Jinho Song

NUMERICAL INVESTIGATION OF THE SPREADING AND HEAT TRANSFER CHARACTERISTICS OF EX-VESSEL CORE MELT

The flow and heat transfer characteristics of the ex-vessel core melt (corium) were investigated using a commercial CFD code along with the experimental data on the spreading of corium available in the literature (VULCANO VE-U7 test). In the numerical simulation of the unsteady two-phase flow, the volume-of-fluid model was applied for the spreading and interfacial surface formation of corium with the surrounding air. The effects of the key parameters were evaluated for the corium spreading, including the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The results showed a reasonable trend of corium progression influenced by the changes in the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The modeling of the viscosity appropriate for corium and the radiative heat transfer was critical, since the front progression and temperature profiles were strongly dependent on the models. Further development is required for the code to consider the formation of crust on the surfaces of corium and the interaction with the substrate.

Effect of melt water interaction configuration on the process of steam explosion

ABSTRACT Steam explosion experiments are performed at various modes of melt water interaction configuration using prototypic corium melt. The tests are performed to simulate both melt water interaction in a partially flooded cavity and melt water interaction in a cavity with submerged reactor. The tests are performed using zirconia and corium melts. The behavior of melt jet fragmentation during the flight in the air and fragmentation and mixing of melt jet in water is investigated by a high-speed video visualization and by comparison of debris size distribution and morphology of debris. Strength of steam explosion is estimated by measuring dynamic pressure and dynamic force.

Study of Two-Phase Natural Circulation Cooling of Core Catcher System Using Scaled Model

A two-phase natural circulation cooling has been proposed to remove melted core decay heat by external core catcher cooling system during sever accident scenario. In this paper, two types of the core catcher cooling loops, one with heated loop and the other adiabatic loop simulated with air water system are analytically studied. First, a scaling analysis was carried out for natural circulation flow in a closed loop. Based on the scaling analyses, simulation of two-phase natural circulation is carried out both for air–water and steam–water system in an inclined rectangular channel. The heat flux corresponding to the decay heat is simulated with steam generation rate or air flux into the test section to produce equivalent flow quality and void fraction. Design calculations were carried out for typical core catcher design to estimate the expected natural circulation rates. The natural circulation flow rate and two-phase pressure drop were obtained for different heat inputs or equivalent air injection rates expressed as void fraction for a select downcomer pipe size. These results can be used to scale a steam water system using scaling consideration presented. The results indicate that the air–water and steam water system show similar flow and pressure drop behavior.

Steam Explosion Experiments Using ZrO2 and ZrO2/UO2 Mixture

Korea Atomic Energy Research Institute (KAERI) has been carrying an experimental research program on the steam explosion named “Test for Real cOrium Interaction with water (TROI)” since 1997. The objective of the program is to investigate whether the corium would lead to an energetic steam explosion and to measure the conversion ratio of the energetic steam explosion. In the first series of tests using several kg of ZrO2 where the melt/water interaction were made in the water pool at 30 ∼ 95 °C, either a quenching or a spontaneous steam explosions was observed. In the second series of tests using the mixture of UO2 /ZrO2 performed in a similar manner as that of ZrO2 , it also resulted in either a quenching or energetic steam explosion. The morphology of debris and pressure profile clearly indicate the differences in those two phenomena. The process parameters including the dynamic pressure, dynamic impulse, water and melt temperature, static pressure inside the containment chamber were measured.Copyright