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JAEA Reports

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2020 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2021-025, 159 Pages, 2022/01

JAEA-Technology-2021-025.pdf:46.66MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2020. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring for classifying the importance of measurement points, a score map was created for Fukushima Prefecture and the 80 km zone from the FDNPS, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2020 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.

JAEA Reports

Investigations on distribution of radioactive substances owing to the Fukushima Dai-ichi Nuclear Power Station Accident in the fiscal year 2019 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2020-014, 158 Pages, 2020/12

JAEA-Technology-2020-014.pdf:23.82MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2019. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring to classify the importance of measurement points, we created a score map of Fukushima Prefecture and that within 80 km from the FDNPS based on the "score" method developed in 2018. The way of monitoring radioactive materials in land area was examined and the representativeness of monitoring points was proposed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2019 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.

Journal Articles

Vertical distribution of $$^{90}$$Sr and $$^{137}$$Cs in soils near the Fukushima Daiichi Nuclear Power Station

Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso; Kobayashi, Taishi*; Iijima, Kazuki

Journal of Radioanalytical and Nuclear Chemistry, 326(1), p.303 - 314, 2020/10

 Times Cited Count:1 Percentile:39.17(Chemistry, Analytical)

JAEA Reports

Investigations on distribution of radioactive substances owing to the FDNPP accident in the fiscal year 2018 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2019-019, 135 Pages, 2020/03

JAEA-Technology-2019-019.pdf:22.01MB

After the accident at TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS), distribution situation survey on radioactive materials have been conducted with financially supported by the Ministry of Education, Culture, Sports, Science and Technology (later the Nuclear Regulatory Agency) from June 2011 to FY2018. Results obtained in the project in FY2018 are presented in this report. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of air dose rate were analyzed. Regarding radiocesium deposition in the soil, depth profile survey in the soil and in-situ measurement were performed. Based on these measurement results, effective half-life of the air dose rate and the deposition were evaluated. Considering radiation monitoring data obtained in previous surveys and the installation positions of existing monitoring posts, we tried to make the "score" of the importance of measurement points. Using the Bayesian hierarchical modeling approach, we obtained a map that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys for the entire region within 80 km from the FDNPS. The measurement results for FY2018 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and environmental sample analysis owing to the comprehensive radiation monitoring plan were carried out.

Journal Articles

Depth profiles of radioactive cesium in soil using a scraper plate over a wide area surrounding the Fukushima Dai-ichi Nuclear Power Plant, Japan

Matsuda, Norihiro; Mikami, Satoshi; Shimoura, Susumu*; Takahashi, Junko*; Nakano, Masakazu; Shimada, Kiyotaka*; Uno, Kiichiro; Hagiwara, Shigetomo; Saito, Kimiaki

Journal of Environmental Radioactivity, 139, p.427 - 434, 2015/01

 Times Cited Count:86 Percentile:96.08(Environmental Sciences)

Journal Articles

3-45MeV/u ion beam dosimetry using thin film dosimeters

Kojima, Takuji; Sunaga, Hiromi; Takizawa, Haruki*; Hanaya, Hiroaki; Tachibana, Hiroyuki*

Radiation Physics and Chemistry, 68(6), p.975 - 980, 2003/12

 Times Cited Count:2 Percentile:19.75(Chemistry, Physical)

Four kinds of film dosimeters well-characterized for low LET radiations were applied to 3-45 MeV/u ions. The dose responses relative to those for low LET radiations are almost one up to about 10 MeV/(mg/cm$$^{2}$$) and gradually become smaller with increase of the stopping power. Overall uncertainty in ion beam dosimetry using these characterized dosimeters is better than $$pm$$5%(1$$sigma$$) including uncertainty in fluence measurement($$pm$$2%). Lateral and depth dose profile measurements were achievable using characterized Gafchromic dosimeters with the spatial resolution of better than 1 and 10 $$mu$$m, respectively.

Journal Articles

Power profile evaluation of the JCO precipitation vessel based on the record of the $$gamma$$-ray monitor

Tonoike, Kotaro; Nakamura, Takemi*; Yamane, Yuichi; Miyoshi, Yoshinori

Nuclear Technology, 143(3), p.364 - 372, 2003/09

 Times Cited Count:2 Percentile:19.75(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Measurements of power profile in TRACY supercritical experiment by detecting epithermal neutrons

Nakajima, Ken; Yanagisawa, Hiroshi; Miyoshi, Yoshinori

JAERI-Tech 2003-028, 31 Pages, 2003/03

JAERI-Tech-2003-028.pdf:1.38MB

We have tried to measure the power profile in the TRACY supercritical experiment with high accuracy by detecting epithermal neutrons. In order to measure the epithermal neutrons, a cadmium covered $$^{235}$$U fission chamber was used, and polyethylene, a neutron moderator, was set inside the cadmium to enhance the neutron detection efficiency. In addition, a lead shield was used to reduce the noise current due to gamma-rays. The measured results were compared with the ones using a thermal neutron detector, and it was found that the time delay effect in the thermal neutron detection, which was caused by the flight time of neutrons to reach the detector, distorted the power profile and reduced its peak value. The reduction ratio of peak power was about 4% for the relatively slow power change with the inserted reactivity of 1.5$, but it became over than 40% for the rapid power change with the reactivity of about 3$.

Journal Articles

Modified quasi-steady-state method to evaluate the mean power profiles of nuclear excursions in fissile solution

Nakajima, Ken; Yamamoto, Toshihiro; Miyoshi, Yoshinori

Journal of Nuclear Science and Technology, 39(11), p.1162 - 1168, 2002/11

 Times Cited Count:6 Percentile:41.16(Nuclear Science & Technology)

A modified quasi-steady-state method has been developed to evaluate the mean power during a nuclear excursion in fissile solution. The original method used the critical equation based on the one-group theory to calculate the reactivity. However, the one-group approximation reduces the calculation accuracy and the geometrical buckling used in the critical equation is not applicable to complex geometries. Then, we have modified the method to use the feedback coefficients of reactivity. Although the modified method requires an external calculation to obtain the feedback coefficients, it is applicable to complex geometries and gives more accurate results than the one-group approximation. Moreover, a new method to calculate the boiling power has been developed. using the experimental data of a supercritical experiment facility, SILENE. Experimental analyses were conducted to validate the new method for supercritical xperiments using CRAC and TRACY. The results showed good agreements with the experiments.

JAEA Reports

PLUTON:Three-group neutronic code for burnup analysis of isotope generation and depletion in highly irradiated LWR fuel rods

Lemehov, S.; Suzuki, Motoe

JAERI-Data/Code 2001-025, 338 Pages, 2001/08

JAERI-Data-Code-2001-025.pdf:26.87MB

PLUTON is a three-group neutronic code analyzing, as functions of time and burnup, the change of radial profiles, together with average values, of power density, burnup, concentration of trans-uranium elements, plutonium buildup, depletion of fissile elements, and fission product generation in water reactor fuel rod with standard UO2 , UO2-Gd2O3 , inhomogeneous MOX, and UO2-ThO2 . The PLUTON code, which has been designed to be run on Windows PC, has adopted a theoretical shape function of neutron attenuation in pellet, which enables users to perform a very fast and accurate calculation easily. The present code includes the irradiation conditions of the Halden Reactor which gives verification data for the code. The total list of trans-uranium elements included in the calculations consists of 92U233-239, 93Np237-239, 94Pu238-243, 95Am241-244 (including isomers), and 96Cm242-245. Verification has been performed up to 83 GWd/tU, and a satisfactory agreement has been obtained.

Journal Articles

Improvement of critical heat flux correlation for research reactors using plate-type fuel

Kaminaga, Masanori; Yamamoto, Kazuyoshi; Sudo, Yukio

Journal of Nuclear Science and Technology, 35(12), p.943 - 951, 1998/12

 Times Cited Count:13 Percentile:72.4(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Improvement of CHF correlations for research reactors using plate-type fuels

Kaminaga, Masanori; Yamamoto, Kazuyoshi; Sudo, Yukio

Proceedings of 8th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-8), Vo.3, p.1815 - 1822, 1997/00

In research reactors, plate-type fuel elements are generally adopted so as to produce high power densities and are cooled by a downward flow. A core flow reversal from a steady-state forced downward flow to an upward flow due to natural convection should occur during operational transients such as "Loss of the primary coolant flow". Therefore, in the thermal hydraulic design of research reactors, critical heat flux (CHF) under a counter-current flow limitation (CCFL) or a flooding condition are important to determine safety margins of fuel against CHF during a core flow reversal. The authors have proposed a CHF correlation scheme for the thermal hydraulic design of research reactors, based on CHF experiments for both upward and downward flows including CCFL condition. When the CHF correlation scheme was proposed, a subcooling effect for CHF correlation under CCFL condition had not been considered because of a conservative evaluation and a lack of enough CHF data to determine the subcooling effect on CHF. A too conservative evaluation is not appropriate for the design of research reactors because of construction costs etc. Also, conservativeness of the design must be determined precisely. In this study, therefore, the subcooling effect on CHF under the CCFL conditions in vertical rectangular channels heated from both sides were investigated quantitatively based on CHF experimental results obtained under uniform and nonuniform heat flux condition. As a result, it was made clear that CHF in this region increase linearly with an increase of the channel inlet subcooling and a new CHF correlation including the effect of channel inlet subcooling was proposed.

Oral presentation

Estimation of depth profile of radiocesium in soil based on characteristics of $$gamma$$-ray spectra obtained by airborne radiation monitoring

Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sato, Tomohiko*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa

no journal, , 

A large amount of radiocesium ($$^{134}$$Cs & $$^{137}$$Cs) were released into the atmosphere as a result of 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. To estimate the impact of the accident to the environment, dose rate around FDNPP have been measured by MEXT. Dose rate nearby FDNPP, however, still stay high even though decontamination work was carried out, which means it is necessary to develop an effective decontamination method promptly. Information of depth profile of radiocesium in soil is required to realize it, though, most of measurement methods have trouble due to collection and measurement of soil samples. As we have developed the radiation measurement techniques using unmanned aerial vehicle to measure dose rate distribution over wide areas for years, we attempt to establish the estimation method of depth profile of radiocesium in soil based on characteristics of $$gamma$$-ray spectra obtained by airborne radiation monitoring in this paper.

Oral presentation

Distribution of radionuclides near the Fukushima Dai-ichi Nuclear Power Station

Iijima, Kazuki; Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso

no journal, , 

In this study, in order to estimate the on-site distribution, the concentrations of several radionuclides in off-site topsoil were evaluated along six traces of the radioactive plumes, and the characteristic of spatial distribution and depth profile was discussed. The tendency of inventories of Sr-90 and Pu-238 observed in off-site was consistent with that of observed in the previous on-site sampling, indicating that the estimation of on-site distribution of radionuclides based on the off-site was applicable. Concentration of Cs-137 drastically decreased from top of the surface to around 10 cm depth, then gradually decreased, suggesting that Cs-137 was strongly adsorbed at upper part. Surprisingly, the profile of Pu-239+240 was quite different from that of Pu-238, while it was similar to Am-241. It was considered that the behavior of Am-241 was strongly reflected by that of Pu-241, a parent of Am-241, and the deposition event of Pu-239+240 and Pu-241 was different from that of Pu-238.

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