Yanhua Yang

A MIXED CORE FOR SUPERCRITICAL WATER-COOLED REACTORS

In this paper, a new reactor core design is proposed on the basis of a mixed core concept consisting of a thermal zone and a fast zone. The geometric structure of the fuel assembly of the thermal zone is similar to that of a conventional thermal supercritical water-cooled reactor (SCWR) core with two fuel pin rows between the moderator channels. In spite of the counter-current flow mode, the co-current flow mode is used to simplify the design of the reactor core and the fuel assembly. The water temperature at the exit of the thermal zone is much lower than the water temperature at the outlet of the pressure vessel. This lower temperature reduces the maximum cladding temperature of the thermal zone. Furthermore, due to the high velocity of the fast zone, a wider lattice can be used in the fuel assembly and the nonuniformity of the local heat transfer can be minimized. This mixed core, which combines the merits of some existing thermal SCWR cores and fast SCWR cores, is proposed for further detailed analysis.

CFD Application to Hydrogen Risk Analysis and PAR Qualification

A three dimensional computation fluid dynamics (CFD) code, GASFLOW, is applied to analyze the hydrogen risk for Qinshan-II nuclear power plant (NPP). In this paper, the effect of spray modes on hydrogen risk in the containment during a large break loss of coolant accident (LBLOCA) is analyzed by selecting three different spray strategies, that is, without spray, with direct spray and with both direct and recirculation spray. A strong effect of spray modes on hydrogen distribution is observed. However, the efficiency of the passive auto-catalytic recombiners (PAR) is not substantially affected by spray modes. The hydrogen risk is significantly increased by the direct spray, while the recirculation spray has minor effect on it. In order to simulate more precisely the processes involved in the PAR operation, a new PAR model is developed using CFD approach. The validation shows that the results obtained by the model agree well with the experimental results.

System Simulation of Nuclear Power Plant by Coupling RELAP5 and Matlab/Simulink

Since RELAP5 code has general and advanced features in thermal-hydraulic computation, it has been widely used in transient and accident safety analysis, experiment planning analysis, and system simulation, etc. So we wish to design, analyze, verify a new Instrumentation And Control (I&C) system of Nuclear Power Plant (NPP) based on the best-estimated code, and even develop our engineering simulator. But because of limited function of simulating control and protection system in RELAP5, it is necessary to expand the function for high efficient, accurate, flexible design and simulation of I&C system. Matlab/Simulink, a scientific computation software, just can compensate the limitation, which is a powerful tool in research and simulation of plant process control. The software is selected as I&C part to be coupled with RELAP5 code to realize system simulation of NPPs. There are two key techniques to be solved. One is the dynamic data exchange, by which Matlab/Simulink receives plant parameters and returns control results. Database is used to communicate the two codes. Accordingly, Dynamic Link Library (DLL) is applied to link database in RELAP5, while DLL and S-Function is applied in Matlab/Simulink. The other problem is synchronization between the two codes for ensuring consistency in global simulation time. Because Matlab/Simulink always computes faster than RELAP5, the simulation time is sent by RELAP5 and received by Matlab/Simulink. A time control subroutine is added into the simulation procedure of Matlab/Simulink to control its simulation advancement. Through these ways, Matlab/Simulink is dynamically coupled with RELAP5. Thus, in Matlab/Simulink, we can freely design control and protection logic of NPPs and test it with best-estimated plant model feedback. A test will be shown to illuminate that results of coupling calculation are nearly the same with one of single RELAP5 with control logic. In practice, a real Pressurized Water Reactor (PWR) is modeled by RELAP5 code, and its main control and protection system is duplicated by Matlab/Simulink. Some steady states and transients are calculated under control of these I&C systems, and the results are compared with the plant test curves. The application showed that it can do exact system simulation of NPPs by coupling RELAP5 and Matlab/Simulink. This paper will mainly focus on the coupling method, plant thermal-hydraulic model, main control logics, test and application results.Copyright

The Flowing and Heat Transfer Models of Turbulent Flow in Rolling Motion

The flowing and heat transfer characteristics of turbulent flow in tubes in rolling motion are investigated theoretically. The flowing and heat transfer models of turbulent flow in rolling motion are established. The correlations of frictional resistance coefficient and Nusselt number are derived. The results are also validated with experiments. The effects of several parameters on Nusselt number are investigated. The oscillating amplitude of Nusselt number is in direct ratio with Prandtl number and rolling frequency approximately. The more the flowing velocity is, the less the effect of rolling motion on the flow is. The variation of initial phase difference between Nusselt number and rolling motion with rolling frequency is very limited.Copyright

Experimental Studies on Breakup and Fragmentation Behavior of Molten Tin and Coolant Interaction

Jet breakup and fragmentation behavior significantly affect the likelihood (and ultimate strength) of steam explosion, but it is very challenging to assess the potential damage to reactor cavity due to general lack of knowledge regarding jet breakup phenomena. In this study, the METRIC (mechanism study test apparatus for melt-coolant interaction) was launched at Shanghai Jiao Tong University to investigate FCI physics. The first five tests on molten tin and water interactions are analyzed in this paper. Significant breakup and fragmentation were observed without considerable pressure pulse, and intense expansion of droplets in local areas was observed at melt temperature higher than 600°C. The chain interactions of expansion all ceased, however, and there was no energetic steam explosion observed. Quantitative analysis on jet breakup length and debris was studied to investigate the effect of the melt temperature, initial diameter of the jet, and so on. Furthermore, the results of tests were compared with current theories. It is found that melt temperature has strong impact on fragmentation that need to be embodied in advanced fragmentation models.

A Numerical Analysis Research on Earlier Behavior of Molten Droplet Covered with Vapor Film at the Stage of Triggering and Propagation in Steam Explosion

When the molten fuel with high temperature falls into the cavity water, it will be dispersed into droplets which are covered with vapor films due to the rapid heat transfer with phase transition. This situation cannot be simply described by liquid-liquid or gas-liquid systems. And there are no sufficient experimental studies on the behavior of droplet covered with vapor film because of the rapid reaction and the difficulty in capture of the film configuration. In this paper, a multiphase code with the volume of fluid (VOF) method is used to simulate the earlier behavior of droplet when vapor film exits. The earlier behavior is defined as behavior of the droplet before its disintegration. Thermal effect and pure hydrodynamic effect are, respectively, considered. The simulation results indicate that the film thickness and material density have significant effect on the earlier behavior of droplet. The situation assumed in Ciccarelli and Frost’s model (1994) is observed in current simulation of earlier thermal droplet behavior. The effect of triggering pressure pulse on earlier hydrodynamic behavior is also discussed and it indicates that vapor film has little effect on the hydrodynamic droplet deformation when the intensity of the pressure pulse is very high.

Numerical Simulation of Thermal Behavior of a Molten Droplet Covered With Vapor Film

When the molten fuel with high temperature falls into the cavity water, it will be dispersed to droplets which are covered with vapor films due to the rapid heat transfer with phase transition. This situation cannot be simply described by liquid-liquid nor gas-liquid systems. And there are not sufficient experimental studies on the behavior of droplet covered with vapor film because of the rapid reaction and the difficulty in capture of the film configuration. In this paper, A multi-phase code with the Volume of Fluid Method (VOF) is developed to simulate the behavior of droplet covered with vapor film. Thermal effect is considered. The simulation results indicate that the film thickness and material density have significant effect on the behavior of droplet. The situation assumed in Ciccarelli and Frost’s model is observed in current simulation of thermal droplet behavior.Copyright

CFD Modeling of Mass Transfer in the Flow Through an Orifice With ζ-f Model

Mass transfer enhancement is an important element in flow-accelerated corrosion (FAC). In the present paper the ζ-f model and a compound wall treatment have been tested for high Schmidt number mass transfer in a simple fully developed pipe flow and a flow through an orifice. The test shows that the mass transfer can be well predicted in both flows when the wall is fully resolved with the ζ-f model. The superior performance of the ζ-f model in the flow through an orifice can be attributed to avoiding the utilization of the dimensionless wall distance in the model. However, when the compound wall treatment is utilized together with the ζ-f model, mass transfer can be reasonably predicted only when uτ = Cμ1/4kp1/2 is a fair assumption, as demonstrated in the computation for the fully developed pipe flow. With the compound wall treatment the ζ-f model predicts shorter reattachment length and higher mass transfer rate in the flow through an orifice.Copyright

Analysis for Inverse Flow in Moderator Channels of Supercritical Water Cooled Reactor

This paper mainly talks about supercritical water cooled reactor (SCWR) fuel assembly which has special character such as moderator channels, two flue pin rows between the moderator channels and the thermal zone of fuel bundle. SABER (Sub-channel Analysis Based on Extended pressure Range) is used for sub-channel analysis of the fuel assembly. It is a self-developed sub-channel thermal-hydraulic analysis code. The code was originally developed to analyze SCWRs. After adding an extended computational cell structure and some new boundary conditions, SABER can simulate the complex flow (the opposite flow direction between moderator channels and coolant channels) in the fuel assembly. SABER can also compute heat exchange between moderator channels and cooling channels. The phenomenon of inverse flow occurs in the moderator channels, was found by sub-channel analysis. The phenomenon is caused by the different heating situation around moderator channels. Some sensitivity analysis of this phenomenon was analyzed in the paper.Copyright

Pressure Drop of Perforated Orifice in Single-Phase Flow

This study studied the performance of perforated orifices by a new method, namely field synergy theory (FST). Pressure loss was obtained theoretically by connecting flow field and pressure loss, and pointed out the direction to optimization. To validate the theory, pressure loss was measured experimentally under different orifice structures by changing the parameters of porosity, thickness, hole diameter, hole distribution, and etc. Theoretical results showed that pressure loss was determined by the synergy of velocity and velocity gradient over the flow field passing the orifice. Pressure loss increased as the synergy being stronger. To decrease pressure loss, it was the most effective to decrease the synergy with the biggest weight. The comprehensive performance of a perforated orifice is better than a standard one. All the structure parameters should be optimized to improve the performance of a perforated orifice.Copyright