Effects of vent size and wind on dispersion of hydrogen leaked in a partially open space; Studies by numerical analysis

部分開放空間中の水素漏洩拡散におけるベントサイズと風況の影響; 数値解析による研究

寺田 敦彦  ; 永石 隆二 

Terada, Atsuhiko; Nagaishi, Ryuji

燃料デブリを含む放射性廃棄物の移送、保管、処分過程でみられる部分開放空間内での水素の漏洩挙動を明らかにするために、CFDを用いて、Hallwayモデルのベントサイズやその周囲の風況の影響を研究した。Hallwayモデルは、側面に1つのドアベントと天井に1つのルーフベントをもった部分開放空間の実験モデルである。Hallwayモデルの室底部から水素が漏洩された場合では、室内の水素濃度の上昇は小さかった。水素がルーフベントから排出されるとともにドアベントから外気が流入する煙突効果が起こる際にコアンダ効果で流入した外気の流れが底部に偏流する現象が生じたことが原因と考えられる。室内の水素濃度は、ベントサイズを変化することで室内に流入する外気量とともに変化した。また、室外の風況によって、ドアベント側から風が吹いた場合には低下し、ドアベントと反対側から風が吹いた場合には上昇した。ドアベントからの外気の吹き込みとルーフベントからの水素の排出のバランスに影響を与えたと考えられる。

In order to understand dispersion of hydrogen leaked in a partially open space practically, which can be considered as a basic model for all processes of transfer, treatment, storage and disposal of radioactive materials containing fuel debris in the decommissioning of nuclear facilities after a severe accident, by using a CFD code, the effects of vent size and outer wind on the H dispersion were analytically studied by adopting the experimental Hallway model, which has H release hole on the ceiling, one vent on the Roof vent and Door vent. Air flowed in the model from the Door vent, while H was discharged outside from the Roof vent. The discharged amount of H increased in conjunction with the air inflow when the size of Roof and or Door vents was increased. The effect of wind depended on the direction to the Door vent: wind from the same direction as the Door vent promoted the H discharge, while wind from the opposite direction suppressed. The dispersion characteristics of indoor leaked H was clarified for comparing model tests with the same Froude number and different scales. It was found from the analysis results of comparing model tests with the same Froude number and different scales that when the H leaked into the room and diffused to the air, the flow generated by the buoyancy of mixed gas created the stack effect which caused the natural ventilation by drawing in the air from the outside through vent. In addition, it was speculated that the H concentration decreased after its leak by quickly mixing with the air which flowed in from the vents and reached to the floor due to the Coanda effect, which is the effect of the free jet being drawn to a nearby wall.