マイクロ波加熱下における突沸防止対策の検討

A Study on measures to prevent flashing under microwave heating

土田 隼久*; 金子 暁子*; 藤原 広太*; 瀬川 智臣 ; 川口 浩一  ; 石井 克典 

Tsuchida, Toshihisa*; Kaneko, Akiko*; Fujiwara, Kota*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori

再処理工程では、硝酸ウラニル・硝酸プルトニウム混合溶液をマイクロ波加熱脱硝法により、混合酸化物粉末に転換している。本研究では非接触で突沸を防止する方法として、レーザー照射による突沸防止効果の検討を行った。蒸留水を入れたガラス管に赤外線レーザーを水平方向から照射した状態でマイクロ波加熱を行った結果、レーザー照射位置付近から核沸騰が生じることを確認し、マイクロ波加熱を継続すると断続的な核沸騰の末に過加熱状態となり突沸現象が生じた。これはマイクロ波のエネルギーが赤外線レーザーに比べて大きいことが理由と考えられた。

In the reprocessing process of spent fuels, a liquid mixture of U/Pu nitrate solution is converted to U/Pu mixed oxide powder by the microwave heating denitration method. The cylindrical vessel, which is expected to have a higher speed and capacity than the conventional flat vessel, generates flashing and spilling during microwave heating, and it has been clarified that the shape of the vessel and the microwave power reduce the occurrence of flashing. The anti-flashing effect of laser irradiation was investigated as a non-contact method to prevent flashing. As the laser radiated distilled water in the glass vessel, nucleate boiling occurred from the vicinity of the laser irradiation position. When microwave heating was continued, intermittent nucleate boiling was followed by overheating, which resulted in the flashing phenomenon. In order to prevent flashing, it is necessary to use lasers with a higher power or to improve the energy density by focusing on the laser beam.