Laboratory experiment on runoff of particles deposited on land surface by rainfall at accidents in the decommissioning stage

Shimada, Taro; Namekawa, Masakazu*; Miwa, Kazuji; Takeda, Seiji

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02

It is supposed that radioactive dust deposited at the land surface will be moved downstream and concentrated at the depression by overland flow at heavy rain after the accidental release of radioactive dusts accumulated at the filters in the decommissioning stage of nuclear facilities. The authors are developing a calculation code to evaluate distribution changes of radioactivity on the surface and public dose considering the conditions such as rainfall, topography and types of cover surface. It is necessary to construct methods for setting parameter values used for the calculations based on the actual situation. Therefore, the parameter values were obtained by the experiments where FeO powder spread on the cover surface such as smooth and aged-asphalt, concrete and bare soil, was eroded by overland flow and raindrops and they were collected at the lower end of the slope at a minute interval. The collected weights of overland flow and FeO powder were measured. Based on the Manning's roughness coefficient for smooth asphalt already known as a fixed value, the erosion velocity coefficient was evaluated. Then Manning's roughness coefficients for other cover surfaces were obtained using the erosion velocity coefficient. Manning's roughness coefficients were slightly smaller than the range of literature values. In addition, elevations for the cover surface were measured by 3D scanner as point cloud data, and the surface roughness were evaluated. The values of surface roughness and Manning's roughness coefficients had a correlation. It indicated a possibility to utilize the surface roughness to set the Manning's roughness coefficient for the evaluation of radioactivity distribution change by heavy rainfall.

Penetration factor and indoor deposition rate of elementary and particulate iodine in a Japanese house for assessing the effectiveness of sheltering for radiation exposures

Hirouchi, Jun; Takahara, Shogo; Komagamine, Hiroshi*; Kato, Nobuyuki*; Matsui, Yasuto*; Yoneda, Minoru*

Journal of Radiological Protection, 41(3), p.S139 - S149, 2021/09

https://doi.org/10.1088/1361-6498/ac025b

Sheltering is one of the countermeasures for protection against radiation exposures in nuclear accidents. The effectiveness of sheltering is often expressed by the reduction factor, that is the ratio of the indoor to the outdoor cumulative radioactivity concentrations or doses. The indoor concentration is mainly controlled by the air exchange rate, penetration factor, and indoor deposition rate. The penetration factor and indoor deposition rate depend on the surface and opening materials. We investigated experimentally these parameters of I and particles. The experiment was performed in two apartment houses, three single-family houses, and chambers. The obtained penetration factor ranged 0.3 1 for particles of 0.3 1 m and 0.15 0.7 for I depending on the air exchange rate. The indoor deposition rate for a house room ranged 0.007 0.2 h for particles of 0.31 m and 0.21.5 h for I depending on floor materials.

Performance of in situ gamma-ray spectrometry in the assessment of radioactive cesium deposition around the Fukushima Daiichi Nuclear Power Plant

Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi

Radiation Physics and Chemistry, 179, p.109205_1 - 109205_11, 2021/02

https://doi.org/10.1016/j.radphyschem.2020.109205

In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with several dose rate levels around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr(Ce) detectors to assess the radioactive cesium deposition in the ground. The diverse levels of radioactivity of Cs were then distributed to six survey sites from 30 to 3000 kBq m in the measurement period of October 2018. A method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site.

Geographical distribution of ground deposition density and ambient dose rate, and temporal change of dose rate

Saito, Kimiaki

Tokyo Denryoku Fukushima Daiichi Genshiryoku Hatsudensho Jiko Ni Yoru Kankyo Osen No Kenkyu Chosa No Shinten To Kadai (Internet), p.8 - 10, 2020/07

no abstracts in English

Importance of root uptake of CO on C transfer to plants impacted by below-ground CH release

Ota, Masakazu; Tanaka, Taku*

Journal of Environmental Radioactivity, 201, p.5 - 18, 2019/05

https://doi.org/10.1016/j.jenvrad.2019.01.012

CH released from deep underground radioactive waste disposal facilities can be a belowground source of CO owing to microbial oxidation of CH to CO in soils. Environmental C models assume that the transfer of CO from soil to plant occurs via foliar uptake of CO. Nevertheless, the importance of CO root uptake is not well understood. In the present study, belowground transport and oxidation of CH were modeled and incorporated into an existing land surface CO model (SOLVEG-II) to assess the importance of root uptake on CO transfer to plants. Performance of the model in calculating the belowground dynamics of CH was validated by simulating a field experiment of CH injection into subsoil. The model was then applied to C transfer in a hypothetical ecosystem impacted by continuous CH input from the water table (bottom of one-meter thick soil). In a shallowly rooted ecosystem with rooting depth of 11 cm, foliar uptake of CO was significant, accounting for 80% of the C accumulation in the leaves. In a deeply rooted ecosystem (rooting depth of 97 cm), where the root penetrated to depths close to the water-table, more than half (63%) the C accumulated in the leaves was transferred by the root uptake. We found that CO root uptake in this ecosystem depended on the distribution of methane oxidation in the soil; all C accumulated in the leaves was transferred by the root uptake when methane oxidation occurred at considerable depths (e-folding depths of 20 cm, or 80 cm). These results indicate that CO root uptake contributes significantly to CO transfer to plants if CH oxidation occurs at great depths and roots penetrate deeply into the soil.

Estimation of discharge rate of Cs-137 from urbanized catchment based on the decrease in deposition amount on urban components

Yoshimura, Kazuya

KEK Proceedings 2018-7, p.36 - 40, 2018/11

https://lib-extopc.kek.jp/preprints/PDF/2018/1825/1825007.pdf

no abstracts in English

Radionuclide transport behavior

Hidaka, Akihide

Enerugi Rebyu, 35(9), p.20 - 24, 2015/09

http://ci.nii.ac.jp/naid/40020565747

Operation of nuclear power plant causes accumulation of radionuclides in fuel rods as a result of nuclear fission of uranium and plutonium. During severe accidents, large amount of radionuclides are released from fuel and transport in the reactor coolant system and/or the containment. When the containment fails or its confinement function is lost, radionuclides could be released into the environment. Meanwhile, radionuclides can be removed by condensation onto wall, natural deposition such as gravitational settling, the engineered safety features (ESF) such as containment spray and so on. After various processes described above, the species, amounts and timing of radionuclide released into the environment is called source terms. The behavior of radionuclide can be described mechanistically by condensation or evaporation of gaseous radionuclide, deposition, growth and removal of aerosol by ESF. Present paper summarizes the radionuclide behavior during severe accidents.

Analyses of radio-nuclides release and transport in VEGA-1 and -3 tests with VICTORIA2.0 code

Hidaka, Akihide*; Kudo, Tamotsu; Kida, Mitsuko; Fuketa, Toyoshi

JAERI-Research 2005-001, 67 Pages, 2005/02

JAERI-Research-2005-001.pdf:3.38MB

In the VEGA program to investigate radionuclides release from irradiated fuel during severe accidents, the analyses are being performed with VICTORIA2.0 code for comprehensive understanding of radionuclides release and transport phenomena. The VEGA-1 and -3 tests were analyzed in the present study. The correlation for Cs diffusion coefficient in fuel grain obtained from VEGA-1 was applied to the release analysis of VEGA-3. The calculated release of Cs agreed well with the measurement. The correlation was applied to subsequent Cs transport and deposition analyses. The calculation underpredicted the total mass of Cs deposited onto the test apparatuses because nucleation of aerosol and its growth were underestimated due to the consideration of aerosol nucleation originated only from released FP in VICTORIA2.0. A sensitivity analysis with aerosol seeds for heterogeneous nucleation showed a reasonable agreement with the measured Cs distribution. It turned out that additional aerosol seeds besides the released FP be considered when the VICTORIA2.0 code is applied to the VEGA test analyses.

A New method for determining HT deposition velocity and dependence of the velocity on environmental factors

Koarashi, Jun; Amano, Hikaru; Atarashi-Andoh, Mariko; Iida, Takao*; Koma, T.*

Radiation Protection Dosimetry, 93(3), p.237 - 243, 2001/00

https://doi.org/10.1093/oxfordjournals.rpd.a006435

no abstracts in English

Outline of ART Mod2 code for analysis of radionuclide transport during severe accidents

Hidaka, Akihide

RIST News, (30), p.2 - 14, 2000/10

no abstracts in English