Study on optimizing microwave heating denitration method and powder characteristics of uranium trioxide

Segawa, Tomoomi; Kawaguchi, Koichi; Kato, Yoshiyuki; Ishii, Katsunori; Suzuki, Masahiro; Fujita, Shunya*; Kobayashi, Shohei*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*

Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 9 Pages, 2019/05

A solution of plutonium nitrate and uranyl nitrate is converted into a mixed oxide by microwave heating denitration method. In the present study, for improving the efficiency of microwave heating and achieving high-temperature uniformity to produce homogeneous UO powder, the microwave heating test of potassium chloride and uranyl nitrate solution, and numerical simulation analysis were conducted. The potassium chloride agar was adjusted to the dielectric loss, which is close to that of the uranyl nitrate solution and the optimum support table height was estimated to be 50 mm for denitration of the uranyl nitrate solution by microwave heating. The adiabator improved the efficiency of microwave heating denitration. Moreover, the powder yield was improved by using the adiabator owing to ease of scraping of the denitration product from the bottom of the denitration vessel.

Mechanism of flashing phenomena induced by microwave heating

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.

Hydrogen behavior in primary precipitate of F82H steel; Atomistic calculation based on the density functional theory

Watanabe, Yoshiyuki; Iwakiri, Hirotomo*; Murayoshi, Norihiko*; Kato, Daiji*; Tanigawa, Hiroyasu

Plasma and Fusion Research (Internet), 10, p.1205086_1 - 1205086_2, 2015/12

https://doi.org/10.1585/pfr.10.1205086

In this paper, formation energy of isolated hydrogen atom in CrC has been theoretically investigated with atomistic calculation based on the density functional theory. The lowest calculated formation energy of a hydrogen atom is -0.48 eV with a trigonal bipyramidal configuration surrounded by five regular Cr lattice atoms. A comparison of the formation energy of hydrogen atom in bcc-iron may indicate that hydrogen atoms in F82H steel are more energetically favorable in CrC-based precipitate rather than Fe-based matrix, leading to an increase of the tritium retention in the precipitate.

Development of solubility improvement technology for nitric acid of plutonium dioxide in scrap MOX powder

Kato, Yoshiyuki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 14(2), p.75 - 85, 2015/06

https://doi.org/10.3327/taesj.J14.014

In the MOX pellet fabrication process, the MOX powder is mixed, granulated and is pressed and finally sintered MOX pellet. In addition only a little part of MOX powder disperses in a globe box and adheres to its wall and floor. The scattered MOX powder becomes dirty. This waste MOX powders have been called as dirty MOX powders and stored. MOX powders which do not meet the specification are rejected from the MOX pellet fabrication process. By the conventional method, MOX powder is pelletized once. The pellet was dissolved with hot nitric acid. Recovery is possible by extracting plutonium out of a nitric acid solution. In this study, a simple method to recover MOX was developed. Generally, MOX powders cannot dissolved in a nitric acid at room temperature. And then, MOX powders are reacted with silicon compound (SiC) and dissolved in a nitric acid at room temperature. Nearly 70% of plutonium was recovered with uranium.

Heating efficiency of microwave heating direct denitration of a mixture of uranyl nitrate and plutonium nitrate

Kato, Yoshiyuki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(2), p.62 - 73, 2014/05

https://doi.org/10.3327/taesj.J13.019

A mixture of plutonium nitrate and uranyl nitrate solution is co-converted to MOX by the microwave heating method developed by JAEA. The heating efficiency is very important to improve throughput or energy-saving performance in this conversion process. In this study, the efficiencies were measured using both experimental and engineering scale microwave ovens, changing the chemical form of solution and its location in the oven. In addition, the distributions of electromagnetic field strength and its absorption concentration in the solution were numerically evaluated by an electromagnetic field analysis code, MWS 2009. The experimental results could almost be explained by the numerical analyses.

Morphology of stress corrosion cracking due to exposure to high-temperature water containing hydrogen peroxide in stainless steel specimens with different crevice lengths

Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Kaji, Yoshiyuki

Journal of Nuclear Materials, 441(1-3), p.348 - 356, 2013/10

https://doi.org/10.1016/j.jnucmat.2013.05.073

Crack growth tests were performed in high-temperature water containing hydrogen peroxide (HO) to evaluate the relationships between the crevice structure and HO on stress corrosion cracking (SCC) growth morphology of stainless steel (SS). Small compact tension (CT) specimens with different fatigue pre-crack lengths were prepared. 20300 ppb HO was injected into the high-temperature water at 561 K. Intergranular SCC (IGSCC) was observed only near the side grooves of the CT specimens. Owing to pre-crack shortening, the IGSCC area expanded to the central region of the CT specimens. The effects of HO on SS appeared intensely near the surfaces exposed to high levels of HO. The calculations for the percentage of HO remaining showed that the effects of HO flowed from both sides of the crack were more obvious than those flowed from the crack mouth.

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

Kato, Yoshiyuki

Journal of Nuclear Science and Technology, 49(10), p.999 - 1009, 2012/10

AA2012-0237.pdf:1.28MB

https://doi.org/10.1080/00223131.2012.723176

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.

Evaluating techniques and phenomena of Stress Corrosion Cracking (SCC) in Light Water Reactors (LWRs); SCC evaluating techniques for predicting core internal and pipe aging of LWRs, technical data collection (Contract research)

Yamamoto, Masahiro; Kato, Chiaki; Sato, Tomonori; Nakano, Junichi; Ugachi, Hirokazu; Tsukada, Takashi; Kaji, Yoshiyuki; Tsujikawa, Shigeo*; Hattori, Shigeo*; Yoshii, Tsuguyasu*; et al.

JAEA-Review 2012-007, 404 Pages, 2012/03

JAEA-Review-2012-007.pdf:36.72MB

There are many LWRs which have been operated for more than 20 years in Japan and it is expected that technique corresponding to aging plants are necessary established for safety operation in LWRs. A lot of troubles related to SCC are reported and many investigations are concerned with SCC mechanism and technical evaluation. In this paper, those research data were collected as possible widely and reviewed systematically. Current circumstances concerned with SCC in LWRs were reviewed specifically as follows: SCC incidents, SCC evaluation methods for crack initiation and propagation, the investigations concerned with SCC mechanism and monitoring technique for corrosive environment. Influences with reactor types (BWR, PWR), materials (stainless steels, Ni alloys) and SCC evaluating methods (laboratories and actual plants) were summarized as graphs and tables easy to understand in common/difference points concerned with SCC. From these arranged results, future themes were considered and remarked SCC phenomenon was summarized in actual plants. As for SCC evaluations under the accelerate conditions in the laboratory test, it was suggested that a computational prediction and modeling including statistical technique and microscopic analysis in crack initiation were important. Furthermore it was suggested that monitoring techniques predicting SCC initiation and grasping plant circumstance in operation and feasibility in actual plants were important.

Development of pressing machine with a die wall lubrication system for the simplified MOX pellet fabrication method in the FaCT project

Sudo, Katsuo; Takano, Tatsuo; Takeuchi, Kentaro; Kihara, Yoshiyuki; Kato, Masato

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Japan Atomic Energy Agency has been contracted to advance the Fast Reactor Cycle Technology Development project. As one part of the project, a simplified MOX pellet fabrication method has been developed for fast reactor fuels. In previous reports, feasibility of a simplified MOX pellet fabrication method was confirmed through hot and cold laboratory-scale experiments. The die wall lubrication pressing technology was one of the important technologies included in the development of the simplified MOX pellet fabrication method. In the work described here, a pressing machine with a die wall lubrication system was developed, and MOX pellet fabrication experiments were carried out on the kilogram MOX scale.

High temperature oxidation of FBR structural materials in carbon dioxide and in air

Furukawa, Tomohiro; Kato, Shoichi; Inagaki, Yoshiyuki; Aritomi, Masanori*

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 5 Pages, 2011/10

A key problem in the application of a supercritical carbon dioxide (CO) turbine cycle to a fast breeder reactor is the corrosion of structural materials brought about by supercritical CO at high temperatures. In this study, high-temperature oxidation tests on the structural materials were performed in carbon dioxide pressurized at 0.2 and 1 MPa, and in air, and the oxidation behavior were compared. Results of investigating the effect of CO pressure including the previous reports tested at 10 MPa and at 20 MPa, the effect was hardly observed for all steels. In air environment, weight gain caused by high temperature oxidation was much lower than that in CO.