Accidental Release Of Radioactivity Research Articles

Origin and age of an ongoing radioactive contamination of soils near La hague reprocessing plant based on 239+240Pu/238Pu and 241Am/241Pu current ratios and 90Sr and Ln(III) soil contents

Nuclear reprocessing plants are sources of environmental contamination by gaseous or liquid discharges. Numerous radionuclides are of concern, with actinides and 90Sr being the most radiotoxic. Environmental radioactivity survey programs mostly use γ-spectrometry to track contaminations because γ-spectrometry is very cost effective and can be carried out on raw samples. On the other hand, the determination of β- or α-emitting radionuclides in environmental samples requires rather sophisticated analytical methods, and are thus dedicated to specific goals. However, measuring radionuclides such as Pu, Am, and Sr often provides more information about the presence of a current or prior contamination and on its origin, based on the isotopic composition of the samples. We found that the analysis of 241Pu, 239+240Pu, 241Am, and 90Sr of a few selected soil samples taken near the nuclear reprocessing plant of La Hague, France, revealed the presence of a previous environmental contamination originating from several incidents in La Hague site involving atmospheric transfer and leaks in flooded waste pits. The 241Am-241Pu dating method indicated a contamination period prior to 1983. The presence of elevated levels of light non-radioactive lanthanides and yttrium in the soil samples confirmed the involvement of cold fuel. Our results demonstrate how long-lived actinides are likely to reveal a long-term contamination of the environment by spent fuel. Our study indicates that there is a requirement to use more sophisticated tools than γ-spectrometry when surveying the environments surrounding industrial plants for nuclear power and nuclear reprocessing with a potential for the accidental release of radioactivity into the environment.

A summary of fission-product-transport phenomena during SGTR severe accidents

A steam-generator-tube rupture (SGTR) in a pressurized-water reactor is a design-basis accident with which plants have been designed to cope. Its specific significance is in its potential to bypass the containment thereby providing a pathway for radioactivity release to the environment. In combination with significant core damage, uncontrolled SGTR may lead to accidental release of radioactivity in the form of aerosol particles and gaseous compounds.In this paper, we describe the phenomena identification and ranking tables (PIRT) prepared as an international collaboration for uncontrolled SGTR in connection with core damage. This PIRT is limited to fission-product transport and retention in the steam generator and release to the auxiliary building, i.e., the source term. The phenomena affecting the fission-product retention in the steam generator and release to the environment were divided into those relevant in a dry steam-generator secondary side, and those relevant in a flooded secondary side. Rankings were given to 17 phenomena in the dry and 16 phenomena in the flooded secondary side regarding their: i) impact on the source term, ii) the availability of experimental data applicable to SGTR severe-accident conditions, and iii) the availability of codes/models to describe the phenomenon under the conditions of SGTR severe accidents.The SGTR boundary conditions and the considered phenomena are briefly described. The results are given in the form of ranking tables separately for the dry and flooded steam generator secondary side. The most important phenomena and their interactions with other phenomena are discussed with references to existing data and models. The most important uncertain phenomena in the dry steam generator scenario are particle bounce and fragmentation; whereas inertial impaction and retention by droplets in the jet region are the most uncertain ones in the flooded configuration. The need for improved knowledge is, though, tempered by overall high aerosol retention in the latter scenario. The applicability of the existing data and models for SGTR accident analysis is considered in the discussion.

Influence of the migration of radioactive contaminants in soil, resident occupancy, and variability in contamination on isodose lines for typical Northern European houses

In the remedial phase following an accidental radioactive release, it is important that soil decontamination measures are carried out on the areas that contribute most to the radiation dose. In this study, the newly developed concept of isodose lines was applied to the area around typical Swedish dwellings to identify these areas. The influence of the most common building materials in Sweden, wood and brick, and the importance of the positions of doors and windows on the isodose lines were demonstrated for specific positions inside the houses, as well as for the entire house, assuming the residents exhibit typical resident occupancy. Decontamination of the areas within certain isodose lines was shown to result in a greater dose reduction than decontaminating the same area of soil within a certain distance of the house. Furthermore, the impact of vertical migration of the radioactive contaminants in the soil on the isodose lines was studied, showing that the area enclosed by isodose lines decreases over time as the contaminants migrate deeper into the soil. The resulting isodose lines and their change over time are dominated by the downward movement of the contamination in the upper layer of soil. The impact of the variability in contamination on the final isodose lines and their dependence on building materials are demonstrated.

The common field lampricide 3-trifluoromethyl-4-nitrophenol is a potential radiosensitizer in fish cells

PurposeTo evaluate if the common field lampricide 3-trifluoromethyl-4-nitrophenol (TFM) that is intended to eradicate the invasive species sea lampreys in the Great Lakes has the potential to sensitize radiation responses in cells from non-targeted native fish Materials and methodsThe TFM toxicity was assessed acutely and chronically with the clonogenic fish cell line eelB. The acute toxicity (24-h exposure) was determined by the fluorescent cell viability probe Alamar Blue. The chronic toxicity was determined either by Alamar Blue (7-d exposure) or the clonogenic survival assay (14-d exposure). Pre- and post-exposure of fish cells to environmentally relevant TFM concentrations following gamma irradiation were performed. Clonogenic survival was determined to assess the damage level of radiation-induced reproductive cell death. ResultsThe chronic toxicity tests were more sensitive than the acute toxicity tests. The 14-d EC50 using the clonogenic survival endpoint was 2.09 ± 0.28 μg/mL and was statistically similar to the 7-d EC50 (1.85 ± 0.07 μg/mL) based on the Alamar Blue-based cytotoxicity endpoint. Post-exposure of cells to environmentally relevant TFM concentrations following irradiation did not have any effect as compared to the irradiation alone group. In contrast, pre-exposure of cells to TFM following irradiation had a negative additive effect when the total radiation dose was 2 Gy, but not 0.1 or 0.5 Gy. ConclusionOur results suggest that the common field lampricide TFM is a potential radiation sensitizer in cells from non-targeted native fish. This could be a health problem of concern for non-targeted native fish if a large accidental radioactive release occurs.

Numerical Study of Long-Term Radioactivity Impact on Foodstuff for Accidental Release Using Atmospheric Dispersion Model

The radiological consequences of a potential atmospheric release of $$^{131}$$ I, $$^{137}$$ Cs, $$^{133}$$ Xe and $$^{90}$$ Sr for hypothetical accident appropriate to a 10 MW research reactor were calculated. The Gaussian model CROM (Screening Model for Environmental Assessment) was used to compute the accidental radioactive release under emergency exposure situation and the estimation of yearly average dose by different exposure pathways. The realistic assessment of radiation level due to the abnormal occurrence operation of nuclear installations such as foods consumption, external irradiation, inhalation and ingestion has been examined. In this study, the evaluation of the dose results, to a continuous emissions rate under dry and wet deposition process, was estimated onto six reference groups of public covering the period from the new born infant to more than 17 years old as defined by the International Commission on Radiological Protection. The obtained modeling results were compared to the limits values prescribed by IAEA and Euratom recommendations. The findings indicate that the ground concentrations were found to be significant and mostly sensitive to the emission conditions, when the total deposition exceeds the contamination limits. The short-lived isotopes have much more influence on the concentration on foodstuff. The activity concentration of $$^{131}$$ I is significantly higher in animal products and vegetables, while the $$^{137}$$ Cs is dominant in fruits vegetables. In contrast, the Noble gas $$^{133}$$ Xe is significantly lower.

Optimization of exposure and countryside waste management for different accidental radioactive release

Since the Fukushima accident, Japanese scientists have been intensively monitoring ambient radiations in the highly contaminated territories situated within 80 km of the nuclear site. The surveys that were conducted through mainly carborne, airborne and in situ gamma-ray measurement devices, enabled to efficiently characterize the spatial distribution and temporal evolution of air dose rates induced by Caesium-134 and Caesium-137 in the terrestrial systems. These measurements revealed that radiation levels decreased at rates greater than expected from physical decay in 2011-2012 (up to a factor of 2), and dependent on the type of environment (i.e. urban, agricultural or forest). Unlike carborne measurements that may have been strongly influenced by the depuration of road surfaces, no obvious reason can be invoked for airborne measurements, especially above forests that are known to efficiently retain and recycle radiocaesium.The purpose of our research project is to develop a comprehensive understanding of the data acquired by Japanese, and identify the environmental mechanisms or factors that may explain such decays. The methodology relies on the use of a process-based and spatially-distributed dynamic model that predicts radiocaesium transfer and associated air dose rates inside/above a terrestrial environment (e.g., forests, croplands, meadows, bare soils and urban areas).Despite the lack of site-specific data, our numerical study predicts decrease rates that are globally consistent with both aerial and in situ observations. The simulation at a flying altitude of 200 m indicated that ambient radiation levels decreased over the first 12 months by about 45% over dense urban areas, 15% above evergreen coniferous forests and between 2 and 12% above agricultural lands, owing to environmental processes that are identified and discussed. In particular, we demonstrate that the decrease over evergreen coniferous regions might be due the combined effects of canopy depuration (through biological and physical mechanisms) and the shielding of gamma rays emitted from the forest floor by vegetation. Our study finally suggests that airborne surveys might have not reflected dose rates at ground level in forest systems, which were predicted to slightly increase by 5 to 10% during the same period of time.

Automatic Mapping of Monitoring Data

This paper presents an approach, based on universal kriging, for automatic mapping of monitoring data. The performance of the mapping approach is tested on two datasets containing daily mean gamma dose rates in Germany reported by means of the national automatic monitoring network (IMIS). In the second dataset an accidental release of radioactivity in the environment was simulated in the South-Western corner of the monitored area. The approach has a tendency to smooth the actual data values, and therefore it underestimates extreme values, as seen in the second dataset. However, it is capable of identifying a release of radioactivity provided that the number of sampling locations is sufficiently high. Consequently, we believe that a combination of applying the presented mapping approach and the physical knowledge of the transport processes of radioactivity should be used to predict the extreme values.

Simulation of radioactive plume gamma dose over a complex terrain using Lagrangian particle dispersion model

FLEXPART-WRF is a versatile model for the simulation of plume dispersion over a complex terrain in a mesoscale region. This study deals with its application to the dispersion of a hypothetical air borne gaseous radioactivity over a topographically complex nuclear site in southeastern France. A computational method for calculating plume gamma dose to the ground level receptor is introduced in FLEXPART using the point kernel method. Comparison with another similar dose computing code SPEEDI is carried out. In SPEEDI the dose is calculated for specific grid sizes, the lowest available being 250 m, whereas in FLEXPART it is grid independent. Spatial distribution of dose by both the models is analyzed. Due to the ability of FLEXPART to utilize the spatio-temporal variability of meteorological variables as input, particularly the height of the PBL, the simulated dose values were higher than SPEEDI estimates. The FLEXPART-WRF in combination with point kernel dose module gives a more realistic picture of plume gamma dose distribution in a complex terrain, a situation likely under accidental release of radioactivity in a mesoscale range.

Hints to discriminate the choice of wet deposition models applied to an accidental radioactive release

In nuclear emergency management, wet deposition modelling is of crucial importance for correctly evaluating soil contamination after an atmospheric release. Wet deposition is generally divided into two main processes: in-cloud scavenging (rainout) and below-cloud scavenging (washout). The large number of schemes proposed in the literature for both processes reflects the uncertainties in our current understanding of these phenomena. There is presently no scientific consensus to discriminate between the two processes. In order to improve our understanding of the magnitude of modelling uncertainties, a comprehensive sensitivity analysis was performed by focusing on representation of wet deposition fluxes. A large number of model configurations involving different deposition schemes and modelling options were evaluated by comparison with available observations of soil contamination. The objective is to establish a priority rank order of wet deposition schemes for soil contamination modelling.

Determination of the maximum individual dose exposure resulting from a hypothetical LEU plate-melt accident

The objective of this study was to provide an estimate of the potential impact of accidental radioactive release from the testing cell of the Egyptian second research reactor ETRR-2 on the dose level of public around the reactor. The assessment was performed for two cases: an evaluation of the impact that accidental release has on the dose that would be received by public around the reactor in case of proper operation of testing cell filtration system; and an assessment of the potential dose in case of loss of testing cell filtration system. The results show that the filtration system has a great role in decreasing the dose received by an individual located outside the reactor to a dose level lower than the annual permissible dose.

Key factors in imprecision in radiological emergency response assessments using the NAMEmodel

In the very early stages of response to an accidental release of radioactivity leading toenvironmental contamination, it is likely that only limited measurements of radioactivity inthe local environment will be available on which to base decisions concerning protectionmeasures and radiation monitoring activities. Model predictions will be used to aidunderstanding of the radiological situation and to form a basis for emergency healthprotection decisions. This paper presents an analysis of the relative importance ofcontributors to the imprecision associated with emergency response calculations based on afew off-site measurements, using predictions from the UK Met Office’s NAME III(Numerical Atmospheric dispersion Modelling Environment version 5.2) dispersion model.The results presented extend those from a previous study in which a simple Gaussianplume model was used and confirm the key parameters contributing to imprecision. Thepotential extent of the sheltering countermeasure resulting from a hypotheticalrelease in real weather conditions occurring in 2007 and 2008 is also presented.

Study of the radioecological sensitivity of rice to radioactive contamination

This study focused on the radioecology of rice and explored how the French specificities of rice cultivation can be taken into account in risk assessment. The objective of the study was to characterize the radioecological sensitivity of rice with respect to an accidental release of radioactivity. We want to know if a uniform and specific deposit would involve the same contamination on representative paddy fields of Camargue. To model the transfer of the radionuclides in the rice caryopsis following an accidental atmospheric pollution, we used the classical modelling for the cereals which considers first the interception by the foliage (modelled by an interception ratio) then the translocation to the grain (modelled by a translocation factor). The values of the parameters (interception ratio, translocation factor and yield) were regionalized with the agronomical software ORIZA2000, developed by the IRRI (International Rice Research Institute). We partly calibrated ORIZA2000 for a French rice variety: Ariete, thanks to physiological data provided for International Cooperation Centre in Agronomical Research for Development (CIRAD). ORIZA2000 proposes a daily follow-up of the leaf area index which can be correlated with the interception ratio. Five simulations with various climates, irrigation managements, and technical uses have been inputted on ORIZA2000. The data inputted were extracted from the database AGROSYST from the French Institute for Agronomical Research (INRA) and from the CIRAD. We established two scenarios of contamination. The first one consisted in a single contamination of water. In this case, there is almost no difference between simulations. However, in each simulation (except for organic farming) it is relevant to notice that the fourth depletion of water leads to a significant variation of contamination. The second contamination scenario consisted in a double contamination of water and of air. In that case, technical practices are responsible of the highest source of variability of the grain contamination. The variability of the contamination is mainly due to the variability of the yield which has in the radioecological modelling a dilution effect. The rice produced by organic farming is more sensitive than the rice produced by conventional farming because of low yields.

Bayesian Inference and Markov Chain Monte Carlo Sampling to Reconstruct a Contaminant Source on a Continental Scale

AbstractA methodology combining Bayesian inference with Markov chain Monte Carlo (MCMC) sampling is applied to a real accidental radioactive release that occurred on a continental scale at the end of May 1998 near Algeciras, Spain. The source parameters (i.e., source location and strength) are reconstructed from a limited set of measurements of the release. Annealing and adaptive procedures are implemented to ensure a robust and effective parameter-space exploration. The simulation setup is similar to an emergency response scenario, with the simplifying assumptions that the source geometry and release time are known. The Bayesian stochastic algorithm provides likely source locations within 100 km from the true source, after exploring a domain covering an area of approximately 1800 km × 3600 km. The source strength is reconstructed with a distribution of values of the same order of magnitude as the upper end of the range reported by the Spanish Nuclear Security Agency. By running the Bayesian MCMC algorithm on a large parallel cluster the inversion results could be obtained in few hours as required for emergency response to continental-scale releases. With additional testing and refinement of the methodology (e.g., tests that also include the source geometry and release time among the unknown source parameters), as well as with the continuous and rapid growth of computational power, the approach can potentially be used for real-world emergency response in the near future.

Key sources of imprecision in radiological emergency response assessments

In the first few hours after an accidental release of radioactivity to the atmosphere it islikely that limited measurements of radioactivity in the environment will be available onwhich to make decisions concerning protection measures and radiation monitoringactivities, and that monitoring data will be supplemented by the predictions of models.There will be imprecision associated with these predictions, partly resulting from lack ofknowledge (for example, about the nature of the release and the actual stateof the weather), partly due to imprecision in the models themselves and partlydue to intrinsic imprecision associated with the accuracy of the measurements.This study considers the relative importance of the key parameters influencingassessment imprecision and discusses the implications for emergency response systems.

Food safety and acceptance of management options after radiological contaminations of the food chain

After an accidental radioactive release leading to contamination of the food chain, countermeasures may be used to reduce the radiological health risk to the population and to bring social reassurance. This paper analyses public acceptance and consumer’s behaviour for various countermeasures for contaminated milk as revealed by a recent public survey in Belgium. The survey instrument used was Computer Assisted Personal Interviewing. A simulated news bulletin was included for a fast and realistic briefing on the situation investigated. The results show that clean feeding of dairy cattle and disposal of contaminated milk are the preferred options in case of contaminations above legal norms. For contaminations below legal norms, normal consumption of milk seems better accepted than disposal. Nonetheless, the expressed consumer’s behaviour reveals a precautionary tendency: the presence of radioactivity at some step in the food chain could lead to avoiding purchasing products from affected areas. Finally, public trust building is revealed as a key element of a successful countermeasure strategy.

CUMULATIVE DOSE ASSESSMENT USING THERMOLUMINESCENCE PROPERTIES OF PORCELAIN ISOLATORS AS EVIDENCE OF A SEVERE RADIATION ACCIDENT IN THE REPUBLIC OF SAKHA (YAKUTIA), RUSSIA, 1978

The cumulated absorbed doses in four electric porcelain isolators collected at the site of the "Kraton-3" underground nuclear explosion in the Republic of Sakha (Yakutia), Russia, were evaluated using the thermoluminescence technique. The doses attributable to the accidental radioactive release from the explosion ranged from 1.2 to 10 Gy; the maximal value was detected for the isolator collected near the "Kraton-3" borehole. The measured thermoluminescence doses for two of the four samples analyzed are in reasonable agreement with the estimates of external gamma dose presented by earlier investigators of the site.

Bayesian Updating of Atmospheric Dispersion After a Nuclear Accident

Summary We consider a Bayesian forecasting system to predict the dispersal of contamination on a large scale grid in the event of an accidental release of radioactivity. The statistical model is built on a physical model for atmospheric dispersion and transport called MATCH. Our spatiotemporal model is a dynamic linear model where the state parameters are the (essentially, deterministic) predictions of MATCH; the distributions of these are updated sequentially in the light of monitoring data. One of the distinguishing features of the model is that the number of these parameters is very large (typically several hundreds of thousands) and we discuss practical issues arising in its implementation as a realtime model. Our procedures have been checked against a variational approach which is used widely in the atmospheric sciences. The results of the model are applied to test data from a tracer experiment.

Better use of European (regional) resources.

In case of an accidental release of radioactivity and subsequent contamination of the food chain, many samples need to be collected and analysed, and this is far from being a simple issue. The determination of contamination levels requires accredited laboratories, approved and certified procedures and methods, transparency and above all prompt results, as stakeholders in general cannot afford waiting. Adequate decisions require fixed norms, stable in time, and accepted internationally. Moreover, an effective policy relies on traceability of products as well. There are huge requirements of harmonisation of procedures, traceability of data, database management, priority settings etc. Accredited laboratories tend to make use of reliable techniques but these have been optimised for low radiation levels and high accuracy for routine analyses, often in the framework of radiological surveillance of the territory, drinking waters or the food chain. It is obvious that such procedures, although very accurate and sensitive, are not suited for urgent decisions in crisis situations. Similarly, accredited analysis methodologies may start from large quantities of product in order to decrease limits of detection; however, this involves sometimes long times for drying or chemical treatment, introducing important delays. Furthermore, large quantities of samples would simply result in the saturation of the analytical capabilities of one country. Adequate actions and informed decisions during a nuclear accident will require an analytical infrastructure that individual countries do not have; hence there is a clear need to establish regional collaboration and co-operation. This paper includes an example of such collaborative work and mutual assistance, and also touches on how sharing tools for decision making, analytical resources, sample collection procedures and analysis would promote trust, reliablity in the results, a common approach toward minimizing the effects of a radiological disaster and above all unity. Last but not least, this paper also poses a challenge: Nuclear accident management implies that all responsible parties have to guarantee that decision support systems have access to data and information in the best available and consistent manner. This will not be achieved in an independent and isolated manner.

Regulation of nuclear radiation exposures in India

India has a long-term program of wide spread applications of nuclear radiations and radioactive sources for peaceful applications in medicine, industry, agriculture and research and is already having several thousand places in the country where such sources are being routinely used. These places are mostly outside the Department of Atomic Energy (DAE) installations. DAE supplies such sources. The most important application of nuclear energy in DAE is in electricity generation through nuclear power plants. Fourteen such plants are operating and many new plants are at various stages of construction. In view of the above mentioned wide spread applications, Indian parliament through an Act, called Atomic Energy Act, 1964 created an autonomous body called Atomic Energy Regulatory Board (AERB) with comprehensive authority and powers. This Board issues codes, guides, manuals, etc., to regulate such installations so as to ensure safe use of such sources and personnel engaged in such installations and environment receives radiation exposures within the upper bounds prescribed by them. Periodic reports are submitted to AERB to demonstrate compliance of its directives. Health, Safety and Environment Group of Bhabha Atomic Research Centres, Mumbai carries out necessary surveillance and monitoring of all installations of the DAE on a routine basis and also periodic inspections of other installations using radiation sources. Some of the nuclear fuel cycle plants like nuclear power plants and fuel reprocessing involve large radioactive source inventories and have potential of accidental release of radio activity into the environment, an Environmental Surveillance Laboratory (ESL) is set up at each such site much before the facility goes into operation. These ESL’s collect baseline data and monitor the environment throughout the life of the facilities including the de- commissioning stage. The data is provided to AERB and is available to members of the public. In addition, a multi-tier system of AERB permissions is in place to ensure that all aspects of safety have been considered before permission to operate is granted. The stages where permission of AERB is essential are site selection, design data, and several stages during construction and operation. The details required by AERB include provision for treatment and storage of radioactive waste, de-commissioning procedures and provision of costs. In addition to AERB, nuclear power plants have to comply with the requirements of Ministry of Environment and Forests and get their clearance. This is given on the basis of Environmental Impact Assessment Report which should satisfy the authorities that no ecological damage will be caused and the facility will not have adverse effect on the environment. In addition, the State Pollution Control Board where the facility is to be located has to permit the site of the plant for its proposed discharges into the environment. It is largely due to the above comprehensive regulatory controls that none of the plants in India had any accident during the last 3–4 decades of operation. The type of measurements carried out by the ESL’s and results from a few typical ESL’s will be presented.

A study of atmospheric dispersion of radionuclides at a coastal site using a modified Gaussian model and a mesoscale sea breeze model

Ground level concentration and sky-shine dose due to radioactive emissions from a nuclear power plant at a coastal site have been estimated using the standard Gaussian Plume Model (GPM) and the modified GPM suggested by Misra (Atmospheric Environment 14 (1980) 397), which incorporates fumigation effect under sea breeze condition. The difference in results between these two models is analysed in order to understand their significance and errors that would occur if proper choice were not made. Radioactive sky-shine dose from 41Ar, emitted from a 100 m stack of the nuclear plant is continuously recorded by environmental gamma dose monitors and the data is used to validate the modified GPM. It is observed that the dose values increase by a factor of about 2 times than those of the standard GPM estimates, up to a downwind distance of 6 km during sea breeze hours. In order to examine the dispersion of radioactive effluents in the mesoscale range, a sea breeze model coupled with a particle dispersion model is used. The deposited activity, thyroid dose and sky-shine radioactive dose are simulated for a range of 30 km. In this range, the plume is found to deviate from its straight-line trajectory, as otherwise assumed in GPM. A secondary maximum in the concentration and the sky-shine dose is also observed in the model results. These results are quite significant in realistically estimating the area affected under any unlikely event of an accidental release of radioactivity.