Changqi Yan

Optimization Design of the Weight of Reactor Coolant Pump

Reactor coolant pump is a key equipment in nuclear power plants, which has direct impact on the overall weight and the arrangement of nuclear power plants. The optimization design of the weight of the reactor coolant pump is carried out based on colony complex algorithm. Gradient crossover genetic algorithm is also used to optimize the weight of the pumps inner motor for attaining the optimization result of the pump. Both the algorithms are developed ourselves. The results show that the optimized weight is 12.482% less than the prototypes, the optimization effect is obvious. The start-up transient and flow coast down transient of the optimized pump are analyzed. The results indicate that the optimized results are feasible. The effects of the operating parameters of primary loop and rotating speed of pump on the weight of reactor coolant pump, and the effects of relevant parameters on the weight of motor is also analyzed in this paper. The corresponding results can provide a reference for engineering design.

Study on the Behaviors of a Conceptual Passive Containment Cooling System

The containment is an ultimate and important barrier to mitigate the consequences after the release of mass and energy during such scenarios as loss of coolant accident (LOCA) or main steam line break (MSLB). In this investigation, a passive containment cooling system (PCCS) concept is proposed for a large dry concrete containment. The system is composed of series of heat exchangers, long connecting pipes with relatively large diameter, valves, and a water tank, which is located at the top of the system and serves as the final heat sink. The performance of the system is numerically studied in detail under different conditions. In addition, the influences of condensation heat transfer conditions and containment environment temperature conditions are also studied on the behaviors of the system. The results reveal that four distinct operating stages could be experienced as follows: startup stage, single phase quasisteady stage, flashing speed-up transient stage, and flashing dominated quasisteady operating stage. Furthermore, the mechanisms of system behaviors are thus analyzed. Moreover, the feasibility of the system is also discussed to meet the design purpose for the containment integrity requirement. Considering the passive feature and the compactness of the system, the proposed PCCS is promising for the advanced integral type reactor.

Experimental Study of a Gas Separator for MSR Gas Removal System

An independent gas removal system was firstly put up by Oak Ridge National Laboratory (ORNL) for Molten Salt Breeder Reactor (MSBR) to remove fission gas such as Xenon etc. from molten salt (LiF–BeF–UF), where the gas separator is a key equipment for which high separation efficiency and low pressure drop are required. Swirl vanes and recovery vanes are installed around the inlet and outlet of the gas separator. With reference to the design of ORNL, a new gas separator was designed for a conceptual design of a small molten salt research reactor.An experimental loop was also fabricated to test the local pressure drop and separation efficiency of the new designed gas separator using of water and air as working fluid. The separation efficiency is measured by comparing the gas flow rate from the bubble generator and that at the outlet of the separator using of high speed video camera. The tests were conducted with the water flow rates covering 10–30 m3/h and an average void fraction of 0.3%. Besides, the shape of gas cores is found necessary to estimate the working performance of gas separators. High separation efficiency comes with a stable and straight gas core, and the gas will be taken off from two ends of the gas separator. What’s more, the result shows that low concentration of gas does not increase the pressure drop compared with the condition of liquid only, except when it exceeds a certain level. Finally, local flow resistance of the gas separator was also obtained under low gas concentration condition, showing that the resistance factor is nearly unvaried with a value of 5.Copyright

Experimental Study of Density Lock in Passive Residual Heat Removal System

Conceptual design of advanced passive residual heat removal system in which density lock is applied is proposed, moreover theoretical analysis and experimental study on its feasibility is carried out. According to the design, atmospheric-pressure experimental loop is built so that researches on working performance of density lock in the system are done at steady-state operation and pump trip conditions. The results show that at steady-state operation conditions, density lock can keep close in a long run, which will separate passive residual heat removal system from primary circuit system. As a result, passive residual heat removal system is in the non-operating conditions, which do not influence normal operation of reactors. At the pump trip conditions, density lock can be automatically opened quickly, which will make primary and passive heat removal system communicated. The natural circulation is well established in the two systems, and is enough to ensure removal of residual heat. In addition, experimental study on operating reliability of density lock is made on the condition of small flow surge. The result show that the flow surge do not lead to the failure of the function of density lock, but bring about a little position change of temperature interface in the density lock, moreover, a new balance steady state will arrive very soon.

Visualized Experiment of Bubble Behaviors in a Vertical Narrow Rectangular Channel Under Natural Circulation Condition

The characteristics of bubble behavior have been in particular interest for decades due to its significant contribution to understanding the mechanism of heat transfer. In the present work, visualized experiment is conducted to study the bubble characteristics in subcooled flow boiling of a narrow rectangular channel under natural circulation. The experiments were performed at pressures of 0.2 MPa, with inlet subcooling ranging from 20 to 60 K and heat flux ranging from 100 kW/m2 to 300 kW/m2. A high-speed digital camera is used to capture the pictures of bubble behaviors. A sequence of image processing algorithms is used deal with the original bubble images to get relevant bubble parameters. We observe the whole process of a single sliding bubble lifetime and found most of bubbles slide along the heating surface after detaching the nucleation sites. Five typical sliding bubble growth paths are observed in the present experimental conditions. According to the analysis of the experimental data, it can be found that the liquid subcooling and wall superheat are the main factors that affect the bubble size during sliding in narrow rectangular channel under natural circulation condition. Due to the difference of driving force, the sliding velocity of bubble in forced circulation is always larger than that in natural circulation. At the same time, the bubble velocity changes significantly at different heat flux and shooting location.

The Surge Line Stress Analysis Model Setup With the Consideration of Thermal Stratification

In this paper, we deal with a typical pressurizer surge line in a conventional pressurized water reactor (PWR). This study is performed to develop an understanding of thermal stratification phenomenon, which may occur in the surge line during either normal condition or transient process, in the pressurizer surge line. The pressurizer surge line model of Daya Bay nuclear power plant is used as base analysis model, in which the hot leg is taken into account. The transient temperature distribution required to assess the phenomenon along the pressurizer surge line is obtained through CFD analysis technology using ANSYS FLUENT. The temperature loads are transferred to ANSYS Mechanical for stress evaluation for the heat up transient process. Subsequently, the usage factor is calculated on the basis of ASME Section-III design curve. The possible mitigation scheme for the thermal stratification phenomenon of changing the layout angles is also simulated and analyzed in detail. The results show that the thermal stratification phenomenon will occur both in normal operating condition and in heat up transient process. The circumfluent effect makes the thermal stratification phenomenon exhibit unique profile due to the introduction of the hot leg. The continuous spray mass flow rate may influence both the temperature difference and the occurrence range for the thermal stratification phenomenon. The stress analysis incorporating both temperature load and pressure load is performed for pressurizer surge line model with hot leg for the conservative and complete heat up case.Copyright

REMOVAL EFFICIENCY OF IODINE AT SATURATED STEAM IN SUBMERGED VENTURI SCRUBBER

Sever accident due to molten core of Nuclear Power Plant causes the production of steam which carries the radioactive iodine. It is important to retain the radioactive iodine from contaminated gas and steam before it is released into the environment. The purpose of this research is to investigate the removal efficiency of iodine in a submerged venturi scrubber for saturated steam at 100°C. Venturi Scrubber is submerged in a venturi tank filled with liquid which is alkaline by adding sodium hydroxide (NaOH) and sodium thiosulphate (Na2S2O3) in scrubbing water. Saturated Steam of 100 °C is injected into an experimental loop. Iodine removal efficiency is investigated for saturated steam at various compressed gas flow rate 330, 420, and 510 kg/s. Inlet and outlet concentration are measured at the sampling points of an experimental loop to calculate the iodine removal efficiency. The maximum removal efficiency of 99.4% is achieved at gas mass flow rate of 510 kg/s.Copyright

Two-Phase Slug Flow in a Narrow Rectangular Channel Under Inclined Conditions

The characteristics of two-phase slug flow in a narrow rectangular channel with cross section of 3.25 mm × 43 mm under vertical and inclined conditions are investigated using a high speed video camera system. It is found that the velocity of Taylor bubble in vertical continuous slug flow could be well predicted by the Nicklin et al. (1962) correlation, in which C0 is given by the correlation of Ishii (1977), and the drift velocity given by the correlation of Sadatomi et al. (1982) or Clanet et al. (2004). For low two-phase superficial velocity (FrTP ≤ 3.5), the Taylor bubble velocities gradually increase with the increasing in inclination angles and almost approximate the maximum value for θ = 30°. For high two-phase superficial velocity (FrTP > 3.5), the influence of the inclination angles on the Taylor bubble velocity is insignificant, and the bubble velocity under vertical condition is slight lower than those under inclined conditions. For the inclined cases, the nose of Taylor bubble is deviated from the centerline and its position is the function of the two-phase superficial velocity as well as the inclination angle.Copyright

Application of Dual-Adaptive Niched Genetic Algorithm in Optimal Design of Nuclear Power Components

Genetic algorithm (GA) has been widely applied in optimal design of nuclear power components. Simple genetic algorithm (SGA) has the defects of poor convergence accuracy and easily falling into the local optimum when dealing with nonlinear constraint optimization problem. To overcome these defects, an improved genetic algorithm named dual-adaptive niched genetic algorithm (DANGA) is designed in this work. The new algorithm adopts niche technique to enhance global search ability, which utilizes a sharing function to maintain population diversity. Dual-adaptation technique is developed to improve the global and local search capability at the same time. Furthermore, a new reconstitution operator is applied to the DANGA to handle the constraint conditions, which can avoid the difficulty of selecting punishment parameter when using the penalty function method. The performance of new algorithm is evaluated by optimizing the benchmark function. The volume optimization of the Qinshan I steam generator and the weight optimization of Qinshan I condenser, taking thermal-hydraulic and geometric constraints into consideration, is carried out by adopting the DANGA. The result of benchmark function test shows that the new algorithm is more effective than some traditional genetic algorithms. The optimization design shows obvious validity and can provide guidance for real engineering design.Copyright

Experimental Study on Resistance Characteristics in a 3 × 3 Rod Bundle

Experimental study on resistance of air-water two-phase flow in a vertical 3 × 3 rod bundle was carried out under normal temperature and pressure. The rod diameter and pitch were 8 mm and 11 mm, respectively. The ranges of gas and liquid superficial velocity were 0.013∼3.763 m/s and 0.076∼1.792 m/s, respectively. The result indicated that the existing correlations for calculating frictional coefficient in the rod bundle and local resistance coefficient could not give favorable predictions on the single-phase experimental data. For the case of two-phase flow, eight correlations for calculating two-phase equivalent viscosity poorly predicted the frictional pressure drop, with the mean absolute errors around 60%. Meanwhile, the eight classical two-phase viscosity formulae were evaluated against the local pressure drop at spacer grid. It is shown that Dukler model predicted the experimental data well in the range of Rel<9000 while McAdams correlation was the best for Rel⩾9000. For all the experimental data, Dukler model provided the best prediction with MRE of 29.03%. Furthermore, approaches to calculate two-phase frictional pressure drop and local resistance were proposed by considering mass quality, two-phase Reynolds number and densities in homogenous flow model, resulting in a good agreement with the experimental data.Copyright