Abstract
Slight amount of hydrogen and oxygen exist in the main steam pipelines of boiling water reactor. These gases are generated by the radiolytic decomposition of the water. The detonation of these gases lead to pipe rupture problems at Hamaoka-1 and Brunsbuttel in 2001. To prevent similar problems, gas accumulation experiments were conducted to investigate accumulation mechanisms of these non-condensable gases. As a result of accumulation experiments, it was shown that non-condensable gas (hydrogen and oxygen) remains in closed pipe due to condensation of steam which caused by cooling effect of a surrounding cold gas. Concentration of accumulated gas is affected by buoyancy force effect to non-condensable gas and gravity effect on condensed water. Therefore, non-condensable gas accumulates easily in vertical pipes, in which non-condensable gas accumulates from the top of the pipes and condensed water is easily vented. Contrary, in case of horizontal pipes, gravity effect to non-condensable gas is small compared to vertical pipes, so non-condensable gas is not likely to accumulate in the pipes. To estimate the failure potential of detonation waves caused by accumulated gases, detonation experiments were conducted with straight tube and 90-degree bend tube. In the straight tube tests, the highest detonation pressure was recorded at the closed end. In the 90-degree bend experiments, pressure time histories revealed pressure loads greater than the straight tube portion at two locations. One is a high pressure peak at the extrados of the bend and the other is a double pressure peak just downstream of the bend outlet. Comparisons of experimental results show that impulse at the closed end of straight tube is greater than two high pressure location of 90-degree bend.
