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The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident caused a significant release of radionuclides into the environment. It is important to explore the timing and amount of radioactive release to terrestrial areas in order to clarify the consequences of the accident, including the dose received by the population living in the areas affected by the accident. In general, backward estimations are performed using air concentrations of radionuclides, but they are difficult to measure when radioactive plumes are passing through, and only spatially and temporally limited measurements are available. Therefore, a new method of backward estimation was developed based on the total cumulative deposition density, which can provide sufficient data in the environment by combining the atmospheric transport, dispersion, and deposition model calculations. Consequently, our estimations show that a major release of 137Cs and 131I occurred on 15, 20, 21, 22, 25, and 30 March 2011, after the accident. The amounts of release estimated by our new method for 137Cs and 131I were 4.9 × 1015 Bq and 120 × 1015 Bq, respectively. These results have no significant contradiction with the estimated results by the previous studies that were based on air concentrations and air dose rates that were measured in terrestrial areas. It was found that our new method is applicable for backward estimation oriented to the dose assessment for the people living in terrestrial areas.

Sheltering is one of the countermeasures used to mitigate radiation exposure during nuclear power plant accidents. The effectiveness of sheltering for inhalation exposure is often expressed by the reduction factor, which is defined as 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. Meanwhile, the air exchange rate depends on surrounding environmental conditions: the wind speed, leakage area normalised by the floor area of the house, and gross building coverage ratio. In this study, the ranges of the uncertainty of the reduction factors for particles and iodine in reactive gas form were investigated under various environmental conditions, and sensitivity analyses were conducted to understand the parameter with the most influence on the uncertainty of the reduction factor. From the results of the uncertainty analyses, the calculated reduction factor was highly variable depending on the environmental condition and the airtightness of the houses. The median and 95th percentile of the reduction factors for the older houses were 0.5 and 0.9 for particles and 0.07 and 0.4 for iodine in reactive gas form, respectively and these ranges were smaller for newer houses. From the results of the sensitivity analyses, the wind speed was the most influential parameter determining the reduction factor. Additionally, the wind speed was less influential for the reduction factor in newer houses.

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 the materials and structure of windows and doors as it is these openings in the building envelope that control penetration. We investigated experimentally these parameters of I2and particles. The experiment was performed in two apartment houses, three single-family houses, and chambers. The obtained penetration factor ranged from 0.3 to 1 for particles of 0.3-1μm and 0.15-0.7 for I2depending on the air exchange rate. The indoor deposition rate for a house room ranged from 0.007 to 0.2 h-1for particles of 0.3-1μm and 0.2-1.5 h-1for I2.

State-of-the-art dose assessment models were applied to estimate doses to the population in urban areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. Assessment results were compared among five models, and comparisons of model predictions with actual measurements were also made. Assessments were performed using both probabilistic and deterministic approaches. Predicted dose distributions for indoor and outdoor workers from a probabilistic approach were in good agreement with the actual measurements. In addition, when the models were applied to assess the doses to the representative person, based on a concept recommended by the International Commission on Radiological Protection and in the International Atomic Energy Agency Safety Standards, it was evident that doses to the representative person obtained with a deterministic approach were always higher than those obtained with a probabilistic approach using the same model.

Radiation exposure is one of most important factors to manage following a nuclear emergency. Actual measurement is the best way to obtain information concerning the dose received by the people in terms of accuracy and reliability. However, in practice, it is difficult to collect measurements from all people affected by nuclear accidents over the whole period of exposure from past to future. Therefore, probabilistic assessment using a model is needed. An assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rates inside and outside houses in Fukushima City. A survey of behavioral patterns was also performed for the same purpose. In addition to our measurement and survey, we took into account the latest insights from the experiences of the Fukushima Daiichi nuclear power plant accident. Comparisons between the assessed and measured results revealed that the time-dependence of doses and the distribution of doses obtained using the developed models agree well with the results of actual measurements. Thus, our probabilistic approach was validated. Based on both our assessment and on our actual measurements, no participants were observed to receive doses in excess of 1 mSv y as of 8 y after the Fukushima Daiichi nuclear power plant accident in Fukushima City.

The IAEA’s model testing programmes have included a series of Working Groups concerned with modelling radioactive contamination in urban environments. These have included the Urban Working Group of Validation of Environmental Model Predictions (1988–1994), the Urban Remediation Working Group of Environmental Modelling for Radiation Safety (EMRAS) (2003–2007), the Urban Areas Working Group of EMRAS II (2009–2011), the Urban Environments Working Group of (Modelling and Data for Radiological Impact Assessments) MODARIA I (2013–2015), and most recently, the Urban Exposures Working Group of MODARIA II (2016–2019). The overarching objective of these Working Groups has been to test and improve the capabilities of computer models used to assess radioactive contamination in urban environments, including dispersion and deposition processes, short-term and long-term redistribution of contaminants following deposition events, and the effectiveness of various countermeasures and other protective actions, including remedial actions, in reducing contamination levels, human exposures, and doses to humans. This paper describes the exercises conducted during the MODARIA I and MODARIA II programmes. These exercises have included short-range and mid-range atmospheric dispersion exercises based on data from field tests or tracer studies, hypothetical urban dispersion exercises, and an exercise based on data collected after the Fukushima Daiichi accident. Improvement of model capabilities will lead to improvements in assessing various contamination scenarios (real or hypothetical), and in turn, to improved decision-making and communication with the public following a nuclear or radiological emergency.

After the Fukushima accident, it became important to determine the quantity of radionuclide ingested by inhabitants. The most common methods currently used to obtain such data are the "market basket" (MB) and "duplicate" (DP) methods. However, it is difficult to conduct monitorings using these methods with sufficient frequency as they are high cost and time-consuming. The present study proposes a new method to estimate the ingestion of radionuclides, based on the time-dependent concentrations of radiocesium in sewer sludge, which addresses the uncertainties of the two common methods. The newly proposed method, which we designate as SL, consists of three steps: (1) the separation of wet weather and dry weather data, (2) determining the mass balance of the wastewater treatment plant (WWTP), and (3) developing a reverse biokinetic model to relate the amount of radionuclides ingested to the amounts contained in the sewer sludge. We tested the new method using the time-dependent radiocesium concentrations in sewer sludge from the WWTP in Fukushima City. The results from the SL method agreed to those from the MB while overestimated those from DP method. The trend lines for all three methods, however, are in good agreement. Sensitivity analyses of SL method indicate further studies on uncertainties of sensitive parameters are deemed necessary to improve the accuracy of the method.

Self-evacuation by a private vehicle is one of the most commonly used methods of public evacuation in the case of a nuclear accident. The aim of this paper is to evaluate the dose-reduction effects of vehicles. To achieve this aim, a model for calculating the dose reduction factor was developed based on the actual shape and weight of Japanese vehicles. This factor is defined as the ratio of dose rate inside a vehicle to that outside. The model was developed based on weight of vehicle to take into account the dose-reduction effects due to not only the steel plate of the vehicle body but also the other assemblies. In addition to model calculation, the dose reduction factors were evaluated by actual measurements in the areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. A comparison between the simulated and the measured results revealed that the dose reduction factors obtained using the developed models were in good agreement with the results of actual measurements. Using this model, we also evaluated the dose reduction factors for cloudshine and groundshine in the case of a nuclear accident. The evaluations were performed for four vehicle models whose weights were 800-1,930 kg. The dose reduction factor for cloudshine with photon energy of 0.4-1.5 MeV was 0.66-0.88, and that for groundshine from Cs was 0.64-0.73. Although these results were obtained under the assumption that Cs is placed only on the ground surface, according to these considerations, if Cs migrated into the ground corresponding to the relaxation mass depth of 10 g cm, the dose reduction factors would be almost 8% less than those for the ground surface.

Information on the radioactivity distribution inside and outside houses is useful for indoor external dose assessments. In this study, we collected both soil samples around the target houses and house material samples (i.e., of the floor, inner wall, ceiling, outer wall, and roof). The radioactivity of the samples was measured using a high-purity germanium detector. The surface contamination densities of the floor, inner wall, ceiling, outer wall, and roof relative to the ground were 3 $\times$ 10$^{-3}$$\sim$7 $\times$ 10$^{-2}$, 6 $\times$ 10$^{-5}$$\sim$4 $\times$ 10$^{-4}$, 7 $\times$ 10$^{-5}$$\sim$3 $\times$ 10$^{-4}$, 2 $\times$ 10$^{-3}$$\sim$1 $\times$ 10$^{-2}$, and 4 $\times$ 10$^{-3}$$\sim$2 $\times$ 10$^{-1}$, respectively. The relative surface contamination densities varied depending on the material, its location, and the orientation of the surface., 家屋内での外部被ばく線量評価において、家屋内外の放射能分布の情報は有用である。本研究では、対象とした家屋周辺の土壌と家材サンプル(床,内壁,天井,外壁,屋根)を収集した。それらサンプルの放射能をHPGe検出器で測定した。地面に対する床,内壁,天井,外壁,屋根の相対表面濃度はそれぞれ3$\times$10$^{-3}$ $\sim$ 7$\times$10$^{-2}$, 6$\times$10$^{-5}$ $\sim$ 4$\times$10$^{-4}$, 7$\times$10$^{-5}$ $\sim$ 3$\times$10$^{-4}$, 2$\times$10$^{-3}$ $\sim$ 1$\times$10$^{-2}$, and 4$\times$10$^{-3}$ $\sim$ 2$\times$10$^{-1}$であった。相対表面濃度は材質,位置及び表面の向きによって異なった。

In order to lift of an evacuation order in evacuation areas and return residents to their homes, human dose assessments are required. However, it is difficult to exactly assess indoor external dose rate because the indoor distribution and infiltration pathways of radionuclides are unclear. This paper describes indoor and outdoor dose rates measured in eight houses in the difficult-to-return area in Fukushima Prefecture and identifies the distribution and main infiltration pathway of radionuclides in houses. In addition, it describes dose rates calculated with a Monte Carlo photon transport code to aid a thorough understanding of the measurements. The measurements and calculations indicate that radionuclides mainly infiltrate through visible openings such as vents, windows, and doors, and then deposit near these visible openings; however, they hardly infiltrate through sockets and air conditioning outlets. The measurements on rough surfaces such as bookshelves implies that radionuclides discharged from the Fukushima-Daiichi nuclear power plant did not deposit locally on rough surfaces.

Dose assessment is an important issue from the viewpoints of protecting people from radiation exposure and managing postaccident situations adequately. However, the radiation doses received by people cannot be determined with complete accuracy because of the uncertainties and the variability associated with any process of defining individual characteristics and in the dose assessment process itself. In this study, a dose assessment model was developed based on measurements and surveys of individual doses and relevant contributors (i.e., ambient dose rates and behavior patterns) in Fukushima City for four population groups: Fukushima City Office staff, Senior Citizens' Club, Contractors' Association, and Agricultural Cooperative. In addition, probabilistic assessments were performed for these population groups by considering the spatial variability of contamination and interpopulation differences resulting from behavior patterns. As a result of comparison with the actual measurements, the assessment results for participants from the Fukushima City Office agreed with the measured values, thereby validating the model and the approach. Although the assessment results obtained for the Senior Citizens' Club and the Agricultural Cooperative differ partly from the measured values, by addressing further considerations in terms of dose reduction effects due to decontamination and the impact of additional exposure sources in agricultural fields, these results can be improved. By contrast, the measurements obtained for the participants from the Contractors' Association were not reproduced well in the present study. To assess the doses to this group, further investigations of association members' work activities and the related dose reduction effects are needed.

On 1 April 2017, around 6 y after the Fukushima Daiichi nuclear power station accident, evacuation orders for large affected areas were lifted, and areas to which people could return were expanded. In the current study, a dose estimation model based on a probabilistic approach has been developed to estimate the external radiation doses children would receive after returning to these areas. The target groups are children from infants to high school students, and the target areas are nine municipalities including evacuation areas as of 5 September 2015. The estimation period is for 4 y starting 1 April 2017. Validation of the model in an area for which individual personal dosimetry measurements were available showed that it is valid for infants, kindergarteners, 3rd and 4th grade elementary school students, 5th and 6th grade elementary school students, and junior high school students. Considering the statement of the International Commission on Radiological Protection, the estimated radiation doses for these five age groups were taken to be the 95th percentiles of the predicted distributions as an index of conservative judgement. As a result of our estimations, the 95th percentile doses to all age groups were less than 20 mSv y in all periods and in all areas. The 95th percentile doses in some areas were less than 1 mSv y, which is the long-term dosimetric target set by the Japanese government. It should be noted that our results are preliminary, being based on several assumptions and limitations regarding environmental contamination conditions and the behavioral patterns of children. To estimate the children's doses precisely, further considerations for these assumptions and limitations will be needed.

Ingestion of contaminated soil is one potential internal exposure pathway in areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. Doses from this pathway can be overestimated if the availability of radioactive nuclides in soils for the gastrointestinal tract is not considered. The concept of bioaccessibility has been adopted to evaluate this availability based on in vitro tests. This study evaluated the bioaccessibility of radioactive cesium from soils via the physiologically-based extraction test (PBET) and the extractability of those via an extraction test with 1 mol/L of hydrochloric acid (HCl). The bioaccessibility obtained in the PBET was 5.3% ± 1%, and the extractability in the tests with HCl was 16% ± 3%. The bioaccessibility was strongly correlated with the extractability. This result indicates the possibility that the extractability in HCl can be used as a good predictor of the bioaccessibility with PBET. In addition, we assessed the doses to children from the ingestion of soil via hand-to-mouth activity based on our PBET results using a probabilistic approach considering the spatial distribution of radioactive cesium in Date City in Fukushima Prefecture and the interindividual differences in the surveyed amounts of soil ingestion in Japan. The results of this assessment indicate that even if children were to routinely ingest a large amount of soil with relatively high contamination, the radiation doses from this pathway are negligible compared with doses from external exposure owing to deposited radionuclides in Fukushima Prefecture.

We quantitatively analyzed changes in residents’ perceptions of the net benefits derived from the Kashiwazaki–Kariwa nuclear power station (KK) before and after the accident at the Fukushima Daiichi plant (FD) following the Great East Japan Earthquake on March 11, 2011. Employing data from two surveys—conducted in January 2010 and December 2011 before and after FD accident, respectively—we found that KK's perceived net benefits declined after the FD accident. This decline resulted from changes in respondents’ relative weightings of KK's costs and benefits rather than heightened expectations of future nuclear accidents. We also found that residents living near nuclear facilities are more concerned about health risks from nuclear accidents than the likelihood of such accidents caused by human error. We suggest that a more effective policy entails changing people's relative weighting of nuclear facilities’ costs and benefits by protecting lives through enhanced evacuation planning and post-disaster support for rehabilitation, although Japan's current nuclear power policy aims to assuage people's risk perceptions by reducing the probability of nuclear accidents to zero.

The α-type isomer of [6,6]-phenyl-C71-butyric acid methyl ester (α-[70]PCBM) has been separated into enantiomers. The structures of (R)- and (S)-α-[70]PCBM were unambiguously identified by X-ray crystallography. Systematic investigations on photovoltaic properties of devices based on the optically active/inactive α-[70]PCBM acceptor and a conjugated polymer donor revealed that the enantiomer separations and combinations have insignificant effects on the device performances.

This study investigates factors in gaps between perceived and actual straight-line distance to Japan’s Kashiwazaki-Kariwa nuclear power plant (KKNPP). The distance to areas in the official accident response plan is defined using straight lines from the NPP, making it important to determine whether area residents understand these distances correctly. Adults living in the two municipalities cohosting the NPP were surveyed randomly in 2005, 2010 and 2011. In this study, we consider three groups of factors — geographical features, personal attributes, and experience in events highlighting nuclear safety. The Niigata-ken Chuetsu-oki earthquake hit the NPP between the first and second of these three surveys, and the Tohoku earthquake and the March 2011 Fukushima nuclear accident occurred between the second and the third surveys. Before the Fukushima accident, overestimations of straight-line distance were common among respondents, and geographical features such as lack of NPP visibility aggravated bias between actual and perceived distance. After the Fukushima accident, underestimation of the distance became common and personal attributes became more influential as the factor of the perceived-actual distance gap.

Cost per severe accident, which can cover various kinds of consequences, namely health effects, economic, social and environmental impacts, has been used as an index for severe accident consequence assessment in the authors' previous studies. Decontamination of the contaminated area was concluded influential to the cost per severe accident, though it employed simple and conservative assumptions, which made further discussion difficult. A new decontamination model is formed to address this issue. A sensitivity analysis using the elementary effects method is performed to identify parameters which have large influence on the cost per severe accident. We identify 25 important parameters, and fix most negligible parameters to their medians to form a simplified decontamination model. Calculations of the cost per severe accident with the simplified model and the full model are performed and compared. The differences of the results of the two model are not significant, which ensure the validity of the simplified ...

Probabilistic dose assessment is one of the useful methods to describe the information on the dose distributions in the population. To use this assessment, statistically characterized data on the pathway-relevant contributors are necessary. The objectives of the paper are to determine the statistical values and the distribution forms of the contributors to external exposures, as well as to identify the causes of the variabilities of them. To achieve the objectives, we have measured and surveyed ambient dose rate and time spent outdoors in Fukushima Prefecture. The measurements and surveys were performed with the cooperation of indoor workers, outdoor workers and pensioners. These results allowed us to determine the statistically characters of the individual doses and its contributors. In addition, these contributors had the variabilities attributed to the spatial distributions of deposited radionuclides, as well as the temporal and interpopulational differences of behavioral patterns., 原子力事故後の汚染地域において被ばくを適切に管理するためには、住民の線量を合理的に評価する手法が必要である。確率論的線量評価手法は、線量分布を評価することで住民の被ばく状況を包括的に把握できる方法の一つである。この評価手法を利用するためには、被ばく要因に係る統計データが必要となる。本研究では、第一に、福島事故後の被ばく状況について外部被ばくに係る被ばく要因の統計データを決定すること、第二に、個人線量の変動性の原因を特定することを目的とした。これらの目的を達成するために、福島県内の屋内作業者や屋外作業者などの協力を得て、住民の個人線量および自宅の空間線量率を測定するとともに、生活行動時間を調査した。また、個人線量を目的変数として、空間線量率と職場屋外での滞在時間を説明変数とする多重回帰分析を実施した。これらの分析の結果として、第一に、被ばく要因の統計分布と統計値を決定できた。第二に、空間線量率や屋外滞在時間のような被ばく要因は汚染の地域差や生活行動時間の個人差・団体差に応じて変動しており、その変動に応じて個人線量にも統計的に有意な違いが観察されることがわかった。

Sheltering is one of the protective actions to reduce external exposures from both the radioactive plume and the deposited radionuclides in a nuclear emergency. The aim of the present study is to provide the data of characteristics of evacuation facilities regarding building materials and structures, and preliminary estimates of shielding efficiency for the use of emergency planning. To achieve this aim, surveys were performed on the evacuation facilities actually used in Japan. In addition, for air submersion and deposited radionuclides, the shielding factors were calculated based on the survey results. The findings indicate that the shielding factors for the radiation due to air submersion were almost within the range of the previous works. The shielding factors, which were calculated with considerations of the radionuclides deposited only on the ground surface, were greater than those of the previous works. To explain the differences between the present study and previous works, an evaluation should be needed taking into account contributions of contaminated roofs.

This case study of the areas that host Kashiwazaki Kariwa NPP compares local citizens' attitude towards the benefits and the drawbacks of hosting the NPP. In December 2011, our survey respondents became more negative about hosting the NPP after the Fukushima accident in March 2011 compared to the survey in January 2010. Another comparison between the November 2005 and the December 2011 surveys provided a different look. The magnitude of the negative shift in Kariwa Village, which saw a large expansion of social welfare programs, was modest in the sense that its 2011 results were similar to its 2005 results. Local tax revenues, subsidies from the national government and the donation from a utility contributed to this budget expansion in Kariwa. The negative shifts from 2005 to 2011 were clear in the other two municipalities which did not see such a large expansion of economic benefits during this period., 著者所属: 日本原子力研究開発機構(JAEA)

To develop an effective emergency plan for a nuclear accident, the size of the precautionary action zone (PAZ) was evaluated using a Level 3 probabilistic safety analysis (PSA) code, the OSCAAR. For accident scenarios identified through a Level 2 PSA analysis for representative boiling water reactor (BWR) and pressurized water reactor (PWR) plants, the absorbed doses to red marrow were calculated as a function of the distance from the accidental site for possible weather sequences in a year, and then the evaluation was made for the distance which satisfies the dose criterion of 1 Gy for acute exposure, as established in the Basic Safety Standards (BSS) of the International Atomic Energy Agency (IAEA). Consequently, the present study indicated that the size of the PAZ should be approximately a 3-km radius under average weather conditions.

Manganese silicide layers were grown on Si(111) substrates by exposure of the Si substrates to MnCl2 vapor. The thermal treatment temperature of 500 °C provided the appropriate growth conditions to form the Mnx Siy (y /x ∼ 2) similar to MnSi1.7 phase. The epitaxial Mnx Siy (y /x ∼ 2) islands grew during the initial growth stage. As the heat treatment time increased, the epitaxial layer became continuous and covered the entire Si(111) substrate surface at the appropriate heat treatment temperature of 500 °C, even though the additional growth of the Mnx Siy (y /x ∼ 1) deposit similar to MnSi phase occurred when the thickness of Mn-silicide layers exceeded the limited layer thickness. These results encouraged us to grow large area Mnx Siy (y /x ∼ 2) layers on Si substrates using this simple growth technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Relocation is one of the long-term protective actions for a nuclear and radiological emergency. The objective of relocation should be taken into account the concepts of “safe living condition” and “return to normality”, and prepare the strategy adopted these concepts. In order to prepare the strategy, we have examined the model using Return Level which is basis on these concepts. We have investigated the dependence of number of people to be relocated, relocation time, avertable collective dose and avertable per caput dose per year to criteria, i.e. Intervention Level and Return Level. From these results, it would be impossible to justify the strategy in terms of cost-benefit analysis. Therefore, to justify the strategies which are taken into account “safe living condition” and “return to normality”, we have to consider the other factor such as social physiological aspects.

Large quantities of radioactive materials were released into the environment as a result of the Fukushima Daiichi Nuclear Power Station accident. Many inhabitants residing in the affected areas are now exposed to radiation in their daily lives. In an attempt to manage this radiation dose, an additional radiation dose of 1 mSv/y was adopted as a long-term dosimetric target. An activity level reading of 0.23 μSv/h was then determined as a guidance value to achieve the target by implementing decontamination measures. The objectives of this study are to assess the effects of decontamination based on this guidance value and to predict any possible future problems with the decontamination strategy. Using a probabilistic approach, we assessed the annual effective dose of indoor workers, outdoor workers, and pensioners in the Fukushima Prefecture. Our probabilistic model considers the variabilities in behavioral patterns and Cs-137 surface-activity levels. Five years after the initial contamination, the 95th percentiles of indoor workers and pensioners in 53 of the 59 municipalities were found to receive annual effective doses of below 1 mSv/y (0.026-0.73 mSv/y). However, for outdoor workers in 25 municipalities, the annual doses were over 1 mSv/y (1.0-35 mSv/y). Therefore, the guidance value is effective for indoor workers and pensioners; to determine whether additional countermeasures for outdoor workers should be implemented, a detailed assessment that uses more realistic assumptions is required.

Ingestion of contaminated soil is one potential internal exposure pathway in areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. Doses from this pathway can be overestimated if the availability of radioactive nuclides in soils for the gastrointestinal tract is not considered. The concept of bioaccessibility has been adopted to evaluate this availability based on in vitro tests. This study evaluated the bioaccessibility of radioactive cesium from soils via the physiologically-based extraction test (PBET) and the extractability of those via an extraction test with 1 mol/L of hydrochloric acid (HCl). The bioaccessibility obtained in the PBET was 5.3% ± 1%, and the extractability in the tests with HCl was 16% ± 3%. The bioaccessibility was strongly correlated with the extractability. This result indicates the possibility that the extractability in HCl can be used as a good predictor of the bioaccessibility with PBET. In addition, we assessed the doses to children from the ingestion of soil via hand-to-mouth activity based on our PBET results using a probabilistic approach considering the spatial distribution of radioactive cesium in Date City in Fukushima Prefecture and the interindividual differences in the surveyed amounts of soil ingestion in Japan. The results of this assessment indicate that even if children were to routinely ingest a large amount of soil with relatively high contamination, the radiation doses from this pathway are negligible compared with doses from external exposure owing to deposited radionuclides in Fukushima Prefecture.

Radiation protection issues on preparedness and response for a severe nuclear accident are discussed in this paper based on the experiences following the accident at Fukushima Daiichi nuclear power plant. The criteria for use in nuclear emergencies in the Japanese emergency preparedness guide were based on the recommendations of International Commission of Radiological Protection (ICRP) Publications 60 and 63. Although the decision-making process for implementing protective actions relied heavily on computer-based predictive models prior to the accident, urgent protective actions, such as evacuation and sheltering, were implemented effectively based on the plant conditions. As there were no recommendations and criteria for long-term protective actions in the emergency preparedness guide, the recommendations of ICRP Publications 103, 109, and 111 were taken into consideration in determining the temporary relocation of inhabitants of heavily contaminated areas. These recommendations were very useful in deciding the emergency protective actions to take in the early stages of the Fukushima accident. However, some suggestions have been made for improving emergency preparedness and response in the early stages of a severe nuclear accident.

We have investigated in-reactor luminescence (IRL) from a silica glass at temperatures ranging from 100 K to 250 K. The IRL consists mainly of a broad emission band peaked at 2.7 eV assigned to oxygen deficient centers produced in the silica glass under the in-reactor irradiation. The 2.7 eV emission intensity linearly increased with the irradiation time and its increasing rate was larger for higher irradiation temperatures. However, this temperature dependence is inconsistent with that for the defect production rate and the cause is not clear at present. The initial intensity of the 2.7 eV IRL band increases with temperature, showing an activation energy of ca 21 meV. This value is much lower than those observed in the temperature dependence of the 2.7 eV photoluminescence (PL) and the cathodeluminescence (CL) induced by 8 keV electron irradiation. These results suggest that in IRL, some electrons excited to higher energy levels than the luminescence level are likely transferred to the luminescence state without thermal activation, resulting in a lower activation energy in their temperature dependence.

We have performed in situ measurements of luminescence from high and low OH silica glasses and a silica single crystal under H+ irradiation. The luminescence spectra showed various emission bands assigned to intrinsic and irradiation-produced defects in silica. With increase of H+ fluence, the intensity of the 2.7 eV band first increased and then gradually decreased, and which were respectively attributed to production of the B2α oxygen deficient centers and their subsequent annihilation by defect clustering or Si precipitation. Such defect formation processes under H+ irradiation were influenced by the amount of intrinsic OH in silica glass, i.e., irradiation-produced defects were more stable in the high-OH silica glass compared with the low-OH silica glass. The detailed analyses of the luminescence of silica single crystal indicated that the defect formation process after some amorphization of silica crystal is fundamentally the same as that in the low-OH silica glass.

In order to investigate the temperature effects on the dynamic radiation damaging process, we have carried out in situ measurements of in-reactor luminescence (IRL) and gamma-ray induced luminescence (GIL) of a silica glass at temperatures ranging from 70 K to 370 K. Both luminescence spectra were found to consist of two broad emission centers at 3.1 eV and 4.1 eV with an additional temperature independent emission around 2.5 eV. The 2.5 eV emission different from the other two showed long tail to the lower energy side and was attributed to the Cherenkov radiation. The 3.1 eV band was attributed to a B2β oxygen deficient center on the basis of our photoluminescence measurement. The intensity of the 3.1 eV IRL increased with increasing temperature up to ca. 200 K and saturated above 200 K, which is clearly different from the reported temperature dependence of 3.1 eV photoluminescence, suggesting the existence of some different relaxation mechanism of excited electron under ionizing radiations.

There has been some concern in reviewing the effectiveness of making decisions on the implementation of protective measures in emergency exposure situations. After the Fukushima Daiichi nuclear power plant accident, temporal changes in the concentration of iodine 131 in tap water were studied using published data from several authorities in Fukushima, Ibaraki, and Tokyo. Averted doses to infants (1-year-old children) due to the intake of iodine 131 through tap water restrictions were also evaluated. Consequently, it was found that the apparent half-life of iodine 131 in tap water was 2.8 days. The averted equivalent doses to the thyroids of 1-year-old children were found to have a maximum value of 8.3 mSv in a local area of Fukushima. Hence, the tap water restrictions implemented by the authorities were considered to be effective in the early phase of the emergency exposure situation.

Many residents are exposed to radiation in their daily lives in the areas contaminated by radioactive materials by the Fukushima Daiichi Nuclear Power Plant accident. To protect the people from radiation exposures adequately, dose assessment is necessary. The aim of this study is to provide the scientifically based quantitative information about a range of received doses to the people from the evacuation areas and the deliberate evacuation areas. To achieve this aim, we adopted a probabilistic approach that can provide the information about a range of doses and their likelihood of occurrence taking into account uncertainty and variability of input data. The dose assessment was performed based on the measurement data of the surface activity concentrations of 137Cs and the results of actual survey on behavioral patterns of the population groups living in Fukushima Prefecture. As the result of assessment, the 95th percentile of the annual effective dose received by the inhabitants evacuated was mainly in the 1–10 mSv dose band in the first year after the contamination. However, the 95th percentile of the dose received by some outdoor workers and inhabitants evacuated from highly contaminated areas was in the 10–50 mSv dose band.

Risk evaluation is an important assessment tool of nuclear safety, and a common index of direct/indirect influences of severe accidents as a compound of risk is necessary then. In this research, various influences of severe accidents are converted to monetary value and integrated. The integrated influence is calculated in a unit of “cost per severe accident” and “cost per kWh”. The authors must emphasize that the aim is not to estimate the accident cost itself but to extend the scope of “risk-informed decision making” for continuous safety improvements of nuclear energy. To calculate the “cost per severe accident” and the “cost per kWh”, typical sequences of severe accidents are picked-up first. Containment failure frequency (CFF) and source terms of each sequence are taken from the results of level 2 probabilistic risk assessment (PRA). The source terms of each sequence is input into the level 3 PRA code OSCAAR which was developed by Japan Atomic Energy Agency (JAEA). The calculations have been made for 248 meteorological sequences, and the results presented in this study are given as expectation values for various meteorological conditions. Using these outputs, the cost per severe accident is calculated. It consists of various costs and other influences converted into monetary values. This methodology is applied to a virtual 1,100 MWe BWR-5 plant. Seismic events are considered as the initiating events. The data obtained from the open documents on the Fukushima Accident are utilized as much as possible. Sensitivity analyses are carried out to identify the dominant influences, sensitive assumptions/parameters to the cost per accident or per kWh. Based on these findings, optimization of radiation protection countermeasures is recommended. Also, the effects of sever accident management are investigated.

We have isolated a novel type of natural tumoricidal product from the basidiomycete strain, Agaricus blazei Murill. Using the double-grafted tumor system in Balb/c mice, treatment of the primary tumor with an acid-treated fraction (ATF) obtained from the fruit bodies resulted in infiltration of the distant tumor by natural killer (NK) cells with marked tumoricidal activity. As shown by electrophoresis and DNA fragmentation assay, the ATF also directly inhibited tumor cell growth in vitro by inducing apoptotic processing; this apoptotic effect was also demonstrated by increased expression of the Apo2.7 antigen on the mitochondrial membranes of tumor cells, as shown by flow-cytometric analysis. The ATF had no effect on normal mouse splenic or interleukin-2-treated splenic mononuclear cells, indicating that it is selectively cytotoxic for the tumor cells. Cell-cycle analysis demonstrated that ATF induced the loss of S phase in MethA tumor cells, but did not affect normal splenic mononuclear cells, which were mainly in the G0G1 phase. Various chromatofocussing purification steps and NMR analysis showed the tumoricidal activity to be chiefly present in fractions containing (1-->4)-alpha-D-glucan and (1-->6)-beta-D-glucan, present in a ratio of approximately 1:2 in the ATF (molecular mass 170 kDa), while the final purified fraction, HM3-G (molecular mass 380 kDa), with the highest tumoricidal activity, consisted of more than 90% glucose, the main component being (1-->4)-alpha-D-glucan with (1-->6)-beta branching, in the ratio of approximately 4:1.

Soft x-ray excited optical luminescence (XEOL) of silica glasses was studied with respect to the excitation x-ray energy (near the Si K-edge) and irradiation time. The luminescence spectra showed emission bands at 3.1 eV and 2.7 eV, assigned to B2β and B2α oxygen deficient centers in silica glasses, and the luminescence yields of these bands changed drastically before and above the Si K-edge. Si K-edge photoluminescence yield (PLY) spectrum of the band at 3.1 eV was similar to Si K-edge XANES spectrum recorded in the photocurrent mode for the same silica sample, except for the negative edge jump in the PLY spectrum. The time evolutions of the band intensity at 3.1 eV were also investigated under the excitation by soft x-ray below and above Si K-edge. The band intensity in both cases decreased slightly with the irradiation. These results indicate that a part of B2β centers in the silica glass probably changed to other types of oxygen deficiencies by the electron excitation effect. In the early stage of the irradiation, a rapid increase in the intensity of the 3.1 eV band was also observed, indicating that soft x-ray irradiation produced luminescence sites such as B2β centers.