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1.
Jun Koarashi Hiroki Fujita Mika Nagaoka 《Journal of Nuclear Science and Technology》2016,53(4):546-553
Quantitative evaluation of the atmospheric discharge of radiocarbon (14C) is of primary importance for accurately assessing the radioecological impact of the operation of the Tokai reprocessing plant (TRP). However, monitoring the atmospheric 14C discharge was not conducted at the TRP prior to October 1991. The main purpose of this study was to establish the chronology of atmospheric 14C discharges for the entire operation period (1977–2014). We found a strong correlation between the 14C discharge and spent fuel reprocessing data obtained after October 1991; we used this correlation to estimate the monthly 14C discharges in the 1977–1991 period. The total amount of atmospheric 14C discharge was estimated at 7741 ± 217 GBq for the entire period, with the largest annual discharge of 978 GBq in 1992. Tree-ring 14C analysis and model calculations using the established discharges were conducted to assess the excess 14C concentrations around the TRP in the past. The results suggested that the excess 14C concentrations were <45 Bq kg?1 C and the annual effective dose via the atmosphere–rice ingestion pathway was as low as 1.2 μSv y?1, indicating no significant radioecological impact of atmospheric 14C discharges from the TRP. 相似文献
2.
Wataru Nitta Keisuke Isogai Clemens Schlosser 《Journal of Nuclear Science and Technology》2013,50(5):712-719
Atmospheric 85Kr and 133Xe activity concentrations were determined from weekly air samples collected at Sapporo, Akita and Chiba, Japan, throughout 2011. The results demonstrated that the Fukushima Dai-ichi Nuclear Power Plant accident in early March 2011 resulted in high 133Xe activity concentrations as well as elevated levels of 85Kr activity; there was a striking increase in the concentrations of both isotopes over the week running from 14 to 22 March as the radioactive plume released from the plant was captured. At Chiba, following the accident, the 85Kr activity concentration increased from 1.38 to 17.7 Bq/m3, while the 133Xe levels increased from below the minimum detectable concentration (MDC ≤ 1.9 × 10?3 Bq/m3) to 1.3 × 103 Bq/m3. Conversely, at Sapporo and Akita, high 85Kr activity concentrations were not observed, due to differences in air transportation mechanisms based on wind directions. Duplicate samples were collected at Chiba to allow the simultaneous analyses of 85Kr and 133Xe at the Japan Chemical Analysis Center and the Bundesamt für Strahlenschutz in Germany and the results were in good agreement. The external effective radiation doses resulting from 85Kr and 133Xe releases following the accident were estimated to be approximately 7.0 × 10?3 and 1.3 μSv, respectively, based on the activity concentrations of these nuclides from March to June in 2011 at Chiba. 相似文献
3.
Masayo Inagaki Taeko Koga Hiroshige Morishima Shojiro Kimura Masatoshi Ohta 《Journal of Nuclear Science and Technology》2013,50(5):531-534
The concentrations of 222Rn existing in air have been studied by using a convenient and highly sensitive Pico-rad detector system at Masutomi spa in Yamanashi Prefecture, Japan. The measurements in air were carried out indoors and outdoors during the winter of 2000 and the summers of 1999 and 2005. The concentrations of 222Rn in spring water in this region were measured by the liquid scintillation method. The concentrations of natural radionuclides contained in soils surrounding spa areas were also examined by means of the γ-ray energy spectrometry technique using a Ge diode detector to investigate the correlation between the radionuclides contents and 222Rn concentrations in air at each point of interest. The atmospheric 222Rn concentrations in these areas were high, ranging from 5 Bq/m3 to 2676 Bq/m3. The radon concentration at each hotel was high in the order of the bath room, the dressing room, the lobby, and the outdoor area near the hotel, with averages and standard deviations of the concentration of 441 ± 79 Bq/m3, 351 ± 283 Bq/m3, 121 ± 5 Bq/m3, and 23 ± 1 Bq/m3, respectively. The source of 222Rn in the air in the bath room is more likely to be the spring water than the soil. The spring water plays carries the radon to the atmosphere. Our measurements indicated that the 222Rn concentration in the air was affected by the 222Rn concentration in spring water rather than that in soil. 相似文献
4.
《Journal of Nuclear Science and Technology》2013,50(11):1474-1480
The distribution of 3H in the atmosphere, vegetations and soil water was observed in the vicinity of Tokai reprocessing plant (TRP) over the period 1990–2004. The annual means of the atmospheric HTO and HT concentrations were in the range of 12–40 mBqm?3 with a significant seasonal variation and 14–51 mBqm?3 with no seasonal variation, respectively. Long-term atmospheric dilution factors, defined as the annual mean of the atmospheric HTO concentration divided by the discharge rate of HTO from the TRP, were estimated to be 10?8–10?6 sm?3. The atmospheric HTO concentrations decreased with distance from the TRP, falling to the current background level in Japan at 5 km off-site. The HTO concentrations observed were compared with those calculated by a simple mathematical model with input data of the monthly 3H discharge rates and actual meteorological conditions. The calculations were correlated well with the observations even for only a little HTO-elevated situation, considering the naturally occurring 3H level in atmospheric vapor around the TRP. Tritium concentrations in vegetation and soil water samples were roughly the same as the atmospheric HTO concentrations, suggesting the rapid equilibrium of 3H concentrations in the atmosphere-soil-vegetation system around the TRP. 相似文献
5.
《Journal of Nuclear Science and Technology》2013,50(11):1215-1227
The tritium concentration in the hydrogen product in Japan's future very high temperature gas-cooled reactor (VHTR) system coupled with a thermochemical water-splitting iodine-sulfur (IS) process (VHTRIS system), named GTHTR300C, was estimated by numerical analysis. The tritium concentration in the hydrogen product significantly depended on undetermined parameters, i.e., the permeabilities of a SO3 decomposer and a H2SO4vaporizer made of SiC. Thus, the estimated tritium concentration in the hydrogen product for the conservative analytical condition ranged from 3.4 × 10?3 Bq/cm3 at STP (38 Bq/g-H2) to 0.18 Bq/cm3 at STP (2,000 Bq/g-H2). By considering the tritium retained by core graphite and the reduction in permeation rate by an oxide film on the heat transfer tube of the IHX and the HI decomposer, the tritium concentration in the hydrogen product decreased to the range from 3.3 × 10?5 Bq/cm3 at STP (0.36 Bq/g-H2) to 5.6 × 10?3 Bq/cm3 at STP (63 Bq/g-H2), which were smaller than those for the conservative analytical condition by factors of about 3.2 × 10?2 and 9.6 × 10?3, respectively. The effectof the helium flow rate in the helium purification system on the tritium concentration in the hydrogen product was also evaluated. 相似文献
6.
7.
Takashi Kodama Hiroshi Kinuhata Yuki Shibata Mikio Kumagai Kazunori Suzuki Shin-Itiro Hayashi 《Journal of Nuclear Science and Technology》2020,57(9):1101-1110
ABSTRACT NO2 and NO generated during a boiling and drying accident, which affects the release of volatilized radioactive Ru into the atmosphere, were examined using various samples including simulated high-level liquid waste and a thermogravimetric analyzer. NO2 and NO in the gas flowing out of the analyzer were measured separately using a NOx analyzer equipped with NO2 and NO sensors. The samples were heated to 600°C at constant heating rates of mainly 0.2 and 1°C min?1 that was adopted taking into account the decay heat of high-level liquid waste. It was found that under 180°C some nitrates in the liquid waste mainly separated their nitrate groups as HNO3 without generating NOx (a mixture of NO and NO2) and above 300°C the residual HNO3 in the waste participated in thermal decomposition generating NOx. The generation rates of NO2 and NO were obtained as a function of time using Arrhenius type equations, and the O2 rate was derived from these equations using the stoichiometry of the reactions that generate NO2, NO, and O2. 相似文献
8.
Daniel Murnick Ozgur Dogru Erhan Ilkmen 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(7-8):708-711
A new ultra sensitive laser-based analytical technique, intracavity optogalvanic spectroscopy (ICOGS), allowing extremely high sensitivity for detection of 14C-labeled carbon dioxide has recently been demonstrated. Capable of replacing accelerator mass spectrometers (AMS) for many applications, the technique quantifies zeptomoles of 14C in sub micromole CO2 samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity, and detection via impedance variations, limits of detection near 10?15 14C/12C ratios have been obtained with theoretical limits much lower. Using a 15 W 14CO2 laser, a linear calibration with samples from 5 × 10?15 to >1.5 × 10?12 in 14C/12C ratios, as determined by AMS, was demonstrated. Calibration becomes non-linear over larger concentration ranges due to interactions between CO2 and buffer gas, laser saturation effects and changes in equilibration time constants. The instrument is small (table top), low maintenance and can be coupled to GC or LC input. The method can also be applied to detection of other trace entities. Possible applications include microdosing studies in drug development, individualized sub-therapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon. 相似文献
9.
Takuya Kobayashi Haruyasu Nagai Masamichi Chino Hideyuki Kawamura 《Journal of Nuclear Science and Technology》2013,50(3):255-264
The source term of the atmospheric release of 131I and 137Cs due to the Fukushima Dai-ichi Nuclear Power Plant accident estimated by previous studies was validated and refined by coupling atmospheric and oceanic dispersion simulations with observed 134Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for 134Cs and 137Cs, the sea surface concentration of 134Cs was calculated using the previously estimated source term and was compared with measurement data. The release rate of 137Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of 131I was refined to follow the radioactivity ratio of 137Cs. As a result, the total amounts of 131I and 137Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.0 × 1017 and 1.3 × 1016 Bq, respectively. 相似文献
10.
Rong Tan Huang 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(24):3212-3216
The temperature effect on the microstructure of the N+-ion implantation-induced Si3N4 buried layer was investigated. The underlying silicon nitride layers were formed in a Si (1 1 1) wafer after implantation of 50 keV nitrogen ions (fluence: 1 × 1017, 2 × 1017 and 5 × 1017 ions/cm2). It was observed that a continuous amorphous layer of about 200 nm thickness was formed in all implanted samples due to the irradiation damage. After 30 min annealing at 900 °C, poly-crystalline Si3N4 products were found by TEM examination in the specimen implanted with 5 × 1017 ions/cm2 dose. In the case of annealing at 1200 °C a continuous single-crystalline α-Si3N4 buried layer was formed indicating that the amorphous layer in the implanted samples could be transformed into three successive layers, which are amorphous SiO2, single-crystal α-Si3N4 and retained defects from surface to inner substrate, respectively. 相似文献
11.
Toyohiko Yano Hiroshi Konishi Saishun Yamazaki Mohd Idzat bin Idris Katsumi Yoshida 《Journal of Nuclear Science and Technology》2017,54(8):891-898
SiC fiber-reinforced SiC matrix composites (SiCf/SiC) are considered as one of the candidates for blanket materials in future fusion reactors and as an advanced fuel cladding material for next-generation fission reactors. Generally, the densification of SiC needs sintering additives and oxides such as Al2O3, Y2O3, and yttrium-aluminum garnet (YAG, Y3Al5O12), which are frequently added to SiC. However, the effects of neutron irradiation on sintering additives are still unclear. In this study, we performed the neutron irradiation of Al2O3, Y2O3, and YAG at fluences up to 2.0–2.5 × 1024 n/m2 (E > 0.1 MeV) at 60–90 °C. The isochronal recovery of the macroscopic volume of Al2O3 against annealing temperature showed smooth and continuous shrinkage at a temperature of up to 1200 °C, and the volume slightly increased above that temperature. In contrast, the volume of Y2O3 showed quick shrinkage at the low temperature range, and slower and smooth recovery was observed up to ~1100 °C. In the case of YAG, the recovery of volume occurred in a step-wise manner at 600–750 °C, and continuous shrinkage occurred at temperatures lower and higher than that temperature range. The activation energies for the macroscopic volume recoveries of three oxides were obtained from the Arrhenius plots of the rate coefficients. Two-stage recovery was observed for Al2O3, whereas more complicated recovery processes were suggested for Y2O3 and YAG. 相似文献
12.
Tadahiro Kin Takaya Kawagoe Shouhei Araki Yukinobu Watanabe 《Journal of Nuclear Science and Technology》2017,54(10):1123-1130
We conducted a feasibility study for producing a high-purity medical radioisotope 64Cu from natural zinc with accelerator-based neutrons. 64Cu isotopes were produced via the 64Zn(n,p) reaction. The accelerator-based neutrons were generated via the C(d,n) reaction using low-energy deuterons of 9 and 12 MeV on a 1-mm-thick carbon target. First, the production purity was estimated using the evaluated nuclear data library JENDL-4.0 and our previously measured thick target neutron yield. We found that even when natural zinc was used as the starting material, significantly high-purity 64Cu could be obtained. Next, irradiation experiments for producing 64Cu using natural zinc were conducted at Kyushu University Tandem Laboratory, with the amounts of 64Cu isotopes and other gamma-emission nuclides measured by a high-purity germanium detector. As a result, high-purity 64Cu isotopes of 1.11(49) × 100 and 3.70 (17) × 100 Bq/g/μC were produced with incident deuteron energies of 9 and 12 MeV, respectively. 相似文献
13.
《Journal of Nuclear Science and Technology》2013,50(10):445-451
The oxidation of UO2 was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO2 to U3O UO7 significantly influenced the rate of the oxidation of the second stage from U3O7 to U3 O8. The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These findings suggest the existence of a close connection between the rate of formation of the U3O7 phase and the rate of the subsequent oxidation of this phase: A slow formation of U3O7 would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U3O7 at 200°C: The increase of annealing time prolonged the induction stage. The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y/)=(1/2.303)kntn . The time exponent n in this equation varied in the range of 1.0~2.5, and the rate constant k of 1.15×10?4~2.04 ×10?1 min?1, depending on the experimental conditions. 相似文献
14.
本文采用涂布法制备了一系列H310BO3/ZnS(Ag)闪烁体转换屏样品,对其成分配比进行了优化。结果表明,最佳的H310BO3/ZnS(Ag)质量比在1∶6~1∶7之间,最佳的黏合剂用量为总质量的25%。利用中子照相设备对转换屏的发光均匀性进行了成像分析,结果显示光输出非常均匀;对楔形镉条进行中子成像,并采用调制传递函数(modulation transfer function,MTF)方法计算了系统分辨率,结果显示,在MTF值为0.1时,对于厚度分别为270(11)、350(14)、404(9)及505(15)μm的转换屏,其相应的系统空间分辨率分别为255.6、315.9、371.0和471.3 μm。 相似文献
15.
Ying Zheng Ken Kurosaki Yuji Ohishi Hiroaki Muta Shinsuke Yamanaka 《Journal of Nuclear Science and Technology》2013,50(5):526-530
Y6UO12 was synthesized by solid-state reactions of Y2O3 and U3O8. The high-density pellet of Y6UO12 was prepared by the spark plasma sintering followed by heat treatment in air for oxygen supplementation. The thermal conductivity (κ) was evaluated using the laser flash method from room temperature to 1173 K. The κ of Y6UO12 decreased with increasing temperature in the whole temperature range, indicating that the phonon contribution was predominant. The room temperature κ value of Y6UO12 was 4.90 Wm?1K?1. The magnitude relationship of κ among Y6UO12, Y6WO12, and Yb6WO12, i.e. κ of Yb6WO12 < κ of Y6UO12 < κ of Y6WO12, was discussed based on the general lattice thermal conductivity theory. 相似文献
16.
《Journal of Nuclear Science and Technology》2013,50(5):447-450
The 17O(n, a)14C cross section has been evaluated for incident neutron energies from 10?5eV to 20MeV for accurate calculation on the 14C production in nuclear reactors. Evaluation was based on the single-level Breit-Wigner formula for the thermal to resonance energy regions. In the higher energy region, a multi-step evaporation model code PEGASUS was used, and the results were normalized using the 16O(n, a) cross section ratio of JENDL-3 evaluation to PEGASUS calculation. Results are given in tabular and graphical forms, and also as one-group cross sections using typical BWR, PWR and FBR spectra of ORIGEN-2. 相似文献
17.
《Journal of Nuclear Science and Technology》2013,50(10):720-722
The potential energy curves of LiHe+, BeHHe+ and FHe+ in the ground state are calculated with a scale factor optimized STO-6G basis set, and these potential curves are compared with those of HHe+, CH3He+, NH2He+ and OHHe+ already reported. In the T→He+ β-decay, ground state daughter ions HHe+, LiHe+ and BeHHe+ are found to be bound, whereas CH3He+, NH2He+, OHHe+ and FHe+ ions dissociate into a He atom and residual fragments. 相似文献
18.
Bhushan Dhabekar S.N. MenonE. Alagu Raja A.K. BakshiA.K. Singh M.P. ChougaonkarY.S. Mayya 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(16):1844-1848
Optically Stimulated Luminescence (OSL) technique has emerged as a serious competitor to Thermally Stimulated Luminescence (TSL) technique in various dosimetric applications, especially after the development of crystalline alumina (Al2O3:C) doped with carbon. Since then, several attempts are being made to develop other possible materials for OSL based dosimetric applications. Efforts conducted in our laboratory in this direction have led to the development of a new phosphor, Lithium Magnesium Phosphate doped with terbium and boron (LiMgPO4:Tb,B). This phosphor is prepared by solid-state diffusion method involving conventional air furnaces with operating temperature 1000 °C and easily amenable to large scale production without compromising primary dosimetric advantages. In this work we present some of the dosimetric OSL characteristics of this phosphor. The phosphor exhibits a main TSL peak at 250 °C. The phosphor also emits OSL, when the irradiated phosphor is stimulated with 470 nm light with the OSL sensitivity 1.3 times that of commercially available Al2O3:C. Photoluminescence (PL) emission spectrum consists of sharp lines characteristics of Tb3+ emission. The OSL discs made out of this phosphor are reusable up to at least 50 cycles, the phosphor exhibits dose linearity up to 1 kGy. Minimum detectable dose is found to be 20 μGy and fading of the OSL signal is found to be about 16% in four days, after which the OSL signal stabilizes. 相似文献
19.
T. Sonoda M. Kinoshita M. Sataka K. Yasunaga 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2010,268(19):3277-3281
In order to understand the properties of ion tracks and the microstructural evolution under accumulation of ion tracks in UO2, 100 MeV Zr10+ and 210 MeV Xe14+ ions irradiation examinations have been done at a tandem accelerator facility of JAEA-Tokai, and it has been observed the microstructure by means of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) in CRIEPI.Comparison of the diameter of ion tracks between UO2 and CeO2 under irradiation with 100 MeV Zr10+ and 210 MeV Xe14+ ions at room temperature clarify that the sensitivity on high density electronic excitation of UO2 is much less than that of CeO2. By the cross-sectional observation of UO2 under irradiation with 210 MeV Xe14+ ions at 300 °C, elliptical changes of fabricated pores that exist till ∼6 μm depth and the formation of dislocations have been observed in the ion fluence over 5 × 1014 ions/cm2. The drastic changes of surface morphology and inner structure in UO2 indicate that the overlapping of ion tracks will cause the point defects, enhance the diffusion of point defects and dislocations, and form the sub-grains at relatively low temperature. 相似文献
20.
《Journal of Nuclear Science and Technology》2013,50(4):585-590
A soft-type neutron-shielding resin has been developed by improving an existing hard-type neutronshielding material using the epoxy-based resin as an additional shielding material. A flexible heat-resistant neutron-shielding material has been developed, which consists of a new polymer-based resin with boron. The neutron shielding performance of the developed flexible heat-resistant resin with the 252Cf neutron source is almost the same as that of polyethylene. The outgases of H, H2, NH4, H2O, CO, O2, C4H10, and CO2 from the developed resin have been measured at high temperature (up to 250°C) by thermal desorption spectroscopy methods. The soft-type resin and the newly developed heat-resistant resin will be applied to prevent the effects of neutron streaming and to control the movement of a vibrated pipe as the seal material around the plumbing in the future fast reactor and innovative fission reactor. 相似文献