Steam explosion HOME > RESEARCH > Nuclear Safety > Steam explosion
 
Background

1. Steam explosion

Steam explosion is one of the risk significant phenomena at the severe accident. It often occurs if hot liquid material comes into contact with cold coolant and the coolant boils at a local area of hot liquid-coolant interaction producing rapid vapor generation. The steam explosion is developed following four steps: premixing, triggering, propagation, and expansion. (Fig. 1.).

 
Fig.1.Transition steps of steam explosion: (a) premixing, (b) triggering, (c) propagation, (d) expansion
 

2. Shock-bubble interaction

As previous researches conducted experiments and simulations about shock propagation in bubbly mixtures, it is known that void fraction and bubble sizes are key components influencing behavior of an underwater shock. Besides, no one knows exactly how they play a role of an absorber because phenomena of shock-bubble interaction vary with initial condition in which the shock-bubble interaction occurs and the bubble clouds are located. Therefore, it is need to verify a mechanism between the pressure shock and the bubble clouds for explaining the various phenomena in terms of a physical view. With an exact model of shock-bubble interaction, it could be used for mitigating a shock and, by extension, be applied to suppression of steam explosion with additional merits which void fraction has. (Fig. 1.).

 
Fig.2. Conjecture description about single bubble behavior after a shock passes
 
Objectives
1. Observation of shock transition with single/multi microbubble
2. Criteria suggestion of mitigation of an underwater shock from shock-bubble interaction
3. Application of shock-bubble interaction to steam explosion for minimizing a shock damage
 
Results
1.Experiment – Micro bubble generation

I setup the experimental instrument which generates micro bubble. The facility consists of water pool, pump and dissolving tank. (Fig. 3.) The picture of micro bubbles from the generator is below. (Fig. 4.) After measuring bubbles using visualization, I have found distribution of size of bubbles where flow rate is 6.5LPM, temperature is 20C, and gauge pressure in the tank is 1bar. (Fig. 5.)

Fig. 3. Schematic design of the microbubble generator.
Fig. 4. Bubble cloud from the microbubble generator.
Fig. 5. Size distribution of each bubble generation.
2. Numerical approach – Shock bubble interaction

I have conducted numerical simulation describing a system of 1-D shock tube containing microbubble clouds. Like Fig. 6, a planar shock is generated at high pressure region in the system and passes downward through the bubbly media. As its shock moves, bubbles gain some energy from the shock and oscillation by dissipating their energy. (Fig. 7.)

Fig. 6. 1-D shock tube system with micro bubbles.
Fig. 7. Time histories derived from shock-bubble interaction.