The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
Tetsuji Imanaka - One of the best experts on this subject based on the ideXlab platform.
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comparison of Radioactivity Release and contamination from the fukushima and chernobyl nuclear power plant accidents
2020Co-Authors: Tetsuji ImanakaAbstract:Although both the Fukushima Daiichi Nuclear Power Plant (FNPP) accident in 2011 and the Chernobyl NPP Unit 4 (CNPP) accident in 1986 are classified as Level 7, the worst nuclear incidence on the International Nuclear and Radiological Event Scale by the International Atomic Energy Agency, there are various differences between the two, including the accident process, Released radionuclide composition, and meteorological and geological conditions. The amounts of iodine-131 (131I) and cesium-137 (137Cs) Released into the atmosphere were about six times smaller after the FNPP accident compared to the CNPP accident. Cesium-137 is the most important radionuclide in considering long-term effects of nuclear accidents. According to Chernobyl laws in Ukraine, Belarus and Russia, depending on the level of 137Cs contamination, the contaminated territories were classified as alienation zone (>1480 kBq m−2), obligatory resettlement zone (555–1480 kBq m−2) and voluntarily resettlement zone (185–555 kBq m−2). The areas of the corresponding zones around FNPP were 272, 459 and 1405 km2, respectively, which were 11–15 times smaller compared to the CNPP accident. Meanwhile, the number of affected people around FNPP was only three to five times smaller compared to CNPP, reflecting the higher population density for the FNPP accient. Cumulative exposures for the 1st year 1 m above ground (normalized to the initial 137Cs deposition of 1 MBq m−2) were 63 mGy for the FNPP accident, while it was 500 mGy for the CNPP accident because more various radionuclides were emitted in case of the CNPP accident than the FNPP accident. Cumulative exposures at 30 years were evaluated to be 500 mGy and 970 mGy for the FNPP accident and the CNPP accident, respectively.
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fukushima 1 and chernobyl comparison of Radioactivity Release and contamination
2016Co-Authors: Tetsuji ImanakaAbstract:Accident process, Radioactivity Release and ground contamination are compared between the Fukushima-1 accident and the Chernobyl accident. The area of ground severely contaminated around Chernobyl is more than ten times larger than around Fukushima-1. The composition of ground contamination is also different between Chernobyl and Fukushima-1. Other than radiocesiums (134Cs and 137Cs), radionuclides such as 95Z, 95Nb, 103Ru and 140La contribute significantly radiation exposure during the first year in Chernobyl, while their contribution is negligible in Fukushima-1. Cumulative radiation exposure during the first year per initial 137Cs deposition of 1 MBq m−2 is 500 mGy and 63 mGy in Chernobyl and Fukushima-1, respectively. For 30 year, they are 970 mGy and 500 mGy in Chernobyl and Fukushima-1, respectively.
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comparison of the accident process Radioactivity Release and ground contamination between chernobyl and fukushima 1
Journal of Radiation Research, 2015Co-Authors: Tetsuji Imanaka, Gohei Hayashi, Satoru EndoAbstract:In this report, we have reviewed the basic features of the accident processes and Radioactivity Releases that occurred in the Chernobyl accident (1986) and in the Fukushima-1 accident (2011). The Chernobyl accident was a power-surge accident that was caused by a failure of control of a fission chain reaction, which instantaneously destroyed the reactor and building, whereas the Fukushima-1 accident was a loss-of-coolant accident in which the reactor cores of three units were melted by decay heat after losing the electricity supply. Although the quantity of radioactive noble gases Released from Fukushima-1 exceeded the amount Released from Chernobyl, the size of land area severely contaminated by 137 Cesium ( 137 Cs) was 10 times smaller around Fukushima-1 compared with around Chernobyl. The differences in the accident process are reflected in the composition of the discharged Radioactivity as well as in the composition of the ground contamination. Volatile radionuclides (such as 132 Te- 132 I, 131 I, 134 Cs and 137 Cs) contributed to the gamma-ray exposure from the ground contamination around Fukishima-1, whereas a greater variety of radionuclides contributed significantly around Chernobyl. When Radioactivity deposition occurred, the radiation exposure rate near Chernobyl is estimated to have been 770 μGy h −1 per initial 137 Cs deposition of 1000 kBq m −2 , whereas it was 100 μGy h −1 around Fukushima-1. Estimates of the cumulative exposure for 30 years are 970 and 570 mGy per initial deposition of 1000 kBq m −2 for Chernobyl and Fukusima-1, respectively. Of these exposures, 49 and 98% were contributed by radiocesiums ( 134 Cs+ 137 Cs) around Chernobyl and Fukushima-1, respectively.
Vaclav Smidl - One of the best experts on this subject based on the ideXlab platform.
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inverse modelling for real time estimation of radiological consequences in the early stage of an accidental Radioactivity Release
Journal of Environmental Radioactivity, 2016Co-Authors: Petr Pecha, Vaclav SmidlAbstract:Abstract A stepwise sequential assimilation algorithm is proposed based on an optimisation approach for recursive parameter estimation and tracking of radioactive plume propagation in the early stage of a radiation accident. Predictions of the radiological situation in each time step of the plume propagation are driven by an existing short-term meteorological forecast and the assimilation procedure manipulates the model parameters to match the observations incoming concurrently from the terrain. Mathematically, the task is a typical ill-posed inverse problem of estimating the parameters of the Release. The proposed method is designated as a stepwise re-estimation of the source term Release dynamics and an improvement of several input model parameters. It results in a more precise determination of the adversely affected areas in the terrain. The nonlinear least-squares regression methodology is applied for estimation of the unknowns. The fast and adequately accurate segmented Gaussian plume model (SGPM) is used in the first stage of direct (forward) modelling. The subsequent inverse procedure infers (re-estimates) the values of important model parameters from the actual observations. Accuracy and sensitivity of the proposed method for real-time forecasting of the accident propagation is studied. First, a twin experiment generating noiseless simulated “artificial” observations is studied to verify the minimisation algorithm. Second, the impact of the measurement noise on the re-estimated source Release rate is examined. In addition, the presented method can be used as a proposal for more advanced statistical techniques using, e.g., importance sampling.
Muyi Ni - One of the best experts on this subject based on the ideXlab platform.
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individual dose due to Radioactivity accidental Release from fusion reactor
Journal of Hazardous Materials, 2017Co-Authors: Muyi NiAbstract:Abstract As an important index shaping the design of fusion safety system, evaluation of public radiation consequences have risen as a hot topic on the way to develop fusion energy. In this work, the comprehensive public early dose was evaluated due to unit gram tritium (HT/HTO), activated dust, activated corrosion products (ACPs) and activated gases accidental Release from ITER like fusion reactor. Meanwhile, considering that we cannot completely eliminate the occurrence likelihood of multi-failure of vacuum vessel and tokamak building, we conservatively evaluated the public radiation consequences and environment restoration after the worst hypothetical accident preliminarily. The comparison results show early dose of different unit Radioactivity Release under different conditions. After further performing the radiation consequences, we find it possible that the hypothetical accident for ITER like fusion reactor would result in a level 6 accident according to INES, not appear level 7 like Chernobyl or Fukushima accidents. And from the point of environment restoration, we need at least 69 years for case 1 (1 kg HTO and 1000 kg dust Release) and 34–52 years for case 2 (1 kg HTO and 10kg–100 kg dust Release) to wait the contaminated zone drop below the general public safety limit (1mSv per year) before it is suitable for human habitation.
Petr Pecha - One of the best experts on this subject based on the ideXlab platform.
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inverse modelling for real time estimation of radiological consequences in the early stage of an accidental Radioactivity Release
Journal of Environmental Radioactivity, 2016Co-Authors: Petr Pecha, Vaclav SmidlAbstract:Abstract A stepwise sequential assimilation algorithm is proposed based on an optimisation approach for recursive parameter estimation and tracking of radioactive plume propagation in the early stage of a radiation accident. Predictions of the radiological situation in each time step of the plume propagation are driven by an existing short-term meteorological forecast and the assimilation procedure manipulates the model parameters to match the observations incoming concurrently from the terrain. Mathematically, the task is a typical ill-posed inverse problem of estimating the parameters of the Release. The proposed method is designated as a stepwise re-estimation of the source term Release dynamics and an improvement of several input model parameters. It results in a more precise determination of the adversely affected areas in the terrain. The nonlinear least-squares regression methodology is applied for estimation of the unknowns. The fast and adequately accurate segmented Gaussian plume model (SGPM) is used in the first stage of direct (forward) modelling. The subsequent inverse procedure infers (re-estimates) the values of important model parameters from the actual observations. Accuracy and sensitivity of the proposed method for real-time forecasting of the accident propagation is studied. First, a twin experiment generating noiseless simulated “artificial” observations is studied to verify the minimisation algorithm. Second, the impact of the measurement noise on the re-estimated source Release rate is examined. In addition, the presented method can be used as a proposal for more advanced statistical techniques using, e.g., importance sampling.
Yu B Kholina - One of the best experts on this subject based on the ideXlab platform.
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radioecological state of lakes in the southern ural impacted by Radioactivity Release of the 1957 radiation accident
Journal of Environmental Radioactivity, 1997Co-Authors: I I Kryshev, G N Romanov, L N Isaeva, Yu B KholinaAbstract:This paper is concerned with the distribution of 90Sr and 137Cs in lake ecosystems in the southern Urals which were affected by the 1957 radiation accident. In 1992, the levels of 90Sr in the most highly contaminated lakes, which were removed from economic usages, were as follows: 17–120 Bq l−1 in water, 70–110kBq kg−1 in fish and 2.9–5.2 kBq kg−1 in aquatic plants. In the lakes which are used in the fishery, the levels of 90Sr are 0.05–0.5 Bq l−1 in water and 4–550 Bq kg−1 in fish. The levels of 137Cs in these lakes are 0.03–0.6 Bql−1 in water and 2–33 Bq kg−1 in fish. In the first few years following the accident, a dose rate level of 10−2 Gy day−1 to molluscs, bottom-dwelling fish and aquatic plants could be exceeded in the most highly contaminated lakes of Uruskul' and Berdyanish. In 1992, the background exposure level for fish from these lakes was still exceeded by a factor of 1000. In the other lakes, the doses to aquatic organisms were considerably lower. Doses to the population from lake fish consumption do not exceed 10−3 Sv year−1.