A model for radiological consequences of nuclear power plant operational atmospheric releases

A dynamic dose and risk assessment model is developed to estimate radiological consequences of atmospheric emissions from nuclear power plants. Internal exposure via inhalation and ingestion, external exposure from clouds and radioactivity deposited on the ground are included in the model. The model allows to simulate interregional moves of people and multi-location food supply in the computational domain. Any long-range atmospheric dispersion model which yields radionuclide concentrations in air and on the ground at predetermined time intervals can easily be integrated into the model. The software developed is validated against radionuclide concentrations measured in different environmental media and dose values estimated after the Chernobyl accident. Results obtained using the model compare well with dose estimates and activities measured in foodstuffs and feedstuffs.     

14C content in vegetation in the vicinities of Brazilian nuclear power reactors

(14)C specific activities were measured in grass samples collected around Brazilian nuclear power reactors. The specific activity values varied between 227 and 299 Bq/kg C. Except for two samples which showed (14)C specific activities 22% above background values, half of the samples showed background specific activities, and the other half had a (14)C excess of 1-18%. The highest specific activities were found close to the nuclear power plants and along the main wind directions (NE and NNE). The activity values were found to decrease with increasing distance from the reactors. The unexpectedly high (14)C excess values found in two samples were related to the local topography, which favors (14)C accumulation and limits the dispersion of the plume. The results indicate a clear (14)C anthropogenic signal within 5 km around the nuclear power plants which is most prominent along northeastwards, the prevailing wind direction.     

The Bulgarian Emergency Response System for dose assessment in the early stage of accidental releases to the atmosphere

The Bulgarian Emergency Response System (BERS) is being developed in the Bulgarian National Institute of Meteorology and Hydrology since 1994. BERS is based on numerical weather forecast meteorological information and a numerical long-range dispersion model accounting for the transport, dispersion, chemical and radioactive transformations of pollutants. In the present paper, the further development of this system for a mixture of radioactive gaseous and aerosol pollutants is described. The basic module for the BERS, the numerical dispersion model EMAP, is upgraded with a “dose calculation block”. Two scenarios for hypothetical accidental atmospheric releases from two NPPs, one in Western, and the other in Eastern Europe, are numerically simulated. The effective doses from external irradiation, from air submersion and ground shinning, effective dose from inhalation and absorbed dose by thyroid gland formed by 37 different radionuclides, significant for the early stage of a nuclear accident, are calculated as dose fields for both case studies and discussed.     

A box model for calculation of collective dose commitment from radioactive waterborne releases to the baltic sea

To meet the new regulations of maximum yearly releases from Swedish nuclear power plants issued by the Swedish National Radiation Protection Institute, and to make realistic calculations of collective dose commitment derived from radionuclides discharged to the Baltic Sea, a box model AQUAPATH-BALTIC has been developed. The model calculates radionuclide concentrations in 25 boxes for discharges into given compartments and takes into consideration the dispersion rates of the water masses, the sediment-water interaction and radioactive decay. The calculated concentrations in water and sediment at steady state are then used to evaluate individual and collective intakes of activity and external exposures. The radiation doses to the global population following discharges to the Baltic Sea are also calculated.     

Predictive model for the (14)C radioactivity in a plant following an exposure to airborne (14)CO(2) gas

This paper provides details of a dynamic compartment model for estimating the (14)C radioactivity in an agricultural plant exposed to an amount of airborne (14)CO(2) gas. The plant, in the model, is divided into two compartments, the plant body (shoot and root) and ears, to predict the radioactivity of different parts of a plant. The carbon transports from, to and between the compartments are described by the processes of a photosynthesis, respiration, and translocation. The carbon transport fluxes of these processes are determined from the growth rates of a plant, which are usually easily attained. The model predictions showed that the present model could converge to a region where the specific activity model is applicable when the elapsed exposure time was extended up to the harvest time of a plant. The (14)C activity of a plant was greatly affected by the elapsed exposure time, the developmental stages of a plant at an exposure time, and the airborne (14)C activity during an exposure. It was expected that the peak of the ears' (14)C activity appeared when the exposure time was close to the ears-maturity date. The model predictions agreed reasonably well with the measured (14)C radioactivity of the rice plants that were artificially exposed to (14)CO(2) of a high (14)C source for a short period of time in an exposure box.     

Background and anthropogenic radionuclide derived dose rates to freshwater ecosystem: nuclear power plant cooling pond: reference organisms

The radiological assessment of non-human biota to demonstrate protection is now accepted by a number of international and national bodies. Therefore, it is necessary to develop a scientific basis to assess and evaluate exposure of biota to ionizing radiation. Radionuclides from the Ignalina Nuclear Power Plant (Lithuania) were discharged into Lake Druksiai cooling pond. Additional radionuclide migration and recharge to this lake from a hypothetical near-surface, low-level radioactive waste disposal, to be situated 1.5 km from the lake, had been simulated using RESRAD-OFFSITE code. This paper uses ERICA Integrated Approach with associated tools and databases to compare the radiological dose to freshwater reference organisms. Based on these data, it can be concluded that background dose rates to non-human biota in Lake Druksiai far exceed those attributable to anthropogenic radionuclides. With respect the fishery and corresponding annual committed effective human dose as a result of this fish consumption Lake Druksiai continues to be a high-productivity water body with intensive angling and possible commercial fishing.     

Uncertainties of internal dose assessment for animals and plants due to non-homogeneously distributed radionuclides

The dose conversion coefficients (DCCs) for the assessment of internal absorbed dose rate in reference animals and plants have been generally calculated assuming a homogeneous distribution of radionuclides within the body. Realistic scenarios of internal exposure must account for some radionuclides which tend to concentrate in specific organs or tissues. To study the effect of such inhomogeneous distributions, internal DCCs have been calculated assuming both a central and an eccentric point source. The analysis of the results showed that uncertainties of the whole body DCC due to non-homogeneous radionuclide distribution are less than 30% for photons and electrons for all considered organisms. For electrons, the uncertainties are negligible below certain energies, dependent on the size of the organisms. Additionally, the organ doses due to the accumulation of the radionuclide in an organ are also described and organ/whole body doses ratios are estimated.     

Statistical characteristics of radionuclide concentration field around a nuclear power plant

A Markov chain model with two states is used for investigating the space and time structure of the concentration field around an elevated continuous source. The concentration field is computed with a time-dependent Gaussian puff dispersion model run with observed meteorological data as input. Spatial distributions of transition probability, Besson persistence coefficient and order of Markov chain are presented for tritium routinely released from a nuclear power plant located about 100 miles east of Bucharest, Romania.     

Cost assessment of ventilation and averted dose due to radon in dwellings

The inhalation dose due to radon and its progenies could be averted by ventilation in dwellings; however, on the other hand the increased ventilation augments the heating cost. Therefore a cost-benefit analysis could contribute to optimise the ventilation rate. In our current work we applied our former defined parameters of the optimising procedure to assess the optimised ventilation and radon concentration in dwellings with average parameters. To assess the inhalation dose rates the time-dependent concentrations of all the progenies were calculated in case of periodic and continuous ventilation as well, at three different radon entry rates (5, 10, 20kBqh(-1)). The optimal ventilation rates in case of continuous ventilation are 0.22, 0.40 and 0.66h(-1), respectively. By these conditions the optimal radon concentration takes 160-210Bqm(-3). According to the more detailed analysis the periodic ventilation gives, in general, a better solution than the continuous one. The Monte Carlo simulations provided a large uncertainty; therefore, before the practical application of the results the uncertainty should be decreased taken into account the local conditions.     

The influence of a coal-fired power plant operation on radionuclide concentrations in soil

Fifty-two soil samples in the vicinity of a coal-fired power plant (CFPP) in Figueira (Brazil) were analyzed. The radionuclide concentration for the uranium and thorium series in soils ranged from <9 to 282 Bq kg(-1). The range of 40K concentration in soils varied from <59 to 412 Bq kg(-1). The CFPP (10 MWe) has been operating for 35 years and caused a small increment in natural radionuclide concentration in the surroundings. This technologically enhanced natural radioactivity (TENR) was mainly due to the uranium series (234Th, 226Ra and 210Pb) and was observable within the first kilometer from the power plant. The CFPP influence was only observed in the 0-25 cm soil horizon. The soil properties prevent the radionuclides of the 238U-series from reaching deeper soil profiles. The same behavior was observed for 40K as well. No influence was observed for 232Th, which was found in low concentrations in the coal.     

Distribution of carbon 14 in the terrestrial environment close to French nuclear power plants

For 10 years, (14)C measurements have been performed around French nuclear power plant sites, both in zones influenced and zones not influenced by gaseous releases. Examining the results from these measurements in the terrestrial environment shows that the discharges have a very slight impact on the radiocarbon level (with a relative increase in the specific activity of the order of 3 Bqkg(-1)C in the influenced areas). In correlation, there is a near-negligible increase in dose, on average less than 0.1 microSvyr(-1), with reference to a dose from background radiation, which is of the order of 10 microSvyr(-1). The deltaC13 values are very similar between the influenced zone and the non-influenced zone, with a mean of -27 per thousand. The mean DeltaC14 varies from 101 per thousand in the non-influenced zone to 123 per thousand in the influenced zone. Moreover, a general reduction in (14)C concentration was found, with a time constant of the order of 95 years. The current level of (14)C specific activity in terrestrial environment is estimated to be 242+/-6 Bqkg(-1)C.     

A dynamic model of the global iodine cycle and estimation of dose to the world population from releases of iodine-129 to the environment

A dynamic linear compartment model of the global iodine cycle has been developed for the purpose of estimating radiological impacts on the world population from releases of ¹²⁹I to the environment. The time-invariant fractional transfer rates, which describe the transport of ¹²⁹I between environmental compartments comprising the atmosphere, hydrosphere, lithosphere, and terrestrial biosphere, are estimated from an analysis of available data on concentrations for naturally occurring stable iodine and data on the global hydrologic cycle. The global radiological impacts on man from a given release of ¹²⁹I are estimated from the calculated compartment inventories as a function of time and models for the intake of iodine by a reference adult. For a constrant population of 12.2 billion, the estimated worldwide complete population dose commitment to the thyroid is 76 man-Sv/GBq (2.8 × 10⁵ man-rem/Ci) released. Estimated values of the incomplete population dose commitment at various times after a global-scale release to the atmosphere are also presented.     

Development of a dynamic transfer model of (14)C from the atmosphere to rice plants

A dynamic compartment model was investigated to describe ¹⁴C accumulation in rice plants exposed to atmospheric ¹⁴C with temporally changing concentrations. In the model, rice plants were regarded to consist of three compartments: the ear and the mobile and immobile carbon pools of the shoot. Photosynthetically fixed carbon moves into the ear and the mobile carbon pool, and these two compartments release a part of this carbon into the atmosphere by respiration. Carbon accumulated in the mobile carbon pool is redistributed to the ear, while carbon transferred into the immobile carbon pool from the mobile one is accumulated there until harvest. The model was examined by cultivation experiments using the stable isotope, ¹³C, in which the ratios of carbon photosynthetically fixed at nine times during plant growth to the total carbon at the time of harvest were determined. The model estimates of the ratios were in relatively good agreement with the experimental observations, which implies that the newly developed compartment model is applicable to estimate properly the radiation dose to the neighboring population due to an accidental release of ¹⁴C from nuclear facilities.     

Parameterization of a dynamic specific activity model of 14C transfer from surface water-to-humans

Carbon-14 is a particularly interesting radionuclide from the perspective of dose estimation because it mixes readily with stable CO2, and hence enters the food-chain as fundamental biomolecules. A model was developed for the situation of 14C releases to surface waters, where there are distinct changes in the water 14C activity concentrations throughout the year. The model computes the specific activity in water, phytoplankton, fish, crops, meat, milk and air, following a typical irrigation-based food-chain scenario. This paper describes the derivation of the required 14C-specific parameter values. Many of the key parameters are not commonly measured, at least not in the context of dose assessment. Thus, inference from other sources of data was required, and this is the scientific contribution described in this paper. The best estimates and appropriate measures of statistical dispersion are provided. This required consideration of both the temporal and spatial averaging domains to ensure they were correct for parameters as defined in the model. The model coupled with these parameter values represents several new developments for modelling 14C transfers.     

Extension of sensitivity and uncertainty analysis for long term dose assessment of high level nuclear waste disposal sites to uncertainties in the human behaviour

Biosphere dose conversion factors are computed for the French high-level geological waste disposal concept and to illustrate the combined probabilistic and deterministic approach. Both ¹³⁵Cs and ⁷⁹Se are used as examples. Probabilistic analyses of the system considering all parameters, as well as physical and societal parameters independently, allow quantification of their mutual impact on overall uncertainty. As physical parameter uncertainties decreased, for example with the availability of further experimental and field data, the societal uncertainties, which are less easily constrained, particularly for the long term, become more and more significant. One also has to distinguish uncertainties impacting the low dose portion of a distribution from those impacting the high dose range, the latter having logically a greater impact in an assessment situation. The use of cumulative probability curves allows us to quantify probability variations as a function of the dose estimate, with the ratio of the probability variation (slope of the curve) indicative of uncertainties of different radionuclides. In the case of ¹³⁵Cs with better constrained physical parameters, the uncertainty in human behaviour is more significant, even in the high dose range, where they increase the probability of higher doses. For both radionuclides, uncertainties impact more strongly in the intermediate than in the high dose range. In an assessment context, the focus will be on probabilities of higher dose values. The probabilistic approach can furthermore be used to construct critical groups based on a predefined probability level and to ensure that critical groups cover the expected range of uncertainty.     

The role of planktonic organisms in accumulation and transfer of radioactive contaminants in the cooling reservoir of a nuclear power plant

The results of long-term studies (1985–2006) on the state of planktonic communities and their capacity for accumulation of radioactive contaminants in the cooling reservoir of the Beloyarsk Nuclear Power Plant (BNPP) have been summarized. The changes in the population density and biomass of planktonic organisms have been estimated in different water areas of the Beloyarsk Reservoir. The levels of radionuclide accumulation by phyto- and zooplankton in the reservoir and technological channels of the BNPP have been determined. The contributions of two nuclear power enterprises (the BNPP and the Institute of Reactor Materials) to the accumulation of radionuclides by planktonic organisms have been evaluated. The rates of radionuclide accumulation by phyto- and zooplankton have been estimated and compared with those of other components of the aquatic biocenosis.     

Dynamic model for the assessment of radiological exposure to marine biota

A generic approach has been developed to simulate dynamically the uptake and turnover of radionuclides by marine biota. The approach incorporates a three-compartment biokinetic model based on first order linear kinetics, with interchange rates between the organism and its surrounding environment. Model rate constants are deduced as a function of known parameters: biological half-lives of elimination, concentration factors and a sample point of the retention curve, allowing for the representation of multi-component release. The new methodology has been tested and validated in respect of non-dynamic assessment models developed for regulatory purposes. The approach has also been successfully tested against research dynamic models developed to represent the uptake of technetium and radioiodine by lobsters and winkles. Assessments conducted on two realistic test scenarios demonstrated the importance of simulating time-dependency for ecosystems in which environmental levels of radionuclides are not in equilibrium.     

Preliminary analysis of single flash combined with binary system using thermodynamic assessment: a case study of Dieng geothermal power plant

This paper addressed the performance of single flash combined with a binary system that was proposed in the Dieng geothermal power plant by applying thermodynamic assessment methods. A set of mathematical equations from the plant was developed and solved iteratively using engineering equation solver. The results showed that the available exergy of the produced fluid from production wells is 66,204 kW. The performance of an existing single-flash power plant indicated 24,300 kW of net power output. The proposed design of single flash combined with a binary system improves the power output by 17.16% to 27,786 kW. The second law efficiency increases from 36.7% to 41.97% while the first law efficiency increases from 11.62% to 13.61%.     

POSEIDON/RODOS models for radiological assessment of marine environment after accidental releases: application to coastal areas of the Baltic, Black and North Seas

In the framework of the developments of the European system RODOS (Real-time On-line DecisiOn support System) for emergency response to nuclear accident, the computer code POSEIDON, that was developed to assess the radiological consequences of radioactive releases into marine environment, was adapted to cope with emergency conditions, in situations of radioactive discharges into the oceans from direct deposition from the atmosphere, sunken ships and containers, from discharges of rivers and estuaries and from coastal run-off. Based on the box model developed within the 'Marina' project, POSEIDON can calculate the dose effects from radionuclide releases in the coastal waters of Europe integrated over long time periods. A dynamic food chain model was implemented to deal with the short-term dynamical uptake of radioactivity by specific marine plants and organisms. POSEIDON has been installed on a UNIX platform to be fully compatible with RODOS input/output databases and on a Windows platform with an interface based on web technology. The 3D hydrodynamic model THREETOX is a part of the POSEIDON/RODOS system. It has been applied to coastal areas of the Baltic Sea, the Black Sea, and the North Sea. to derive the parameters for a flexible system of well-defined model compartments to be adapted to emergency conditions. The activity concentrations in water and in the marine food web were calculated by means of POSEIDON for radioactive fallout resulting from bomb testing, from the Chernobyl accident, and from routine discharges from nuclear facilities. POSEIDON's model results were compared with measurement data, and with calculation results from THREETOX. The model results agreed with the measurement data sufficiently.