ナトリウム燃料残渣の炭酸ガス安定化実験

Experimental Study of Prevention Measures against Sodium Combustion Residuum Reignition

石川 浩康 ; 大野 修司  ; 宮原 信哉  

Ishikawa, Hiroyasu; Ohno, Shuji; Miyahara, Shinya

空気雰囲気におけるナトリウム燃焼を窒素ガスによって強制的に停止させた場合、その燃焼残渣を50程度の低温まで冷却しても空気雰囲気とすることによって、再び着火する場合がある。燃焼残渣がどのような場合に再着火するかを映像記録と化学分析から調査し、また、燃料残渣を湿り炭酸ガスで安定化させることにより低温での再着火を防止できることを実験的に確認した。

Nitrogen gas can be an extinguisher or a mitigating in the case of sodium leak and fire accident in an air atmonphere, which may occur at a liquid metal cooled nuclear power plant. However sodium combustion residuum sometimes reignites in the air atmosphere even at room temperature when it was produced by nitrogen gas injection to the burning sodium. In this study we have been investigating the cause of reignition and prevention measures. Experiments were carried out with small type test equipment, which can handle 1g order sodium fire and extinguishment. Sodium combustion residua, which were made by our equipment and sampled, were analyzed by X-ray diffraction and chemical analyses. The chemical analysis of reignitable residua showed that the residuum contained metallic sodium of about 40Wt-%(61mol-%)to 60-wt %(76mol-%) and most of the rest was sodium-monoxide (Na2O).Sodium-peroxide (Na2O2) was also included in less than 1wt-% of the residuu. Sodium or Na2O cannot ignite by itself in the air atmosphere at room temperature in a few minutes. Therefore the reignition seems to be due to increase in the local temperature that is caused by oxidizing heat of Na and by adiabatic effect of Na2O. It is important to deactivate this dispersed sodium on oxygen for prevention of the residuum reigntion, hence it is considered as a rational measure to change the sodium to sodium-carbonate. Our experments showed that the dispersed sodium on the exterior of residuum could be changed to carbonate by a mixture by a mixture of carbon-dioxide(CO2) gas (2 to 8vol-%),humidity (0.6 to 3vol-%) and mitrogen gas. The deactivated residuum did not reignite in the air atmospherebe bwlow 473K.