Steady-State and Transient Analysis in Single-Phase Natural Circulation of ABV-6M

This paper discusses the results of the thermal-hydraulic investigations of natural circulation. The RELAP5/MOD3.4 computer code has been used to simulate the natural circulation in an ABV-6M Nuclear Power Plant (NPP), and steady-state and transient operational characteristics are researched. Some results can be listed as follows. In the steady-state analysis, the relationship between the reactor power and the mass flow rate of primary loop, and the temperature difference of core inlet and outlet are obtained. The comparisons between the RELAP5 results and the theoretic calculation data indicate good general agreement. Besides, the mass flow rate of natural circulation will increase and the flow will become stable more quickly when the reactor power increases on the condition of the system with a fixed construction. The trends of the thermal parameters are obtained and the temperature envelope curve of secondary circuit fluid is ascertained. In the transient analysis, some perturbations, such as the fluctuations of feedwater temperature and feedwater mass flow rate, have influence on the system performance. Then, the comparisons between taking an action and not taking an action on Nitrogen Pressurizer are obtained when these small perturbations occur. It is turn out that the safety of natural circulation loop is sensitive to some small perturbations.