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Harjo, S.
Isotope News, (793), p.13 - 16, 2024/06
no abstracts in English
Uchibori, Akihiro; Okano, Yasushi
Isotope News, (793), p.32 - 35, 2024/06
The design of a containment vessel in a sodium-cooled fast reactor was optimized from simulation on the hypothetical severe accident including sodium leakage and combustion. The simulation method is one of the base technologies of the design optimization system, ARKADIA. The simulation was performed on the different design conditions including volume of the containment vessel and the safety equipment as optimization parameters. The iterative simulation successfully found that the safety under this accident was kept even in the downsized containment vessel by selecting an effective safety equipment. This study demonstrated that the developed method has basic capability for design optimization in ARKADIA.
, 
, and X-ray spectrum analysisOshima, Masumi*; Goto, Jun*; Hayakawa, Takehito*; Asai, Masato; Kin, Tadahiro*; Shinohara, Hirofumi*
Isotope News, (790), p.19 - 23, 2023/12
When analyzing samples that contain many radionuclides at various concentrations, such as radioactive waste or fuel debris, it is difficult to apply general spectrum analysis methods and is necessary to chemically separate each nuclide before quantifying it. The chemical separation is especially essential for analysis using a liquid scintillation counter (LSC). In this report, the authors explain the newly developed spectral determination method (SDM) in which the entire spectrum is fitted to quantify radioactivity of nuclides mixed in a sample. By applying the SDM to - and X-ray spectrum measured by LSC and -ray spectrum measured by Ge detector simultaneously, the authors demonstrated that radioactivity of 40 radionuclides mixed in a sample at concentrations varying by two orders could be quantified, which is useful to simplify chemical separation process in radionuclide quantification.
Yamaguchi, Akiko; Okumura, Masahiko; Takahashi, Yoshio*
Isotope News, (789), p.20 - 23, 2023/10
Radium is a radioactive element produced from uranium and thorium and is important for environmental contamination issues around uranium mines and for geological disposal. In addition, radium is used in radiometric dating and cancer therapy, making it important not only in environmental chemistry but also in many other fields, including geochemistry and nuclear medicine. However, because radium is a radioactive element with no stable isotopes, spectroscopic measurement of radium is difficult, and little information at the molecular level has been obtained so far. In this study, we have clarified the molecular-level information of hydrated radium for the first time in the world by combining extended X-ray absorption fine structure (EXAFS) measurements and first-principles molecular dynamics simulations.
Furuta, Takuya
Isotope News, (787), p.20 - 23, 2023/06
Carbon ion radiotherapy has an advantage over conventional radiotherapy such that its superior dose concentration on the tumor helps to reduce unwanted dose to surrounding normal tissues. Nevertheless, a little dose to normal tissues, which is a potential risk of secondary cancer, is still unavoidable. In the current dose assessment, however, only assessment around target volume is performed for the tumor control and prevention of acute radiation injury of fatal organs. We therefore developed a system called RT-PHITS for CIRT to reproduce the carbon ion radiotherapy including the production and transport of secondary particles based on treatment planning data using PHITS. Using this system, whole-body dose assessment of patients in the past carbon ion radiotherapy can be performed. By comparing the dose assessment to the epidemiologic records of the patients, the relation between dose exposure of non-target organs and incidence of side effects such as secondary cancer will be elucidated.
Tsubota, Yoichi
Isotope News, (787), p.28 - 31, 2023/06
In the fuel debris retrieval process during the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), radioactive particulates are generated in the primary containment vessel (PCV). Particulates containing 
nuclides (-aerosols), which have a particularly large internal exposure effect, are important to be monitored in addition to confinement measures in the PCV. The research group of the Japan Atomic Energy Agency (JAEA) summarized the four requirements for measuring -aerosols in the harsh environment of the 1F-PCV as follows: "reliable operation in a high humidity environment", "measurement of -aerosols without using filter paper", "measurement of high concentration of -aerosols", and "selective measurement of -aerosols". The IAAM was developed as an instrument that satisfies these four criteria. The IAAM was developed as an "in-situ" -aerosol measurement device that combines air heating, a flat-type flow path, direct measurement of -aerosol, usage of multi-channel photomultiplier tube, and an optimized scintillator thickness. Performance verification tests have demonstrated that the IAAM can be used for real-time measurement of -aerosol concentration in air, and that it can measure more than 30 times of -aerosol concentration expected in the 1F-PCV. In the future, we will continue to verify the measurement of -aerosol concentration at various sites and aim to apply the system to such sites.
Miyamoto, Yutaka; Suzuki, Daisuke; Tomita, Ryohei; Tomita, Jumpei; Yasuda, Kenichiro
Isotope News, (786), p.22 - 25, 2023/04
no abstracts in English
Matsuda, Shohei; Yokoyama, Keiichi
Isotope News, (786), p.6 - 9, 2023/04
no abstracts in English
Yoshitomi, Hiroshi
Isotope News, (786), p.26 - 29, 2023/04
no abstracts in English
Nishio, Katsuhisa
Isotope News, (785), p.36 - 40, 2023/02
no abstracts in English
Nakayama, Hiromasa; Onodera, Naoyuki; Satoh, Daiki
Isotope News, (785), p.20 - 23, 2023/02
We developed the local-scale high-resolution atmospheric dispersion and dose assessment system (LHADDAS) for safety and consequence assessment of nuclear facilities and emergency response to nuclear accidents or deliberate releases of radioactive materials in built-up urban areas. This system comprises three parts, namely, preprocessing of input files, main calculation by a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) or a real-time urban dispersion simulation model based on a lattice Boltzmann method (CityLBM), and postprocessing of dose calculation by a simulation code powered by lattice dose-response functions (SIBYL). LHADDAS has a broad utility and performs excellently in (1) simulating turbulent flows, plume dispersion, and dry deposition under realistic meteorological conditions; (2) simulating real-time tracer dispersion using a locally mesh-refined lattice Boltzmann method; and (3) estimating the air dose rates of radionuclides from air concentrations and surface deposition in consideration of the influence of individual buildings and structures. This system is promising for use in safety assessment of nuclear facilities (as an alternative to wind tunnel experiments), detailed pre/post-analyses of local-scale radioactive plume dispersion in case of nuclear accidents, and quick response to emergency situations resulting from deliberate release of radioactive materials by terrorist attacks in central urban district areas.
Ogawa, Tatsuhiko; Hirata, Yuho; Matsuya, Yusuke; Kai, Takeshi
Isotope News, (784), p.13 - 16, 2022/12
Track-structure calculation, a method to simulate every secondary electron production reaction explicitly, has been extensively used as an important techniques in various fields such as radiation biology, material irradiation effect, and radiation detection. However, it requires the dielectric function of the target materials, which is not well known except for liquid water. Therefore we developed a model to perform track-structure calculation based on a systematic formula of secondary electron production cross section and that of stopping power. The model can therefore perform track-structure calculation regardless of the availability of dielectric function measurement data. Stopping range, and energy deposition radial distribution calculated by this model agreed well with the earlier experimental data and calculation by precedent codes. The lineal energy in tissue-equivalent gas calculated by this model agreed with measurement data taken from literature, showing distinct difference from that in liquid water. This model was implemented to PHITS Ver3.25, the general-purpose radiation transport simulation code of JAEA, being distributed to users as the first track-structure calculation model applicable to arbitrary materials available in general-purpose transport code.
Ota, Masakazu; Koarashi, Jun
Isotope News, (784), p.28 - 31, 2022/12
In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with 
Cs. However, Cs transfer processes determining the tree contamination (particularly for stem wood, a prominent commercial resource) remain insufficiently understood. We propose a model (SOLVEG-R) for simulating dynamic behavior of Cs in a forest tree-litter-soil system and applied it to contaminated forests of cedar plantation and natural oak stand in Fukushima to elucidate relative impact of distinct Cs transfer processes determining the tree contamination. The transfer of Cs to the trees occurred mostly (
99%) through surface uptake of Cs trapped by needles and bark during the fallout. Root uptake of soil Cs was several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, internal contamination of the trees proceeded through an enduring recycling (translocation) of Cs absorbed on the tree surface. A significant surface uptake of Cs through bark was suggested, contributing to 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining uptake occurred at needles) of the total uptake by the trees. It was suggested that the activity concentration of Cs in stem wood of the trees at these sites are currently (as of 2021) decreasing by 3% per year, mainly through radioactive decay of Cs and partly through dilution effect from tree growth.
Oka, Toshitaka
Isotope News, (784), p.43 - 44, 2022/12
We participated in Young Scientists Project Career Paths for Researchers held at the 59th Isotope and Radiation Research Presentation Meeting, where we heard from four lecturers and discussed how to encourage students to enter doctoral programs.
Mochizuki, Akihito; Ishii, Eiichi
Isotope News, (784), p.23 - 27, 2022/12
no abstracts in English
Sumita, Takehiro; Ikeda, Atsushi
Isotope News, (783), p.28 - 32, 2022/10
no abstracts in English
Kyono, Atsushi*; Yamamoto, Genichiro*; Yoneda, Yasuhiro; Okada, Satoru*
Isotope News, (783), p.23 - 27, 2022/10
Mineral traps are attracting attention as an underground storage method for carbon dioxide. Carbon dioxide laden groundwater reacts with basalt to form magnesite. The formed magnesium carbonate phase varies in many ways, but we tried to clarify the structure because all of them pass through amorphous magnesium carbonate. Pair distribution function using high-energy X-ray diffraction revealed that amorphous magnesium carbonate has a structure similar to that of hydromagnesite. It can be said that it is a safe sequestration method as a carbon dioxide storage technology.
Iwamoto, Osamu
Isotope News, (783), p.2 - 5, 2022/10
no abstracts in English
Sato, Tomonori; Hata, Kuniki; Kaji, Yoshiyuki; Taguchi, Mitsumasa*; Seito, Hajime*; Inoue, Hiroyuki*; Tada, Eiji*; Abe, Hiroshi*; Akiyama, Eiji*; Suzuki, Shunichi*
Isotope News, (782), p.40 - 44, 2022/08
The stagnant water in the reactor building at Fukushima Daiichi Nuclear Power Station (1F) is exposed to the radiation from fuel debris and radioactive species. This water contains much amounts of impurities from the seawater which was injected in the emergency cooling. The impurities will affect the radiolysis and corrosive conditions in the water under irradiation. So, the water radiolysis data, corrosion data of steels under irradiations, and the evaluated potential impacts of corrosion in the decommissioning process of 1F are arranged as the database for corrosion under irradiation. This paper introduces the outline of this database.
Sato, Yuki
Isotope News, (781), p.19 - 23, 2022/06
no abstracts in English
