Kerma conversion factors for modern glass buildings in radioactively contaminated areas.

To improve the estimation of external gamma irradiation from deposited radioactivity in urban environments a model of a modern office or residential building with glass facades was set up with eleven different building heights. Kerma conversion factors for the floors inside the building from contamination on different types of surfaces were determined by using the Monte Carlo code MCNP6 for the primary gamma energies 0.3 , 0.662 and 3.0 MeV and for three different environmental scenarios. The kerma conversion factors were expressed as formulas for each possible deposition area for contaminants. The importance of the determined factors was shown by comparing them to previously generally used factors for multistorey house blocks.

Introducing the concept of the isodose for optimisation of decontamination activities in a radioactive fallout scenario.

In the recovery phase after a radioactive release incident, it is important to be able to focus decontamination operations on the areas that contribute most to the radiation dose. Monte Carlo simulations were applied to determine the shielding effect of a building against radiation from various directions, also giving information on the dose contributions at various locations inside the building from specific areas outside. The concept of the isodose was developed to optimise decontamination activities, and was applied as isodose lines to define the smallest areas that lead to a certain dose reduction through decontamination of areas surrounding the building. The shape and position of the isodose lines depend on the building's geometry, wall thickness, and material, and on the observation point inside the building. Calculations have been made with a surface resolution of 1 m2 for four observation points in a modular building, assuming depositions of 137Cs and 60Co on the ground surface and on the roof, as well as 1 cm below the ground surface to represent ground penetration. For example, a ten times as large area would have to be decontaminated to increase the dose reduction from 10% to 30%, if it is assumed that all the contamination is located at a depth of 1 cm.

Modeling of the fate of radionuclides in urban sewer systems after contamination due to nuclear or radiological incidents.

After an accidental radioactive contamination by aerosols in inhabited areas, the radiation exposure to man is determined by complex interactions between different factors such as dry or wet deposition, different types of ground surfaces, chemical properties of the radionuclides involved and building development as well as dependence on bomb construction e.g. design and geometry. At short-term, the first rainfall is an important way of natural decontamination: deposited radionuclides are washed off from surfaces and in urban areas the resulting contaminated runoff enters the sewer system and is collected in a sewage plant. Up to now the potential exposure caused by this process has received little attention and is estimated here with simulation models. The commercial rainfall-runoff model for urban sewer systems KANAL++ has been extended to include transport of radionuclides from surfaces through the drainage to various discharge facilities. The flow from surfaces is modeled by unit hydrographs, which produce boundary conditions for a system of 1d coupled flow and transport equations in a tube system. Initial conditions are provided by a map of surface contamination which is produced by geo-statistical interpolation of γ-dose rate measurements taking into account the detector environment. The corresponding methodology is implemented in the Inhabited Area Monitoring Module (IAMM) software module as part of the European decision system JRODOS. A hypothetical scenario is considered where a Radiation Dispersal Device (RDD) with Cs-137 is detonated in a small inhabited area whose drainage system is realistically modeled. The transition of deposited radionuclides due to rainfall into the surface runoff is accounted for by different nuclide-specific entrainment coefficients for paved and unpaved surfaces. The concentration of Cs-137 in water is calculated at the nodes of the drainage system and at the sewage treatment plant. The external exposure to staff of the treatment plant is estimated. For Cs-137 radiation levels in the plant are low since wash-off of cesium from surfaces is an ineffective process.

Car-borne gamma spectrometry: a virtual exercise in emergency response.

In recent years car-borne gamma spectrometry has expanded from its role as a geological survey platform to being a useful asset in searching for orphan sources and for surveying in the aftermath of an incident involving the release of radioactive materials. The opportunities for gaining practical experience in the field however are limited by cost considerations and practicability. These limitations are exacerbated by the fact that field data can differ significantly from data generated in the laboratory. As a means of exercising existing emergency measuring/surveying capability and introducing car-borne measurements to a larger group, a virtual exercise was devised. The exercise ORPEX (Orphan Sources and Fresh Fallout Virtual Exercise in Mobile Measurement) featured two typical emergency scenarios: a search for orphan sources and surveying to delineate fallout from a local release point. Synthetic spectral data were generated for point sources and inserted into genuine car-borne measurement data. Participants were presented with a typical software tool and data and were asked to report source locations and isotopes within a time limit. In the second scenario, synthetic data representing fallout from a local fire involving radioactive material were added to real car-borne data, participants being asked to produce maps identifying and characterising the regions of contamination. Fourteen individual organisations from seven different countries supplied results which indicated that for strong sources of isotopes with simple spectra featuring high energy peaks, location and identification was not a problem. Problems arose for isotopes with low energy signals or that presented a weak signal even when visible for extended periods. Experienced analysts tended to perform better in identification of sources irrespective of experience with mobile measurements whereas those with experience in such measurements were more confident in providing more precise estimates of location. The results indicated the need for the inclusion of less frequently encountered sources in field exercise related to mobile measurements.

Malevolent use of radioactive materials: an international exercise in the analysis of gamma-spectrometric data.

The past years have seen a broadening in the focus of emergency preparedness and first response towards situations involving the malevolent use of radioactive materials in a variety of contexts. Many of these contexts are such that first responders and responsible authorities may be faced with isotopes and activities that present significant challenges with respect to identification and quantification using gamma ray spectrometry. The MALRAD international exercise was designed to provide a practice opportunity for authorities and laboratories to work with synthetic gamma-spectrometric data generated in response to seven hypothetical scenarios involving radioactive materials. Scenarios were based as far as practical upon earlier events and participants had one week to provide as much information as possible about the sources based on the provided data. Results indicate that in cases of single isotopes, irrespective of the detector type involved, all participants were in a position to identify sources and provide estimates of activity. For situations involving shielded sources or special nuclear materials most participants were in a position to provide indications as to what the sources were but only a few participants were in a position to provide detailed information.

Modelling remediation options for urban contamination situations.

The impact on a population from an event resulting in dispersal and deposition of radionuclides in an urban area could be significant, in terms of both the number of people affected and the economic costs of recovery. The use of computer models for assessment of urban contamination situations and remedial options enables the evaluation of a variety of situations or alternative recovery strategies in contexts of preparedness or decision-making. At present a number of models and modelling approaches are available for different purposes. This paper summarizes the available modelling approaches, approaches for modelling countermeasure effectiveness, and current sources of information on parameters related to countermeasure effectiveness. Countermeasure information must be applied with careful thought as to its applicability for the specific situation being modelled. Much of the current information base comes from the Chernobyl experience and would not be applicable for all types of situations.

Requirements for estimation of doses from contaminants dispersed by a 'dirty bomb' explosion in an urban area.

The ARGOS decision support system is currently being extended to enable estimation of the consequences of terror attacks involving chemical, biological, nuclear and radiological substances. This paper presents elements of the framework that will be applied in ARGOS to calculate the dose contributions from contaminants dispersed in the atmosphere after a 'dirty bomb' explosion. Conceptual methodologies are presented which describe the various dose components on the basis of knowledge of time-integrated contaminant air concentrations. Also the aerosolisation and atmospheric dispersion in a city of different types of conceivable contaminants from a 'dirty bomb' are discussed.

Modelling the long-term consequences of a hypothetical dispersal of radioactivity in an urban area including remediation alternatives.

The Urban Remediation Working Group of the International Atomic Energy Agency's EMRAS (Environmental Modelling for Radiation Safety) program was organized to address issues of remediation assessment modelling for urban areas contaminated with dispersed radionuclides. The present paper describes the second of two modelling exercises. This exercise was based on a hypothetical dispersal of radioactivity in an urban area from a radiological dispersal device, with reference surface contamination at selected sites used as the primary input information. Modelling endpoints for the exercise included radionuclide concentrations and external dose rates at specified locations, contributions to the dose rates from individual surfaces, and annual and cumulative external doses to specified reference individuals. Model predictions were performed for a "no action" situation (with no remedial measures) and for selected countermeasures. The exercise provided an opportunity for comparison of three modelling approaches, as well as a comparison of the predicted effectiveness of various countermeasures in terms of their short-term and long-term effects on predicted doses to humans.

Estimation of health hazards resulting from a radiological terrorist attack in a city.

In recent years, the concern for protection of urban populations against terror attacks involving radiological, biological or chemical substances has attracted increasing attention. It sets new demands to decision support and consequence assessment tools, where the focus has traditionally been on accidental exposure. The aim of the present study was to illustrate issues that need to be considered in evaluating the radiological consequences of a 'dirty bomb' explosion. This is done through a worked example of simplified calculations of relative dose contributions for a specific 'dirty bomb' scenario leading to atmospheric dispersion of 90Sr contamination over a city area. Also, the requirements of atmospheric dispersion models for such scenarios are discussed.

Improvement of modelling capabilities for assessing urban contamination: the EMRAS Urban Remediation Working Group.

The Urban Remediation Working Group of the International Atomic Energy Agency's Environmental Modelling for Radiation Safety (EMRAS) programme was established to improve modelling and assessment capabilities for radioactively contaminated urban situations, including the effects of countermeasures. An example of the Working Group's activities is an exercise based on Chernobyl fallout data in Ukraine, which has provided an opportunity to compare predictions among several models and with available measurements, to discuss reasons for discrepancies, and to identify areas where additional information would be helpful.

An assessment of cumulative external doses from Chernobyl fallout for a forested area in Russia using the optically stimulated luminescence from quartz inclusions in bricks.

Optically stimulated luminescence (OSL) has been used for estimation of the accumulated doses in quartz inclusions obtained from two fired bricks, extracted in July 2004 from a building located in the forested surroundings of the recreational area Novie Bobovichi, the Bryansk Region, Russia. The area was significantly contaminated by Chernobyl fallout with initial (137)Cs ground deposition level of approximately 1.1 MBq m(-2). The accumulated OSL doses in sections of the bricks varied from 141 to 207 mGy, of which between 76 and 146 mGy are attributable to Chernobyl fallout. Using the OSL depth-dose profiles obtained from the exposed bricks and the results from a gamma-ray-survey of the area, the Chernobyl-related cumulative gamma-ray dose for a point detector located in free air at a height of 1m above the ground in the study area was estimated to be ca. 240 mGy for the time period starting on 27 April 1986 and ending on 31 July 2004. This result is in good agreement with the result of deterministic modelling of the cumulative gamma-ray dose in free air above undisturbed ground from the Chernobyl source in the Bryansk Region. Over the same time period, the external Chernobyl-related dose via forest pathway for the most exposed individuals (e.g., forest workers) is estimated to be approximately 39 mSv. Prognosis for the external exposure from 1986 to 2056 is presented and compared with the predictions given by other investigators of the region.

New developments to support decision-making in contaminated inhabited areas following incidents involving a release of radioactivity to the environment.

The Chernobyl accident demonstrated that releases from nuclear installations can lead to significant contamination of large inhabited areas. A new generic European decision support handbook has been produced on the basis of lessons learned on the management of contaminated inhabited areas. The handbook comprises detailed descriptions of 59 countermeasures in a standardised datasheet format, which facilitates a comparison of features. It also contains guidance in the form of decision flowcharts, tables, check lists and text to support identification of optimised solutions for managing the recovery of inhabited areas within a framework consistent with ICRP recommendations. A new comprehensive inhabited-area dose model is also being developed for implementation in the ARGOS and RODOS decision support systems. Shortcomings of previous models are demonstrated. Decision support modelling in relation to malicious dispersion of radioactive matter in inhabited areas is also discussed. Here, the implications of, e.g., particle sizes and dispersion altitude are highlighted.

137Cs and 90Sr in live and dead reindeer lichens (genera Cladonia) from the "Kraton-3" underground nuclear explosion site.

The contents of 137Cs and 90Sr have been determined in 29 samples of live and dead reindeer lichens (genera Cladonia) collected at the "Kraton-3" underground nuclear explosion site (65.9 degrees N 112.3 degrees E, event year--1978) in Yakutia, Russia in 2002. The area contamination was within the range of 0.36-700 and 0.13-770 kBq m(-2) for 137Cs and 90Sr, respectively. The dead organisms were on average much more contaminated than the live ones. Vertical fractionation of the live lichen carpet demonstrated maximal activity concentrations of both radionuclides in the lower older section of the plants, while for the dead lichens the maximal activity concentrations of 137Cs were detected in the upper part. The vertical distribution of 90Sr was more or less homogeneous in the cushions of dead lichens. Elevated levels of 137Cs and 90Sr activity concentrations were also detected in the re-establishing young lichens growing over the residua of some dead lichens.

Requirements of future models for inhabited areas.

Models for inhabited areas are used in a variety of applications for accidental or continuous releases of radioactivity to atmosphere. Pathways of interest are external exposure from radioactive material in the cloud or deposited on indoor and outdoor surfaces and people, inhalation from the plume and from material resuspended from the ground. In developing a model for inhabited areas it is necessary to consider what the end users may need and ensure that the model is appropriate for the application; different levels of detail may be appropriate for different applications. This paper considers the main processes governing exposure in inhabited areas, commenting on the extent to which we understand them and how well current models reflect this understanding. It also identifies where the authors believe future modelling is needed and the key areas where the current inhabited area models could be improved.

Estimation of doses received in a dry-contaminated residential area in the Bryansk region, Russia, since the Chernobyl accident.

In nuclear preparedness, an essential requirement is the ability to adequately predict the likely consequences of a major accident situation. In this context it is very important to evaluate which contributions to dose are important, and which are not likely to have significance. As an example of this type of evaluation, a case study has been conducted to estimate the doses received over the first 17 years after the Chernobyl accident in a dry-contaminated residential area in the Bryansk region in Russia. Methodologies for estimation of doses received through nine different pathways, including contamination of streets, roofs, exterior walls, and landscape, are established, and best estimates are given for each of the dose contributions. Generally, contaminated soil areas were estimated to have given the highest dose contribution, but a number of other contributions to dose, e.g., from contaminated roofs and inhalation of contaminants during the passage of the contaminated plume, were of the same order of magnitude.

Reduction of external dose in a wet-contaminated housing area in the Bryansk Region, Russia.

An investigation of the feasibility of reducing the external dose rate in a recreational housing area located between the settlements of Guta and Muravinka, Bryansk Region, Russia, which had been contaminated by the Chernobyl accident more than a decade earlier was made. Removal of contaminated topsoil was carried out over an area of about 2000 m2, optimising the thickness of the removed layer according to an assessment of the vertical contaminant distribution. A layer of clean sand was applied to shield against radiation from residual contamination in the ground. Careful monitoring of dose rates in reference positions showed that this could reduce the dose rate outdoors by about a factor of 6. The replacement of a roof was found to reduce the dose rate considerably inside the house. A cost analysis of the operation is presented.

Long-term stability of decontamination effect in recreational areas near the town Novozybkov, Bryansk Region, Russia.

In 1995 and 1997, experimental decontamination campaigns were carried out in two recreational areas, Novie Bobovichi and Guta-Muravinka, near the town of Novozybkov, Bryansk Region, Russia. These areas were strongly affected by the Chernobyl fallout in 1986. In order to examine the long-term stability of the clean-up procedures, a programme has been carried out to continuously monitor the radiological situation in and around the decontaminated areas. This follow-up program consists of regular (1-3 times per year) measurements of absorbed gamma-dose rate in air (DR) at reference indoor and outdoor locations, repeated DR measurements on a grid, and gamma-spectrometric analysis of soil and other environmental samples. Very similar dynamics of the Chernobyl-related DR, mostly attributed to radiocaesium decay, were found in all the locations. For the period under study (September 1995-May 2003), the half-lives (years) for the reduction in radiocaesium-dependent DR contribution due to contaminant migration (in the following termed 'DRM half-lives') were, respectively, 52+/-26, 57+/-23, 43+/-21, 46+/-15, and 80+/-56 for the following locations: untreated outdoors, treated outdoors, untreated indoors, treated indoors, and undisturbed forest-grassland plots outside the recreational areas. These relatively high values of the current DRM half-lives correspond very well with the results of soil core analyses, which showed no time-dependent changes in the mean mass depths of the (137)Cs distribution, neither at treated nor at undisturbed plots. The following signs of natural restoration of the disturbed forest-meadow ecosystems have been observed at treated areas: formation of a new litter layer, development of grassy spots, mushroom growths and new generations of pines and birches. The levels of the (137)Cs content in grass and mushrooms from treated plots were one or two orders of magnitude lower, than those registered in the samples from untreated areas. The follow-up study demonstrates the long-term stability and efficiency of the decontamination carried out. There are two main reasons for the sustainment of the effects: careful implementation of adequate clean-up procedures and natural strong fixation of radiocaesium in soil-associated matrices of the ecosystems.

Deposition of contaminant aerosol on human skin.

Over recent years, it has been established that deposition of various types of pollutant aerosols (e.g., radioactive) on human skin can have serious deleterious effects on health. However, only few investigations in the past have been devoted to measurement of deposition velocities on skin of particles of the potentially problematic sizes. An experimental programme has shown the deposition velocities on skin of particles in the ca. 0.5-5 microm AMAD range to be high and generally associated with great variations. A series of investigations have been made to identify some of the factors that lead to this variation. Part of the variation was found to be caused by differences between individuals, whereas another part was found to be related to environmental factors. The identification of major influences on skin contaminant deposition is important in estimating health effects as well as in identifying means for their reduction.

Measurement of contaminant removal from skin using a portable fluorescence scanning system.

The residence time of particulate contamination on the human body is a factor that has an important impact on the accuracy of exposure assessment in the aftermath of an accidental release of radionuclides to the atmosphere. Measurements of particle clearance from human skin were made using an illumination system to excite fluorescence in labelled silica particles and a CCD camera and image processing system to detect this fluorescence. The illumination system consists of high-intensity light emitting diodes (LEDS) of suitable wavelengths arranged on a portable stand. The physically small size of the LEDs allows them to be positioned close to the fluorescing surface, thus maximising the fluorescent signal that can be obtained. The limit of detection was found to be 50 microg of tracer particle per cm2. Experiments were carried out to determine the clearance rates of 10 microm and 3 microm particles from the skin. Results show that, in the absence of any mechanical rubbing of the skin, the clearance of particles from the skin followed an approximately exponential decay with a half-time of 1.5-7.8 h. Skin hairiness and degree of human movement were found, in addition to particle size, to have an important influence on particle fall-off rate.

The STRATEGY project: decision tools to aid sustainable restoration and long-term management of contaminated agricultural ecosystems.

The STRATEGY project (Sustainable Restoration and Long-Term Management of Contaminated Rural, Urban and Industrial Ecosystems) aimed to provide a holistic decision framework for the selection of optimal restoration strategies for the long-term sustainable management of contaminated areas in Western Europe. A critical evaluation was carried out of countermeasures and waste disposal options, from which compendia of state-of-the-art restoration methods were compiled. A decision support system capable of optimising spatially varying restoration strategies, that considered the level of averted dose, costs (including those of waste disposal) and environmental side effects was developed. Appropriate methods of estimating indirect costs associated with side effects and of communicating with stakeholders were identified. The importance of stakeholder consultation at a local level and of ensuring that any response is site and scenario specific were emphasised. A value matrix approach was suggested as a method of addressing social and ethical issues within the decision-making process, and was designed to be compatible with both the countermeasure compendia and the decision support system. The applicability and usefulness of STRATEGY outputs for food production systems in the medium to long term is assessed.