The overall goal of this experiment and simulation is to investigate the siphon breaking phenomenon in order to improve the design and analysis of the siphon breaker of a research reactor. This episode can help answer a few questions in our research reactor safety feat, such as how to prevent a recurrent accident. The main advantage with this technique is that the siphon breaking phenomenon can be easily and accurately analyzed.
The data for this experiment were collected at the two-phase flow lab of the Pohang University of Science and Technology. This schematic provides an overview of its features and the equipment used to monitor it. There is an upper tank with a 57.6 cubic meter capacity.
It includes an optional orifice assembly. The lower tank is 8.3 meters below the upper tank and has a capacity 70 cubic meters. Any water deposited there can be reused via a return pump.
The piping system has a 16 inch pipe. There are both lower and upper rupture points referred to as Loss of Coolant Accident, or LOCA, sites. The siphon breaker line ends in the upper tank, 11.6 meters above the lower pipe rupture point.
Two absolute pressure transducers and three differential pressure transducers monitor the system. There is also an ultrasonic flow meter. Four cameras record regions of the experiment through observation windows.
The experiments investigated the effects of varying LOCA size, siphon breaker line size, siphon breaker types, and presence of the orifice. This apparatus at the Handong Global University is a 1/8 scale model of the facility that will be used to demonstrate the experimental protocol. Compare its schematic with that of the original facility.
All of the relevant features are in place, but on a manageable scale. Prepare for the experiment by ensuring that all monitoring instrumentation is in place and ready to operate. Next, consider the range of experimental conditions to be studied.
This demonstration will use 1/2 inch and 1/4 inch siphon breaker lines. In addition, the LOCA site will have a one inch or two inch opening, created by attaching appropriate pipes. This apparatus has its experimental conditions set.
A 1/2 inch siphon breaker line is in position and connected to the pipe leading from the tank to the LOCA. The first experiment will use the lower LOCA at the end of this pipe. The experiment starts with a LOCA size of one inch.
When all preparations have been made, fill the upper tank with water. Check the initial water level before proceeding. With the instruments recording, return to the lower LOCA site.
There, open the valve to start water flow and begin the test. Collect data until the water flow into the lower tank has stopped. Close the lower LOCA valve before continuing.
After saving the collected data, prepare for the next test condition. This requires removing the pipe that sets the LOCA size. Replace the pipe with the next pipe diameter for the planned tests.
In this case, one with a two inch opening. When the upper tank is filled again, open the lower LOCA site to collect data in this configuration. The third test requires changing the siphon breaker line.
Remove the 1/2 inch line from its position. Replace it with the 1/4 inch siphon breaker line, which is the next diameter line for these tests. Once again, fill the upper tank and perform the test.
If necessary, continue conducting tests for all configurations, including changes in LOCA position. The next step is to study the experiments by computer simulation. This is the initial screen of Siphon Breaker Simulation Program.
To check parameters, click on the Show Parameters button. The new screen shows the parameters used for the simulation. After changing the input as necessary, click OK to return to the initial screen.
Next, click the Run button. When prompted, enter the time interval the simulation will cover. Click OK to be taken to a water level graph.
In the graph, the water level is shown as a function of time over the chosen time interval. Analyze the graph to determine if siphon breaking occurs with the given parameters. To check other outputs, select the appropriate check box below the plot.
For the pressure plot, click on the p2 box. Click on the waterlevel box to remove the original plot. To show the flow rate, click on the q12 box.
Remove the pressure plot by clicking on p2 again. When done, click Save the data button to create the data text file. Confirm the action in the pop-up dialogue box.
Click OK to return to the home screen. Then, click Exit to leave the program. The data file will be in the same directory as the simulation program.
Its contents allow detailed study of the numerical simulation results. These are data from a full scale experiment at the two-phase flow lab of the Pohang University of Science and Technology. The black circles represent Differential Pressure data.
The gray triangles represent Absolute Pressure data. Both sets refer to the left vertical axis. The red crosses are Water Flow rate data, which use the right vertical axis.
There are three stages of the experiment. First is the Loss of coolant. Second is Siphon breaking.
Third is the Steady State. This plot allows comparison of experimental results for water flow rate with output from the software simulation. The blue squares are data for a 12 inch LOCA opening, and the blue line is for the associated simulation.
Data for a 16 inch LOCA opening are shown with red circles, and the red line is the simulation results. Here is another test of the model. The horizontal position of a black circle is the experimentally measured Undershooting height.
The vertical position is the Undershooting height from a simulation. The blue line corresponds to the case of the values from experiment and simulation being equal. The plot suggests the model can be used for analysis of siphon breaking.
The implications of this technique extend toward diagnostics of the safety of a research reactor because the program can predict entire siphon breaking demonstration in case there was a recurrent accident by pipe rupture. Once mastered, each simulation can be done in five minutes if performed properly. It is important to remember that the input parameters for simulation should be entered in of the siphon breaker design conditions.
At this development, this technique paved the way for researchers in the field of siphon breaker design to explore safety in research reactor. After watching this video, you should have a good understanding of how to design and analyze the siphon breaker of a research reactor.
