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Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Kato, Yoshiyuki; Kawaguchi, Koichi; Ishii, Katsunori
Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 7 Pages, 2018/11
Mixed uranium oxide and plutonium oxide powder is produced from uranyl nitrate and plutonium nitrate mixed solution by the microwave heating denitration method in the spent fuel reprocessing process. Since the microwave heating method is accompanied by a boiling phenomenon, it is necessary to fully grasp the operating conditions in order to avoid flashing and spilling in the mass production of denitrification technology for the future. In this research, it was clarified that the heat transfer coefficient became lower as the dielectric constant increased. The dominant factor of the blowing up phenomena is supposed to be generation of the innumerable bubble rather than bubble's growth.
Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Yamada, Yoshikazu; Kato, Yoshiyuki; Ishii, Katsunori
Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 8 Pages, 2018/07
Mixed uranium oxide and plutonium oxide powder is produced from uranyl nitrate and plutonium nitrate mixed solution by the microwave heating denitration method in the spent fuel reprocessing process. Since the microwave heating method is accompanied by a boiling phenomenon, it is necessary to fully grasp the operating conditions in order to avoid flashing and spilling in the mass production of denitrification technology for the future. In this research, it was confirmed that a potassium chloride aqueous solution as a simulant of uranyl nitrate aqueous solution with high dielectric loss cause loss of microwave at the solution surface as the dielectric loss increased with the increase of KCl concentration by experimental and electromagnetic field analysis, and revealed that the change in the heating condition affects the generation of flushing.
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.
Yamaki, Tatsunori*; Abe, Yutaka*; Kaneko, Akiko*; Segawa, Tomoomi; Kawaguchi, Koichi; Yamada, Yoshikazu
Proceedings of the 22nd International Conference on Nuclear Engineering 2014 (ICONE-22), Vol.2A, p.V02AT09A011_1 - V02AT09A011_10, 2014/07
Uranium and plutonium mixed nitrate solution of the spent nuclear fuel is converted to uranium and plutonium mixed oxide (MOX) powder by the microwave heating direct denitration method in co-conversion process of the nuclear fuel cycle. The cylindrical denitration vessel can be expected to realize high-speed and high-capacity processing against traditional shallow vessel. However, flushing and overflow phenomena of solution have been confirmed in cylindrical vessel. Thus, It is required to be clarified that the generation condition and generation mechanism of flushing phenomena during microwave heating for the safety of the operating condition and the optimum design of the equipment. The craiteria of flushing phenomena and the relationship between the released power by evaporation and the absorbed power in water is confirmed by the experimental results from the microwave heating. It is found that the flow structure is changed and the outer surface is heated according to the increase of the concentration of KCl by the microwave heating experiment with using the KCl solution and KCl jelly as a simulated solution of the uranium and plutonium mixed nitrate solution.
Murakami, Yoshio
Hyomen Kagaku, 12(8), p.520 - 524, 1991/00
no abstracts in English
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.
Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Chonan, Fuminori*; Yuasa, Tomohisa*; Yamaki, Tatsunori*; Segawa, Tomoomi; Yamada, Yoshikazu
no journal, ,
no abstracts in English
Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Yamada, Yoshikazu
no journal, ,
A mixed solution of uranyl nitrate and plutonium nitrate is converted to MOX raw powder by the microwave heating de-nitration method in nuclear fuel reprocessing. Since the microwave heating causes a boiling phenomenon, it is necessary to sufficiently confirm operating conditions to prevent flushing and overflow phenomena of solution. In this study, visualization observation of the microbubble generation and growth behavior near the liquid surface, measuring of bubble diameters, calculating the frequency of nucleation and estimating the quantity of heat of required for generation and growth of microbubbles were performed for the purpose of clarifying the generation mechanism of the flushing phenomena caused by microwave heating. As a result of comparative study with the amount of heat of released by flushing, it was confirmed that the quantities of the heat of released by flushing and the heat of required for generation and growth of microbubbles agree on the order.
Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Yamada, Yoshikazu; Kato, Yoshiyuki; Ishii, Katsunori
no journal, ,
Mixed uranium oxide and plutonium oxide (MOX) powder is produced from uranyl nitrate and plutonium nitrate mixed solution by the microwave heating denitration method in the spent fuel reprocessing process. Since the MH method is accompanied by a boiling phenomenon, it is necessary to fully grasp the operating conditions in order to avoid flashing and spilling in the mass production of denitrification technology for the future. In this research, for the purpose of clarifying the mechanism of flashing phenomenon during microwave heating, the generation mechanism of bubbles that innumerably occur at the time of flashing is considered. When the contact angle at the heterogeneous nucleation of bubbles was 177 
C, the theoretical value of the heterogeneous nucleation approximately agreed with the experimental value at the time the superheat degree was found to be close to 35 C.
Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Kato, Yoshiyuki; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
The microwave heating denitration method is used in the spent fuel reprocessing process of the nuclear fuel cycle. Since the microwave heating method is accompanied by a transient boiling phenomenon, it is necessary to grasp the operating conditions and to clarify the mechanism of flashing and spilling in order to avoid it. In this study, by assuming the flashing model for the purpose of the clarification of the flashing mechanism by microwave heating, the flashing mechanism of instantaneous generation and growth is considered by calculating the generation frequency and volume of bubble from the visualization result at flushing. The mechanism of flashing phenomenon during microwave heating is thought that the significant flushing phenomenon occurs by the process that a large amount of nanobubbles are generated at a solid-fluid interface in a overheated liquid phase, the bubble group grows exponentially and collapses, and its internal pressure releases.
Kobayashi, Shohei*; Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Kato, Yoshiyuki; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
The microwave heating denitration method is used in the spent fuel reprocessing process. In order to develop the mass production of denitrification technology for the future, it is necessary to fully grasp the operating conditions to avoid flashing and overflow phenomena of solution. In this research, the conditions of the generation of flashing are evaluated using the potassium chloride aqueous solution as the simulated solution, and the concentration of potassium chloride and the microwave output as parameters. It is found that it is difficult to occur the flashing phenomenon as the concentration of potassium chloride increases.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Futsuta, Akihiro*; Fujiwara, Kota*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
To investigate the influence of the dielectric properties of a solution or a spacer on the heating process of the solution, a low dielectric Teflon or an airogel having a very low dielectric property almost equivalent to air was placed as a spacer directly below the vessel. And the influence of the geometry and the dielectric properties of the sample and the spacer on the heating properties of the sample were evaluated. The heating efficiency obtained by the experiment tended to decrease as the spacer height increased. It was confirmed that the heating efficiency obtained by the electromagnetic analysis almost agreed with the experimental results by a support height of 50 mm. When Teflon was used as a spacer, microwaves entered from the bottom of the solution, whereas when airogel was used as a spacer, microwaves tended to enter from the top of the solution, and it was clarified that the dielectric characteristics of the spacer were the heating characteristics of the sample.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Fujiwara, Kota*; Futsuta, Akihiro*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
The microwave heating denitration method is used in the nuclear fuel cycle. To clarify the mechanism of flashing phenomena during microwave heating, it was focused on the frequency of bubble nucleation in heterogeneous nucleation and considered the bubbles generated in the solution. From the visualization observation results, it was verified that a new bubble was generated below the single bubble. The bubbles generated at the gas-liquid interface are considered to be caused by heterogeneous nucleation. Moreover, the calculation results revealed that bubbles were generated at a large contact angle. It is suggested that many bubbles are generated at the gas-liquid interface, and many bubbles generated by heterogeneous nucleation in the superheated liquid phase influence the generation of flashing.
Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Fujiwara, Kota*; Futsuta, Akihiro*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
In the reprocessing process in the nuclear fuel cycle, a solution of plutonium nitrate and uranyl nitrate is converted into a mixed oxide by microwave heating denitration method. The objective of this study is to clarify the mechanism of the flashing phenomenon and to clarify the effect of the microwave heating characteristics of a high dielectric constant solution on the flashing phenomenon. Microwave heating experiments were conducted using KCl aqueous solution, which is the high dielectric constant solution simulating the reprocessing solution. It was clarified that the growth rate of bubbles in the KCl aqueous solution decreased with the time of microwave heating compared with distilled water. It is thought that in the KCl aqueous solution, the heating efficiency at the center of the solution is lower than that in the surroundings, and the growth rate of bubbles is reduced so that the flashing phenomenon does not easily occur in the high dielectric constant solution.
Tsuchida, Toshihisa*; Kaneko, Akiko*; Fujiwara, Kota*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
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.
Tsuchida, Toshihisa*; Kaneko, Akiko*; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori
no journal, ,
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. In this study, it was investigated the effect of laser irradiation as a non-contact method of preventing flashing. Microwave heating of a glass vessel filled with distilled water irradiated horizontally with an infrared laser caused intermittent nucleate boiling near the laser irradiation point, resulting in an overheating state, which caused a flashing phenomenon. In contrast, a high-power Yb pulsed laser can give a higher energy density than the infrared laser and is expected to generate more cavitation, and therefore there is a good possibility that flashing can be prevented.
Kawaguchi, Koichi; Segawa, Tomoomi; Ishii, Katsunori; Tsuchida, Toshihisa*; Hamdan, N.*; Kaneko, Akiko*
no journal, ,
Laser beam was irradiated to water heated by the microwave, and generated bubble was observed using high speed camera. Increased frequency of bubble generation in the section including the position of laser beam irradiation was observed. At the end, although flashing occurred, there was a tendency to be delayed compared to laser non-irradiation.
