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Journal Articles

Flushing phenomena and flow structure by microwave heating

Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Chonan, Fuminori*; Yuasa, Tomohisa*; Yamaki, Tatsunori*; Segawa, Tomoomi; Yamada, Yoshikazu

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 8 Pages, 2017/07

From the observation results, in the process of flushing, the behaviors leading to flushing were classified divided into three types. First type is that first generation bubble from heating leads to flushing. Second type is that nucleate boiling continues during heating and stop, finally single bubble generates and leads to flushing. Third type is defined that gradual evaporation occurs without bubbles. It was revealed that the total quantities of heat released by flushing are approximately equal when assuming the flushing mechanism, it can be triggered that a large amount of micro bubbles are instantaneously generated and grew.

Journal Articles

The Criteria of flushing phenomena under microwave heating

Yamaki, Tatsunori*; Abe, Yutaka*; Kaneko, Akiko*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu; Fujii, Kanichi*

Journal of Nuclear Science and Technology, 52(2), p.241 - 250, 2015/02

 Times Cited Count:3 Percentile:60.55(Nuclear Science & Technology)

In the Microwave Heating de-nitration method developed in Japan, a mixed solution of uranyl nitrate and plutonium nitrate recovered from the spent fuel in the reprocessing plant is converted directly to mixed oxide (MH-MOX) powder. This MH-MOX powder is utilized to fabricate MOX fuel with UO$$_{2}$$ powder for FBR. The MH method is accompanied with transient boiling phenomena such as overflow and flushing. Toward high-speed and high-capacity conversion by MH-method in the future, it is required to avoid overflow and flushing and to understand optimal design conditions for design and operation. At the first step for these objectives, basic knowledge of transient boiling phenomena by the MH-method has been acquired with using distilled water. It was observed that generation of singular bubble triggered flushing and distilled water just before flushing was superheated by a temperature 10 degrees centigrade higher than boiling temperature. Based on these results, it is clarified that the occurrence criteria of flushing correlate with absorbed power in the water and released power from the water surface.

Oral presentation

Study on flushing phenomena by microwave heating

Yamaki, Tatsunori*; Kaneko, Akiko*; Abe, Yutaka*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu; Suzuki, Masahiro; Fujii, Kanichi*

no journal, , 

To use recovered uranium and plutonium as raw material of nuclear fuel, reprocessing solution (uranium and plutonium mixed nitrate solution) of the spent nuclear fuel is converted to uranium and plutonium mixed oxide (MOX) powder. Microwave heating direct denitration method is one of such methods to convert nitrate solution to MOX powder. The cylindrical denitration vessel can be expected to realize high-speed and high-capacity processing against traditional shallow vessel. Flushing and overflow phenomena of solution have been confirmed in cylindrical vessel. The research was conducted in order to clarify mechanism of the flushing and overflow phenomena during microwave heating. It was found that there was tendency of flushing in the case of short vessel diameter and high initial water level when magnetron power was constant. It was confirmed that the liquid temperature just before flushing was superheat.

Oral presentation

Study on flushing phenomena generated by microwave heating

Yamaki, Tatsunori*; Kaneko, Akiko*; Abe, Yutaka*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu

no journal, , 

In Japan, the microwave heating method is adopted in the conversion process of reprocessing facility for spent fuels of a nuclear reactor. When the scale-up of the conversion process is considered, visualization observation of flushing phenomena by microwave heating was experimented in order to optimize the structure of denitration containers depending on the scale of throughput. Evaluation of the effects of the diameter of a container, initial level of liquid, and microwave power on the conditions for the generation of flusing was conducted, and it was clarified that the mechanism of the generation of flushing and dominant factor.

Oral presentation

Effect of dielectric characteristics on transient boiling phenomena induced by microwave heating

Yamaki, Tatsunori*; Abe, Yutaka*; Kaneko, Akiko*; Kanagawa, Tetsuya*; Kitazawa, Toshihide*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu

no journal, , 

For practical application of high-volume production of microwave heating denitration method, it is required to avoid the transient boiling phenomena of overflow and flushing during microwave heating and to optimize the design condition of vessel shape and microwave outpot. The boiling phenomena and flow structure of KCl aqueous solution by microwave heating were measured with the KCl concentration as a parameter. Flushing phenomena does not become difficult to occur and flow structure becomes disordered to be created the vortex structure according to increase of the KCl concentration. From the results of measuring the temperature distribution of side cross-section surface of the KCl jelly, near the center is mainly heated in the case of the water jelly. On the other hand, around the jelly is mainly heated in the KCl jelly. It is clarified that the generation condition of flushing and the boiling phenomena are significantly influenced by the difference of water and KCl solution.

Oral presentation

Criteria and mechanism of transient boiling phenomena induced by microwave heating

Yamaki, Tatsunori*; Abe, Yutaka*; Kaneko, Akiko*; Kanagawa, Tetsuya*; Kitazawa, Toshihide*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu

no journal, , 

A mixed solution of uranyl nitrate and plutonium nitrate recovered from the spent fuel is converted directly to mixed oxide (MOX) powder in the microwave heating de-nitration process of the reprocessing plant. This research aimed at elucidating occurrence criteria and mechanism of flushing phenomena in order to avoid transient boiling phenomena such as overflow and flushing, and understand optimal design conditions. Flushing conditions were clarified by evaluating the correlation between absorbed power in the distilled water and released power by evaporation.

Oral presentation

Mechanism of flushing phenomena induced by microwave heating

Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Chonan, Fuminori*; Yuasa, Tomohisa*; Yamaki, Tatsunori*; Segawa, Tomoomi; Yamada, Yoshikazu

no journal, , 

no abstracts in English

7 (Records 1-7 displayed on this page)
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