In this application, based on the CGN_NHR1.0 model library, an overall simulation model of the intermediate loop of the low-temperature heating reactor was built using a visual drag-and-drop modeling method. The multi-domain coupling and collaborative simulation
verification were carried out using the MBSE method. The typical working condition selected was the step reduction of rated full power (100% FP) to 70% FP load disturbance. Oriented by the SysML functional requirements, a joint simulation framework for reactor physics, thermal-hydraulic, and control systems was constructed. The simulation conditions were divided into two stages: the first 100 seconds of the system maintained a steady state operation, and at the 100-second moment, a 70% FP step load reduction disturbance was applied. The simulation results showed that the various thermal-hydraulic parameters of the intermediate loop could return to stability within 450 seconds after the disturbance occurred, and the dynamic response performance of the system control was better than the design-expected indicators. Research has confirmed that the SysML-Modelica joint modeling approach is applicable to the design and analysis of complex nuclear energy systems. The "requirement driven - functional mapping - dynamic verification" closed-loop verification mode constructed in this study can provide reliable theoretical and methodological support for the digital design and development of nuclear energy equipment.