Abstract: Heat pipe reactors have advantages such as compact structure, stable operation, and high inherent safety, showing significant potential for specialized applications including space power systems and energy supply in remote areas. However, in such scenarios, the systems are often subject to transient conditions like load fluctuations and reactivity perturbations, making their self-regulating capability crucial to operational autonomy and safety. In this study, the system-level self-regulating characteristics of U-50Zr metal-fueled heat pipe reactor core coupled with an open-cycle air Brayton system were investigated. To address the high computational cost of 3D high-fidelity models, which were unsuitable for long-duration system simulations, an equivalent lumped-parameter model was developed. Its consistency with the 3D model in terms of trend and key parameters was verified under multiple transient scenarios. Using this model, the transient characteristics of the system under ±5% load disturbances and step reactivity insertions of ±10 pcm and ±50 pcm were simulated and analyzed. The results indicate that the system regains steady state within approximately 1 520 s under ±5% load disturbances, and within approximately 1 620 s under reactivity disturbances of ±10 pcm and ±50 pcm, while the heat transfer power of the heat pipes remains below the corresponding limiting values throughout the transients, demonstrating good self-regulating capability and safety margin. To further evaluate the advantages of the proposed design, a comparison was made with a SUPERHERO heat pipe reactor that used UN ceramic fuel and a clad-based design. The results show that although both cores exhibit similar trends under the same disturbances, the U-50Zr metal-fueled core offers a more direct heat transfer path, faster thermal response, and consequently more rapid temperature and reactivity feedback, leading to a shorter recovery time to steady state. This work provides insights for the design and control optimization of metal-fueled heat pipe reactor systems.