values suggesting that the fuel cooling and overall reactor safety are not compromised during load-follow operation with the selected control scheme. Future work includes optimization of the control as well as considering other states of the fuel cycle.