Atmospheric Dispersion Calculations Research Articles

An Integrated Solution for Nuclear Power Plant On-Site Optimal Evacuation Path Planning Based on Atmospheric Dispersion and Dose Model

Safety in nuclear energy utilization is crucial. In the event of a radioactive release incident, coupled with meteorological uncertainties, a radioactive plume can impact personnel evacuation. This paper presents an integrated solution for radionuclide release accident assessment and emergency evacuation decision making. The solution consists of three processes: atmospheric dispersion calculation, dose calculation, and path planning. The individual processes are connected through data exchange, thus allowing users to choose specific models based on experience. The proposed scheme combination is the Gaussian plume model, the dose conversion factor method, and an improved Dijkstra’s path planning algorithm. This algorithm, combined with dispersion and dose results, weighs nodes using the moving expected dose, facilitating the path with minimum dose risk. A program for Atmospheric Diffusion and Dose Calculation (ADDC) is developed based on the recommended scheme. Advantages include ease of use, minimal data requirements, data accessibility, and efficient evacuation. Dose estimates and optimal evacuation routes can be obtained quickly and at very low cost in response to rapidly changing environmental conditions. In a case study at a Chinese planned nuclear plant, we consider a spent fuel pool water loss scenario, assessing dose risks from 2020 to 2022 meteorological statistics. In dose calculation, results reveal that during an SFP drying accident, the radiation dose in the core area (100 m away) can reach 30–150 mSv within 2 h, and at 500 m away, it can reach 5–15 mSv. The dose in all downwind directions can drop below 250 mSv within 60 m. In path planning, results reveal the program is capable of accurately and efficiently calculating the minimum dose evacuation route. The program’s path reduces the effective dose by up to 67.3% compared to the shortest route, enhancino safety, and guiding post-accident decision making and planning.

Verification of the NACAC atmospheric dispersion calculation using a hypothetical accident in a neighboring nuclear power plant

Calculating atmospheric dispersion in a hypothetical nuclear accident plays an essential role as a predictive tool in nuclear emergency planning. The Nuclear Accident Consequence Analysis Code (NACAC) has been developed as an in-house code by the Thailand Institute of Nuclear Technology to develop its capability for understanding the transboundary radiological effect of a hypothetical nuclear accident. To verify the performance of the NACAC, a comparison between the calculated results using the NACAC with those from the well-developed Java-based Real-time On-line Decision Support (JRODOS) code is performed with representative cases of all seasons in a year. Two hypothetical severe accidents at the Fangchenggang pressurized water reactor, namely, (i) a loss of off-site power and (ii) a large-break loss of coolant, are utilized as the initial boundary conditions. The air concentration characteristic maps obtained from both codes are analyzed, revealing that the dominant radionuclide dispersion pathways are similar in all study cases. The air concentration, ground concentration, and total effective dose rate at several locations up to 500 km away from the release point are directly compared. Typically, the calculated results from the two codes are in reasonable agreement. However, for specific locations and directions, the NACAC predictions of the concentrations and total effective dose rate are lower than those from the JRODOS. These differences may be influenced by the different trajectory calculations between the two codes, which resulted in varying plume densities in certain areas. However, it does not significantly affect the radiation effect assessment. The NACAC still provides a total effective dose rate corresponding to the JRODOS, lower than one mSv throughout the main dispersion direction.

Near-range atmospheric dispersion of an anomalous selenium-75 emission

On May 15th of 2019, an anomalous emission of selenium-75 was detected at the stack of the Belgian Reactor 2 (BR2) in Mol. Although the release exceeded the prescribed limits for BR2, there was no harm to the population or food chain and so the event was classified as INES 1. However, it was very interesting from the perspective of near-range atmospheric dispersion. This publication brings together all available information at the near range – stack-monitored source term data, on-site meteorological data, ambient dose equivalent rates, deposition and concentration measurements – in one dataset that covers the initial puff release on May 15th, 2019 as well as a residual release through early November 2019. To demonstrate the consistency of this dataset, supporting atmospheric transport and dispersion calculations are performed using a Gaussian plume model. These calculations, in turn, are supported by near-range Flexpart calculations in the context of the residual release.

An integrated method for atmospheric dispersion and corresponding risks: Application to ITU TRIGA Mark II research reactor

The prediction of the present and future impact of radioactivity release is important. However, there are several models and options to choose from. An integrated approach is proposed in this study and it is implemented to Istanbul Technical University (ITU) TRIGA Mark II Research Reactor. The procedure was divided into six steps including quantification of the source term, specification of meteorological data, atmospheric dispersion model selection, atmospheric dispersion and deposition calculation, biosphere and geosphere transport calculation, and finally dose and risk calculation. The acquisition of data and parameters for these steps were discussed in detail to provide insight to users of the integrated method. The evaluation of wind direction and speed defined in the safety analysis report of the reactor showed that the average wind direction at the reactor site altered from NE direction to NE-NNE over time but speed stayed almost the same. The maximum-total cloudshine and groundshine as a result of annual exposure rate were found as 21.1 μSv/yr at ITU Ayazağa Campus. For inhalation, Ba-140 and I-131 were found to have the highest risk in mortality and morbidity, respectively. The same is true for Sr-90 and I-131 in the lifetime intake of food while in the lifetime intake of tap water, Sr-90 is the leading radioisotope for both mortality and morbidity risks. However, all calculated values are quite low considering the survival rates. Moreover, the results of the study provides useful insight into the understanding of necessities while shedding light on limitations.

Backward Estimation of Atmospheric Release of 137Cs and 131I Using Total Cumulative Deposition in Terrestrial Areas Following the Fukushima Daiichi Nuclear Power Plant Accident.

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.

Systematic Approach to Transboundary Radioactivity Monitoring for Accidents in External Nuclear Power Plants

AbstractPast nuclear accidents demonstrated that radioactive materials from an accident in a nuclear power station (NPS) can disperse to other countries or even across the globe. This means all countries need to be prepared to respond to a nuclear power emergency even if they have no nuclear power program. This study aims to propose a structured framework to enable transboundary radio activity monitoring of accidental releases in external NPSs in such a country with limited calculation resources. A trial calculation of a hypothetical release from an interfacing system loss of coolant accident (ISLOCA) in Unit 1 of Fangchenggang NPS during different representative meteorological scenarios is carried out to demonstrate the usability of the proposed framework. It was found that a relatively large release can reach the border of Thailand within 24 h when the wind along the dispersion pathway is basically in northeast direction with significant amount of rainfall, though it may not be able to trigger the alarm at the radiation monitoring stations. However, it is highly likely that the release that fulfills the aforementioned conditions be detected by one of the stations within 48 h-timeframe. As the trial calculation could deliver insightful findings with limited calculation resources, the proposed transboundary atmospheric dispersion calculation framework can be used in other nonnuclear power countries to prepare for emergency response to accidents in external NPSs.

Inter-comparison of transboundary atmospheric dispersion calculations: A summary of outputs from the ASEAN NPSR benchmark exercise

Previous nuclear power plant (NPP) severe accidents have raised great concern in Southeast Asia on the issue of transboundary atmospheric dispersion of an accidental release from an external NPP. This study presents the inter-comparison of atmospheric dispersion calculations performed by different calculation codes employing Lagrangian particle model or Gaussian puff model with Southeast Asia weather data during the northeast monsoon period. The test case is a hypothetical accident in Fangchenggang NPP with a hypothetical source term. Radionuclide concentration and radiation dose distribution maps along with specified values at specific locations are compared to demonstrate the similarities and differences of each calculation code. All calculation codes can generally capture the dispersion pathway, though only those employing Lagrangian particle model can record microscale changes in wind direction. Analysis of predicted exposure extent and lead time shows that radioactive plume contributing to the radiation dose of several μSv/day can reach one or more ASEAN countries within the 24-h timeframe. This information can be used to design appropriate risk communication strategy to dispel unnecessary public anxiety or to plan for more extensive radiation monitoring capability. For this purpose, Gaussian puff model can be used to provide initial information which can be later confirmed by Lagrangian particle model.

Prediction of the exposure of atmospheric releases from Baltic nuclear power plant to members of the public and non-human biota

The article presents a long-term prediction of radiation doses to members of the public and reference organisms of biota from planned radioactive atmospheric releases by the Baltic nuclear power plant with VVER-1200. The calculation of atmospheric dispersion and radiation dose to the population have performed on the basis of general models presented in the IAEA Safety Report Series No. 19. The radiation doses to non-human biota have calculated using the ERICA Tool. Annual effective dose to the population near the Baltic NPP are expected to be below 2.1 μSv. The dose rate of reference organisms will not exceed 0.6 nGy/h. The main contribution to the irradiation of both population and non-human biota will be made by 14C and 3H. It has recommended to include these radionuclides in the radioecological monitoring program of natural and agricultural ecosystems in the area where the Baltic NPP is located.

Consequences of selecting different subsets of meteorological data to utilize in deterministic safety analysis

Atmospheric dispersion calculation of radiological releases can be done for different purposes such as deterministic or probabilistic safety analysis, environmental impact assessment, emergency preparedness and response. The characteristics of the weather conditions used in such assessments have a significant effect on the results, thus it is vital to select appropriate meteorological data for the calculation. In this paper, we conduct a study on deterministic safety analysis of radiological releases and investigate the effects of using different subsets of a meteorological database for such assessments.We demonstrate that conducting deterministic dose assessment with a large site specific dataset of meteorological measurements and the use of a dose percentile is more beneficial than using one set of meteorological parameters. This is because variations in the meteorological condition have considerable effect on the dose results when using one set of meteorological parameters (e.g. worst case scenario) and less when a large meteorological database is used. We show that there can be a significant difference in the maximum dose computed with a large (at least annual with hourly resolution) meteorological database when there is a lack of data points or conversion of the parameters is needed, thus the 100th dose percentile is not optimal for verification of safety criteria fulfillment. It is better to use a relatively high percentile (e.g. from 80th to 99th), partly because it behaves more robustly and also because the use of the maximum dose (100th percentile) would be overly conservative. In case of meteorological data not being available for a sufficient temporal domain (e.g. data available for only one year or less), a multiplication factor – determined based on conservative assumptions and extensive studies on the possible spread of meteorological conditions and their effect at a given location – can be used for the comparison of a selected dose percentile with the safety limit.A 5-years long meteorological database provided by a meteorological measurement system was used in this study as an example to demonstrate and calibrate the methodology on a real database. The methods presented in this work are universal, they can be used in deterministic safety analysis of other nuclear facilities, and the results can facilitate the development of optimal meteorological databases.

Radioxenon Releases from A Nuclear Power Plant: Stack Data and Atmospheric Measurements

An analysis of a data set consisting of 3 years of high time resolution radioxenon stack measurements from the three nuclear reactors at the Forsmark nuclear power plant in Sweden, as well as measurements of atmospheric radioxenon in Stockholm air, 110 km away, is presented. The main causes for the stack releases, such as the function of the xenon mitigation systems, presence of leaking fuel elements, and reactor operations such as shutdown and startup, are discussed in relation to the stack data. The relation between radioxenon releases and reactor operation is clearly illustrated by the correlation between the stack measurements and thermal reactor power. In general, the isotopic ratios of the Stockholm measurements, which are shown to mainly originate from Forsmark releases, agree well with stack measurements, and with a modeled reactor operational sequence. Results from a forward atmospheric dispersion calculation agree very well with observed plume arrival times and widths, and with some exceptions, also with absolute activity concentrations. The results illustrates the importance of detailed knowledge of radioxenon emissions from nuclear power plants when interpreting radioxenon measurements for nuclear test ban verification, and provide new input to this kind of analysis. Furthermore, it demonstrates the possibility to use sensitive radioxenon detection systems to remotely detect and verify reactor operation.

Reanalysis of environmental qualification radiation parameters for Kuosheng nuclear power plant

Abstract Kuosheng BWR-6 plant, owned by Taiwan Power Company, is currently operating at core thermal power of 2 971 MWt. The purpose of this study is to develop a method used to calculate the radiation dose at the reactor auxiliary building and at various rooms accommodating safety-related equipment during the design basis Loss of Coolant Accident (LOCA). The method integrates various aspects, including core inventory calculation using ORIGEN2 code, radioactive material transport and removal calculation using RADTRAD code, activity release calculation based on Technical Specification leakage limit and RADTRAD output, atmospheric dispersion calculation using ARCON96 code, and dose calculation using gamma energy and spectrum based finite cloud model. The assumptions used are based on the Regulatory Guide 1.89 revision 1. The calculation shows that the original Environmental Qualification(EQ) radiation parameters defined in the FASR, for the safety-related electrical and instrumental control equipment in the reactor auxiliary building, can be relaxed significantly and the radiation environment during accident could be reclassified, from “harsh environment” to “mild environment”.

Large-eddy simulation studies for predicting plume concentrations around nuclear facilities using an overlapping technique

We propose, in emergency response to nuclear accidents, a practical and quick local-scale atmospheric dispersion calculation method using an overlapping technique. First, we pre-calculated large-eddy simulations (LESs) of plume dispersion around an actual nuclear facility under idealised atmospheric conditions with 36 wind-direction cases and made a dataset of the 10-minute averaged concentrations for each wind direction case. Then, we conducted LESs of plume dispersion for 1-hour periods under realistic atmospheric conditions using the meteorological data and estimated the spatial distributions of the 1-hour averaged concentrations by overlapping the pre-calculated concentration data depending on the frequency of the mean wind directions. It is shown that the concentration distribution patterns are well reproduced in comparison to those under the realistic conditions. It is concluded that the atmospheric dispersion calculation method using the overlapping technique has potentially a high performance in emergency responses to nuclear accidents.

Large-eddy simulation studies for predicting plume concentrations around nuclear facilities using an overlapping technique

We propose, in emergency response to nuclear accidents, a practical and quick local-scale atmospheric dispersion calculation method using an overlapping technique. First, we pre-calculated large-eddy simulations (LESs) of plume dispersion around an actual nuclear facility under idealised atmospheric conditions with 36 wind-direction cases and made a dataset of the 10-minute averaged concentrations for each wind direction case. Then, we conducted LESs of plume dispersion for 1-hour periods under realistic atmospheric conditions using the meteorological data and estimated the spatial distributions of the 1-hour averaged concentrations by overlapping the pre-calculated concentration data depending on the frequency of the mean wind directions. It is shown that the concentration distribution patterns are well reproduced in comparison to those under the realistic conditions. It is concluded that the atmospheric dispersion calculation method using the overlapping technique has potentially a high performance in emergency responses to nuclear accidents.

Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface

Within the lowest kilometer of the Earth’s atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing of heat and moisture also play a role. The variance (square of the standard deviation) of the fluctuation around the mean wind speed is a measure of the kinetic energy content of the turbulence. This kinetic energy can be resolved into the spectral distributions, or spectra, as functions of eddy size, wavenumber, or frequency. Spectra are derived from Fourier transforms of wind records as functions of space or time corresponding to wavenumber and frequency spectra, respectively. Atmospheric spectra often exhibit different subranges that can be distinguished and scaled by the physical parameters responsible for: (1) their generation; (2) the cascade of energy across the spectrum from large- to small-scale; and (3) the eventual decay of turbulence into heat owing to viscosity effects on the Kolmogorov microscale, in which the eddy size is only a fraction of a millimeter. This paper addresses atmospheric turbulence spectra in the lowest part of the atmospheric boundary layer—the so-called surface layer—where the wind shear is strong owing to the nonslip condition at the ground. Theoretical results dating back to Tchen’s early work in 1953 ‘on the spectrum of energy in turbulent shear flow’ led Tchen to predict a shear production subrange with a distinct inverse-linear power law for turbulence in a strongly sheared high-Reynolds number wall-bounded flow, as is encountered in the lowest sheared part of the atmospheric boundary layer, also known as the eddy surface layer. This paper presents observations of spectra measured in a meteorological mast at Høvsøre, Denmark, that support Tchen’s prediction of a shear production subrange following a distinct power law of degree −1 in the lowest part of the atmospheric surface layer with the form where is the surface friction velocity and is the wavenumber. Tchen’s turbulence theory is shown to be able to predict the measured spectra of the wind velocity component parallel to the mean wind direction for eddy sizes larger than the measurement height above the ground. An amended analytical model for the near-neutral surface layer spectrum is then proposed. This model, which is applicable to the scaling of the spectrum at all heights in the surface layer, is obtained by a combination of Kaimal’s classical spectral model for scaling the inertial subrange with Tchen’s 1953 and 1954 proposed shear production subrange theory. The shear production-amended spectral model is compared with observations of ensemble-averaged near-neutral spectra selected during a nine-month measurement period from recordings from six sonic anemometers at heights of 10, 20, 40, 60, 80, and 100 m in the meteorological tower at the test site for large wind turbines in Høvsøre, Denmark. Finally, potential applications of the new spectral model are discussed, in particular for use within the lowest one-third of the surface layer in which the production subrange component of the spectrum is most prominent. The new spectral model can supply wavenumber-resolved turbulent kinetic energies for the prediction of wind loads on buildings, bridges, and wind turbines, and its spectral parameterization can also be used for scale-dependent parameterization of, e.g., surface-released atmospheric dispersion calculations for regions close to the ground.

Reducing the Danger from Fires in Spent Fuel Pools

ABSTRACTThis article reviews the case of the spent fuel fire that almost happened at Fukushima in March 2011, and shows that, had the wind blown the released radioactivity toward Tokyo, 35 million people might have required relocation. It then reviews the findings by the United States Nuclear Regulatory Commission (NRC) in 2013 that the consequences of a loss-of-water event could be drastically reduced if spent fuel were moved to dry storage after 5 years of pool cooling but that the probability of a spent fuel pool fire is too low to make this a requirement. Our atmospheric dispersion and deposition calculations using HYSPLIT for hypothetical releases from the Peach Bottom plant in Pennsylvania find average interdicted areas and populations requiring relocation larger than NRC estimates presented to the National Academy of Sciences (NAS) and support the NAS findings of errors and omissions in the NRC's cost-benefit calculations. Political pressures from industry on the NRC may be biasing its analyses toward regulatory inaction.

The Sensitivity of Atmospheric Dispersion Calculations in Near-field Applications: Modeling of the Full Scale RDD Experiments with Operational Models in Canada, Part I.

Three radiological dispersal devices were detonated in 2012 under controlled conditions at Defence Research and Development Canada's Experimental Proving Grounds in Suffield, Alberta. Each device comprised a 35-GBq source of (140)La. The dataset obtained is used in this study to assess the MLCD, ADDAM, and RIMPUFF atmospheric dispersion models. As part one of a two-part study, this paper focuses on examining the capabilities of the above three models and evaluating how well their predictions of air concentration and ground deposition match observations from the full-scale RDD experiments.

Radiation Modeling and Finite Cloud Effects for Atmospheric Dispersion Calculations in Near-field Applications: Modeling of the Full Scale RDD Experiments with Operational Models in Canada, Part II.

Three radiological dispersal devices were detonated in 2012 under controlled conditions at Defence Research and Development Canada's Experimental Proving Grounds in Suffield, Alberta. Each device comprised a 35-GBq source of (140)La. The dataset obtained is used in this study to assess the MLCD, ADDAM, and RIMPUFF atmospheric dispersion models. As a continuation of Lebel et al. (2016), this paper examines different methodologies for making dose estimates with atmospheric dispersion models.

The long distance transport of airborne Ambrosia pollen to the UK and the Netherlands from Central and south Europe.

The invasive alien species Ambrosia artemisiifolia (common or short ragweed) is increasing its range in Europe. In the UK and the Netherlands, airborne concentrations of Ambrosia pollen are usually low. However, more than 30 Ambrosia pollen grains per cubic metre of air (above the level capable to trigger allergic symptoms) were recorded in Leicester (UK) and Leiden (NL) on 4 and 5 September 2014. The aims of this study were to determine whether the highly allergenic Ambrosia pollen recorded during the episode could be the result of long distance transport, to identify the potential sources of these pollen grains and to describe the conditions that facilitated this possible long distance transport. Airborne Ambrosia pollen data were collected at 10 sites in Europe. Back trajectory and atmospheric dispersion calculations were performed using HYSPLIT_4. Back trajectories calculated at Leicester and Leiden show that higher altitude air masses (1500 m) originated from source areas on the Pannonian Plain and Ukraine. During the episode, air masses veered to the west and passed over the Rhône Valley. Dispersion calculations showed that the atmospheric conditions were suitable for Ambrosia pollen released from the Pannonian Plain and the Rhône Valley to reach the higher levels and enter the airstream moving to northwest Europe where they were deposited at ground level and recorded by monitoring sites. The study indicates that the Ambrosia pollen grains recorded during the episode in Leicester and Leiden were probably not produced by local sources but transported long distances from potential source regions in east Europe, i.e. the Pannonian Plain and Ukraine, as well as the Rhône Valley in France.Electronic supplementary materialThe online version of this article (doi:10.1007/s00484-016-1170-7) contains supplementary material, which is available to authorized users.

Atmospheric Transport Models for Hazardous Releases: Variability and Uncertainties – Findings of COST Action ES1006 and Operational Experiences

Atmospheric transport models are in use to model the airborne transport of toxic or radioactive gases or aerosols in large, regional or very local scale events. Different approaches are available, ranging from simple parametric models and Gaussian methods to Lagrangian dispersion models and advanced CFD-based modelling suites. The variety of the models implemented in today’s emergency response systems, used in crisis management and emergency response planning, therefore ranges from very simple, robust and fast approaches to highly sophisticated model systems taking into account changes in the meteorological conditions in time and space, terrain and building effects etc. The various methodologies have advantages and disadvantages with respect to their computational efficiency, accuracy, reliability of the results and many more. For any accidental release scenario, authorities may come to different decisions and a variety of instructions may be given to emergency responders, depending on the simulation tools applied.Which variability in model results can be expected in emergency cases depending on the atmospheric transport model used? How can these uncertainties be explained? How may these be handled in real time application? These questions are addressed in the paper.The performance of different models for local hazardous releases in built-up areas is illustrated by selected results from model evaluation exercises undertaken in the frame of COST Action ES 1006: non-blind and blind test cases, for continuous as well as for puff releases, sensitivity studies and applications of the same model by different users. A comprehensive overview of all results of these model evaluation exercises is given by Baumann-Stanzer et al. (2015).Regional to large scale atmospheric dispersion calculations from different emergency response tools, e.g. for radiological hazards, may also render significant differences in the simulated affected areas – due to different meteorological input but even in case of identical meteorological input and source term due to differences in the applied model physics. This is exemplified and discussed based on a model comparison study using the model systems TAMOS, RODOS and ESTE: comparisons of model results based on the same meteorological forecasts under various weather conditions and for different release scenarios.

NOAA’s HYSPLIT Atmospheric Transport and Dispersion Modeling System

Abstract The Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT), developed by NOAA’s Air Resources Laboratory, is one of the most widely used models for atmospheric trajectory and dispersion calculations. We present the model’s historical evolution over the last 30 years from simple hand-drawn back trajectories to very sophisticated computations of transport, mixing, chemical transformation, and deposition of pollutants and hazardous materials. We highlight recent applications of the HYSPLIT modeling system, including the simulation of atmospheric tracer release experiments, radionuclides, smoke originated from wild fires, volcanic ash, mercury, and wind-blown dust.