Fate of anthropogenic radionuclides (90Sr, 137Cs, 238Pu, 239Pu, 240Pu, 241Am) in seawater in the northern Benguela upwelling system off Namibia.

A baseline study on anthropogenic radioactivity in the Namibian marine ecosystem, which is part of the northern Benguela upwelling system, known as one of the most productive ocean areas in the world, has been performed. A scientific cruise carried out in 2014 covering inshore and offshore areas, exhibiting different oceanographic features, has provided a basis for better understanding the distributions, ratios and inventories of six anthropogenic radionuclides (90Sr, 137Cs, 238Pu, 239Pu, 240Pu and 241Am) in seawater. Although 3H was also measured, due to extremely low levels, its behaviour was not studied. The main source of 90Sr, 137Cs, 239Pu, 240Pu and 241Am in the samples analysed was proven to be global fallout, a finding further confirmed by 240Pu/239Pu and 90Sr/137Cs ratios. Furthermore, the 238Pu SNAP-9A satellite accident signal was confirmed once again through the determination of the 238Pu/239+240Pu activity ratio. Inshore and offshore samples showed different patterns due to the unique oceanographic features of this upwelling system. The levels of anthropogenic radionuclides, comprehensively assessed for the first time in this region, are comparable with the few existing data and filled a critical gap for the Southern Atlantic Ocean.

Long term 7Be deposition in Romania.

This study is based on monthly 7Be deposition data at 29 of the stations of Romania's National Environmental Radioactivity Surveillance Network (NERSN), with different geographical and climatological conditions, extending over periods up to 17 years (1979-1995). The 7Be activity in each monthly sample from each station was determined using high-resolution gamma-ray spectrometry performed at the Environmental Radioactivity Laboratory, Bucharest-Afumati. The annual dynamics of atmospheric deposition of 7Be at each NERSN station showed a strong seasonal trend, very similar to the precipitation regime, with the highest values being observed in spring/summer and the lowest in winter. But the annual 7Be deposition fluxes varied broadly from station to station and year to year, from a minimum of 164 Bq/m2/y (Bechet, 1989) to a maximum of 1388 Bq/m2/y (Baia Mare, 1988). This large space-time variability of deposition was mainly due to the variability of the precipitation regime. The analysis of experimental data confirms the strong correlation of 7Be deposition data with precipitation, air temperature and the number of sunspots. Wet and dry deposition data are presented and discussed for four stations where separate dry and wet 7Be deposition measurements were performed.

From radiometry to chronology of a marine sediment core: A 210Pb dating interlaboratory comparison exercise organised by the IAEA.

Laboratories from 14 countries (with different levels of expertise in radionuclide measurements and 210Pb dating) participated in an interlaboratory comparison exercise (ILC) related to the application of 210Pb sediment dating technique within the framework of the IAEA Coordinated Research Project. The laboratories were provided with samples from a composite sediment core and were required to provide massic activities of several radionuclides and an age versus depth model from the obtained results, using the most suitable 210Pb dating model. Massic concentrations of Zn and Cu were also determined to be used for chronology validation. The ILC results indicated good analytical performances while the dating results didn't demonstrate the same degree of competence in part due to the different experience in dating of the participant laboratories. The ILC exercise enabled evaluation of the difficulties faced by laboratories implementing 210Pb dating methods and identified some limitations in providing reliable chronologies.

Impact of Saharan dust events on radionuclides in the atmosphere, seawater, and sediments of the northwest Mediterranean Sea.

In February 2004, anthropogenic radionuclides (137Cs, 236U, 239Pu and 240Pu), transported from the Sahara Desert, were observed in the Monaco air, and later in water and sediment samples collected at the DYFAMED site in the northwest (NW) Mediterranean Sea. While 236U and 137Cs in Saharan dust particles showed a high solubility in seawater, Pu isotopes were particle reactive in the water column and in the sediment. The impact of the Saharan deposition was found at 0-1.0 cm of the sediment core for 236U and 137Cs, and between 1.0 and 1.5 cm for Pu isotopes. The excess of 236U was observed more in the water column than in the sediment, whereas the 239+240Pu total inventories were comparable in the water column and the sediment. This single-day particle event represented 72% of annual atmospheric deposition in Monaco. At the DYFAMED site, it accounted for 10% (137Cs) and 15% (239+240Pu) activities of sinking particles during the period of the highest mass flux collected at the 200 and 1000 m water depths, and for a significant proportion of the total annual atmospheric input to the NW Mediterranean Sea (28-37% for 137Cs and 34-45% for 239+240Pu). Contributions to the total 137Cs and 239+240Pu sediment inventories were estimated to be 14% and 8%, respectively. The Saharan dust deposition phenomenon (atmospheric input, water column and sediment) offered a unique case to study origin and accumulation rates of radionuclides in the NW Mediterranean Sea.

Modelling of marine radionuclide dispersion in IAEA MODARIA program: Lessons learnt from the Baltic Sea and Fukushima scenarios.

State-of-the art dispersion models were applied to simulate (137)Cs dispersion from Chernobyl nuclear power plant disaster fallout in the Baltic Sea and from Fukushima Daiichi nuclear plant releases in the Pacific Ocean after the 2011 tsunami. Models were of different nature, from box to full three-dimensional models, and included water/sediment interactions. Agreement between models was very good in the Baltic. In the case of Fukushima, results from models could be considered to be in acceptable agreement only after a model harmonization process consisting of using exactly the same forcing (water circulation and parameters) in all models. It was found that the dynamics of the considered system (magnitude and variability of currents) was essential in obtaining a good agreement between models. The difficulties in developing operative models for decision-making support in these dynamic environments were highlighted. Three stages which should be considered after an emergency, each of them requiring specific modelling approaches, have been defined. They are the emergency, the post-emergency and the long-term phases.

IAEA's ALMERA network: Supporting the quality of environmental radioactivity measurements.

The International Atomic Energy Agency coordinates and provides methodological and analytical quality support to the network of Analytical Laboratories for the Measurement of Environmental Radioactivity (ALMERA), comprising 150 laboratories in 84 countries. Annual proficiency tests (PTs) are organized for the network laboratories using sets of different samples typically encountered in environmental and food monitoring laboratories. The PT system is designed to respond to the needs of the network for rapid response and reliable measurement results, and to metrological principles and international standards and guides. Comparison of performance of ALMERA and non-ALMERA laboratories in PTs indicates that the "PT - method development - training - PT" strategy adopted for capability building is beneficial to the network.

Certified reference materials for radionuclides in Bikini Atoll sediment (IAEA-410) and Pacific Ocean sediment (IAEA-412).

The preparation and characterization of certified reference materials (CRMs) for radionuclide content in sediments collected offshore of Bikini Atoll (IAEA-410) and in the open northwest Pacific Ocean (IAEA-412) are described and the results of the certification process are presented. The certified radionuclides include: (40)K, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (234)U, (238)U, (239)Pu, (239+240)Pu and (241)Am for IAEA-410 and (40)K, (137)Cs, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (235)U, (238)U, (239)Pu, (240)Pu and (239+240)Pu for IAEA-412. The CRMs can be used for quality assurance and quality control purposes in the analysis of radionuclides in sediments, for development and validation of analytical methods and for staff training.

A comparison of marine radionuclide dispersion models for the Baltic Sea in the frame of IAEA MODARIA program.

Four radionuclide dispersion models have been applied to simulate the transport and distribution of (137)Cs fallout from Chernobyl accident in the Baltic Sea. Models correspond to two categories: box models and hydrodynamic models which solve water circulation and then an advection/diffusion equation. In all cases, interactions of dissolved radionuclides with suspended matter and bed sediments are included. Model results have been compared with extensive field data obtained from HELCOM database. Inventories in the water column and seabed, as well as (137)Cs concentrations along 5 years in water and sediments of several sub-basins of the Baltic, have been used for model comparisons. Values predicted by the models for the target magnitudes are very similar and close to experimental values. Results suggest that some processes are not very relevant for radionuclide transport within the Baltic Sea, for instance the roles of the ice cover and, surprisingly, water stratification. Also, results confirm previous findings concerning multi-model applications.

Detection of Fukushima Daiichi nuclear power plant accident radioactive traces in Monaco.

Daily air monitoring of radionuclides in the Principality of Monaco (43°73'N, 7°43'E) after the Fukushima Daiichi nuclear power plant accident showed that only Iodine-131 ((131)I) and Caesium isotopes ((134)Cs and (137)Cs) were detected. The peak of (131)I varied and reached its maximum between March 29th and April 5th, meanwhile both peaks of (134)Cs and (137)Cs arrived later and attained a maximum between April 1st and 4th. Their maximum activity concentrations in air were 354, 30, and 37 µBq m(-3) respectively. The (134)Cs to (137)Cs activity ratio was close to 1, which is different from that one observed after the Chernobyl accident (around 0.54). Up to 95% of caesium isotopes were washed out by wet scavenging during 27-28th of March, where the maximum deposition rates of (134)Cs and (137)Cs (13.7 and 19.1 mBq m(-2) day(-1), respectively) were observed. The significant input of (134)Cs and (137)Cs into the Mediterranean seawater column (30 m depth) was detected later, on the 24th of May. Radioisotopes of caesium and iodine were found far above the applied detection limits, but still with no concern for harmful radiation exposure and public health. The contamination gradually decreased in air and activity concentrations returned to background values after one or two months.

Seabed gamma-ray spectrometry: applications at IAEA-MEL.

The technique of underwater gamma-ray spectrometry has been developed to complement or replace the traditional sampling-sample analysis approach for applications with space-time constraints, e.g. large areas of investigation, emergency response or long-term monitoring. IAEA-MEL has used both high-efficiency NaI(Tl) and high-resolution HPGe spectrometry to investigate contamination with anthropogenic radionuclides in a variety of marine environments. Surveys at the South Pacific nuclear test sites of Mururoa and Fangataufa have been used to guide sampling in areas of high contamination around ground zero points. In the Irish Sea offshore from the Sellafield nuclear reprocessing plant, a gamma-ray survey of seabed sediment was carried out to obtain estimates of the distribution and subsequently, for the inventory of 137Cs in the investigated area.

Kara Sea radioactivity assessment.

Investigations following five international expeditions to the Kara Sea have shown that no radiologically significant contamination has occurred outside of the dumping sites in Novaya Zemlya bays. Increased levels of radionuclides in sediment have only been observed in Abrosimov and Stepovoy Bays very close to dumped containers. Evaluations of radionuclide inventories in water and sediment of the open Kara Sea and Novaya Zemlya bays as well as soil from the shore of Abrosimov bay have shown that radionuclide contamination of the open Kara Sea is mainly due to global fallout, with smaller contributions from the Sellafield reprocessing plant, the Chernobyl accident run-off from the Ob and Yenisey rivers and local fallout. Computer modelling results have shown that maximum annual doses of approximately 1 mSv are expected for a hypothetical critical group subsisting on fish caught in the Novaya Zemlya bays whereas populations living on the mainland can be expected to receive doses at least three orders of magnitude lower.

Underwater gamma surveys of Mururoa and Fangataufa lagoons.

Underwater gamma-ray spectrometry is an effective alternative or complement to traditional sampling and laboratory analyses for applications such as contamination assessment in emergency situations, long-term monitoring of radioactive releases or investigation of sunken radioactive objects. This technique was recently used in a seabed contamination study undertaken at the South Pacific nuclear weapons test sites of the Mururoa and Fangataufa atolls in order to guide and focus sediment core sampling in the areas with highest gamma-emitting radionuclide levels. 60Co inventories estimated on the basis of the underwater gamma-ray spectrometry survey were in good agreement with results previously obtained by traditional sediment sampling and laboratory analysis.

Transport of radionuclides from the Mururoa and Fangataufa atolls through the marine environment.

A dispersion of radionuclides (3H, 90Sr, 137Cs, 239Pu) potentially released from the Mururoa and Fangataufa atolls through the South Pacific Ocean has been studied by means of computer models. The models used consisted of three differently structured compartmental models for the regional field and a hydrodynamic world ocean model for the far-field simulations. The outcome of regional modelling is predicted activity concentrations with time in different regions of French Polynesia (over up to 10,000 years for plutonium). The far-field model simulates large-scale dispersion in the South Pacific Ocean over periods of up to 50 years. The overall result suggests that there will not be radioactive contamination of any radiological interest at inhabited sites in French Polynesia or anywhere else in the ocean at present or in the future.

Benchmarking of numerical models describing the dispersion of radionuclides in the Arctic Seas.

As part of the International Arctic Seas Assessment Project (IASAP) of the International Atomic Energy Agency (IAEA), a working group was created to model the dispersal and transfer of radionuclides released from radioactive waste disposed of in the Kara Sea. The objectives of this group are: (1) development of realistic and reliable assessment models for the dispersal of radioactive contaminants both within, and from, the Arctic ocean; and (2) evaluation of the contributions of different transfer mechanisms to contaminant dispersal and hence, ultimately, to the risks to human health and environment. With regard to the first objective, the modelling work has been directed towards assessment of model reliability and asone aspect of this, a benchmarking exercise has been carried out. This paper briefly describes the benchmark scenario, the models developed and used, and discusses some of the benchmarking results. The role of the exercise within the modelling programme of IASAP will be discussed and future work described.