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Journal Articles

Electron-tracking Compton camera imaging of technetium-95m

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

AA2018-0639.pdf:2.39MB

 Times Cited Count:0 Percentile:0.01(Multidisciplinary Sciences)

Imaging of $$^{95m}$$Tc radioisotope was conducted using an electron tracking-Compton camera (ETCC). $$^{95m}$$Tc emits 204, 582, and 835 keV $$gamma$$ rays, and was produced in the $$^{95}$$Mo(p,n)$$^{95m}$$Tc reaction with a $$^{95}$$Mo-enriched target. The recycling of the $$^{95}$$Mo-enriched molybdenum trioxide was investigated, and the recycled yield of $$^{95}$$Mo was achieved to be 70% - 90%. The images were obtained with each of the three $$gamma$$ rays. Results showed that the spatial resolution increases with increasing $$gamma$$-ray energy, and suggested that the ETCC with high-energy $$gamma$$-ray emitters such as $$^{95m}$$Tc is useful for the medical imaging of deep tissue and organs in the human body.

Journal Articles

Local structure analysis of ZrN, and Dy$$_{0.5}$$Zy$$_{0.5}$$N surrogate materials for fast reactor nitride fuel

Yoneda, 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 Dy$$_{0.5}$$Zr$$_{0.5}$$N, are fabricated for the purpose of investigating the crystal structure. Lattice parameters of Dy$$_{1-x}$$Zr$$_x$$N followed the Vegard's low, in spite of the large lattice mismatch ($$sim$$ 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.

Journal Articles

Atomic structure of ion tracks in Ceria

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:33 Percentile:95.98(Instruments & Instrumentation)

We have investigated atomic structure of ion tracks in CeO$$_{2}$$ 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.

Oral presentation

Atomic structure of ion tracks in fluorite structure oxides; Comparison with CeO$$_{2}$$ and ZrO$$_{2}$$

Takaki, Seiya

no journal, , 

Oxide ceramics with fluorite-structure have been studied as advanced nuclear application, so it is important to clarify the irradiation-induced microstructure. Especially, radiation damage induced by fission fragments with 70-100 MeV, induce high-density electronic excitation in the materials to result in forming cylindrical defect, so called ion track. This study aims to clarify and compare with the structure of ion tracks in CeO$$_{2}$$ and cubic ZrO$$_{2}$$ (YSZ) irradiated with swift heavy ions. 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. On the other hand, the size and the areal density of ion tracks in YSZ is smaller than those of CeO$$_{2}$$. The difference of ion tracks between CeO$$_{2}$$ 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.

Oral presentation

High density electronic excitation damage in fluorite structure oxides

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$$_{2}$$ and cubic ZrO$$_{2}$$ (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$$_{2}$$ 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$$_{2}$$. The difference of ion tracks between CeO$$_{2}$$ 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.

Oral presentation

Study on fabrication and property of nitride fuel for MA transmutation

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$$_{x}$$Zr$$_{1-x}$$N 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).

Oral presentation

Study on fabrication and property of nitride fuel for MA transmutation

Takaki, Seiya; Takano, Masahide

no journal, , 

Nitride fuel with ZrN or TiN matrix have been studied for transmutation of minor actinide (MA). These are supposed to be designed as solid solution or 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 the present study, we are aimed to clarify composition and temperature dependence of thermal conductivity and electric conductivity of Dy$$_{x}$$Zr$$_{1-x}$$N solid solution as MA surrogate nitride fuel in order to understand the thermal conduction mechanism of MA nitride fuel physically. In addition to, we introduce studies about pyrochemical compatibility between Dy$$_{x}$$Zr$$_{1-x}$$N (x=0, 0.3) 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).

Oral presentation

Interrelationship between thermal and electrical conductivity of (Dy,Zr)N solid solution simulating nitride fuel for MA transmutation

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 Dy$$_{x}$$Zr$$_{1-x}$$N solid solution as surrogate nitride fuel with MA in order to understand the dependence of the MA nitride fuel physically.

Oral presentation

Lattice expansion in ZrN and Dy$$_{0.3}$$Zr$$_{0.7}$$N irradiated by 200 MeV Xe ions

Takaki, 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 Dy$$_{0.3}$$Zr$$_{0.7}$$N increase with increasing ion fluence.

Oral presentation

Interrelationship between thermal and electrical conductivity of (Dy,Zr)N solid solution simulating nitride fuel

Takaki, Seiya; Takano, Masahide

no journal, , 

Nitride fuel with ZrN matrix have been studied for transmutation of minor actinide (MA). Although composition and temperature dependence of thermal conductivity for safety evaluation of the fuel have been studied with a little of MA, there is little information about physical explanation of thermal conduction for MA nitride fuel. In the present study, we are aimed to clarify composition and temperature dependence of thermal conductivity of Dy$$_{x}$$Zr$$_{1-x}$$N solid solution as surrogate nitride fuel with MA in order to understand the dependence of the MA nitride fuel physically. We found thermal conductivity by using laser flash methods and electrical contribution of thermal conductivity by measuring electrical conductivity, which revealed that electrical conductivity is responsible for thermal conductivity.

Oral presentation

Sintering experiments of Dy$$_{0.3}$$Zr$$_{0.7}$$N under a variety of milling conditions

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 (MA). 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 Dy$$_{0.3}$$Zr$$_{0.7}$$N 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 time (from 10 to 150 min) and employing either tungsten carbide (WC) or silicon nitride (Si$$_{3}$$N$$_{4}$$) milling cup and balls. The measurement of specific surface area clarifies that finer powder can be obtained with WC. However, the achieved densities of the sintered pellets, as a function of specific surface area of the milled powder, show that the denser pellets can be obtained with Si$$_{3}$$N$$_{4}$$ in spite of the smaller specific surface area. These results suggest that the distortion in the powder particles influences the behaviour of grain growth during the sintering.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 3; Lattice and bulk expansion of nitride fuel pellet by self-irradiation damage

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 $$^{244}$$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.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 4; Correlation of milling condition and sintered density of nitride fuel surrogate material

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 Dy$$_{0.3}$$Zr$$_{0.7}$$N 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$$_{3}$$N$$_{4}$$ in spite of the smaller specific surface area.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 5; Chemical compatibility between cladding and fuel surrogate materials

Harada, Makoto; Takaki, Seiya; Takano, Masahide

no journal, , 

T91 ferrite steel is considered as cladding of nitride fuels for transmutation of Minor Actinides. In this study, chemical compatibility between cladding and fuel surrogate materials was investigated in two different conditions. One condition was in over melting point of cladding and in short term. The other condition was in predicted operation temperature (773K, 923K, 1023K) and in long term. Surrogate fuel materials were ZrN and Dy$$_{0.3}$$Zr$$_{0.7}$$N, and cladding materials were T91 and SUS316L steel. After the reaction tests, cross sections of specimens were examined by SEM/EDS to characterize the extent of reaction and diffusion. In the melting test, reaction layers didn't exist, but some particles of surrogate fuel materials were observed in cladding layer. In predicted operation temperature test, all specimen had no reaction layers. In conclusion, cladding and fuel surrogate materials have excellent chemical compatibility.

Oral presentation

Lattice and bulk expansion of $$^{244}$$Cm-doped nitride induced by self-irradiation damage at room temperature

Takano, 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 $$alpha$$ 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.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 4; Correlation of milling condition and sintered density of nitride fuel surrogate material

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, Dy$$_{0.3}$$Zr$$_{0.7}$$N 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.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 10; Application of pore former for density control in surrogate fuel sintering process

Takaki, Seiya; Takano, Masahide

no journal, , 

In order to obtain fundamental knowledge for controlling sintered density with pore former regarding nitride fuel for MA transmutation, various types of polymer particles are added to Dy$$_{0.3}$$Zr$$_{0.7}$$N and they are sintered. We report the results of sintering test added with pore former for Dy$$_{0.3}$$Zr$$_{0.7}$$N.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 14; Dimensional recovery of He-accumulated nitride pellet containing Cm by annealing

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$$^{circ}$$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 1300$$^{circ}$$C, the nitride pellet still had expansion value of 0.6%, that should be taken into account when designing the pellet-cladding gap.

Oral presentation

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 16; Application of pore former for density control of TRU nitride pellets

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 Dy$$_{0.3}$$Zr$$_{0.7}$$N as surrogate nitride fuel.

Oral presentation

Application of pore former for density control in (Pu,Zr)N sintering process

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 Dy$$_{0.3}$$Zr$$_{0.7}$$N as surrogate nitride fuel.

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