Session: 14-11 Student Paper Competition

Paper Number: 64595

Start Time: August 4, 2021, 03:00 PM

64595 - Effects of Non-Condensable Gas on Characteristics of Natural Circulation Flow of Isolation Condenser 

 An isolation condenser (IC) is one of the passive core cooling systems and equipped in boiling water reactors. In case of emergency, the IC is used to cool the reactor core by condensing steam. Because the IC uses natural circulation flow, it does not require electricity to operate.

 During the Fukushima Daiichi accident, the ICs succeeded to operate after the earthquake. However, all electric power sources were lost by Tsunami and the isolation valves on ICs were closed automatically by the fail-safe design, which led to restart failure of the ICs. On the other hand, Tokyo Electric Power Company pointed out that even if all the valves were opened, there was possibility that the ICs were not able to restart by hydrogen generated in the core.

 The objective of the current study is to evaluate an effect of non-condensable gas on the cooling performance of the IC. We conducted experiments using natural circulation loop with non-condensable gas injection, where helium was used to simulate hydrogen effect on the IC.

 The IC simulator at Hokkaido University has an accumulator; which has 2 heaters inside and generate steam, and it is connected to a U-shaped heat transfer tube, set horizontally, and 907 mm in length. Because the driving force corresponds to the water head difference, the heat transfer tube and the water pool are set 4 m above the accumulator. The simulator has 5 pressure sensors, one mass flowmeter, and 6 thermocouples at the heat transfer tube. The power of heaters was set to 9 kW and the accumulator produced steam of 5 MPa at maximum.  

 Natural circulation flow was generated when the pressure in the experimental loop increased enough. Then, the pressure and the natural circulation flow rate gradually decreased with time. After the long term operation, the experimental system reached quasi-steady state in which the heat removal rate and the heat input from the electric heaters were balanced. The pressure at a quasi-steady state was increased with increasing amount of injected helium. Since the differential pressure at the down comer increased by the helium injection, the accumulated helium may affect the increase of system pressure.

Presenting Author: Tetsuya Takada Hokkaido University

Authors:

Tetsuya Takada Hokkaido University
Yasunori Yamamoto Hokkaido University
Kosuke Ono Hokkaido University