Wet granulation of mixed oxide powders de-nitrated by the microwave heating

マイクロ波加熱によって脱硝されたMOX粉末の湿式造粒

加藤 良幸 

Kato, Yoshiyuki

FBR用簡素化MOX燃料ペレット製造プロセスにおけるマイクロ波脱硝MOX粉末の湿式造粒性能を調査した。3枚羽根の撹拌羽根とチョッパーを備えた撹拌造粒機を使用して評価した。粉末物性は、SEM観察,粒度分布及び粉末流動性で評価した。この結果、水分添加率が12.5-13.5wt%と狭帯域の条件ではあるが、数ミクロンの原料粉末が直径120-140mの顆粒となり、粉末流動性が30未満であったものを73超えまでに改善でき、製品収率も90%超と良好な結果が得られた。焼結性能に大きな影響を与える比表面積は、低下させることなく原料粉末と同等であった。水分添加率が9wt%未満では、粉末流動性は原料粉末と変わらず、顆粒はみられなかった。この要因は、原料粉末中の毛細管(空間)に吸収されることによるものと追加実験の結果から推測された。水分添加率が14wt%超では、粉末流動性は飽和して変化しないが、製品収率が減少した。この狭帯域の水添加率と強い結合力は、顆粒形成を推測するペンデュラ状態とジョージ法の標準理論に基づき理解された。

Performance of wet granulation for MOX powder de-nitrated by the microwave heating de-nitration method was investigated in order to fabricate MOX fuel pellets for FBR at an extremely simplified process. An agitating granulator equipped with three blades and a chopper was used and the performance was evaluated. Characteristics of raw powder and granules were evaluated from SEM observation, granulometry and flow-ability measurement. We could obtain the granules of 120-140 m in diameter from the raw powder of several micron in a narrow range of water addition ratio 12.5-13.5 wt% with a flow-ability 73 and a product yield 90%. Specific surface area which is the index of sintering performance was almost same as the one of raw powder. When the ratio was 9 wt%, flow-ability did not change from the one of raw powder 30 and no granule was observed. It was estimated from an additional experiment that the reason was capillaries (or voids) in the raw powder. When the ratio was larger than 14 wt%, flow-ability saturated and product yield decreased. This narrow range of water addition ratio and strong binding force were successfully understood based on the standard theory of granulation supposing a pendular state and Gorge method.