Gyoodong Jeun

Boiling characteristics of dilute polymer solutions and implications for the suppression of vapor explosions

Quenching experiments of hot solid spheres in dilute aqueous solutions of polyethylene oxide polymer and surfactant have been conducted for the purpose of investigating the physical mechanisms of the suppression of vapor explosions in this polymer solutions. Two spheres of 22.2 and 9.5 mm-diameter were tested in the polymer solutions of various concentrations and pool temperatures from 30°C to its boiling point. The minimum film boiling temperature in 30°C liquid rapidly decreased from over 700°C for pure water to about 150°C as the polymer concentration was increased up to 300 ppm for a 22.2 mm sphere, and it decreased to 350°C for a 9.5 mm sphere. This trend is observed consistently in the heated pool up to its boiling temperature, while the tests with surfactant solutions do not show an appreciable reduction in the minimum film boiling temperature. The ability of suppression of vapor explosions by dilute polyethylene oxide solutions against an external trigger pressure was tested by dropping molten tin into the polymer solutions at 25°C. It was observed that in 50 ppm solutions more mass fragmented than in pure water, but it produced weaker explosion pressures. The explosion was completely suppressed in 300 ppm solutions with the external trigger. The debris size distributions of fine fragments smaller than 0.7 mm were shown to be almost identical regardless of the polymer concentrations.

Transient Analysis of Natural Circulation Nuclear Reactor REX-10

As research regarding small- and medium-sized nuclear reactors (SMRs) has rapidly increased worldwide, the Regional Energy Research Institute for Next Generation (RERI) is designing a new conceptual nuclear reactor, called the Regional Energy rX-10MWt (REX-10). The REX-10 is an integral-type nuclear reactor and adopts natural circulation for heat removal. Since the REX-10 is designed for district heating and small-scale power generation near residential areas, it has to guarantee safety under all circumstances. Thus, the REX-10 Test Facility (RTF) is designed to evaluate the natural circulation behavior in the REX-10. On the basis of a theoretical model and reactor safety, two experimental parameters (heater power and feedwater flow rate) were chosen and various transient experiments are conducted. As a result of six transient experiments, the RTF guarantees safety against abrupt changes in the experimental parameters. Furthermore, all the experiments are simulated by using the MARS code. In most cases, the results of the MARS code show good agreement with the experimental results. However, in case of the chiller trip, the MARS code overestimates the temperature and generates a fluctuation of the primary flow. However, both results show a similar trend after the fluctuation is finished.

Three-Dimensional Modeling of Debris Mixing and Sedimentation in Severe Accidents Using the Moving Particle Semi-Implicit Method Coupled with Rigid Body Dynamics

Abstract Particle mixing and sedimentation, related to corium debris bed formation and coolability in severe accidents, is investigated using a new computational fluid dynamics tool: the Analysis of Debris Dynamics and Agglomeration (ADDA) code. ADDA was developed based on an enhanced numerical method combining the moving particle semi-implicit algorithm with a rigid body dynamic model. The analysis successively simulates the entire process of debris bed formation, including corium jet breakup, mixing, and sedimentation. The methodology allows identification of key characteristics in the formation of the corium debris bed. Two-dimensional (2-D) and three-dimensional (3-D) simulations were utilized to model the detailed flow structures and mixing phenomena, along with the final sedimentation process, and were compared to the Q21 QUEOS test performed at Forschungszentrum Karlsruhe, Germany. For the analysis of debris bed formation, it is recommended that full 3-D simulations be utilized to provide enhanced accuracy related to corium debris field prediction. The 2-D simulations were found to be insufficient because of the debris field dependence on particle agglomeration and mixing, prior to debris settling.

A Study on the Impact and Solidification of Liquid Metal Droplets during Thermal Spray Deposition onto a Substrate with Concentric Grooves or Ridges

In this study, a numerical investigation has been performed on the spreading and solidification of a coating material droplet onto the rigid substrate in the thermal spray process. The computational model is validated through the comparison of the predicted numerical result and the experimental data for flat substrate. An analysis of the deposition formation on a substrate with small concentric grooves or ridges was performed. To examine the characteristic of the impact and solidification of a liquid droplet on the substrate with concentric grooves or ridges, a parametric study was conducted with various shapes and sizes of concentric grooves or ridges.

A Study on the Steady-State and Transient Behavior of Natural Circulation in REX-10

Research regarding small- and medium-sized nuclear reactors (SMRs) has increased because of multipurpose applications and increased safety. According to this tendency, a new conceptual nuclear reactor, the Regional Energy rX-10MWt (REX-10), is being designed. REX-10 adopts a way to remove heat by natural circulation and integrates the primary systems within a reactor pressure vessel. To evaluate the steady-state and transient behavior of natural circulation in REX-10, a NAtural Circulation TEst Reactor (NACTER) is designed using the scaling law. The ratio of the height and core power are 1/3 and 1/500, respectively. This research can be divided into three parts - a steady-state experiment, a transient experiment, and MARS (Multidimensional Analysis for Research Safety) code analysis. To investigate the natural circulation characteristics under the steady-state conditions, two parameters were chosen and various experiments were conducted. As a result of the steady-state experiment, we show that the most important parameter that affects the natural circulation behavior is the heater power. In addition, we carried out a transient experiment. The results of the transient experiment are that the NACTER facility is well controlled and guarantees safety in abrupt changes in experimental conditions. Finally, MARS code simulations were conducted. The MARS code results show good agreement with the experimental results.