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observation of radiation-induced defects in ZrN under electron irradiation in HVEMRahman, M. M.*; Yamamoto, Tomokazu*; Matsumura, Sho*; Takaki, Seiya; Takano, Masahide; Costantini, J. M.*; Yasuda, Kazuhiro*
Nuclear Instruments and Methods in Physics Research B, 549, p.165289_1 - 165289_8, 2024/04
Nucleation-and-growth process of radiation-induced defects in zirconium nitride (ZrN) has been investigated 
under electron irradiation by using a high voltage transmission electron microscope (HVEM) under electron irradiation by using a high voltage transmission electron microscope (HVEM).
Yoneda, Yasuhiro; Tsuji, Takuya; Matsumura, Daiju; Okamoto, Yoshihiro; Takaki, Seiya; Takano, Masahide
Physica B; Condensed Matter, 663, p.414960_1 - 414960_9, 2023/08
Times Cited Count：0 Percentile：0.00(Physics, Condensed Matter)We performed various synchrotron X-ray measurements to extract local and average structures of DyN-ZrN solid solutions. We performed the nanoscale structural analysis by combining X-ray absorption fine structure and high-energy X-ray diffraction. The DyN-ZrN solid solution has a rock-salt type cubic crystal structure, and there are instabilities such as the chemical order of the metal site and the distribution of the bond length of the nitrogen site.
Hatsukawa, Yuichi*; Hayakawa, Takehito*; Tsukada, Kazuaki; Hashimoto, Kazuyuki*; Sato, Tetsuya; Asai, Masato; Toyoshima, Atsushi; Tanimori, Toru*; Sonoda, Shinya*; Kabuki, Shigeto*; et al.
PLOS ONE (Internet), 13(12), p.e0208909_1 - e0208909_12, 2018/12
Times Cited Count：5 Percentile：38.54(Multidisciplinary Sciences)Imaging of 
Tc radioisotope was conducted using an electron tracking-Compton camera (ETCC). Tc emits 204, 582, and 835 keV 
rays, and was produced in the 
Mo(p,n)Tc reaction with a Mo-enriched target. The recycling of the Mo-enriched molybdenum trioxide was investigated, and the recycled yield of Mo was achieved to be 70% - 90%. The images were obtained with each of the three rays. Results showed that the spatial resolution increases with increasing -ray energy, and suggested that the ETCC with high-energy -ray emitters such as Tc is useful for the medical imaging of deep tissue and organs in the human body.
Zr
N irradiated by 200 MeV Xe ionsTakaki, Seiya; Takano, Masahide; Ishikawa, Norito
Progress in Nuclear Science and Technology (Internet), 5, p.204 - 207, 2018/00
NaCl-type structured nitrides, such as ZrN and TiN, have potential applications to inert matrix fuels for the transmutation of minor actinides (MA) in accelerator-driven systems (ADS), because of their excellent thermal properties. Understanding of radiation damage with fission fragments is one of the essentials to clarify the microstructural stability of those materials under high-density electronic excitation induced by swift heavy ions. However, very little information about such damage in nitride fuels is available. The present study aims to obtain the knowledge of high-density electronic excitation damage in nitride fuels. XRD analysis has shown that the lattice parameter and the lattice strain of the irradiated ZrN and DyZrN increase with increasing ion fluence.
ZyN surrogate materials for fast reactor nitride fuelYoneda, Yasuhiro; Tsuji, Takuya; Matsumura, Daiju; Okamoto, Yoshihiro; Takaki, Seiya; Takano, Masahide
Transactions of the Materials Research Society of Japan, 42(2), p.23 - 26, 2017/04
ZnN is a possible candidate for the diluent material for nitride fuels containing transuranium elements. Pellets of inert matrix material ZrN, and surrogate nitride fuel material DyZrN, are fabricated for the purpose of investigating the crystal structure. Lattice parameters of Dy
Zr
N followed the Vegard's low, in spite of the large lattice mismatch (
7%) between DyN and ZrN. Local structure analysis was performed by X-ray absorption fine structure (XAFS) and atomic pair-distribution function (PDF) methods. The Zr-N nearest neighbor bond distance changed as changing the Dy composition. The complex local structure of DyN and ZrN is related to the preferable effects of ZrN.
Takaki, Seiya*; Yasuda, Kazuhiro*; Yamamoto, Tomokazu*; Matsumura, Sho*; Ishikawa, Norito
Nuclear Instruments and Methods in Physics Research B, 326, p.140 - 144, 2014/05
Times Cited Count：42 Percentile：94.02(Instruments & Instrumentation)We have investigated atomic structure of ion tracks in CeO
irradiated with 200 MeV Xe ions by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM observations under inclined conditions showed continuous ion tracks with diffraction and structure factor contrast, and the decrease in the atomic density of the ion tracks was evaluated. High resolution STEM with high-angle annular dark-field (HAADF) technique showed that the crystal structure of the Ce cation column is retained at the core region of ion tracks, although the signal intensity of the Ce cation lattice is reduced over a region nm in size. Annular bright field (ABF) STEM observation has detected that the O anion column is preferentially distorted at the core region of ion tracks within a diameter of 4 nm.
Takaki, Seiya; Yasuda, Kazuhiro*; Matsumura, Sho*; Ishikawa, Norito
no journal, ,
Advanced nuclear application materials are irradiated by fast neutrons, electrons, a particles and fission fragments, so formation of radiation damage and microstructure evolution are induced by pile-up effect of those radiation. Behavior of point defects in materials which has ion and covalent bonding is influenced by electronic excitation. Especially, high-density electronic excitation damage induced by fission fragments, induce to form cylindrical defect, so called ion track in the materials to result in influence for microstructural evolution in fuel materials. This study aims to clarify the structure of ion tracks in CeO and cubic ZrO (YSZ) irradiated with swift heavy ions by using several transmission electron microscopies. It was shown that the density of vacancy at the core damage region of ion tracks is increased and the O anion lattice is preferentially disordered at such region. In addition to, high density dislocation was formed in CeO with irradiated by high fluence. This result support STEM observation. In case of YSZ, the size and the areal density of ion tracks is smaller than those of CeO. The difference of ion tracks between CeO and YSZ is presumably due to the difference in the recovery process from the thermal spike regime, which is influenced by the presence of structural vacancy in oxide sublattice.
Takaki, Seiya; Takano, Masahide
no journal, ,
Nitride fuel with ZrN matrix have been studied for transmutation of minor actinide (MA). These are supposed to be designed as ZrN solid solution or TiN compounds with MA nitride from 20mol% to 40mol%. From the above, composition and temperature dependence of thermal conductivity for safety evaluation of the fuel have been studied with a little of MA. In the present study, we are aimed to clarify composition and temperature dependence of thermal conductivity of Dy
ZrN solid solution as surrogate nitride fuel with MA in order to understand the dependence of the MA nitride fuel physically. In addition to, we introduce studies about pyrochemical compatibility between the simulated fuel and candidate material for cladding, and entrusted to Japan Atomic Energy Agency by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).
ZrN irradiated by 200 MeV Xe ionsTakaki, Seiya; Takano, Masahide; Ishikawa, Norito
no journal, ,
NaCl-type structured nitrides, such as ZrN and TiN, have potential applications to inert matrix fuels for the transmutation of minor actinides (MA) in accelerator-driven systems (ADS), because of their excellent thermal properties. Understanding of radiation damage with fission fragments is one of the essentials to clarify the microstructural stability of those materials under high-density electronic excitation induced by swift heavy ions. However, very little information about such damage in nitride fuels is available. The present study aims to obtain the knowledge of high-density electronic excitation damage in nitride fuels. XRD analysis has shown that the lattice parameter and the lattice strain of the irradiated ZrN and DyZrN increase with increasing ion fluence.
Takaki, Seiya; Harada, Makoto; Takano, Masahide
no journal, ,
It is necessary to control the pellet densities for the purpose of securing margin against swelling for nitride fuel for transmutation of minor actinide. Appropriate polymer particles will be applied as a pore former in order to decrease the density. This study aimed to investigate the influence of various milling parameters on the densities of sintered DyZrN solid solution as surrogate nitride fuel in order to obtain fundamental knowledge for controlling sintered density with pore former. The sintered pellet densities are studied under various milling condition. The measurement of specific surface area clarifies that finer powder can be obtained with WC. However, the achieved densities of the sintered pellets show that the denser pellets can be obtained with Si
N
in spite of the smaller specific surface area.
Takaki, Seiya; Takano, Masahide
no journal, ,
Regarding nitride fuel for nuclear transformation of minor actinides, in order to obtain fundamental knowledge for sintering density control by adding pore former, under the various grinding conditions, DyZrN simulated nitride fuel Sintering experiments were carried out. Although the sintered density of the simulated nitride fuel increases with the increase of the specific surface area of the pulverized powder, it can be confirmed that the sintered density decreases as the strain in the grain increases.
Takano, Masahide; Takaki, Seiya
no journal, ,
To clarify the influence of high temperature He gas release on the MA transmutation fuel behavior, annealing experiments on a Cm-bearing nitride pellet were carried out after two years of storage at room temperature, and the results were compared with those on the Cm-bearing dioxide. Just before the annealing, the nitride pellet showed the large expansion value of 1.1%, which suggests that vacancies in grains formed voids at room temperature. During the annealing experiments, the gas swelling of the nitride pellet due to He release above 800
C was relatively slight. From the microstructure images, smaller grains and higher open-porosity of the nitride pellet resulted in the slight gas swelling. After the annealing at 1300C, the nitride pellet still had expansion value of 0.6%, that should be taken into account when designing the pellet-cladding gap.
Takaki, Seiya; Takano, Masahide; Otobe, Haruyoshi
no journal, ,
We will report the application of pore former for density control of TRU nitride fuels. The pore former was selected using DyZrN as surrogate nitride fuel.
Takaki, Seiya; Takano, Masahide; Otobe, Haruyoshi
no journal, ,
We will report the application of pore former for density control of TRU nitride fuels. The pore former was selected using DyZrN as surrogate nitride fuel.
Sitompul, Y.*; Aoki, Takayuki*; Watanabe, Seiya*; Sugihara, Kenta; Takaki, Tomohiro*
no journal, ,
A cumulant Lattice Boltzmann Method (LBM) with Multiphase Field (MPF) and Adaptive Mesh Refinement (AMR) has been developed to model foam formation with stable thin liquid films. The proposed method has been successfully employed to simulate 3D foam formation with many bubbles, maintaining mass conservation and using a large density ratio. In addition, we have extended the proposed method to include heat transfer calculations. To demonstrate the effectiveness of the foam as a thermal insulation layer, we simulated 2D foam formation and compared the heat transfer in a cup of water with and without foam. Preliminary results show that the foam effectively acts as a thermal insulator, retaining the water temperature by preventing the natural air convection and acting like a stagnant air layer.
Takaki, Seiya; Otobe, Haruyoshi; Takano, Masahide
no journal, ,
Nitride fuel with ZrN inert matrix has been studied as a candidate for the transmutation fuel of minor actinides (MA) in an accelerator-driven system (ADS). The pellet densities were designed to be about 85 % of the theoretical density to ensure a margin against swelling, but a dense microstructure is required. One of promising method of controlling the sintering density is by using a pore former (PF). This study aims to investigate the appropriate PF using (Dy,Zr)N as a surrogate nitride fuel with MA and evaluate its technical feasibility through sintering tests of (TRU,Zr)N (TRU: Np, Pu). Three types of polymer particles (A: stearic acid, B: polyester, C: polyethylene) as PF were mixed with (Dy,Zr)N powder respectively, and then the mixed powder was compacted and sintered to obtain the pellets. The dependence of oxygen and carbon impurity concentrations on PF type and concentration was not clear, whereas the pellets mixed with A had numerous cracks formed perpendicular to the direction of compaction. From the above, B and C were used as candidate PFs in the demonstration tests of (TRU,Zr)N. The sintered pellets were prepared using (TRU,Zr)N powder mixed with selected PFs. The sintered density of the pellets decreased linearly with PFs addition concentration as in the (Dy,Zr)N tests, and the almost no clacks occurred in the pellets. We can therefore conclude that B and C are fully applicable to control the sintering density of MA-containing pellets for ADS.
Takaki, Seiya; Ishikawa, Norito; Rahman, M. M.*; Yasuda, Kazuhiro*
no journal, ,
Nitride ceramics, which have excellent nuclear and thermal properties, are being researched and developed as next generation reactor fuel materials. However, compared to oxide ceramics and metals, there is an overwhelming lack of irradiation tests and post-irradiation examinations, which are essential for fuel design and safety evaluation. It is important to obtain mechanistic knowledge on irradiation and damage processes to replace or supplement the limited irradiation test data. In this study, we report the results of ion irradiation tests and nanoindentation hardness tests focusing on high density electronic excitation damage, which is one of the damage elementary processes, and obtained important findings for fuel design that suggest the disappearance of micropores due to irradiation.
Takaki, Seiya; Takano, Masahide
no journal, ,
Nitride fuel with ZrN matrix have been studied for transmutation of minor actinide (MA). These are supposed to be designed as ZrN solid solution or TiN compounds with MA nitride from 20 mol% to 40 mol%. From the above, composition and temperature dependence of thermal conductivity for safety evaluation of the fuel have been studied with a little of MA. In future, it is important to understand the heat conduction mechanism in detail when evaluating irradiation effect on thermal conductivity. In the present study, we are aimed to clarify composition and temperature dependence of thermal conductivity of DyZrN solid solution as surrogate nitride fuel with MA in order to understand the dependence of the MA nitride fuel physically.
Takano, Masahide; Takaki, Seiya
no journal, ,
In the fuel containing minor actinides with high concentrations, lattice defects and He atoms accumulates quickly due to the self-irradiation damage of alpha-decay. The lattice expansion arising from the defects accumulation is well-known phenomenon, however, the knowledge relating to the bulk expansion have not been obtained yet. In this work we prepared a nitride fuel pellet containing 
Cm as a main alpha-emitter, and obtained data on the relationship between lattice and bulk expansion as a function of storage duration at room temperature.
Cm-doped nitride induced by self-irradiation damage at room temperatureTakano, Masahide; Takaki, Seiya
no journal, ,
To understand behavior of the nitride fuel for minor actinide transmutation, lattice and bulk expansion of the nitride fuel pellet induced by 
self-irradiation at room temperature was investigated. Lattice parameter and dimensions of the (Pu,Cm,Zr)N nitride fuel pellet were repeatedly measured at room temperature as a function of storage period, and their relationship was considered. The lattice expansion followed the model equation well, and saturated to 0.49%, which is greater than that for CmN. The higher density of metallic elements in (Pu,Cm,Zr)N can be the main cause of the greater expansion. On the other hand, both the pellet diameter and height increased with the expansion curve similar to the lattice expansion, and saturated approximately to 0.5%. From this similarity we have found that the main cause of the bulk expansion is the lattice expansion due to the accumulation of Frenkel defects.
