Na漏えい燃焼に関する基礎実験; NaOH溶融プール中への連続Na滴下による燃焼状況及び炭素鋼の損傷評価

Basic experiment on the sodium leak combustion; Examination of sodium combustion and liner material damage by sodium continuously dropped into the high-temperature NaOH molten pool

吉田 英一; 古川 智弘  ; 青砥 紀身 

Yoshida, Eiichi; Furukawa, Tomohiro; Aoto, Kazumi

Na漏えい燃焼実験IIにおける床ライナ材の欠損要因を実験的に究明する一環として、高温NaOH溶融プール中にNaを連続滴下し、Naの燃焼状況及び炭素鋼SM400Bの損傷状況を調べた(平成8年10月に実験実施)。実験は、Na漏えい燃焼実験IIにおける漏えい中期以降と考えられる環境を大まかに模擬したものである。Na滴下温度は496、トータルのNa滴下量は約1200g、NaOH溶融プール温度は初期時で660690、NaOH量は約2500g(液深約28mm)である。この時のNa滴下速度は平均約1.8g/secで、滴下高さは約700mmである。これらの実験結果、次のようなことが明らかになった。滴下された燃焼NaはNaOH溶融プール中に潜って消えることはなく、溶融プール上で燃焼浮遊物を形成し、移動しながら燃焼した。この場合、溶融プールは燃焼浮遊物で全面的に覆われることはなく、常に大気界面を有していた。燃焼生成物はNaOH溶融プールに混入・溶解し、本実験の範囲内では燃焼最後まで溶融体を形成していた。また、溶融体の液面近傍部をピークに炭素鋼(JIS G3106 SM400B)の板状試験片及びNaOH容器の壁面で顕著な腐食減肉が生じた。このような材料の腐食減肉の現象は、Naが溶融体の大気界面で浮遊しながら燃焼し、これから生成されるNa2O2の供給が主な要因となって、溶融塩型腐食の機構が作用したものと考えられた。

The purpose of this basic experimentis to clarify the cause of damage of the liner material, which recognized by the Sodium Leak and Combustion Test II. In this experiment, the liquid sodium continuously dropped into the high-temperature NaOH molten pool, to investigate sodium combustion phenomenon in the NaOH pool and damage of the liner material SM400B. The drop temperature of sodium is 496C, and the amount of dropped sodium is about 1200g. The temperature of NaOH molten pool is 660-690C in the initial stage, and the amount of NaOH is about 2500g. The average drop (leak) rate is l.8g/sec, and the height of above the NaOH molten pool is about 700mm. The following results were obtained. The fallen sodium continued to burn during floating on the NaOH molten pool. In this case, the NaOH molten pool was not totally covered with the combustion products, and the molten pool always had the atmosphere interface. The combustion products were mixed and melted in the NaOH molten pool. The maximum reduction of thickness was occured in the level vicinity of NaOH molten pool. Plate test specimens of 3mm thickness were separated in the level vicinity during periods of combustion. And, in the NaOH container, the metal loss of largest about 2.5 mm was recognized at the level vicinity. It is considered that the remarkable metal loss in the level vicinity indicates the involvement of molten salt-type corrosion mechanism with the atmosphere interface. The above mentioned results were obtained from the basic experiment. These results gave the important information to evaluate the damage mechanism of the floor liner material.