Puff Release Research Articles

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.

Evaluating the added value of multi-input atmospheric transport ensemble modeling for applications of the Comprehensive Nuclear Test-Ban Treaty organization (CTBTO)

The Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) runs to date operationally an atmospheric transport modeling chain in backward mode based on operational deterministic European Centre for Medium-Range Weather Forecasts-Integrated Forecasting System (ECMWF-IFS) and on National Centers for Environmental Prediction-Global Forecast System (NCEP-GFS) input data. Meanwhile, ensemble dispersion modeling is becoming more and more widespread due to the ever increasing computational power and storage capacities. The potential benefit of this approach for current and possible future CTBTO applications was investigated using data from the ECMWF-Ensemble Prediction System (EPS). Five different test cases - among which are the ETEX-I experiment and the Fukushima accident - were run in backward or forward mode and - in the light of a future operational application - special emphasis was put on the performance of an arbitrarily selected 10- versus the full 51-member ensemble. For those test cases run in backward mode and based on a puff release it became evident that Possible Source Regions (PSRs) can be meaningfully reduced in size compared to results based solely on the deterministic run by applying minimum and probability of exceedance ensemble metrics. It was further demonstrated that a given puff release of 4E10 Bq of Se-75 can be reproduced within the meteorological uncertainty range [1.9E9 Bq,1.7E13 Bq] including a probability for not exceeding an assumed upper limit source term using simple scaling of a measurement with the corresponding ensemble metrics of backward fields. For the test cases run in forward mode it was found that the control run as well as 10- and 51-member medians all exhibit similar performance in time series evaluation. Maximum rank difference adds up to less than 10% with reference to possible rank values [0,4]. The maximum difference in the Brier score for both ensembles is less than 3%. The main added value of the ensemble lies in producing meteorologically induced concentration uncertainties and thus explaining observed measurements at specific sites. Depending on the specific test case and on the ensemble size between 27 and 74% of samples all lie within concentration ranges derived from the different meteorological fields used. In the future uncertainty information per sample could be used in a full source term inversion to account for the meteorological uncertainty in a proper way. It can be concluded that a 10-member meteorological ensemble is good enough to already benefit from useful ensemble properties. Meteorological uncertainty to a large degree is covered by the 10-member subset because forecast uncertainty is largely suppressed due to concatenating analyses and short term forecasts, as required in the operational CTBTO procedure, on which this study focuses. Besides, members from different analyses times are on average unrelated. It was recommended to Working Group B of CTBTO to implement the ensemble system software in the near future.

Source term estimation in the presence of nuisance signals

Many source-term estimation algorithms for atmospheric releases assume the measured concentration data are influenced only by the releases of interest. However, there are situations where identifying a short-term release from an unknown location in the presence of long-term releases from a different location is of interest. One such example is determining if part or all of a typical magnitude concentration of a radioactive isotope in a sampler came from a nuclear explosion, such as the explosion announced by DPRK in 2013, while medical isotope facilities and nuclear power plants were also operating in the region.An estimation algorithm has been developed for the case where a short-duration release is confounded by a long-term nuisance signal associated with an additional release location. The technique is demonstrated using synthetic release data for a hypothetical medical isotope production facility and a hypothetical puff release from a different location. The algorithm successfully determines the location (within 30 km) and time-varying release rate (within a factor of 2) for the medical isotope production facility and the location (within 60 km), time (within 6 h), and release magnitude (within a factor of 4) of the puff release.

UDINEE: Evaluation of Multiple Models with Data from the JU2003 Puff Releases in Oklahoma City. Part I: Comparison of Observed and Predicted Concentrations

In a complex environment such as an urban area, accurate prediction of the atmospheric dispersion of airborne harmful materials such as radioactive substances is necessary for establishing response actions and assessing risk or damage. Given the variety of urban atmospheric dispersion models available, evaluation and inter-comparison exercises are vital for assessing quantitatively and qualitatively their capabilities and differences. To that end, the European Commission/Directorate General Joint Research Centre with support from the European Commission/Directorate General-Migration and Home Affairs, and with the contribution of the U.S. Defense Threat Reduction Agency, launched the Urban Dispersion INternational Evaluation Exercise (UDINEE) project. Within UDINEE, nine atmospheric dispersion models are evaluated and intercompared. Sulphur hexafluoride concentrations from puffs released near the ground during the Joint Urban 2003 (JU2003) field experiment are used in UDINEE to evaluate atmospheric dispersion models. The JU2003 experiment is chosen because UDINEE aims at the better understanding of modelling capabilities for radiological dispersal devices in urban areas, and the neutrally-buoyant puff releases performed in the JU2003 experiment are the closest scenario to this purpose. The present study evaluates the capability of models at simulating the presence and concentration levels of the tracer at sampling locations. The fraction of predicted concentrations and time-integrated concentrations within a factor-of-two of observations are less than 0.36 and 0.4 respectively. The analysis reveals an improvement in the performance of models by using time-varying inflow conditions. Since the simulation of the dispersion of puff release is particularly challenging, the results of UDINEE could constitute a benchmark for future model developments.

Computational source term estimation of the Gaussian puff dispersion

The hazardous or toxic chemical releases have a detrimental impact on public safety. Estimating source parameters is of particular importance in aiding emergency response and post-assessment. Source term estimation from sensor measurements with a given Gaussian puff dispersion model is a typical inverse problem, which can be transformed into an optimization problem. In this paper, we employed the particle swarm optimization, the Nelder–Mead method, and their hybrid method to solve the optimization problem. Furthermore, we proposed a three-dimensional neighborhood topology which considerably improves performance of the particle swarm optimization. We implemented all these algorithms in JAVA on an embedded system to make a preliminary estimation of the accidental puff release. Numerical experiments with synthetic datasets show that the particle swarm optimization maintains a balance between computation time, accuracy, robustness, and implementation complexity. In contrast, the hybrid algorithm has an advantage in computation time at the expense of more sophisticated implementation.

Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity

Results from numerical simulations of the mixing of two puffs of scalars released in a turbulent flow channel are used to introduce a measure of mixing quality, and to investigate the effectiveness of turbulent mixing as a function of the location of the puff release and the molecular diffusivity of the puffs. The puffs are released from instantaneous line sources in the flow field with Schmidt numbers that range from 0.7 to 2400. The line sources are located at different distances from the channel wall, starting from the wall itself, the viscous wall layer, the logarithmic layer, and the channel center. The mixing effectiveness is quantified by following the trajectories of individual particles with a Lagrangian approach and carefully counting the number of particles from both puffs that arrive at different locations in the flow field as a function of time. A new measure, the mixing quality index Ø, is defined as the product of the normalized fraction of particles from the two puffs at a flow location. The mixing quality index can take values from 0, corresponding to no mixing, to 0.25, corresponding to full mixing. The mixing quality in the flow is found to depend on the Schmidt number of the puffs when the two puffs are released in the viscous wall region, while the Schmidt number is not important for the mixing of puffs released outside the logarithmic region.

Prediction of dosage-based parameters from the puff dispersion of airborne materials in urban environments using the CFD-RANS methodology

One of the key issues of recent research on the dispersion inside complex urban environments is the ability to predict dosage-based parameters from the puff release of an airborne material from a point source in the atmospheric boundary layer inside the built-up area. The present work addresses the question of whether the computational fluid dynamics (CFD)–Reynolds-averaged Navier–Stokes (RANS) methodology can be used to predict ensemble-average dosage-based parameters that are related with the puff dispersion. RANS simulations with the ADREA-HF code were, therefore, performed, where a single puff was released in each case. The present method is validated against the data sets from two wind-tunnel experiments. In each experiment, more than 200 puffs were released from which ensemble-averaged dosage-based parameters were calculated and compared to the model’s predictions. The performance of the model was evaluated using scatter plots and three validation metrics: fractional bias, normalized mean square error, and factor of two. The model presented a better performance for the temporal parameters (i.e., ensemble-average times of puff arrival, peak, leaving, duration, ascent, and descent) than for the ensemble-average dosage and peak concentration. The majority of the obtained values of validation metrics were inside established acceptance limits. Based on the obtained model performance indices, the CFD-RANS methodology as implemented in the code ADREA-HF is able to predict the ensemble-average temporal quantities related to transient emissions of airborne material in urban areas within the range of the model performance acceptance criteria established in the literature. The CFD-RANS methodology as implemented in the code ADREA-HF is also able to predict the ensemble-average dosage, but the dosage results should be treated with some caution; as in one case, the observed ensemble-average dosage was under-estimated slightly more than the acceptance criteria. Ensemble-average peak concentration was systematically underpredicted by the model to a degree higher than the allowable by the acceptance criteria, in 1 of the 2 wind-tunnel experiments. The model performance depended on the positions of the examined sensors in relation to the emission source and the buildings configuration. The work presented in this paper was carried out (partly) within the scope of COST Action ES1006 “Evaluation, improvement, and guidance for the use of local-scale emergency prediction and response tools for airborne hazards in built environments”.

Solution for sudden contamination transport through air duct system: Under a puff release

When a chemical or biological agent is suddenly released into ventilation ducts, agent concentration along the whole ductwork should be promptly and accurately determined. In this work, an advection-diffusion model was suggested to calculate the agent transport in the air ducts. A node model was constructed for the agent dispersion at the duct junctions. Under a puff injection of the agent in the ductwork, the two models were integrated to derive the theoretical solution for the concentration dynamics. An experiment, using DEHS (diethylhexyl sebacate) aerosols as the representative agent pollution, was conducted to present the concentration dynamics within an air ductwork. Well agreement was observed between the theoretical predictions and the experimental results even with the extremely large sectional area. In this study, time characteristics were further defined and discussed to investigate the continuous normal distribution pattern of agent concentration along the flow direction in the ductwork. Such discussion helped to determine the exact time when the agent arrived at and traveled through a certain location after a puff release. It was also used to obtain the potential exposure at the outlets of the ductwork. The present work was expected to assist the early-warning and source identification of a potential chemical or biological agent attack in the ventilation ductwork.

Synthesis of α-ionyl-β-d-glucoside and its property of flavor release

A flavor precursor α-ionyl-β-d-glucoside (IG) was synthesized by Koenigs–Knorr method, and its structure was characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform-infrared spectroscopy, and electro spray ionization mass spectroscopy (MS). Thermal degradation behaviors of the intermediate α-ionyl-tetra-O-acetyl-β-d-glucoside (IAG) and IG were analyzed by thermogravimetry and online pyrolysis (Py)-gas chromatography–MS. Flavor release property of IG was investigated with cigarettes as the carrier. The results indicated that fracture temperature of glycosidic bond was about 200 °C for IAG, and was about 190 °C for IG. Py of IAG and IG could generate several aroma compounds such as megastigmatriene, α-ionol, α-ionone, and 3-oxo-α-ionol. IG added in cigarettes could be pyrolyzed to release α-ionol, α-ionone, and 3-oxo-α-ionone, and increase the release amount of megastigmatrienone in mainstream smoke during smoking. The release amount of characteristic flavor components in mainstream smoke remain stable after the cigarette sample with IG placed in standard condition for 30 days, and there was no significant difference in the single puff release amounts, which confirmed the flavor release stability and uniformity of IG under heating treatment.

Proximity risk assessment for two sensitive chemical plants based on the accident scenario consequence analysis

ABSTRACTPetrochemical complexes include high risk interconnected plants processing large quantities of dangerous/flammable substances, complex reactors of high thermal sensitivity operated under severe conditions of high productivity and associated equipment, vessels or separation units operating at intense temperature and pressures. Such plant design/operation problems contribute quite frequently to the occurrence of small incidents or rare major accidents including domino effects. The study applies classical boiling liquid expanding vapour explosion fire and toxic puff release models to evaluate the effects and consequences of different accident scenarios involving two neighbouring risk plants, with exemplifications for the aniline and maleic anhydride synthesis plants. A proposed joint probability index of human casualties, related to thermal radiation doses and toxic material released around plants, points out the influence of production capacity and plant proximity on the severity of accident consequences and domino‐effect occurrence. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

A More Extensive Investigation of the Use of Ensemble Forecasts for Dispersion Model Evaluation

Abstract An ensemble forecast is used as input to a Lagrangian particle dispersion model to study the effect that analysis errors in the numerical weather prediction assimilation cycle have on dispersion modeling. The wind and temperature fields from a control forecast are first compared with radiosonde measurements to quantify the quality of the forecast. It predicts, on average, a less stable atmosphere near the surface, whereas the average deviations in wind speed and wind direction are small. The dispersion model then simulates a tracer puff release from the European Tracer Experiment (ETEX), by using the ensemble forecast as input. The spread in the ensemble forecast is calculated by comparing the predicted puff concentrations for each ensemble member with those from the control forecast. It was found that ensemble members that were close to the control forecast when one statistical measure was calculated were not necessarily close when another was used. The ensemble spread is then quantified by comp...

Variability of eddy diffusivity in the stratosphere deduced from vertical distributions of N2O and CFC-12

The vertical distributions of eddy diffusivity in the stratosphere, calculated from the vertical mixing ratio profiles of N 2 O and CFC-12, are discussed. A photochemical equilibrium model has been formulated to evaluate the eddy diffusivity in the stratospheric altitude region of about 17–38 km. An attempt has been made to study the temporal variability from the measured vertical profiles during the balloon flights in the years of 1987, 1990 and 1994 conducted from a tropical site, Hyderabad (17.5 °N, 78.6 °E). The present calculated eddy diffusion coefficients are higher than those estimated earlier using a similar procedure (Massie and Hunten, 1981) for average midlatitudinal conditions. Richardson numbers are also calculated from the wind and temperature profiles and the persistence of turbulent layers are studied. A probable range of eddy diffusion coefficients is proposed for the equatorial region. The lower limit agrees well with the values of NAS (1979) and the higher limit, almost constant over the complete altitude region (≈7 × 10 4 cm 2 s −1 ), roughly follows the in situ measurements using puff release experiments over the same location.

CLOUD: A vapour-aerosol dispersion model accounting for plume 3D motion and heat and mass transfer between phases

The CLOUD (concentration levels of unconfined dispersion) code has been developed, the nucleus of which is an innovative two-phase fluid dispersion model characterized by conservation equations for mass, momentum, energy and species, averaged over a volume slice transverse to the direction of plume motion. The initial and boundary conditions for the above equations are determined either by using auxiliary models or by direct input of the space distribution, and respectively of the time evolution, of the relevant variables. The initial conditions model for an instantaneous, puff release has been based on an experimental programme carried out at the Swiss Federal Institute of Technology. The boundary conditions for semi-continuous, jet releases have been based on literature models for critical two-phase flow at the rupture. The code has been validated with data from three large scale release test series: the Desert Tortoise series (ammonia), the Goldfish series (HF), and the Thorney Island series (heavy gas).

Tropospheric dispersion: the first ten days after a puff release

Dispersion from a puff released in the atmospheric boundary layer in mid-latitudes is simulated with a Lagrangian global multiple-particle model using analysed three-dimensional wind fields. Quantitative measures of the spread are computed and used to assess the influence of the synoptic system into which the puff is released, and the ways in which turbulent diffusion can contribute to the total spread. the nature of the dispersion over ten days is examined to elucidate the controlling meteorology and kinematics during the various phases which could be identified. the results are compared with measurements made from constant-level balloons. A time index is proposed to characterize large-scale dispersion from a point source.

Tropospheric dispersion: The first ten days after a puff release

AbstractDispersion from a puff released in the atmospheric boundary layer in mid‐latitudes is simulated with a Lagrangian global multiple‐particle model using analysed three‐dimensional wind fields. Quantitative measures of the spread are computed and used to assess the influence of the synoptic system into which the puff is released, and the ways in which turbulent diffusion can contribute to the total spread. the nature of the dispersion over ten days is examined to elucidate the controlling meteorology and kinematics during the various phases which could be identified. the results are compared with measurements made from constant‐level balloons. A time index is proposed to characterize large‐scale dispersion from a point source.

Inadequate use of pressurized aerosols by asthmatic patients [author's transl

The purpose of this study was to determine in a population of asthmatics, the number of patients who correctly used the pressurized aerosols (bronchodilator drugs or steroids) spontaneously, or after training sessions. 115 asthmatics (in- or outpatients, 14-70 years old) were asked to use their inhaler in the presence of an observer. The inhalation technique was considered correct when (1) the puff release was coordinated with a deep inspiration and (2) when the inspiration was followed by a few seconds' breath-holding. The patients were divided into two groups: a trained group of 46 patients who were observed for 1 month or more after the two above-mentioned maneuvres had been demonstrated to them by a physician and the need for correct use strongly emphasized. The other group (the untrained group) comprised 69 patients who were presumably using their inhalers according to the manufacturer's instructions: (1) expiration; (2) inspiration and actuation, and (3) apnea. In the trained group 52% of the patients were classified by the observer as correct users, as compared to 28% in the untrained group. The results were not influenced by sex. age or occupational differences. These observations suggest that a majority of asthmatics probably derived incomplete benefit from the use of pressurized aerosols. Although training apparently results in a more efficient use of the canisters, this study shows that training sessions must be repeated, and the results checked at regular intervals by a member of the medical staff. In subjects who repeatedly fail to achieve a correct inhalation technique the drug should be given by another route.

ADPIC—A Three-Dimensional Particle-in-Cell Model for the Dispersal of Atmospheric Pollutants and its Comparison to Regional Tracer Studies

Abstract A hybrid Lagrangian-Eulerian atmospheric transport-diffusion model was developed to calculate the three-dimensional distribution of atmospheric pollutants in transient-region flow fields. This Atmospheric Diffusion Particle-in-Cell (ADPIC) code was validated against several existing closed-form analytical solutions including a puff release in steady, unidirectional shear flow, and a puff release with scale-dependent horizontal and vertical eddy diffusion coefficients. These tests showed that the ADPIC results were within a 5% error when compared to the analytic solutions. Regional (100 km) tracer studies at the National Reactor Test Station Idaho Falls, Idaho, and at the Savannah River Laboratory, Aiken, S. C., were also used to compare the code against field measurements.

An Inert Gas Tracer System for Monitoring the Real-Time History of a Diffusing Plume or Puff

Abstract A brief description is given of the Hanford inert gas tracer system employed in atmospheric diffusion studies. Among the advantages of the system are the detailed histories of concentration generated simultaneously at 64 field positions, and the ability to disperse instantaneous point sources (puffs) as well as longer duration releases (plumes). Concentration measurements are made to a distance of 800 m from the source. Sample data resulting from a puff and a plume release are given. A minor amount of data analysis follows. Mean effective transport height resulting from the ground-level puff release are found to increase from 0.9 m at 200 m from the source to 1.7 m at a distance of 800 m. For the continuous plume, corresponding effective transport heights from a release 1 m above the surface were found to be 1.2 m and 1.6 m. For the puff, the ratio of σz to σv was found to be 3.9 at 200 m from the source, and 4.2 at 800 m.