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Hirooka, Shun; Nakamichi, Shinya; Matsumoto, Taku; Tsuchimochi, Ryota; Murakami, Tatsutoshi
Frontiers in Nuclear Engineering (Internet), 2, p.1119567_1 - 1119567_7, 2023/03
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 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.
Tsuchimochi, Ryota; Kato, Masato; Hirooka, Shun; Matsumoto, Taku; Uno, Hiroki*; Ogasawara, Masahiro*; Sugata, Hiromasa*
no journal, ,
Thermal expansion and specific heat of CaF, 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
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.
Nakamichi, Shinya; Tsuchimochi, Ryota; Omi, Koyo; Yamada, Yoshikazu
no journal, ,
no abstracts in English
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.
Nakajima, Tatsuya; Kato, Masato; Tsuchimochi, Ryota; Hirooka, Shun; Watanabe, Masashi; Nakamichi, Shinya; Murakami, Tatsutoshi; Ishii, Katsunori
no journal, ,
no abstracts in English
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 were carried out. We confirmed that the specific heat of CaF
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.
Kato, Masato; Tsuchimochi, Ryota; Matsumoto, Taku; White, J.*; McClellan, K.*
no journal, ,
no abstracts in English
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 and Gd
O
were used as simulating materials of UO
and PuO
, respectively. A shrinkage rate measurement on CeO
and Gd
O
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
and Gd
O
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.
Hirooka, Shun; Matsumoto, Taku; Kato, Masato; Tsuchimochi, Ryota; Ogasawara, Masahiro*
no journal, ,
Fluorite compounds such as actinide oxide and CaF 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
C makes the experiment difficult, and the reported data are scattered. In this work, measurement of specific heat was carried out on CaF
, SrF
and (Ca,Sr)F
for the relatively lower melting temperature of below 1500
C. (Ca,Sr)F
which has lower melting temperature than CaF
and SrF
showed the rapid increase of specific heat and the peak at lower temperature. It is expected that UO
, PuO
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.
Matsumoto, Taku; Tsuchimochi, Ryota; Hirooka, Shun; Kato, Masato; White, J.*; McClellan, K.*
no journal, ,
The thermal diffusivity, thermal expansion and heat capacity of CaF was measured with LFA, DIL and DSC up to 1250
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.
Takato, Kiyoto; Nishina, Masahiro; Tsuchimochi, Ryota; Hayashizaki, Kohei; Segawa, Tomoomi; Kawaguchi, Koichi; Ishii, Katsunori; Makino, Takayoshi; Okumura, Kazuyuki
no journal, ,
no abstracts in English
Tsuchimochi, Ryota; Hirooka, Shun; Sunaoshi, Takeo*; Yamada, Tadahisa*
no journal, ,
no abstracts in English
Hirooka, Shun; Tsuchimochi, Ryota; Matsumoto, Taku; Nakamichi, Shinya; Murakami, Tatsutoshi
no journal, ,
no abstracts in English