静止ナトリウム液滴燃焼基礎実験(II)

A Basic experimental study on combustion of suspended sodium droplet (II)

佐藤 研二*

not registered

高速炉の冷却材の液体ナトリウムの,漏えい事故時の燃焼挙動に関しては,これまでの工学的な取り組みに加えて現象論的にも解明していくことが重要である。本実験研究は,昨年度に引き続きナトリウム液滴の着火挙動に焦点をあて,懸垂して静止状態の液滴を気流中で着火・燃焼させ、液滴の初期温度,直径および周囲の気流速度が着火挙動におよぼす影響を調べることを目的とした。実験で,液体ナトリウム供給装置先端の細管ノズル下端において生成・保持された高温液滴を,ある瞬間から上向きの空気流にさらし,着火現象とその後の燃焼現象の様子をデジタル方式の高速度ビデオカメラを用いて観察した。最初に,分析に適した画像を得る方法を探るために昨年度と同じ装置を用いて予備的実験を行い,外部照明の有無と画像の関係,画像データの処理方法について検討した。続いて,未反応状態の液滴を短時間で空気流中にさらすことが確実にできるよう実験装置の改造を行い,湿分が無視できる酸素・窒素混合の疑似乾燥空気雰囲気で本実験を行った。装置の改造等の効果により,良好な条件で実現された現象の鮮明な画像が一部ながら得られ,着火過程における,液滴表面の状態、発光分布の時間変化等をより詳しく把握することができ,流速の影響の検討も行った。実験回数が限られたため,温度の影響については調べることができなかった。

For appropriate understanding and/or prediction of the combustion behavior of sodium, working as liquid coolant in fast breeder reactors, in case of leakage accident, phenomenological analyses of the behavior must be also important along with conventional engineering approach. Following our previous study in the last year, the major objective of this experimental research is to elucidate the effects of the initial temperature and diameter of droplet, and of the air flow velocity on ignition process of a sodium droplet, by exposing a suspended droplet to the air flow at room-temperature. In the experiments, a high-temperature droplet suspended from the end of a fine stainless steel nozzle of the liquid sodium supply system was exposed to an upward air flow, and the ignition and succeeding combustion phenomena were observed by using high-speed color video recording system. In the preliminary study, the effects of lighting and image data processing on obtaining pictures suitable to analyses were investigated with the apparatus used in the previous study. After the experimental apparatus was modified partially in order to expose the unreacted droplet to the air flow more quickly, main experiments were performed in synthetic dry air or oxygen-nitrogen mixture of 21% oxygen. Good quality pictures of the phenomena achieved under good conditions were recorded even fbr a few cases. The details of the ignition process of a sodium droplet, including the aspects of the surface and light emission, were examined, and the effects of the air flow velocity were discussed. Since number of performed experimental runs was small, the effect of the initial droplet temperature were not examined.