在我国能源结构转型压力剧增，环境污染日益严重的背景下，一体化自然循环反应堆因能提供安全、清洁、经济的能源而受到关注。当前，对于在高压条件下采用汽-气稳压器的一体化自然循环反应堆的稳态自然循环特性以及动态稳压特性的研究相对较少，有待进一步研究。 本文建立了采用汽-气稳压器的一体化自然循环实验系统（HRTL-200Ⅱ），对其稳态自然循环特性和动态稳压特性进行实验研究。同时，对自然循环系统稳态流动-阻力特性等问题进行了理论分析；建立了非平衡态汽-气稳压器模型，并对其中涉及的壁面冷凝传热模型提出改进。 论文首先建立HRTL-200Ⅱ一体化自然循环实验系统。在系统压力为5.0~7.0MPa的条件下，实验研究了加热功率、加热段入口阻力系数、主回路压力、加热段出口过冷度、二回路压力和流量等因素对稳态自然循环特性的影响，研究结果表明在高温、高压条件下一体化自然循环反应堆可以建立稳定的全功率自然循环，为一体化自然循环反应堆的研发设计和稳定运行提供数据支撑。 针对自然循环稳态流动-阻力特性，理论推导得到稳态自然循环流量分别与加热功率和系统总阻力之间存在幂函数关系并得到实验验证，首次揭示了流动状态和系统阻力对自然循环系统稳态流动-阻力特性的影响； 同时，针对一体化布置方案中存在的问题，从理论上证明忽略上升段和下降段之间的传热以及热源和热阱的温度分布采用线性假设对自然循环能力带来的误差在一定范围内可以忽略。 对于HRTL-200Ⅱ实验系统的动态稳压特性进行实验研究。实验结果表明在功率阶跃条件下，主回路系统压力的变化存在跟随滞后，并且加热段出口过冷度会迅速减小，这在一定程度上会影响反应堆的安全性。同时，实验研究了二回路调节和主回路初始条件对HRTL-200Ⅱ实验系统动态稳压特性的影响，所得结果可以为采用一体化汽-气稳压器的一体化自然循环反应堆的安全运行提供指导。 为了进一步研究HRTL-200Ⅱ实验系统的动态稳压特性，建立了适用于高压条件的非平衡态汽-气稳压器模型，并与HRTL-200Ⅱ实验系统的动态实验结果进行比较，验证了模型的准确性。针对高压条件，建立了存在非凝结气体的高压水蒸汽壁面凝结传热模型，揭示了压力对存在非凝结性气体的水蒸汽壁面冷凝传热影响的机理，并将此模型用于汽-气稳压器模型中。

In the background of increasing pressure of the energy restructuring and the serious environmental pollution in our country, the integrated natural circulation reactor has received extensive attention for the ability of providing clean, safe and economical energy. At present, the steady-state natural circulation characteristic and the transient behavior of gas-steam pressurizer under high pressure need to be further studied in the integrated natural circulation reactor with gas-steam pressurizer. In this paper, the integrated natural circulation test loop with the gas-steam pressurizer (HRTL-200Ⅱ) has been established, and the experimental study on the steady-state natural circulation characteristic and the transient behavior of the gas-steam pressurizer is set in HRTL-200Ⅱ. In addition, the theoretical investigation of the flow-resistance performance in the steady-state natural circulation is presented. The non-equilibrium gas-steam pressurizer model has been established and the improvement on the steam condensation heat transfer model in presence of non-condensable gas is also proposed. The test loop of HRTL-200Ⅱ has been established firstly. Under the system pressure of 5.0~7.0MPa, the experimental study on the effect of the heating power, the inlet resistance coefficient of the core, the total pressure, the outlet sub-cooling of the core, the pressure and the mass flow rate in the second loop on the steady-state natural circulation characteristic is set in HRTL-200Ⅱ. The experimental result proves that the integrated natural circulation reactor can establish the steady full power natural circulation under high pressure and high temperature, which provides the data support for the design and operation of the integrated natural circulation reactor. For the flow-resistance characteristic in the steady-state natural circulation, the power function relations of G~Q^m and △pf~G^q are obtained in theory and have been validated by the experiments of HRTL-200Ⅱ. The power function relations reveal the effect of the flow regime and the system resistance on the flow-resistance characteristic in the steady-state natural circulation. Moreover, for the problems existing in the integral arrangement, the quantitative analysis result shows that the errors of the natural circulation capacity caused by neglecting the heat transfer between the hot-leg and the cold-leg, and the linear assumption in the temperature distribution of the hot source and hot sink can be neglected within limits. Experimental research on the transient behavior of the gas-steam pressurizer in HRTL-200Ⅱhas been carried out. The experimental result indicates that under the condition of the power step-up，the hysteresis phenomenon exist in the dynamic response characteristic of the system pressure and the outlet sub-cooling of the core decreases rapidly, which will influence the nuclear reactor safety. In addition, the effect of the secondary loop regulation and the initial parameters in the primary loop on the transient behavior of the gas-steam pressurizer is also studied experimentally, which provides the guidance of the safe operation of the integrated natural circulation reactor with the gas-steam pressurizer. In order to make further research on the transient behavior of the gas-steam pressurizer in HRTL-200Ⅱ, the non-equilibrium gas-steam pressurizer model under high pressure has been established. The model validation is carried out by comparing with the experimental result of HRTL-200Ⅱ, which proves the correctness of the established non-equilibrium gas-steam pressurizer model. The steam condensation heat transfer model in presence of non-condensable gas under high pressure is also proposed, and it provides theoretical insights into the pressure’s influence mechanism to the steam condensation heat transfer in presence of non-condensable gas. As a result, this established model has been applied to the non-equilibrium gas-steam pressurizer model.