[en] Full text: Marine sediments may act as a sink for radionuclides originating from atmospheric fallout (e.g. Chernobyl accident), for radionuclides in discharges from nuclear installations (e.g. Sellafield, UK) for river transported radionuclides, and radionuclides released from nuclear waste dumped at sea (e.g. fjords at Novaya Zemlya). In order to assess short and long term consequences of radionuclides entering the marine ecosystem, the role of sediments as a relatively permanent sink and the potential for contaminated sediments to act as a diffuse source should be focused. The retention of radionuclides in sediments will depend on the source term, i.e. the physico-chemical forms of radionuclides entering the system and on interactions with various sediment components. Radionuclides associated with particles or aggregating polymers are removed from the water phase by sedimentation, while sorption to surface sediment layers is of relevance for ionic radionuclide species including negatively charged colloids. With time, transformation processes will influence the mobility of radionuclides in sediments. The diffusion into mineral lattices will increase fixation, while the influence of for instance red/ox conditions and bio-erosion may mobilize radionuclides originally fixed in radioactive particles. Thus, information of radionuclides species, surface interactions, transformation processes and kinetics is essential for reducing the uncertainties in marine transfer models. Dynamic model experiments where chemically well defined tracers are added to a sea water-marine sediment system are useful for providing information on time dependent interactions and distribution coefficients. When combined with sequential extraction techniques, information on mobility and rate of fixation is subsequently attained. In the present work experimental results from the Irish Sea and the Kara Sea will be discussed

[en] Northern Russian radio-ecological and nuclear risks are connected with several objective factors: disposal, exploitation, supplying of the cycle of atomic military and ice-breaking fleets; disposal of enterprises and bases for maintenance of ships with nuclear-power installations (NPI) in Murmansk and Archangel regions; place the State Atomic Shipbuilding Center (RSASBC) enterprises in Archangel and partly in Murmansk regions; exploitation of the Kola Atomic Station (APS); functioning of the Novaya Zemlya archipelago nuclear range; functioning Russian Plesetsk cosmo-drome. Technical proposals and projects for radio-ecology in the North are outlined. (R.P.)

[en] Chernaya Bay is a shallow embayment on the southern coast of Novaya Zemlya where three kiloton level underwater nuclear tests were reported to have occurred in 1955-61. Sedimentation rates in Chernaya Bay are low (< 0.1 cm/y) and sediment-depth distribution of radionuclides is governed mainly by biological mixing. Sediments in Chernaya Bay are characterised by ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios of 0.030 and 0.0012, respectively. The reduced yield of ²⁴¹Pu has resulted in a ²⁴¹Am/^239-240Pu activity ratio of 0.05, which increases with increasing distance from its value of 0.05 in Chernaya Bay to fallout levels of 0.30. (R.P.)

[en] Assessment of ⁹⁰Sr and ¹³⁷Cs content in the Black Sea before and after the Chernobyl NPP accident as well as large-scale prognosis of their inventory are presented. About 0.1-0.3 PBq of ⁹⁰Sr and 1.7-2.4 PBq of ¹³⁷Cs deposited to the Black Sea with atmospheric fallout directly after this accident. ⁹⁰Sr content increased up to 1.5 times and ¹³⁷Cs - 5.6 times in 0-100 m layer of the sea. Assessment of ⁹⁰Sr and ¹³⁷Cs contents in biota and bottom sediments was done as well as flux of sedimentation deposit of ¹³⁷Cs in bottom sediments was determined. ⁹⁰Sr and ¹³⁷Cs concentrations in the Sevastopol Bays decreased twice, respectively, during 8 and 10 years after the period since May, 1986. (author)

[en] Full text: This paper presents the first analytical results of man-made radionuclides from sea water samples taken on a research cruise of RV GAUSS conducted in 1995. Whereas surface samples were frequently taken in the Norwegian Sea during the last decades, this is the first extensive set of large-volume subsurface samples which were analysed for transuranium elements (²³⁸Pu, ^239,240Pu, ²⁴¹Am) and radiocesium. The results of radiocesium and americium did not show any enhanced levels of concentration, whether from surface or from subsurface samples. In contrast to these results we found significantly increased concentrations of plutonium in the deep layers of the Norwegian Sea. The ^239,240Pu concentrations found in depths between 140 m and 1250 m exceed up to seven times the concentrations known to exist in the Northeast Atlantic. The geographical extent of these enhanced concentrations covers the area between 60 deg N and at least 70 deg N. On a transect off the Norwegian Coast, the highest concentrations are found approximately 150 km off and along the coast. The isotopic ratio of plutonium nuclides found here is consistent with the long-time mean ratio of the discharges from the Sellafield reprocessing plant. As the cruise covered the Norwegian Sea with 21 surface stations including 13 depth profiles down to the seabed, we are in the position to give an estimation of plutonium inventory of the Norwegian Sea during summer 1995. As the current releases from the Sellafield works do not correspond with the amount of plutonium found here, other possible sources, mechanisms of releases and transport pathways to the Norwegian Sea are discussed

[en] Full text: Since 1980 seawater samples have been taken yearly in the German Bight on 9 fixed stations for tritium analysis. The initial mean value of 1.9 Bq/l measured in 1980 changed to a concentration of 1.1 Bq/l in 1992 and is now increasing to 2.8 Bq/l in 1995. The accumulated effect to the German Bight derived from the tritium sources discharging into the adjacent seas is calculated by transfer factors. The calculations take into account the yearly liquid discharges from the nuclear reprocessing plants and power stations into the British and French coastal waters as well as the tritium concentration in the Atlantic and North Sea water, the rain water input and the freshwater tributaries to the southern North Sea. The activity values used are taken both from literature and own measurements. The results show that the nuclear weapons fallout was the predominant source in 1980. Nowadays the nuclear power industry is the main source of tritium concentration in the German Bight. The poster demonstrates the temporal development of the activity concentration measured in relation to the calculated contributions. The geographic locations of the sample stations and the sites of the sources are displayed. Moreover, the individual sources and their tritium discharges (in 1993, as an example) as well as the transfer factors used are listed

[en] Anthropogenic ¹²⁹I discharged by the nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France) is a promising new tracer of physical and biogeochemical processes in the North Atlantic and Arctic Oceans. A sample collected in the eastern subtropical North Atlantic was selected to directly measure the impact of weapons-fallout ¹²⁹I on the oceans. An ¹²⁹I/¹²⁷I ratio of 0.534 ± 0.076 x 10^-10 was found, compared to the pre-anthropogenic radio of ∼ 10^-12. The ratio of ¹²⁹I to ¹³⁷Cs at the 'fallout station' was 2.0 ± 0.3 (atom ratio). ¹²⁹I to ¹³⁷Cs ratios in the Scottish and Norwegian Coastal waters, sampled in 1976 and 1978, are roughly as predicted from the available release data. (R.P.)

[en] ²³²Th and ²³⁰Th concentrations of unfiltered and filtered seawater samples were measured along a depth profile of the Pacific Ocean at the HOT station using isotopic dilution and thermal ionization mass spectrometry. The ²³²Th concentrations are rather constant from below 25 m down to over 2000 m (30-40 x 10⁶ atoms/cm³) and then they increase rapidly towards the bottom (118-336 x 10⁶ atoms/cm³ at 4000 m). The ²³⁰Th concentration increases linearly with depth from 2.6 x 10³ atoms/cm³ at 25 m to 109 x 10³ atoms/cm³ at 4000 m. The relatively high ²³⁰Th concentrations and ²³⁰Th/²³²Th ratios measured at 25 m are consistent with a mixed layer of about 100 m. The linear increase of the ²³⁰Th with depth implies that the effect of eddy diffusion is negligible for most of the water column. The difference in the transport of ²³⁰Th and ²³²Th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent re-mineralization. (author)

[en] Full text: Scenarios concerning accidental releases of radionuclides into water bodies can be found in the open literature, mostly in connection with nuclear power plants located either onshore or inland. However, meager attention has been given to nuclear reactors used as energy sources for propulsion at sea, which are also subject to accidents. Such potential accidents may involve the loss of part of the reactor core to the surrounding water body. In addition of the initial instantaneous releases, one can estimate delayed source terms based on the rate at which radionuclides are dissolved or leached from the solidified material, like part of the core or structural materials in contact with water. Most of such solidified material might be a mixture of uranium, zirconium, iron, calcium, silica, fission and activation products, and transuranium elements as oxides, forming a glassy type solid. Transport models were used to calculate radionuclide concentrations in water resulting from short and delayed source terms. Oceanographic data used in the calculations were taken either from the open literature or from unclassified reports of the Brazilian Navy, being, however, as generic as possible. Time-dependent concentration functions for radionuclides in aquatic food following an accidental release reflect the net result of intake and elimination processes. However, to avoid the complexities of multiple parameters involved in such processes, the model accounts only for trophic transfer of radionuclides, and yet avoids the necessity of analyzing the details of each transfer step used to determine fish, crustacea, molluscs and seaweed accumulation. Swimming and other aquatic sports are not included in the model used for dose calculations because of theirs relatively low importance in comparison with the pathways concerning ingestion of aquatic food

[en] Full text: Distributions of particle-reactive radionuclides ^239,240Pu, ²³⁸Pu, ²¹⁰Pb and ²¹⁰Po measured in the central Arctic Ocean during expeditions on the Canadian icebreakers, CCGS Henry Larsen in 1993 and CCGS Louis St Laurent in 1994 and 1995 reflect their sources, circulation pathways and scavenging histories. Disequilibria between the naturally occurring ²¹⁰Pb (T_1/2 = 22.3 y) and its grandparent ²²⁶Ra (T_1/2 = 1600 y) can be used to determine residence times for dissolved ²¹⁰Pb on the order of 10 to 100 years. Disequilibria is evident throughout the water column in the Arctic Ocean but is greatest in the halo-cline water (100 to 300 m) in the Makarov, Canada and Amundsen Basins where minima in ²¹⁰Pb activities are observed. Vertical distributions of ^239,240Pu, a long-lived radionuclide derived mainly from atmospheric nuclear fallout, are remarkably similar throughout the Arctic Ocean. Profiles are characterized by low activities in the surface mixed layer, increased levels through the halo-cline and maximum values in the Atlantic layer, decreasing to levels below the detection limit at depths greater than 1500 m. Comparison of the ratio of ^239,240Pu to ⁹⁰Sr, a non particle-reactive fallout radionuclide, to the global fallout ratio is used to determine ^239,240Pu removal rates. Both particle-reactive radionuclide distributions are consistent with recent contact of surface and halo-cline water with particle-rich continental shelf regions where ^239,240Pu and ²¹⁰Pb evidently undergo enhanced scavenging from seawater. Atlantic layer water is characterized by fallout ^239,240Pu/⁹⁰Sr ratios and limited ²¹⁰Pb/²²⁶Ra disequilibria, which provides evidence for reduced scavenging and interaction of Atlantic layer water with shelf regions