Passive cooling systems are important to ensure safety in nuclear power plants. The Isolation Condenser (IC) is one of them which condenses the steam from the Reactor Pressure Vessel (RPV) in case of an emergency. The IC contains heat transfer tubes; where the steam will flow, and a water pool to remove heat by boiling heat transfer that is set above the RPV. Because the system is driven by natural circulation, the IC does not require electricity to operate. During the Fukushima Accident, the ICs successfully auto started after the earthquake. However, due to the loss of direct current caused by the Tsunami, the valves might be closed by the fail-safe design, which led to a restart failure of the IC. TEPCO has pointed out that assuming all the valves succeeded to open, there is a possibility that the IC couldn't operate by accumulating hydrogen generated from the core. The objective of our research is to grasp the effect of non-condensable gas inflow in the IC by performing experiments and analyses eventually. As an initial stage, in this study, both experiments with high-pressure steam for operation checking and performance evaluation, and experimental analysis with the TRAC-BF1 code were performed. The IC simulator held by our laboratory has an accumulator; which has 2 heaters inside and generates steam, and it’s connected to the heat transfer pipes which is U-shaped, set horizontally, and 907 mm in length. Because the driving force is the water head difference, the heat transfer tube, and the water pool are set 4 m above the accumulator. The simulator measures the pressure of 6 positions, mass flow rate, and temperature inside and outside of 6 positions of the heat transfer tube. The maximum power of the heaters is 9 kW and the accumulator can produce approximately 7 MPa steam. From the experiment result, we found that all steam was condensed through the heat transfer tube. When the heaters were at maximum power, the position of complete condensate was at about 500 mm from the inlet. Until it reaches a quasi-steady state, pressures of all positions and mass flow rate decreased after the IC started to operate. The pressure throughout the system was approximately at 1 MPa when it reaches a quasi-steady state, and the temperature inside the tube of 355 mm position was at saturation temperature. At the 552 mm position, the temperature was always below saturation temperature which means a complete condensate. The water pool of the simulator is visible so by observing the circumstances of boiling, we can anticipate the point of complete condensate too. The flow rate was at about 2.5 g/s at a quasi-steady state. From the experimental analysis, we found that the position of complete condensate will match when the boundary conditions of the inlet and outlet were fixed for the heat transfer tube. The heat transfer rate will also match in this condition and currently analysis by a loop model containing the whole system of the simulator is under consideration to reproduce the natural circulation flow rate. The final objective of this study is to evaluate the effect of non-condensable gas. The simulator can inject gas and the TRAC code can handle non-condensable gas. Both experiment and analysis considering non-condensable gas will be our future task for this research.


ICONE Competition - ICONE28-POWER2020-16842: Experiment and Analysis on Isolation Condenser Simulator Using Pressurized Steam

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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