A massive earthquake of Richter scale 9.0 followed by a tsunami with waves of 10 to 14m struck the Fukushima Daiichi(FD) nuclear power plant operated by Tokyo Electric Power Company(TEPCO). The power of nuclear power plant was lost, so cooling systems did not operate, and then the accident of hydrogen explosion was occurred. Due to this accident, the hydrogen explosion in severe accident was concerned again.
The hydrogen must be effectively controled or removed for defending the hydrogen explosion, but because of various accident causes and irregularity of hydrogen distribution and behavior, preparing countermeasure for explosion risk reduction is difficult.
In this study, the explosion risk according to hydrogen behavior in severe accident is evaluated, and the new structure of PAR is proposed and analyzed, hydrogen explosion is simulated using the previews results and analyzed at the specified locations in the containment building. Flames and pressure propagations are discussed, and the effect of the pressure impact on a wall in analyzed. The result shows that the high pressures impact on the building wall in the cases of the top and the bottom explosions. A multi-step PAR is proposed and analyzed. The distant between catalysts in firstly tested, and the analysis shows the distant 100mm is the best performance. Then two-step and three-step PAR are simulated and the results are compared with the results of the single step. The multi-step PAR reduces the spontaneous ignition problem and increases the hydrogen reduction rate radically. Two catalyst shapes of crossover and hexagon are proposed and analyzed, and the results are compared with those of conventional honeycomb. Hexagon shapes shows the best performance. As the outer structure of PAR, the guide vane is proposed, and studied. The vane having 150mm hight, 60°angle and attached between vane and catalyst is the best in the case of upward flow. The structure of 150mm hight, 100mm distance and 60°angle is the best in the sideward case, and the structure of 50mm hight, 60°angle and direct attached is the best.