Visualizing an ignition process of hydrogen jets containing sodium mist by high-speed imaging

高速度撮影によるナトリウム混在水素噴流燃焼の着火過程の可視化

土井 大輔  ; 清野 裕 ; 宮原 信哉*  ; 宇埜 正美*

Doi, Daisuke; Seino, Hiroshi; Miyahara, Shinya*; Uno, Masayoshi*

In severe accident scenarios for sodium-cooled fast reactors, it is desirable to gradually consume hydrogen generated by various ex-vessel phenomena without posting a challenge to containment integrity. An effective means is combustion of hydrogen jets containing sodium vapor and mist, but previous studies have been limited to determining ignition thresholds experimentally. The aim of this study was to visualize the ignition process in detail to investigate the ignition mechanism of hydrogen-sodium mixed jets. The ignition experiments of the hydrogen jet containing sodium mist were carried out under a condition of little turbulence. The ignition process was measured with an optical measurement system comprised of a high-speed camera and an image intensifier, and a spatial distribution of luminance was analyzed by image processing. Detail observation revealed that sodium mist particles burned as scattering sparks inside the jet and that hydrogen ignited around the mist particles. Additionally, the experimental results and a simple heat balance calculation indicated that the combustion heat of sodium mist particles could ignite the hydrogen as the heterogeneous ignition source in the fuel temperature range where the mist particle formation was promoted.