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powder induced by helium precipitationSerizawa, 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, which deforms the morphology of the grains and their surfaces Helium was injected into pulverized UO 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.
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：42.72(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; 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.
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 matrix to deform the microstructure. The examination was performed using single and polycrystalline UO 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.
Saito, Kenya*; Kakuta, Akio*; Oi, Noboru*; Nomata, Terumitsu*; Tominaga, Yasuo*; Okoshi, Yoshimi*; Kashibe, Shinji*; Ouchi, Atsuhiro*
PNC TJ4164 88-002VOL2, 24 Pages, 1988/05
PNC-TJ4164-88-002VOL2.pdf:1.53MB
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Saito, Kenya*; Kakuta, Akio*; Oi, Noboru*; Nomata, Terumitsu*; Tominaga, Yasuo*; Okoshi, Yoshimi*; Kashibe, Shinji*; Ouchi, Atsuhiro*
PNC TJ4164 88-002VOL1, 60 Pages, 1988/05
PNC-TJ4164-88-002VOL1.pdf:3.72MB
None
by helium releaseMatsunaga, Junji*; Kashibe, Shinji*; Serizawa, Hiroyuki; Nakajima, Kunihisa; Iwai, Takashi
no journal, ,
Variation of microstructure of UO 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 
C. The formation of a tunnel was observed in the grain boundary after the heat treatment at 1700 C.
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
. The micro-structure of UO 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.
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 fragments and hyperstoichiometric monograin UO
particles fabricated by the transportation method. It was suggested that the difference in the composition of UO is closely related with the condition of the formation of the negative crystal.
and its inner pressureMatsunaga, 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. 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.
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 was used for helium infusion. A sintered CeO pellet was reduced in hydrogen atmosphere at 1073 K for 1 hour. O/Ce ratio of as-sintered CeO and reduced CeO 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 and CeO
. 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. However, such kind of bubble was not found in the stoichiometric CeO. The sizes of intragranular bubbles in CeO 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 matrix and oxygen vacancy would increase solubility of helium.
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 
-emitter. In this paper, we will discuss a mechanism of inter-granular gas bubble produced by the helium injected into UO using HIP.
Serizawa, Hiroyuki; Oishi, Yuji*; Haga, Yoshinori; Yamanaka, Shinsuke*; Tsuru, Tomohito; Kaji, Yoshiyuki; Matsunaga, Junji*; Kashibe, Shinji*
no journal, ,
We found that porous UO 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.
Serizawa, Hiroyuki; Oishi, Yuji*; Haga, Yoshinori; Yamanaka, Shinsuke*; Tsuru, Tomohito; Kaji, Yoshiyuki; Matsunaga, Junji*; Kashibe, Shinji*
no journal, ,
We found that porous UO 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.
