Predicting the environmental risks of radioactive discharges from Belgian nuclear power plants

Radiological risk assessment to marine biota from exposure to NORM from a decommissioned offshore oil and gas pipeline

Scale residues can accumulate on the interior surfaces of subsea petroleum pipes and may incorporate naturally occurring radioactive materials (NORM). The persistent nature of 'NORM scale' may result in a radiological dose to the organisms living on or near intact pipelines. Following a scenario of in-situ decommissioning of a subsea pipeline, marine organisms occupying the exteriors or interiors of petroleum structures may have close contact with the scale or other NORM-associated contaminated substances and suffer subsequent radiological effects. This case study used radiological dose modelling software, including the ERICA Tool (v2.0), MicroShield® Pro and mathematical equations, to estimate the likely radiological doses and risks of effects from NORM-contaminated scale to marine biota from a decommissioned offshore oil and gas pipeline. Using activity concentrations of NORM (²²⁶Ra, ²¹⁰Po, ²¹⁰Pb, ²²⁸Ra, ²²⁸Th) from a subsea pipeline from Australia, environmental realistic exposure scenarios including radiological exposures from both an intact pipe (external only; accounting for radiation shielding by a cylindrical carbon steel pipe) and a decommissioned pipeline with corrosive breakthrough (resulting in both internal and external radiological exposure) were simulated to estimate doses to model marine organisms. Predicted dose rates for both the external only exposure (ranging from 26 μGy/h to 33 μGy/h) and a corroded pipeline (ranging from 300 μGy/h to 16,000 μGy/h) exceeded screening levels for radiological doses to environmental receptors. The study highlighted the importance of using scale-specific solubility data (i.e., K_d) values for individual NORM radionuclides for ERICA assessments. This study provides an approach for conducting marine organism dose assessments for NORM-contaminated subsea pipelines and highlights scientific gaps required to undertake risk assessments necessary to inform infrastructure decommissioning planning.

Ensuring robust radiological risk assessment for wildlife: insights from the International Atomic Energy Agency EMRAS and MODARIA programmes

In response to changing international recommendations and national requirements, a number of assessment approaches, and associated tools and models, have been developed over the last circa 20 years to assess radiological risk to wildlife. In this paper, we summarise international intercomparison exercises and scenario applications of available radiological assessment models for wildlife to aid future model users and those such as regulators who interpret assessments. Through our studies, we have assessed the fitness for purpose of various models and tools, identified the major sources of uncertainty and made recommendations on how the models and tools can best be applied to suit the purposes of an assessment. We conclude that the commonly used tiered or graded assessment tools are generally fit for purpose for conducting screening-level assessments of radiological impacts to wildlife. Radiological protection of the environment (or wildlife) is still a relatively new development within the overall system of radiation protection and environmental assessment approaches are continuing to develop. Given that some new/developing approaches differ considerably from the more established models/tools and there is an increasing international interest in developing approaches that support the effective regulation of multiple stressors (including radiation), we recommend the continuation of coordinated international programmes for model development, intercomparison and scenario testing.

Baseline radioecological data for the soil and selected bioindicator organisms in the temperate forest of Plitvice Lakes National Park, Croatia

The aim of this study was to provide baseline radioecological data for the temperate forest ecosystem in Plitvice Lakes National Park. Emphasis was placed on the determination of naturally occurring radionuclides since there is an acknowledged lack of data for these radionuclides in non-accident conditions in wildlife, even for bioindicator organisms. Activity concentrations of ²³⁸U, ²²⁶Ra, ²¹⁰Pb, ²³²Th, ⁴⁰K, ¹³⁴Cs, and ¹³⁷Cs were measured by gamma spectrometry in soil and bioindicators: earthworms, conifer needles, mosses, and lichens. From the measured activity concentrations, concentration ratios were calculated to quantify the transfer of these radionuclides from soil to bioindicators. Our results show that soil activity concentrations are biased toward results from other studies conducted within the Dinaric mountain region. However, in moss and lichen samples, we measured higher activity concentrations of ²²⁶Ra and lower activity concentrations of ⁴⁰K and ¹³⁷Cs in comparison to similar studies. Also, we estimated lower concentration ratios for all radionuclides from soil to these organisms, except for ²¹⁰Pb, in comparison to generic values. The transfer of ²³⁸U was generally low for all of the bioindicator organisms. For conifer needles, a correlation was found between activity concentrations of ²²⁶Ra and ¹³⁷Cs in soil and related concentration ratios. Correlation was also found between the activity concentration of ⁴⁰K in soil and transfer of ⁴⁰K and ¹³⁷Cs to mosses and lichens. A comparison with literature data highlighted the lack of ²²⁶Ra related concentration ratios for conifer trees and especially for earthworms. Therefore, the results of this study could supplement the sparse data currently available on radionuclide background data in similar ecosystems and related soil-to-wildlife transfer of radionuclides. Dose rate assessments, performed by the ERICA Tool, estimated that 96% of the overall exposure of wildlife in the Park area is due to the background dose rates, while 0.06 μGy h^-1 on average can be attributed as an incremental dose rate from ¹³⁴Cs and ¹³⁷Cs.

Biomonitoring of radioactive contamination of the Yenisei River using aquatic plants

The Yenisei River is contaminated by artificial radionuclides released by one of the Russian facilities producing weapons-grade plutonium (the Mining-and-Chemical Combine, MCC), which has been in operation for 60 years. The paper presents results of long-term monitoring of radionuclide concentrations in six aquatic plant species collected from the 1400 km Yenisei River stretch downstream of the city of Krasnoyarsk. Before the last MCC reactor was shut down (in 2010), up to 30 artificial radionuclides were detected in the plant biomass, and 2 and 5 years after the reactor shutdown, 11 and 3-5 radionuclides, respectively, were detected. The highest concentrations of radionuclides were recorded in Fontinalis antipyretica. The aquatic plant Elodea canadensis, which commonly occurs in the Yenisei River, was used in the cytogenetic study. High frequencies of chromosomal aberrations (up to 33%) were revealed in cells of Elodea canadensis roots from the Yenisei region affected by the MCC radioactive discharge, at dose rates of 45-72 μGy/d, while in the cells of the plant roots from the reference areas, the frequency of chromosomal aberrations was 5-7%, at dose rates below 2 μGy/d. The higher frequencies of chromosomal aberrations in Elodea canadensis collected from the parts of the River with increased concentrations of artificial radionuclides are associated with the radiation factor. The aquatic plant Elodea canadensis can be recommended as a bio-indicator for radioactively contaminated aquatic ecosystems.

Environmental radiological risk assessment of a coal ash and slag disposal site with the use of the ERICA Tool

The aim of this study was to assess the environmental radiological risk of coal ash and slag to terrestrial wildlife. The research site used in this study was a disposal site of coal ash and slag with enhaced content of uranium decay chain radionuclides. With the use of the ERICA Tool, total dose rates to wildlife and risk of resultant radiobiological effects were estimated. As input data for the assessment, experimental activity concentrations of ²³⁸U, ²²⁶Ra and ²¹⁰Pb in coal ash and slag and best estimates of activity concentrations for related daughter radionuclides and ²³⁵U decay chain were used. Where possible, the experimental data for activity concentrations of ²³⁸U, ²²⁶Ra and ²¹⁰Pb in plants and related concentration ratios were used. Results were compared to background dose rates, also estimated by the Tool. The Tool's assessment data indicated internal exposure as the prevalent exposure pathway with ²²⁶Ra and ²¹⁰Po as the main dose contributors. Also, the contribution of ²³⁵U decay chain to the total dose rate was not negligible since for some organisms it represented up to 11% of the total dose rate. The risk of an occurrence of radiobiological effects in plants on the coal ash and slag disposal site can be considered negligible since the estimated total dose rates were below the screening dose of 10 μGyh^-1 and near the dose rates estimated for plants in the control area. However, the estimated dose rates for reference animals and Lichen & Bryophytes were above the screening dose rate for most organisms and on average 13 times higher than the estimated background dose rates. At the given dose rates, an occurrence of different radiobiological effects could not be excluded for animals in close contact with coal ash and slag such as earthworms and small burrowing mammals. A separate assessment performed on an example of reference plants showed that the use of activity concentrations in organisms as input data can result in an order of magnitude smaller estimates of dose rates in comparison to activity concentration in coal and ash as input data. Our study highlighted the need for experimental data in radiological risk assessments to mitigate the conservatism of the ERICA Tool and its tendency to overestimate dose rates.

Does the use of reference organisms in radiological impact assessments provide adequate protection of all the species within an environment?

Non-human biota in radiological risk assessment is typically evaluated using Reference Organisms (ROs) or Reference Animals and Plants (RAPs), for all exposure situations. However, it still remains open whether the use of an increased number of species would improve the ability to demonstrate protectiveness of the environment. In this paper, the representativeness of a broader list of fauna is tested in terms of the geometrical characteristics and habits for radiological risk assessments in the case of routine discharges from a nuclear installation: the Cadarache centre. A list of terrestrial animal species, compiled from ecological inventories carried out around it was evaluated. A first survey around the centre inventoried >400 terrestrial fauna species, which were then filtered to reduce the number to 28 species for which dose assessments were carried out. Despite the differences between geometries for those site-specific species and the ROs (including RAPs), the absorbed dose rates calculated for both were very close (within a factor of two). Regardless of the studied organism, the absorbed dose rates calculated for the discharge scenario were mainly related to internal exposure, particularly for tritium (³H) and carbon 14 (¹⁴C), showing that there would be an acceptable dose rates difference between species from the same organism group. Additionally, sensitivity analyses were conducted to determine if the use of generic, predefined ROs was enough to assure an adequate protection of endangered species. It was observed that for every radionuclide the difference between assessments for site-specific species and ROs are unlikely to exceed a factor of 3. Hence, the result of this evaluation indicates that the use of generic ROs for non-human biota radiological risk assessment covers sufficiently other species, including endangered ones.

A new version of the ERICA tool to facilitate impact assessments of radioactivity on wild plants and animals

A new version of the ERICA Tool (version 1.2) was released in November 2014; this constitutes the first major update of the Tool since release in 2007. The key features of the update are presented in this article. Of particular note are new transfer databases extracted from an international compilation of concentration ratios (CRwo-media) and the modification of 'extrapolation' approaches used to select transfer data in cases where information is not available. Bayesian updating approaches have been used in some cases to draw on relevant information that would otherwise have been excluded in the process of deriving CRwo-media statistics. All of these efforts have in turn led to the requirement to update Environmental Media Concentration Limits (EMCLs) used in Tier 1 assessments. Some of the significant changes with regard to EMCLs are highlighted.

The assessment of ionising radiation impact on the cooling pond freshwater ecosystem non-human biota from the Ignalina NPP operation beginning to shut down and initial decommissioning

The radiological doses to non-human biota of freshwater ecosystem in the Ignalina NPP cooling pond - Lake Druksiai were evaluated for several cases including the plant's operation period and initial decommissioning activities, using the ERICA 1.2 code with IAEA SRS-19 models integrated approach and tool. Among the Lake Druksiai freshwater ecosystem reference organisms investigated the highest exposure dose rate was determined for bottom fauna - benthic organisms (mollusc-bivalves, crustaceans, mollusc-gastropods, insect larvae), and among the other reference organisms - for vascular plants. The mean and maximum total dose rate values due to anthropogenic radionuclide ionising radiation impact in all investigated cases were lower than the ERICA screening dose rate value of 10 μGy/h. The main exposure of reference organisms as a result of Ignalina NPP former effluent to Lake Druksiai is due to ionizing radiation of radionuclides (60)Co and (137)Cs, of predicted releases to Lake Druksiai during initial decommissioning period - due to radionuclides (60)Co, (134)Cs and (137)Cs, and as a result of predicted releases to Lake Druksiai from low- and intermediate-level short-lived radioactive waste disposal site in 30-100 year period - due to radionuclides (99)Tc and (3)H. The risk quotient expected values in all investigated cases were <1, and therefore the risk to non-human biota can be considered negligible with the exception of a conservative risk quotient for insect larvae. Radiological protection of non-human biota in Lake Druksiai, the Ignalina NPP cooling pond, is both feasible and acceptable.