Dose Rate In Areas Research Articles

Integrated radiation air dose rate maps over the 80 km radius of the Fukushima Daiichi Nuclear Power Plant and the entire Fukushima Prefecture during 2011–2022

In this study, we created integrated radiation air dose rate maps in the Fukushima region during 2011–2022 using airborne, car-borne, and walk surveys and fixed-location measurements. We applied a Bayesian geostatistical method to the 80 km radius of the Fukushima Daiichi Nuclear Power Plant and the entire Fukushima Prefecture while considering the history of the evacuation zone lifting in Fukushima. The integrated maps in this study fixed the bias to underestimate the air dose rates in forest areas and created integrated maps with a wider area and time series than previous studies. Furthermore, the results improved our understanding of the spatial heterogeneity of air dose rates. The correlations between walk and airborne surveys and walk and car-borne surveys changed over time (the walk survey includes fixed-location measurements), with the decreasing rates of air dose rate being faster for car-borne surveys, walk surveys, fixed-location measurements, and airborne surveys, in that order. The temporal changes in the variograms indicate that the heterogeneity of the radiocesium distribution in the environment varies with time due to decontamination activities and weathering effects. The trends inside and outside the evacuation zone differ. The temporal changes in the air dose rates from the integrated maps show a decrease between fixed-location measurements and the airborne survey. This decreasing rate mostly reflects the overall decrease in air dose rates. The results of this study could be used to evaluate detailed exposure doses to the public.

Examining External Dose Rates in Mamuju Regency, Indonesia: A Personal Radiation Dosimetry Approach

This study aimed to quantify the individual external radiation exposure in Mamuju, Indonesia. A SmartRad portable personal dosimeter was utilized for this purpose, and data was collected over a period of 30 days. The findings indicate that the dose rate varies from 0.152 to 4.200 μSv/h and cumulatively ranges from 0.1 to 8.4 μSv/day based on an average measurement duration of 160 minutes. The average dose rate in areas with mineral deposits is 11.02 mSv per year. In contrast, the average effective dose in areas without radioactive mineral deposits is 2.6493 mSv per year. The annual average effective dose for individuals was measured at 6.8347 mSv. These findings imply that personal exposure to radiation among the public in Mamuju exceeds the threshold recommended by the International Commission of Radiological Protection.

Gamma radiation dose rate in high-altitude areas in the Bageshwar, Champawat and Pithoragarh districts of Uttarakhand, India.

Radiation has a deteriorating effect on humans as well as on the environment depending on its level, although we have all been exposed to natural gamma radiation from birth. The presence of radionuclides in rocks, soil, plants, and water is a major factor behind the natural gamma radiation. The present study deals with the study of natural gamma radiation at Bageshwar, Champawat and Pithoragarh districts of Uttarakhand. It also consists of seasonal variations in gamma radiation and its relationship with altitude and geology. The purpose of this study was to investigate the influence of altitude and geology on natural gamma radiation dose rate data in high-altitude areas of India. The highest gamma radiation value was 444nSv/h in the summer and 342nSv/h in the winter. The investigation recorded the gamma radiation up to 2542.20maltitude, indicating that the geology of the areas is more relevant than the altitude. Few sites in such a high-altitude zone were found to exceed the value of 200nSv/h, as reported by UNSCEAR. This research is necessary in order to consider the human health and climate changes, both of which are part of the action plan for the United Nation's Sustainable Development Goals (SDG 3, SDG 13).

Changes in air dose rates due to soil moisture content in the Fukushima prefecture forests

Radionuclides released and deposited because of the 2011 Fukushima Dai-ichi Nuclear Power Plant accident caused an increase in air dose rates in Fukushima Prefecture forests. Although an increase in air dose rates during rainfall was previously reported, the air dose rates in the Fukushima forests decreased during rainfall. This study aimed to develop a method to estimate rainfall-related changes in air dose rates, even in the absence of soil moisture data, in Namie-Town and Kawauchi-Village, Futaba-gun, Fukushima Prefecture. Moreover, we examined the relationship between preceding rainfall (Rw) and soil moisture content. The air dose rate was estimated by calculating the Rw in Namie-Town from May to July 2020. We found that the air dose rates decreased with increasing soil moisture content. The soil moisture content was estimated from Rw by combining short-term and long-term effective rainfall using half-live values of 2 h and 7 d and considering the hysteresis of water absorption and drainage processes. Furthermore, the soil moisture content and air dose rate estimations showed a good agreement with coefficient of determination (R2) scores >0.70 and >0.65, respectively. The same method was tested to estimate the air dose rates in Kawauchi-Village from May to July 2019. At the Kawauchi site, variation in estimated value is relatively large due to the presence of water repellency in dry conditions, and the amount of 137Cs inventory was low, so estimating air dose from rainfall remained a challenge. In conclusion, rainfall data were successfully used to estimate soil moisture and air dose rates in areas with high 137Cs inventories. This leads to the possibility of removing the influence of rainfall on measured air dose rate data and could contribute to the improvement of methods currently used to estimate the external air dose rates for humans, animals, and terrestrial forest plants.

Outdoor survey of absorbed dose rate and annual effective dose in Port Said, Marsa Alam-Shalateen and Helwan areas – Egypt.

Outdoor survey of absorbed dose rate and annual effective dose in Port Said, Marsa Alam-Shalateen and Helwan areas – Egypt.

Feasibility study of 3D gamma imaging for improving radiological protection at Sizewell B nuclear power plant.

Nuclear power plants are continuously looking to optimise their radiological monitoring and visualization techniques. At Sizewell B nuclear power plant in the UK, a trial was carried out to judge the feasibility of a gamma imaging system to provide accurate visual representation and characterisation of source terms on an operational pressurized water reactor. Data was collected through a series of scans taken in two rooms within a radiological controlled area at Sizewell B and used to generate radiation "heat maps". This survey type supports As Low As Reasonably Practicable (ALARP) (UK equivalent to ALARA) working in areas with high general area dose rate by gathering radiometric data and generating intuitive visual characterisation of work area source terms.

Surveillance of the seashore using the KATERINA II geo-referenced detection system

In this work, the design and initial demonstration of the KATERINA II detection system for rapid mapping of radionuclides in areas near to seashore is presented. A new development has been realized by integrating a GPS module in KATERINA II detection system and synchronizing its data with the acquired spectra in real-time. The new system may be used in a backpack, for areas with low activity concentration, or can be installed in an unmanned vehicle, for observing and mapping the source(s) of radioactivity, e.g. at the seashore, in areas with high contamination. A quantitative solution is provided for natural and artificial radionuclides, taking into account the characteristics of the detector, the parameters of measurement geometry and a mean beach sand/sediment composition. This paper reports field results for site characterization issues through automated analysis of gamma-ray spectra including low-level and low-energy γ-emitters. Perspectives of the future application of the system in a worldwide basis are related to radionuclides mapping and the assessment of dose rates in seashore areas that may be contaminated due to the operation of nuclear power plants, desalination plants and NORM industries, and/or due to the decommissioning of nuclear installations.

Impact evaluation of typhoons and remediation works on spatiotemporal evolution of air dose rate in two riverside parks in Fukushima, Japan after the Dai-ichi nuclear power plant accident

This study elucidated the impacts of typhoon events and remediation works on the spatiotemporal evolution of the air dose rate in riverside areas frequented by residents. Spatial distribution of the air dose rate and radiocesium concentration in the sediments were measured in two riverside parks located near each other in Fukushima Prefecture, Japan, for 2015–2020. The air dose rates measured by walk surveys were interpolated using ordinary kriging to generate air dose rate maps, to facilitate a comparison between the results at different points in time during the measurement campaigns. After the typhoons that occurred during 2015–2018, the air dose rate near the riverside in one park decreased, but not in the other, because the erosion and sediment deposition patterns differed between them. This could be due to the presence of a dam upstream, which serves a flood mitigation function. However, the extreme event of typhoon Hagibis in 2019 dropped the air dose rates near the riversides in both parks. In contrast to the typhoon events which affected the riverside areas, remediation works such as decontamination undertaken during 2015–2019 reduced the air dose rates around the garden and lawn areas which are frequently used as recreational sites. Modeling the temporal evolutions in the air dose rates for the entire area of the riverside parks revealed that 35% of the reduction was caused by physical decay of radiocesium on average, 14% by vertical migration of radiocesium in the soil through precipitation, and 51% by the three typhoons and remediation works during 2015–2019. The contribution of 20% from the strongest typhoon Hagibis highlights the fact that floods resulting from large typhoons are effective in causing natural attenuation of air dose rates in riverside parks.

Measurement of individual external doses of Tokyo Electric Power Company Holdings employees working in Fukushima Prefecture and the relationship between individual external doses and air dose rates in areas including difficult-to-return zones

Since the Fukushima Daiichi Nuclear Power Station accident, evacuation orders have been lifted except for the difficult-to-return zones (DRZs). Within the DRZs, there has been designated a special zone for reconstruction and revitalisation (SZRR). Decontamination of the SZRR has been promoted so that evacuation orders may be lifted. Previous studies measured individual external doses in the evacuation order-lifted zones (ELZs) and other living areas where the annual additional individual external dose was overall less than approximately 5 mSv y−1. However, there have been few reports about the measurement of individual external doses in a SZRR or outside of an SZRR (O-SZRR). In SZRRs and O-SZRRs, Tokyo Electric Power Company Holdings employees work mainly outdoors. Therefore, the employees’ individual external doses and air dose rates were measured in these zones from March 2020 through January 2021. Our key results were:The median (minimum to maximum) individual external doses at outdoor locations were 0.16 μSv h −1 (0.05–0.63 μSv h−1 ), 0.57 μSv h −1 (0.15–3.92 μSv h−1 ), and 1.36 μSv h −1 (0.14–11.91 μSv h−1 ) for the ELZ, SZRR, and O-SZRR, respectively.The conversion coefficients for the air dose rate measured by airborne monitoring to individual external dose were 0.23, 0.38, and 0.50 for the ELZ, SZRR, and O-SZRR, respectively. The conversion coefficients were below 0.6, which was used in the national government model for estimating external exposure dose from air dose rate. In addition, the conversion coefficients for the SZRR and O-SZRR in air dose rates of less than 1.5 μSv h−1 differed from those obtained for the entire measurement range of this study.The conversion coefficient from air dose rate at a height of 1 m above ground level to individual external dose was researched across a broader and higher range of air dose rates than in the previous study (0.24–20.89 μSv h−1 ). The conversion coefficient is confirmed to be 0.7, similar to previous studies.

Загальний підхід до поводження з паливовмісними матеріалами і супутніми радіоактивними відходами на етапі діяльності з вилучення їх із приміщень об’єкта «Укриття»

After the commissioning of the New Safe Confinement — Shelter object (NSC-SO) complex, radioactive waste (RAW) management activities during the removal of fuel containing materials (FCM) from the SO premises must be carried out with the involvement of NSC systems, including the system of main cranes (SMC), as well as systems and equipment of the technological building (TB), as a component of the NSC. The paper presents a new principled approach to waste management that will be generated during the extraction of FCM from the SO. The transport and technological chains of waste management by their types are considered: FCM, highly active waste and associated RAW. It is noted that the dose rates in many areas of work in the SO can reach 10 Sv/h. In such conditions, the involvement of personnel in physical work should be completely excluded, and the robotics, which will participate in technological operations, should be prepared for work in high ionizing radiation fields. For this reason, the removed FCM cannot be sent for processing to the TB of the NSC, as is done with other RAW (medium-level waste, low-level waste), which were removed from the premises of the SO earlier. It is justified that handling of FCM should be carried out in hermetic protective blocks (block of hot cells). Such cameras should be built in the NSC space as part of the new production building. It is noted that the volume of associated RAW, which will be formed during the extraction of FCM from the SO, will be extremely large. It is practically impossible to carry out their quantitative assessment. The work on the management of associated RAW will be carried out similarly to the work on the removal of FCM. Detected highly active fragments on overall structures should be cut out if possible, and small fragments or detected explosives in building materials are loaded into a transportable container for explosives with their further transfer of the container to the block of hot cameras. The remaining RAW, including radioactively contaminated metal structures and radioactively contaminated concrete structures, are loaded into the container for adjacent RAW and moved to the NSC temporary storage site. Waste removal work should be carried out using a system of a mobile instrument platform of the NSC crane with a remotely controlled robot manipulator (RCRM) attached to it and separate mobile remotely controlled mechanisms (RCM) on their own, depending on their needs. Conclusions are given regarding the sufficiency of infrastructure capabilities for RAW handling at the Chornobyl nuclear power plant and in the Exclusion Zone (EZ), to ensure this activity in general. It is noted that the activities for the preparation of infrastructure facilities for waste management during the removal of FCM from the SO should be directed both to the extension of the operational life of existing facilities and to the construction of new ones.

Dosimetric Study on Natural Background Ionizing Radiation and Impact Assessment on Public Health: A systematic Review in Nigeria

Environmental natural background ionizing radiation contamination and degradation is a global concern because of its negative effect on public health. Public health risk continues to be one of the environmental and public concerns in Nigeria. The emission of natural background ionizing radiation from the outer space, crust of the earth, food, and water and construction materials contributed a lot to the public environmental exposure. The populations’ exposure to background radiation emanated from terrestrial, cosmic, and internal radiation account for 82% which are out of control. Present work was aimed to carry out an investigational study of the natural background ionizing radiation levels, identify locations with high or low BIR and assess the health effect within Nigeria’s communities based on the available data extracted from the literatures and establish a baseline data of exposure rate, absorbed dose rate, annual effective dose equivalent, and excess life cancer risk from outdoor and indoor background radiation. This dosimetric study of natural background radiation in Nigeria is important to monitor the levels of radiation to which people are exposed directly or indirectly. Recently, several studies have been done in Nigeria and different values were reported based on indoor and outdoor background radiation doses. In this paper, a review and literature survey of natural background ionizing radiation was carried out. The data extracted based on indoor and outdoor revealed that Plateau, Oyo, River, Delta and Ondo, Sokoto, Kano and Niger have the highest value of dose rate compared to the world average value. The order of magnitude of the dose rate were Plateau > Oyo > Rive > Delta > Ondo and River > Plateau > Sokoto > Kano > Oyo > Ondo > Delta > Niger for Indoor and outdoor respectively. The highest outdoor & indoor annual effective doses were observed in OYO, Sokoto, Ondo, Delta, Akwanga, Plateau, and River. The results were comparatively greater than the world acceptable limit of 1.0 mSv/y. The order of magnitude of annual effective are OYO > Sokoto > Ondo > Niger Delta and Akwanga > Plateau > Delta > River for outdoor and indoor respectively. The regions with highest excess life cancer risks in Nigeria were observed in Oyo, Akwanga, Ondo, Plateau, River, Kaduna, Anambra, Port court, Abuja, Delta, Ibadan and Kano. Radiation cancer induction values obtained were remarkably high compared to world average value of 0.29×10-3. The amount of radiation absorbed by individual organs exposed to high natural background radiation areas were observed to be highest in tests organ, the order of magnitude were Tests > Bone marrow > Whole body > Lung > Ovaries > Kidney > Liver. But all the estimated mean values of organs doses were remarkably lower than that of world average value. Since the mean absorbed dose rate and annual effective dose in several areas is higher than 0.084µSv/h and 1.0 mSv/year for general public in many locations, long term exposure of the public to these radiations may lead to radiation induced health hazard such as erythema, skin cancer, genetic mutation and sterility.

The Efficiency of Nuclear Ion Exchange Resins Applied in the Primary Circuit Demineralizers of NPP Krško

Chemistry can influence dose rates by two aspects: chemistry conditions applied in the primary circuit and removal of (in)soluble particles. Since the primary coolant activity can have a significant impact on area dose rates and personnel doses, the main objective of purifying the primary coolant is to act on the radioactive source and keep it as low as reasonably achievable. Reduction of occupational exposure maintains confidence among workers and the public. Other factors, such as fuel duty, cycle operation, length and history, materials, steam generator (SG) surface area and particulate redeposition, also have significant contribution to the doses. Ion exchange (IEX) is one of the most common and effective liquid effluents treatment methods in nuclear fuel cycle operations. IEX technology encompasses the sciences of thermodynamics, kinetics, ion chemistry, fluid mechanics, and economics. In the industrial water treatment, cation exchangers are used in combination with downstream anion exchangers or as a mixed bed demineralizer (combination of both cation and anion) for full demineralization. IEX is also an effective treatment method for liquid radioactive waste. In spite of its advanced stage of development, various aspects of ion exchange technology are being studied to improve its efficiency and economy in its application to radioactive waste management and coolant cleaning processes. Over the years desire to improve the efficiency of fine colloidal particles removal and corrosion particulate removal in the primary systems has increased. There is a need for more and more efficient purification in order to decrease worker’s dose during maintenance but also to decrease volumes of radioactive resin waste. Homogenization of products and usage on primary coolant treatment take into account the compromise between source term reductions, liquid and solid waste, and buying and disposal cost. As the disposal costs are much greater than the buying costs, optimization of the lifetime of the purification media, along with an increasing efficiency of pollutant removal is a major goal. One of the effective purification methods for particulate removal is layering of macroporous (MP) resin in clean-up beds, spent fuel pit (SFP) and radwaste beds. Lately, MP resins were also implemented in the primary circuit demineralizers of NPP Krško. The paper evaluates resin purification efficiency of different primary media, and assesses performance of gel and macroporous resin types.

Radiation Monitoring in the Residential Environment: Time Dependencies of Air Dose Rate and 137Cs Inventory

Background: Residential areas have some factors on the external exposure of residents, who usually spend a long time in these areas. Although various survey has been carried out by the government or the research institutions after the Fukushima Daiichi Nuclear Power Plant accident, the mechanism of radiocesium inventory in the terrestrial zone has not been cleared. To better evaluate the radiation environment, this study investigated the temporal changes in air dose rate and 137Cs inventories (Bq/m2) in residential areas and agricultural fields.Materials and Methods: Air dose rate and 137Cs inventories were investigated in residential areas located in an evacuation zone at 5–8 km from the Fukushima Daiichi Nuclear Power Plant. From December 2014 to September 2018, the air dose rate distribution was investigated through a walking survey (backpack survey), which was conducted by operators carrying a γ-ray detector on their backs. Additionally, from December 2014 to January 2021, the 137Cs inventories on paved and permeable grounds were also measured using a portable γ-ray detector.Results and Discussion: In the areas where decontamination was not performed, the air dose rate decreased faster in residential areas than in agricultural fields. Moreover, the 137Cs inventory on paved surfaces decreased with time owing to the horizontal wash-off, while the 137Cs inventory on permeable surfaces decreased dramatically owing to the decontamination activities.Conclusion: These findings suggest that the horizontal wash-off of 137Cs on paved surfaces facilitated the air dose rate decrease in residential areas to a greater extent compared with agricultural fields, in which the air dose rate decreased because of the vertical migration of 137Cs. Results of this study can explain the faster environmental restoration in a residential environment reported by previous studies.

Low dose of external exposure among returnees to former evacuation areas: a cross-sectional all-municipality joint study following the 2011 Fukushima Daiichi nuclear power plant incident

There is little information on the radiation dose levels of returnees to areas once designated as legal no-go zones, after evacuation orders were lifted subsequent to the 2011 Fukushima Daiichi nuclear power plant incident. This study used individual radiation dosimeter monitoring and a location history survey to conduct the most recent dose assessment of external exposure among returnees to former no-go zones. We specifically determined correlation and agreement between external doses and the air dose rate in residential areas and quantified both uncertainty and population variability of the observed data using Monte Carlo (MC) simulation methods. A total of 239 voluntary participants across ten municipalities were analysed; their representativeness of all affected municipal populations was confirmed in terms of air dose rate distribution in residential areas. We found that individual doses were statistically significantly correlated with the air dose rate based on government airborne monitoring. This implies that airborne monitoring can provide sufficient information for understanding dose levels among such returnees. The MC simulations demonstrated that the mean of the annual dose in 2019 (including natural background doses) was 0.93 (95% uncertainty interval 0.53–1.76) mSv, with limited variation between municipalities. As of 2019, this implies that doses from external exposure were very low among returnees and would be associated with a very low likelihood of physical effects according to current scientific consensus. However, these results should be taken with caution due to several study limitations, including selection and participation biases. Regardless, its findings will enhance societal debates about how both individual-dose and government airborne monitoring practices should operate in the future and how the government can improve the public outlook for radiation doses in incident-affected areas.

Temporal decrease in air dose rate in the sub-urban area affected by the Fukushima Dai-ichi Nuclear Power Plant accident during four years after decontamination works

Trends of air dose rate decrease after decontamination works and factors which affect them constitute essential information for radiation protection, such as prediction of external exposure to the public and implementation of measures to reduce such exposure. This study investigated the decrease of air dose rate (ambient dose rate at 1 m above the ground) at 163 points across sub-urban areas in the evacuation zone around the Fukushima Dai-ichi Nuclear Power Plant over the period of four years following the decontamination works carried out in November 2012. The air dose rate on the asphalt pavement decreased faster than on soil surfaces. In addition, air dose rates near the forest decreased at a slower pace than in open fields. These results suggest that the air dose rate in urbanized areas can decrease faster than in other types of land, even after decontamination. Based on comparisons with decrease rates obtained in other studies, the air dose rate tends to decrease faster outside the evacuation zone than inside it. The decrease in air dose rate after decontamination was slower than before decontamination. The contribution of the weathering effect and human activity was estimated to be about 80% and 20% of the ecological decrease rate, respectively.

Gamma Radiation Measurement due to Natural Radioactivity in Hot Water Spring of Behbahan

Introduction: Many people use hot water springs to treat some diseases, such as rheumatism, arthritis, and skin diseases, but they are unaware of the presence of natural radioactive substances that may be found in hot water springs. An effective way to understand the radiation risk of these elements are measuring the dose rate of radiation. In this study, for the first time, gamma dose rate has been measured at the hot water spring of the Garab village in Behbahan city. Materials and Methods: To measure of gamma dose rate in the hot water spring and around it, 6 points were considered and the dose rate in these areas was measured using the RAS-110 Survey meter in four seasons of the year. The dosimeters were also placed at two heights of 5 cm and 1 m, and the dose rate was read and recorded for 20 minutes in any point. Results: The measured absorbed dose rates in air ranged from 49 to 331 nGy/h, in hot water spring areas. The maximum high radiation dose rate was found nearby the principle hot water source (point 1) was measured at 331 nGy/h. The annual effective dose for this place was estimated to be 0.4 mSv. Conclusion: The results of this study showed that the annual effective dose of natural gamma in the hot water spring is higher than the global average and there was a significant difference between the dose rates in different seasons. Also, the effect of height on the amount of radiation is negligible

Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems

As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the “forest” was slower than its decrease in other regions, while that in “urban area” was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the “difficult-to-return zone”. However, the decreasing trend starting from 2013 showed that the decrease in the “zone in preparation for the lifting of the evacuation order” and in the “residence restriction area” was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2–0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9–3.8 and 3.8–9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72–0.77.

Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems

As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the “forest” was slower than its decrease in other regions, while that in “urban area” was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the “difficult-to-return zone”. However, the decreasing trend starting from 2013 showed that the decrease in the “zone in preparation for the lifting of the evacuation order” and in the “residence restriction area” was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2–0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9–3.8 and 3.8–9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72–0.77.

Recommendations to harmonize European early warning dosimetry network systems

After the Chernobyl nuclear power plant accident in 1986, followed by the Fukushima Nuclear power plant accident 25 years later, it became obvious that real-time information is required to quickly gain radiological information. As a consequence, the European countries established early warning network systems with the aim to provide an immediate warning in case of a major radiological emergency, to supply reliable information on area dose rates, contamination levels, radioactivity concentrations in air and finally to assess public exposure. This is relevant for governmental decisions on intervention measures in an emergency situation. Since different methods are used by national environmental monitoring systems to measure area dose rate values and activity concentrations, there are significant differences in the results provided by different countries. Because European and neighboring countries report area dose rate data to a central data base operated on behalf of the European Commission, the comparability of the data is crucial for its meaningful interpretation, especially in the case of a nuclear accident with transboundary implications. Only by harmonizing measuring methods and data evaluation, is the comparability of the dose rate data ensured. This publication concentrates on technical requirements and methods with the goal to effectively harmonize area dose rate monitoring data provided by automatic early warning network systems. The requirements and procedures laid down in this publication are based on studies within the MetroERM project, taking into account realistic technical approaches and tested procedures.

Status of the ITER tokamak nuclear shielding and radiological protection design

Nuclear shielding of the ITER tokamak encompasses several systems and interfaces in a complex radiation environment. Therefore any shielding design has to involve a series of structures, systems and components in an integrated approach. This is evident for the complex ex-vessel radiation environment with streaming and leakage of plasma neutrons and subsequent activation of ex-vessel structures which give raise to excessive shutdown dose rates in accessible areas of the cryostat.The paper reviews recent nuclear analyses related to the performance of primary shields and highlights challenges toward an integrated nuclear shielding design. The general need of propagation of shielding requirements is highlighted in the context of radiation cross talk due to penetrations. Radiation streaming through gaps and penetrations is a key problem in any efficient shield design. The impact on the evolving radiation environment due to several design options along streaming paths such as port gaps, as well as their modeling for nuclear analysis, is presented. Implications regarding design integration and compliance with integrated shielding requirements and ALARA dose are finally given.