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Safety systems play a key role in the nuclear industry. In the past decades, various safety systems have been designed and built to enhance safety level in nuclear power plants. The advanced secondary passive residual heat removal system (ASP) is one of several passive safety systems designed to ensure the safety of the reactor core. Experimental study on transient and steady-state characteristics as well as relevant influence factors of ASP system were conducted by using the high temperature high pressure thermal-hydraulic test facility. The results showed that the C-type heat exchanger could effectively remove the residual heat, and get stronger with the increase of loop pressure. The results also showed natural circulation could be set up with good stability, and get little influence from movement of isolating valves, relief valve as well as water volume in steam generator. Besides, to certificate the reasonability and reliability of the ASP system directly, an integral test was conducted.

The formation and control method of the coolant free surface is one of the key technologies for the design of windowless targets in the Accelerator Driven Systems (ADSs). In this work, a new design of windowless target for ADS based on upward swirling flow is proposed to form a stable free surface without recirculation zones. Experimental and numerical investigations on the free surface flow have been performed in a prototypical windowless target using water as working fluid. The experimental results show that a stable free surface is achieved when the mass flow rate is higher than 4.0 m3/h and the shape of free surface profile greatly depends on the inlet flow rate. CFD simulations have been carried out using VOF method with different turbulent models. The numerical results show that the prediction of BSL Reynolds stress model agrees qualitatively well with the experimental results. The free surface profile of Lead–Bismuth-Eutectic (LBE) in the windowless target is very similar to that of water according to the simulation results. The feasibility of the new windowless target for ADS based on upward swirling flow is preliminary validated.

Natural circulation is one of the most important thermal-hydraulic phenomena that makes the fluid flow along a closed loop without any external driving force. With this merit, it is adopted by the passive heat removal system to bring the residual heat out of the core at accidents, and by the primary system of some new conceptual reactors instead of pumps to drive the coolant in the loop at operation. To investigate the reactor natural circulation and verify system thermal-hydraulic codes, it is a way to construct an integrated effect test facility and perform experiments on it with the scaling criteria. With one-dimensional assumption, the natural circulation system was simplified as the heat source, heat sink and pipes, and described by two groups of equations independently for the single-phase and two-phase flow conditions. Based on these equations, a set of non-dimensional equations were derived and the criteria were obtained both applicable for single-phase and two-phase natural circulation. According to these criteria, the practical application was analyzed and discussed. In the paper, the property similarity was strongly suggested in most cases. Though equal height simulation was widely used in the past, the reduced height simulation is a good way to reproduce three-dimensional (3D) phenomena that are of concern in the investigation. The CHF simulation is not suggested. The mass of metal and its distribution is of concern instead of heat transfer at transient simulation.

A new type of fuel assemblies (FAs) was designed for super critical water reactors (SCWRs). A square FA is composed by 16 rectangular channels. Each channel has 26 fuel rods that are arranged into two rows and enclosed by thermal walls. The gap between each channel acts as water rods as usual design does. Flat absorbers are used as the control rods. They are placed in the gaps. Then computational fluid dynamics (CFD) was used to evaluate the design. The results show mixing vanes can lower the peak cladding temperature of fuel rods. The thermal wall between cold water rods and subchannels should be optimized to produce reasonable heat transfer.Copyright © 2013 by ASME

A new core catcher concept was presented and experimentally investigated in the paper. The new core catcher composed by many vertical cells. Parallel steel plats protecting by the ceramic layer form a vertical channel which can accommodate core molten and cool it from both sides. One cell model was constructed and experimentally studied in the paper. The experiment proved the molten can be solidified and cooled in a very short time.Copyright © 2013 by ASME