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Toward long-term storage of nuclear materials in MOX fuels fabrication facility

Hirooka, Shun; Nakamichi, Shinya; Matsumoto, Taku; Tsuchimochi, Ryota; Murakami, Tatsutoshi

Frontiers in Nuclear Engineering (Internet), 2, p.1119567_1 - 1119567_7, 2023/03

https://doi.org/10.3389/fnuen.2023.1119567

Storage of plutonium (Pu)-containing materials requires extremely strict attention in terms of physical safety and material accounting. Despite the emphasized importance of storage management, only a few reports are available in the public, e.g., experience in PuO $_{2}$ storage in the UK and safety standards in the storage of Pu-containing materials in the US. Japan also stores more U-Pu mixed oxide (MOX) mostly in powder form. Adopting an appropriate storage management is necessary depending on the characteristics of MOX items such as raw powder obtained by reprocessing of spent Light Water Reactor fuels, research and development on the remains of fuel fabrication, which can contain organic materials, and dry-recycled powder during fuel fabrication. Stagnation in fuel fabrications and experience in degradation of MOX containers during extended period of storage have led to the review of the storage method in the Plutonium Fuel Development Center in Japan Atomic Energy Agency. The present work discusses the various nuclear materials, storage methods, experience in degradation of containers that occur during storage, and strategies for future long-term storage.

Oral presentation

A Consideration of utilization of U $_{3}$ O $_{8}$ powder in MOX fuel production

Tsuchimochi, Ryota; Hirooka, Shun; Sunaoshi, Takeo*; Yamada, Tadahisa*

no journal, ,

no abstracts in English

Oral presentation

Measurement of thermal expansion and specific heat of CaF $_{2}$

Tsuchimochi, Ryota; Kato, Masato; Hirooka, Shun; Matsumoto, Taku; Uno, Hiroki*; Ogasawara, Masahiro*; Sugata, Hiromasa*

no journal, ,

Thermal expansion and specific heat of CaF $_{2}$ , which forms the same crystal structure as actinide oxides, were measured by using high-temperature X-ray diffractmeter and differential scanning calorimetry. We confirmed that the specific heat of CaF $_{2}$ explicitly shows the effect of excitation on top of the heat capacity at constant volume and dilatational term. The analysis of the specific heat will be discussed together with the measured data.

Oral presentation

Property measurement of CaF $_{2}$

Tsuchimochi, Ryota; Kato, Masato; Hirooka, Shun; Matsumoto, Taku; White, J.*; McClellan, K.*

no journal, ,

High temperature XRD, Thermal expansion measurement, sound speeds measurement and DSC measurement of CaF $_{2}$ were carried out. We confirmed that the specific heat of CaF $_{2}$ explicity shows the effect of Frenkel defect formation on top of the heat capacity at constant volume and dilatational term. The analysis of the specific heat will be discussed together with the measured data.

Oral presentation

Evaluation of fundamental properties of CaF $_{2}$ , 1; Experimental approach

Kato, Masato; Tsuchimochi, Ryota; Matsumoto, Taku; White, J.*; McClellan, K.*

no journal, ,

no abstracts in English

Oral presentation

In situ analysis of solid solution formation of CeO $_{2}$ and Gd $_{2}$ O $_{3}$

Tsuchimochi, Ryota; Sugata, Hiromasa*; Sunaoshi, Takeo*

no journal, ,

Solid solution reaction of MOX pellet procceds at sintering process, but at what temperature and how fast the reaction proceeds have not been understood. CeO $_{2}$ and Gd $_{2}$ O $_{3}$ were used as simulating materials of UO $_{2}$ and PuO $_{2}$ , respectively. A shrinkage rate measurement on CeO $_{2}$ and Gd $_{2}$ O $_{3}$ mixed compact was carried out in the temperature range of 300K to 1923K. The shringage curve has two positive peaks at around 1213K and 1600K. High temperature X-ray diffraction measurements on CeO $_{2}$ and Gd $_{2}$ O $_{3}$ mixed powder were carried out at 1213K and 1600K for 240 minutes. The solid solution formation was observed at 1600K, but not at 1213K. It is considered that the first shrinkage region at 1213K was caused by initial sintering and the second region at 1600K was caused by mid-final sintering.

Oral presentation

The Bredig transition effect on the thermal conductivity of CaF $_{2}$

Matsumoto, Taku; Tsuchimochi, Ryota; Hirooka, Shun; Kato, Masato; White, J.*; McClellan, K.*

no journal, ,

The thermal diffusivity, thermal expansion and heat capacity of CaF $_{2}$ was measured with LFA, DIL and DSC up to 1250 $^{circ}$ C, then the thermal conductivity was evaluated. We evaluated how the Bredig transition which is one of the unique features of fluorite structure affect on the thermal conductivity.

Oral presentation

Measurement of specific heat on fluorite compounds

Hirooka, Shun; Matsumoto, Taku; Kato, Masato; Tsuchimochi, Ryota; Ogasawara, Masahiro*

no journal, ,

Fluorite compounds such as actinide oxide and CaF $_{2}$ perform a rapid increase and a peak in the specific heat which are attributed by Bredig transition. The behavior is important as a nuclear fuel; however, the fact that the behavior occurs above 2000 $^{circ}$ C makes the experiment difficult, and the reported data are scattered. In this work, measurement of specific heat was carried out on CaF $_{2}$ , SrF $_{2}$ and (Ca,Sr)F $_{2}$ for the relatively lower melting temperature of below 1500 $^{circ}$ C. (Ca,Sr)F $_{2}$ which has lower melting temperature than CaF $_{2}$ and SrF $_{2}$ showed the rapid increase of specific heat and the peak at lower temperature. It is expected that UO $_{2}$ , PuO $_{2}$ and MOX that the high temperature data is limited and scattered could show the similar relationship between the specific heat and the melting temperature. Therefore, the results of the measurements on the fluorite compounds suggest the possibility that the Kopp's law is not applicable to the solid solution of fluoride materials at high temperature.

Oral presentation

A Handheld dust collector to prevent the scatter of the MOX powders around the workplace

Nakamichi, Shinya; Tsuchimochi, Ryota; Omi, Koyo; Yamada, Yoshikazu

no journal, ,

no abstracts in English

Oral presentation

Development of simplified pelletizing process for fast reactor MOX fuels and demonstration experiment, 2; Die wall lubrication technology with using tumbling granular

Takato, Kiyoto; Nishina, Masahiro; Tsuchimochi, Ryota; Hayashizaki, Kohei; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori; Makino, Takayoshi; Okumura, Kazuyuki

no journal, ,

no abstracts in English

Oral presentation

Machine learning sintering density prediction model for MOX fuel pellet

Tsuchimochi, Ryota; Kato, Masato; Nakajima, Tatsuya; Hirooka, Shun; Watanabe, Masashi; Nakamichi, Shinya; Murakami, Tatsutoshi; Ishii, Katsunori

no journal, ,

Uranium and Plutonium mixed oxide (MOX) pellets used as fast reactor fuels have been produced from several raw materials by mechanical blending method. It is essential to control the pellet density which is one of the important fuel specifications, but it is difficult to understand relationships among many parameters in the production. Database for MOX production was prepared from production results of JOYO and MONJU. The input data of eighteen types were chosen from production process and made a data set. A machine learning model for predicting the sintered density of MOX pellets was derived by gradient boosting regressor.

Oral presentation

Challenges in nuclear material storage in Japanese MOX fuel fabrication facilities

Hirooka, Shun; Tsuchimochi, Ryota; Matsumoto, Taku; Nakamichi, Shinya; Murakami, Tatsutoshi

no journal, ,

no abstracts in English

Oral presentation

Machine learning sintering density prediction model for MOX fuel pellet

Nakajima, Tatsuya; Kato, Masato; Tsuchimochi, Ryota; Hirooka, Shun; Watanabe, Masashi; Nakamichi, Shinya; Murakami, Tatsutoshi; Ishii, Katsunori

no journal, ,

no abstracts in English

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Toward long-term storage of nuclear materials in MOX fuels fabrication facility

A Consideration of utilization of U $_{3}$ O $_{8}$ powder in MOX fuel production

Measurement of thermal expansion and specific heat of CaF $_{2}$

Property measurement of CaF $_{2}$

Evaluation of fundamental properties of CaF $_{2}$ , 1; Experimental approach

In situ analysis of solid solution formation of CeO $_{2}$ and Gd $_{2}$ O $_{3}$

The Bredig transition effect on the thermal conductivity of CaF $_{2}$

Measurement of specific heat on fluorite compounds

A Handheld dust collector to prevent the scatter of the MOX powders around the workplace

Development of simplified pelletizing process for fast reactor MOX fuels and demonstration experiment, 2; Die wall lubrication technology with using tumbling granular

Machine learning sintering density prediction model for MOX fuel pellet

Challenges in nuclear material storage in Japanese MOX fuel fabrication facilities

Machine learning sintering density prediction model for MOX fuel pellet