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

https://doi.org/10.1371/journal.pone.0208909

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.

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

https://doi.org/10.1016/j.nimb.2013.10.077

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.

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 DyZrN and they are sintered. We report the results of sintering test added with pore former for DyZrN.

Application of pore former for density control of TRU nitride pellets

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.

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 DyZrN 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 DyZrN (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).

Lattice expansion in ZrN and DyZrN 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 DyZrN increase with increasing ion fluence.

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 800C 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.

High density electronic excitation damage in nitride ceramics

Takaki, Seiya; Ishikawa, Norito; Mohammad Majidur, R.*; 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.

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 DyZrN 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.

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 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.