Refine your search:     
Report No.
 - 
Search Results: Records 1-18 displayed on this page of 18
  • 1

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Effect of hydrogenation conditions on the microstructure and mechanical properties of zirconium hydride

Muta, Hiroaki*; Nishikane, Ryoji*; Ando, Yusuke*; Matsunaga, Junji*; Sakamoto, Kan*; Harjo, S.; Kawasaki, Takuro; Oishi, Yuji*; Kurosaki, Ken*; Yamanaka, Shinsuke*

Journal of Nuclear Materials, 500, p.145 - 152, 2018/03

 Times Cited Count:11 Percentile:77.59(Materials Science, Multidisciplinary)

Journal Articles

Chemical form consideration of released fission products from irradiated fast reactor fuels during overheating

Sato, Isamu; Tanaka, Kosuke; Koyama, Shinichi; Matsushima, Kenichi*; Matsunaga, Junji*; Hirai, Mutsumi*; Endo, Hiroshi*; Haga, Kazuo*

Energy Procedia, 82, p.86 - 91, 2015/07

 Times Cited Count:2 Percentile:17.75(Nuclear Science & Technology)

Experiments simulating overheating conditions of fast reactor severe accidents have been previously carried out with irradiated fuels. For the present study, the chemical forms of the fission products (FPs) included in the irradiated fuels were evaluated by thermochemical equilibrium calculations. At temperatures of 2773 K and 2973 K, the most stable forms of Cs, I, Te, Sb, Pd and Ag are gaseous compounds. Cs and Sb detected in the thermal gradient tube (TGT) in the experiments can take gaseous chemical forms of elemental Cs, CsI, Cs$$_{2}$$MoO$$_{4}$$, CsO and elemental Sb, SbO, SbTe, respectively. By comparing experimental results and the estimations, it is seen CsI thermochemically behaves in a manner that traps it in the TGT, while elemental Cs trends to move as fine particles. The moving behavior of the gaseous FPs will obey not only thermochemical principles, but also those of particle dynamics.

Journal Articles

Variation in the surface morphology of polycrystalline UO$$_{2}$$ powder induced by helium precipitation

Serizawa, Hiroyuki; Matsunaga, Junji*; Shirasu, Noriko; Nakajima, Kunihisa; Kashibe, Shinji*; Kaji, Yoshiyuki

Journal of Asian Ceramic Societies (Internet), 1(3), p.289 - 295, 2013/09

This report addresses the precipitation of helium in polycrystalline UO$$_{2}$$, which deforms the morphology of the grains and their surfaces Helium was injected into pulverized UO$$_{2}$$ particles at 1473 K by hot isostatic pressing (HIP). The specific surface area measured by volumetric gas adsorption instrument implied that small pores should exist on the as-helium-treated sample surface. Field-emission scanning electron microscopy observations showed that numerous shallow basins (approximately 500 nm in radius) with hexagonal fringe were formed on the surface. The basin resembles a ruptured blister whose lid has been forced open. SEM observations showed a uniform polygonal-shaped section of the gas bubble on the fracture surface; this implies that precipitated helium forms a negative crystal in the grain.

Journal Articles

Formation and growth of image crystals by helium precipitation

Serizawa, Hiroyuki; Matsunaga, Junji*; Haga, Yoshinori; Nakajima, Kunihisa; Akabori, Mitsuo; Tsuru, Tomohito; Kaji, Yoshiyuki; Kashibe, Shinji*; Oishi, Yuji*; Yamanaka, Shinsuke*

Crystal Growth & Design, 13(7), p.2815 - 2823, 2013/07

 Times Cited Count:5 Percentile:42.85(Chemistry, Multidisciplinary)

Since the shape of the negative crystal closely relates to the morphology of the crystal habits, the formation and the growth mechanism is important subject in a field of the physical science. Whereas, the negative crystal formed in a large single crystal mass has been arousing interest as an expensive jewelry because of its mysterious appearance and rarity. However, it is difficult to control the shape of this polyhedral cavity embedded in a solid medium arbitrary. Here we report the recent discovery on the growth process of the negative crystal. We found that precipitated helium forms the negative crystal in UO$$_{2}$$; the shape changes drastically with the condition of the helium precipitation. The transformation mechanism was discussed in this article. Our investigation implies that the shape of the negative crystal can be arbitrary controlled by controlling the precipitation condition.

JAEA Reports

Study on helium behavior in oxide fuel, 1; Deformation of microstructure induced by precipitation of helium (Joint research)

Serizawa, Hiroyuki; Matsunaga, Junji*; Haga, Yoshinori; Nakajima, Kunihisa; Kashibe, Shinji*; Iwai, Takashi

JAEA-Research 2011-025, 32 Pages, 2011/11

JAEA-Research-2011-025.pdf:10.17MB

This report deals with the precipitation of helium in UO$$_{2}$$ matrix to deform the microstructure. The examination was performed using single and polycrystalline UO$$_{2}$$ sample. The helium-treated samples under 900 atm at 1473 K were reheat-treated at much more high temperature, 1573 K or 1973 K to release the infused helium. The microstructure of the sample was examined by FIB, FE-STEM and FE-TEM. It was confirmed that precipitated helium atoms form a negative crystal in the grain or the matrix of the single crystal. At 1573 K, helium can be released without formation of intergranular tunnel since the surface diffusion coefficient of helium is large. However, some open grain boundaries were observed in the sample heat-treated at 1973 K. This might be related to the activity of helium in the grain boundary region. The structure of the negative crystal was analyzed from the view point of the thermodynamics of the surface growth.

Oral presentation

Melting temperature measurement of aluminosilicate additive fuel

Matsunaga, Junji*; Une, Katsumi*; Kusagaya, Kazuyuki*; Hirosawa, Takashi; Sato, Isamu

no journal, , 

no abstracts in English

Oral presentation

Bubble swelling of UO$$_{2}$$ by helium release

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Nakajima, Kunihisa; Iwai, Takashi

no journal, , 

Variation of microstructure of UO$$_{2}$$ by precipitation of helium was examined using FIB and FE-TEM. The swelling accompanied by the formation of a gas bubble was evaluated. The number of helium gas bubble increased remarkably at the temperature more than 1300 $$^{circ}$$C. The formation of a tunnel was observed in the grain boundary after the heat treatment at 1700 $$^{circ}$$C.

Oral presentation

Negative crystal fabricated by helium infusion for UO$$_2+x$$

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Nakajima, Kunihisa; Iwai, Takashi; Haga, Yoshinori; Oishi, Yuji*; Yamanaka, Shinsuke*

no journal, , 

The aim of this study is to clarify the behavior of helium precipitated in UO$$_2$$. The micro-structure of UO$$_2$$ matrix deformed by helium infusion was examined by FE-SEM and FE-TEM. It was deduced that the shape of the negative crystal is determined by the balance between the surface energy of the lattice plane and the inner pressure of helium.

Oral presentation

Helium bubbles in UO$$_{2}$$

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Nakajima, Kunihisa; Iwai, Takashi; Haga, Yoshinori; Oishi, Yuji*; Yamanaka, Shinsuke*

no journal, , 

Helium generated in MOX fuel increases inner pressure of fuel rod and helium could also form additional bubbles in fuel pellet by the combination of radiation defects and high temperature. Therefore it is important to understand the behavior of helium in oxide fuel for reliable operation of MOX fuels. In the present study, the helium infusion treatments in high temperature and high pressure of helium were performed for both sintered polycrystalline UO$$_{2}$$ fragments and hyperstoichiometric monograin UO$$_{2+x}$$ particles fabricated by the transportation method. It was suggested that the difference in the composition of UO$$_{2}$$ is closely related with the condition of the formation of the negative crystal.

Oral presentation

Relationship between shape of negative crystal in helium infused UO$$_{2}$$ and its inner pressure

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Nakajima, Kunihisa; Iwai, Takashi; Haga, Yoshinori; Oishi, Yuji*; Yamanaka, Shinsuke*

no journal, , 

In the present study, the helium infusion were conducted at high temperature with highly pressurized helium for both UO$$_{2}$$. Following a high temperature treatment, the negative crystal formed in the sample was examined by FE-SEM. The SEM image was analyzed to measure the area of the surface on the negative crystal which is composed of facetted lattice planes. It was confirmed that the shape of the negative crystal formed in this method is deviated from the equilibrium shape reported previously, which means that the higher inner pressure produced by the helium precipitated in the cavity relate to the shape of the negative crystal.

Oral presentation

Study on formation of helium bubbles in CeO$$_{2-x}$$

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Oishi, Yuji*; Yamanaka, Shinsuke*

no journal, , 

We applied the helium infusion technique by a hot isothermal pressing (HIP) method and CeO$$_{2}$$ was used for helium infusion. A sintered CeO$$_{2}$$ pellet was reduced in hydrogen atmosphere at 1073 K for 1 hour. O/Ce ratio of as-sintered CeO$$_{2}$$ and reduced CeO$$_{2-x}$$ was evaluated by XRD as 2.00 and 1.99, respectively. The helium infusion was conducted under the experimental condition at 1473 K and 50 MPa of helium for CeO$$_{2}$$ and CeO$$_{1.99}$$. As helium treated samples were annealed at 1773 K under atmospheric pressure in argon. By the heat treatment, additional intra- and intergranular bubbles were formed in CeO$$_{1.99}$$. However, such kind of bubble was not found in the stoichiometric CeO$$_{2}$$. The sizes of intragranular bubbles in CeO$$_{1.99}$$ were about less than 100 nm, and intergranular bubbles were larger than those in grain. We at this consider that helium can dissolve into CeO$$_{2}$$ matrix and oxygen vacancy would increase solubility of helium.

Oral presentation

A Discussion for a mechanism on formation of helium bubble in oxide fuel

Matsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Oishi, Yuji*; Yamanaka, Shinsuke*

no journal, , 

In the developing MA-MOX fuel, the accumulation of helium should be serious problem since minor actinides are $$alpha$$-emitter. In this paper, we will discuss a mechanism of inter-granular gas bubble produced by the helium injected into UO$$_2$$ using HIP.

Oral presentation

Primary factor in determing the shape of image crystal

Serizawa, Hiroyuki; Oishi, Yuji*; Haga, Yoshinori; Yamanaka, Shinsuke*; Tsuru, Tomohito; Kaji, Yoshiyuki; Matsunaga, Junji*; Kashibe, Shinji*

no journal, , 

We found that porous UO$$_{2}$$ grain was formed by the precipitation of helium injected by HIP. SEM analysis showed that polyhedral negative crystals were formed in the sample. The shape of the negative crystal changes dramatically with the conditions of helium precipitation. A truncated octahedron-type, an octa-triacontahedron and a pentacontahedron-type negative crystal were observed. The change in the precipitation condition means the variation in the activity of helium in matrix. So, our study implies that the shape of the negative crystal should changes depending on the helium inner pressure enclosed in the negative crystal.

Oral presentation

Shape controlable polyhedron-type cavity; Image crystal

Serizawa, Hiroyuki; Oishi, Yuji*; Haga, Yoshinori; Yamanaka, Shinsuke*; Tsuru, Tomohito; Kaji, Yoshiyuki; Matsunaga, Junji*; Kashibe, Shinji*

no journal, , 

We found that porous UO$$_{2}$$ grain was formed by the precipitation of helium injected by HIP. SEM analysis showed that polyhedral negative crystals were formed in the sample. The shape of the negative crystal changes dramatically with the conditions of helium precipitation. The change in the precipitation condition means the variation in the activity of helium in matrix. So, our study implies that the shape of the negative crystal should changes depending on the helium inner pressure enclosed in the negative crystal. It is difficult to arbitrarily control the shapes of these polyhedral negative crystals embedded in a solid medium. However, the shape of the negative crystal can easily be controlled by helium injection method. In this article, we call shape controlled negative crystal as image crystal. Here, we report a relationship between the surface energy and the shape and discuss the transformation mechanism of image crystal.

Oral presentation

Chemical forms consideration of released fission products from irradiated fast reactor fuels during overheating

Sato, Isamu; Tanaka, Kosuke; Koyama, Shinichi; Matsushima, Kenichi*; Matsunaga, Junji*; Hirai, Mutsumi*; Endo, Hiroshi*; Haga, Kazuo*

no journal, , 

Thermochemical equilibrium calculations of gaseous chemical forms and adhering chemical forms of fission products and fuel elements were performed simulating the heating test condition done for irradiated fuels to discuss the release behavior of fission products from overheated fuels.

Oral presentation

Structure of image crystal in uranium dioxide arised from precipitated helium

Serizawa, Hiroyuki; Kaji, Yoshiyuki; Oishi, Yuji*; Yamanaka, Shinsuke*; Matsunaga, Junji*

no journal, , 

We found that porous UO$$_{2}$$ grain was formed by the precipitation of helium injected by HIP. Scanning electron microscopy analysis showed that polyhedral negative crystals were formed in the sample. The shape of the negative crystal changes dramatically with the conditions of helium precipitation. A truncated octahedron-type, an octa-triacontahedron-type, and a pentacontahedron-type negative crystal were observed. Our study implies that the shape of the negative crystal should change depending on the helium inner pressure enclosed in the negative crystal.

Oral presentation

Mechanical properties of Urania-Zirconia solid solutions with tetragonal and monoclinic structures

Ikeuchi, Hirotomo; Yano, Kimihiko; Ogino, Hideki; Matsunaga, Junji*

no journal, , 

Mechanical properties (micro-hardness, elastic modulus, and fracture toughness) of fuel debris are essential information for defueling work in the Fukushima Daiichi NPP. The Urania-Zirconia solid solution, (U,Zr)O$$_{2}$$, is expected to be separated into cubic phase with low Zr contents and tetragonal or monoclinic phase with high Zr contents during cooling process. In this study, the properties of tetragonal and monoclinic phase are investigated. The (U$$_{1-x}$$Zr$$_{x}$$)O$$_{2.0}$$ samples (x=0.85 for tetragonal phase and 0.95 for monoclinic phase) were prepared by sintering the compacted mixture of UO$$_{2}$$ and ZrO$$_{2}$$ powders at maximum 2673 K. The micro-hardness of samples was lower than what has been expected from trend of cubic phase. The elastic modulus was comparable with cubic phase. The fracture toughness of the tetragonal phase was higher than the other two phases. The stress-induced martensitic transformation around the indent is expected to increase the fracture toughness.

Oral presentation

Accident-Tolerant Fuel R&D Program in Japan

Yamashita, Shinichiro; Mohamad, A. B.; Ioka, Ikuo; Nemoto, Yoshiyuki; Kawanishi, Tomohiro; Kaji, Yoshiyuki; Osaka, Masahiko; Murakami, Nozomu*; Owaki, Masao*; Sasaki, Masana*; et al.

no journal, , 

Japan's Accident Tolerant Fuel (ATF) research and development (R&D) program has been conducted since 2015 in cooperation with power plant providers, fuel venders and universities for making the most use of the experiences in R&D, practical design, and evaluations of fuels and cores of commercial Light Water Reactors (LWRs). An overview of the present R&D progress is given, in relation to the role of Japan Atomic Energy Agency (JAEA) in the program. The ATF candidate materials currently under consideration are the following three claddings: the silicon carbide (SiC) composite which is potentially applicable for Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR), the FeCrAl steel strengthened by dispersion of fine oxide particles (FeCrAl-ODS) for BWR, and Cr-coated zircalloy claddings for PWR. In addition to the cladding materials, R&D on the SiC-made BWR channel box and accident tolerant control rods are also underway.

18 (Records 1-18 displayed on this page)
  • 1