Accidental Release Of Radioactive Material Research Articles

Application of the RODOS decision support system for nuclear emergencies to the analysis of possible consequences of severe accident in distant receptors

The work deals with the implementation of the methodology for the assessment of possible consequences of an accidental release of radioactive material for space distant receptors, and then application to the planned Polish nuclear power plant. The basic idea is, first to identify the worst case scenario for each considered receptor using trajectory analysis, and then to perform integrated simulations of atmospheric dispersion and dose estimation models. The study shows that the methodology for the identification and selection of meteorological conditions based on trajectory analysis is adequate for the proper preparation to making comprehensive computations in the RODOS system. The capabilities of RODOS system have been verified in performing a number of integrated simulations, finally leading to the assessment of possible consequences of the accidental release of radioactive substances to the atmosphere for distant receptors.

Ranking uncertainties in atmospheric dispersion modelling following the accidental release of radioactive material

During the pre-release and early phase of an accidental release of radionuclides into the atmosphere there are few or no measurements, and dispersion models are used to assess the consequences and assist in determining appropriate countermeasures. However, uncertainties are high during this early phase and it is important to characterise these uncertainties and, if possible, include them in any dispersion modelling. In this paper we examine three sources of uncertainty in dispersion modelling; uncertainty in the source term, uncertainty in the meteorological information used to drive the dispersion model and intrinsic uncertainty within the dispersion model. We also explore the possibility of ranking these uncertainties dependent on their impact on the dispersion model outputs.

Use of radar rainfall to model deposition of radionuclides

Accurate precipitation information is necessary for modelling the deposition of radionuclides following an accidental release of radioactive material to the atmosphere. The increase in resolution of numerical weather prediction models (NWP) has led to precipitation which looks more realistic but performs poorly when compared to observations using traditional grid-point statistics. Dispersion models have the ability to use precipitation information derived from radars. This study looks at the differences in estimates of air activity and deposition when precipitation information from a high resolution NWP is replaced by precipitation information from radar. Using a hypothetical release and a year's worth of meteorological data the results show that in around a third of cases there is a significant difference in the amount of deposition estimated when NWP precipitation is used compared to cases where radar precipitation is used. The results also show a small number of cases where air activity concentrations vary significantly between the runs.

Source term estimation of multi‐specie atmospheric release of radiation from gamma dose rates

Determination of a source term of an accidental release of radioactive material into the atmosphere is very important for evaluating emergency situations and their consequences. However, knowledge of the source term and its composition is typically vague and uncertain. One possible way to obtain the source term is inverse modeling in which an atmospheric transport model is combined with field measurements. The most accessible measurements are those from gamma dose rate (GDR) detectors. However, GDR measurements represent a sum of contribution from all nuclides from both plume and deposition which makes the problem particularly difficult. The same difficulty arises when the measurements can not distinguish contribution from another species in the release, such as nuclides attached to different particle sizes. We propose a Bayesian method for recovery of the source term from GDR measurements where a priori knowledge on ratios of different species is given in the form of bounds. This knowledge is incorporated into the model of covariance matrix of the source term. The Bayesian methodology allows to handle uncertain knowledge on the nuclide ratios as well as unknown temporal correlations of the source term. We evaluate and compare the proposed method with other state‐of‐the‐art methods on a twin experiment of a non‐stationary release of 16 nuclides from the Czech nuclear power plant Temelin being registered by the Austrian GDR monitoring network. Real‐world validation of the approach is performed on the latest measurements of concentration and deposition of caesium‐137 from the Chernobyl accident, where we estimate composition of the source term from different particle sizes (species). The estimated source term is in very good agreement with previously reported results and the calculated species ratios are supported by the available observations.

Hydro-sedimentary model as a post-accidental management tool: Application to radionuclide marine dispersion in the Bay of Toulon (France)

The coastal city of Toulon, located in southern France, is the homeport of the French navy's nuclear-powered vessels, and is the largest nuclearized harbour in Europe. Therefore, an accidental release of radioactive material would have major consequences for the marine ecosystem and the economy of the region. A hydro-sedimentary model is presented to better understand the dispersion of a hypothetical release of radionuclides and to gain insights into the potential effects on the surrounding ecosystem, especially on sea sediments. The aim of the model is to provide the foundation of a management tool for experts and stakeholders in decision making in case of an accidental release. We simulate a numerical radionuclide discharge in the military harbour under several climatic conditions and we compute 137Cs, which might have substantial impacts on the marine ecosystem, and 239Pu for its high affinity for solid phase. Results show that wind conditions and solid discharges from the Las River are the primary influences on sediment-bed contamination, and the hydro-sedimentary dynamics following the first days of release have an important influence on the distribution of radionuclides.

Wastelanding: Legacies of Uranium Mining in Navajo Country

In this sophisticated and insightful book, Traci Brynne Voyles argues that the process of “wastelanding” helps explain the history and persistence of environmental injustice. Environmental racism stems not only from constructed discourses of race but also from constructed conceptions of place. Asserting their colonial dominance over the Navajo, Euro-Americans defined indigenous lands in the American Southwest as wasted and useless, making those landscapes, and the people who inhabited them, pollutable. Wastelanding enabled the development of uranium mining and milling on Navajo land, a continuation of the colonial project with dramatic, if slowly evolving, violence inflicted on both the land and people. “The power exerted over environmental resources,” Voyles explains, “and the ways in which those in power construct knowledge about landscapes, are a central part of how what we now call social injustices are produced” (p. ix). In exploring the legacy of uranium mining in Navajo country, Voyles draws from tremendously powerful histories: the forced sterilization of indigenous women paired with the reproductive health impacts of radiation exposure; Navajo houses constructed from radioactive uranium mill tailings; and the virtually unknown Rio Puerco accident in 1979, when the containment barriers of a tailings pond in New Mexico failed and sent a radioactive slurry into the river and through reservation lands—the largest accidental release of radioactive material in American history. From these and other stories Voyles builds a convincing case for connections between colonialism, wastelanding, and environmental injustice. She brings her account to the present by examining grassroots activism regarding land tenure, environmental health, and the prospect of renewed uranium mining, underscoring her historical argument by demonstrating the ongoing link between the demands for decolonization and justice.

Ensemble-based simultaneous emission estimates and improved forecast of radioactive pollution from nuclear power plant accidents: application to ETEX tracer experiment

The accidental release of radioactive materials from nuclear power plant leads to radioactive pollution. We apply an augmented ensemble Kalman filter (EnKF) with a chemical transport model to jointly estimate the emissions of Perfluoromethylcyclohexane (PMCH), a tracer substitute for radionuclides, from a point source during the European Tracer Experiment, and to improve the forecast of its dispersion downwind. We perturb wind fields to account for meteorological uncertainties. We expand the state vector of PMCH concentrations through continuously adding an a priori emission rate for each succeeding assimilation cycle. We adopt a time-correlated red noise to simulate the temporal emission fluctuation. The improved EnKF system rapidly updates (and reduces) the excessively large initial first-guess emissions, thereby significantly improves subsequent forecasts (r = 0.83, p < 0.001). It retrieves 94% of the total PMCH released and substantially reduces transport error (>80% average reduction of the normalized mean square error).

Experimental shielding evaluation of the radiation protection provided by the structurally significant components of residential structures

The human health and environmental effects following a postulated accidental release of radioactive material to the environment have been a public and regulatory concern since the early development of nuclear technology. These postulated releases have been researched extensively to better understand the potential risks for accident mitigation and emergency planning purposes. The objective of this investigation is to provide an updated technical basis for contemporary building shielding factors for the US housing stock. Building shielding factors quantify the protection from ionising radiation provided by a certain building type. Much of the current data used to determine the quality of shielding around nuclear facilities and urban environments is based on simplistic point-kernel calculations for 1950s era suburbia and is no longer applicable to the densely populated urban environments realised today. To analyse a building’s radiation shielding properties, the ideal approach would be to subject a variety of building types to various radioactive sources and measure the radiation levels in and around the building. While this is not entirely practicable, this research analyses the shielding effectiveness of ten structurally significant US housing-stock models (walls and roofs) important for shielding against ionising radiation. The experimental data are used to benchmark computational models to calculate the shielding effectiveness of various building configurations under investigation from two types of realistic environmental source terms. Various combinations of these ten shielding models can be used to develop full-scale computational housing-unit models for building shielding factor calculations representing 69.6 million housing units (61.3%) in the United States. Results produced in this investigation provide a comparison between theory and experiment behind building shielding factor methodology.

Hybrid modeling approach to improve the forecasting capability for the gaseous radionuclide in a nuclear site

Predicted air concentrations of radioactive materials are important for an environmental impact assessment for the public health. In this study, the performance of a hybrid modeling combined with the industrial source complex (ISC) model and an adaptive neuro-fuzzy inference system (ANFIS) for predicting tracer concentrations was investigated. Tracer dispersion experiments were performed to produce the field data assuming the accidental release of radioactive material. ANFIS was trained in order that the outputs of the ISC model are similar to the measured data. Judging from the higher correlation coefficients between the measured and the calculated ones, the hybrid modeling approach could be an appropriate technique for an improvement of the modeling capability to predict the air concentrations for radioactive materials.

New model for agricultural countermeasures in RODOS and ARGOS

Predictions of the effects of agricultural countermeasures are an important part of the decision-making process following an accidental release of radioactive material into the environment. A new model has been developed for this purpose and integrated into the EU decision support systems RODOS and ARGOS. The model is based on the existing food chain model of RODOS and the previous model for simulating agricultural countermeasures in RODOS. The characteristics of the countermeasures and the supporting databases have been derived from the compendia and handbooks developed within the EURANOS project. A wide range of potentially practicable countermeasures is considered on timescales from a day to many years, and endpoints related to their imposition are calculated such that the economic and health impacts can be evaluated. This paper outlines the countermeasures methodology adopted and the databases used and discusses their applicability.

ERIDAS, a computer program for rapid calculation of internal doses from measurements of people in an emergency

In an emergency involving the deliberate or accidental release of radioactive materials, there could potentially be a large number of people who require monitoring for internal contamination. Doses from these measurements will need to be calculated as quickly as possible. Emergency Response Internal Dose Assessment Software (ERIDAS) has been designed for this purpose.

Complementary spectroscopic techniques to model the association of contaminant uranium with structural surfaces

Contaminant uranium poses unique problems for decontamination of former weapons processing and nuclear power facilities, as well as chemical plants, waste storage sites and former mining facilities. In addition, dealing with the possibility of intentional (i.e., a terrorist act) or accidental release of radioactive material in a populated area requires an accurate understanding of the nature of the association of such material with structural surfaces. These surfaces must also be considered in the context of repeated contamination, and the importance of atmospheric exposure, interaction with other possible contaminants, and corrosion or surface degradation due to such exposure must be taken into account. Complementary spectroscopic techniques, especially surface spectroscopies, are essential in developing models for the interaction of contaminants with surfaces and interfaces. In this review (which also presents new data on uranium association with corroding steel surfaces), we collect models of this association as determined by spectroscopic techniques, assess the important considerations in the development of more accurate models, and address some of the questions which remain.

Predictive Contamination of Animal Products Due to the Inhalation of Air and the Ingestion of Soil of Cattle in an Accidental Release of Radioactive Materials - Focusing on Contaminative Influence of Milk

In an accidental release of radioactive materials to the environment, the contaminative influence of animal products due to the inhalation of air and the ingestion of soil of cattle, both of which are considered as minor contaminative pathways in most radioecological models but may be important ones, was investigated with the improvement of the Korean radioecological model DYNACON. Although mathematical models for both contaminative pathways have been established for considering all animal products and incorporated into the model, investigation was limited to milk. As a result, it was found that both pathways are influential in the contamination of milk during the non-grazing period of dairy cows. Precipitation was an influential factor in milk contamination due to the ingestion of soil, especially for 137Cs. In the case of an accidental release during the grazing period of dairy cows, the contaminative influence due to the inhalation of air was negligible irrespective of the existence of precipitation during an accidental release.

The determination of the area affected by relocation after nuclear accidents

Relocation is one of the protective actions that may be introduced to protect the public following an accidental release of radioactive material into the environment. This paper presents the results of a study on the quantitative prediction of the area affected by relocation after nuclear accidents. In this study, the relationship between the areas affected by relocation and the intervention level for implementing relocation as well as source term has been quantitatively described. All the calculations presented in this paper have been done using the European package for accident consequence assessment COSYMA. To estimate the influence of the assumptions made in the calculations on the general applicability of the results, a sensitivity study has been carried out for source term variations and sampling of weather sequences.

Further development of the French-German dispersion model - SODAR pre-processor

Basic concepts, technical applications and details of the updated meteorological pre-processor using SODAR data (MPS) as well as additional meteorological measurements are presented. The pre-processor allows the calculation of boundary-layer parameters, i.e. friction velocity, Monin-Obukhov length and mixing layer height, on the basis of SODAR measurements which serve as input parameters for subsequent dispersion calculations, e.g. within the frame of the DFK model for the calculation of the atmospheric dispersion and radiation exposure related to an accidental release of radioactive material in the near range of a nuclear installation (DFK French-German Commission for Information Interchange on Nuclear Safety). The MPS is an extension to the DFK model which presently only includes the meteorological pre-processor MPT, calculating the boundary layer parameters on the basis of wind-speed data and temperature gradient from tower measurements. The improved DFK model can be implemented within the remote monitoring system of German reactor sites as well as nuclear installations in other countries, provided that either tower data or SODAR data are available as meteorological input.

Models for Decontamination, Relocation and Agricultural Countermeasures in RODOS

Predictions of the effects of decontamination, relocation and agricultural countermeasures are an important part of the decision-making process following an accidental release of radioactive material into the environment. Models and supporting databases have been developed for this purpose and integrated into the EU decision support system, RODOS. A wide range of potentially practicable countermeasures is considered on timescales from a day to many years, and endpoints related to their imposition are calculated such that the economic and health impacts can be evaluated. This paper outlines the countermeasures methodology adopted and the databases used and discusses their applicability on different spatial scales.

Emergency Response Planning at the Nevada Test Site

A robust emergency response plan was an essential part of the underground testing of nuclear weapons at the United States Nevada Test Site (NTS). This plan was designed to help protect the safety and health of test operations personnel and the general public and to minimise social, economic, and environmental consequences in the event of an accidental release of radioactive material into the atmosphere. Meteorological information was a vital element in the formulation of this emergency response plan by a team of senior decision makers. The meteorological basis of the nuclear-test operations emergency response plan is described. Emphasis is placed on the complex, mobile, remote-sensing capability that was placed in the field prior to and during all underground nuclear tests. The system for the prompt electronic communication of these data to the test operations centre and the immediate processing, display, and real-time use of these data by test operations management is portrayed. In addition, the complete mesoscale meteorological monitoring programme, including lightning detection, is described as well as how special mesoscale weather forecasts and test support products were produced and displayed for test management. The radiological assessment technique is summarised and the team effort between the weather forecaster, radiation fallout analyst, the United States Environmental Protection Agency radiological assessment team, and test management is outlined. A typical emergency response plan is described and the process for implementing the plan characterised. The rapid process for electronically displaying meteorological and radiological products on wide-screens during test operations is also described through visual examples. The paper offers a rare view of a comprehensive emergency response capability.

An investigation into the applicability of geostatistical techniques for estimating contamination levels following an accidental release of radioactivity

In the event of an accidental release of radioactive material into the environment appropriate responses will be aided by the analysis and display of the collected data. This paper considers the suitability of using the geostatistical technique of ordinary kriging to interpolate between environmental measurements. Two factors affecting the accuracy of kriged estimates for unsampled locations are investigated, namely the effects of sample size and of spatial distribution. Sample data were generated by a gaussian atmospheric dispersion model and error estimates were determined by comparison of the kriged estimates at unsampled locations with the gaussian model predictions at these locations. Calculations were made for datasets containing between 20 and 80 points, and it was found that even datasets with low numbers of samples gave encouraging results. For example, 40 data points provided estimates with less than 50% error in 70% of the entire region. Estimation errors were smallest for the region of highest values, and highest on the boundary of the region. These results suggest that ordinary kriging can provide useful information in the assessment of post accident radiation monitoring data.

ECOSYS-87: model calculations of the activity in cattle meat related to deposition time and feeding regimes after a nuclear fallout.

The radioecological model ECOSYS-87 was used to evaluate the effect of countermeasures for reducing the ingestion dose by eating cattle meat after an accidental release of radioactive material. Calculations were performed using a database adapted to Swiss conditions for the case that (1) contaminated grass or hay is replaced by clean fodder; (2) the last 100 days before slaughter, taking place one year after an accident, only uncontaminated fodder is given; and (3) alternative feeding regimes are chosen. Seasonal effects were considered by doing all calculations for a deposition at each month of the year. Feeding uncontaminated forage 100 d before slaughter (case 2) proved to be the most effective countermeasure and reduced the integrated activity in meat by 90% to 99%. The effect of replacing contaminated grass (case 1) was less uniform and depended strongly on the time a deposition occurred. In this case the reduction was between 50% and 100% one year after deposition. The substitution of contaminated hay (case 1) was less effective compared to the substitution of grass. The choice of alternative feeding regimes (case 3) led to a reduction of the integrated activity of up to 40% one year after deposition. The present model calculations clearly reveal the importance of the seasonality and demonstrate the usefulness of such calculations as a basis for generating countermeasures in decision support systems.

Particle deposition and plugging in tubes and cracks (with special reference to fission product retention)

The main function of a containment structure enclosing a nuclear reactor is to retain any accidental release of radioactive materials. However, if the containment has leak paths due, for example, to cracks or failed seals, then there is the possibility of particulate matter and gas passing through the opening due to the pressure difference. The work presented in this paper describes in some detail the three main steps reqired to assess the amount of gas and particulate matter that pass into the environment. Step one involves calculation of the gas flow through a tube of non-uniform cross sectional area, step two is concerned with the deposition of small solid particles suspended in the host gas, onto the walls of the tube and, in step three, the rate of buildup of deposit on the tube wall is calculated with the aim of determining the rapidity with which the tube is plugged. We recast the gas dynamics equation into a form suitable for calculating gas flow in non-uniform tubes in the laminar and turbulent flow regimes, from low speed up to critical flow conditions. The results of these calculations are compared with an extensive set of experiments and excellent agreement is found. We briefly outline the various deposition processes that particles can undergo on surfaces and show how the particle concentration in the tube may be calculated. Finally, an equation that determines the shape and rate of formation of a plug is developed. This equation is non-linear and integro-differential in nature, and in order to solve it we develope a method which involves prescibing a geometrical plug shape but allowing the parameters within it to be time dependent. Plugging times and the amounts of particulate and gas that have escaped prior to plugging are calculated. Comparison with experiment is made and reasonable agreement found. A general discussion of the shortcomings of the approach is given together with suggestions for further work.