(Table 4) Concentrations of radionuclides in waters of the Barents and Kara Seas in August 2003

A methodology of experimental simulation of state of spent nuclear fuel that occurs on the sea floor due to some catastrophes or dumping is developed. Data on long-term (more than 2000 days) experiments on estimation of 85Kr and 137Cs release rate from spent nuclear fuel (fragments of irradiated UO2 pellets) were firstly obtained; these estimates prove correctness of a hypothesis offered by us in early 1990s concerning to earlier 85Kr release (by one order of magnitude higher than that of 137Cs) as compared to other fission fragments in case of loss of integrity of fuel containment as a result of corrosion on the sea floor. A method and technique of onboard 85Kr and 137Cs sampling and extraction (as well as sampling of tritium, product of triple 235U fission) and their radiometric analysis at coastal laboratories are developed. Priority data on 85Kr background in bottom layers of the Barents and Kara Seas and 137Cs and 3H in these seas (state of 2003) are presented. Models necessary for estimation of dilution of fission products of spent nuclear fuel and their transport on the floor in accident and dumping regions are developed. An experimental method for examination of state of spent nuclear fuel on the sea floor (one expedition each 2-3 years) by 85Kr release into environment (a leak tracer) is proposed; this release is an indicator of destruction of fuel containment and release of products of spent nuclear fuel in case of 235UO2 corrosion in sea water.

(Table 1) 137Cs and 90Sr concentrations, salinity, and temperature in waters of the southeastern Baltic Sea on October 16, 2001

An analysis of variations in 137Cs and 90Sr concentrations in Baltic Sea surface waters after the accident at the Chernobyl nuclear power plant was performed. Instability of 137Cs concentrations during the short-term observations was found, when they differed 2- to 3-fold. Concentrations of 90Sr appeared to be more stable; meanwhile, their deviations sometimes exceeded ranges of experimental errors. By variations in the monthly average values of radionuclide concentrations in surface waters of the Baltic Sea in 1989-1995, no trend of water self-purification was observed. Theoretical results obtained confirmed a potential of formation and propagation of patches with increased concentrations of 137Cs in the southeastern Baltic Sea. The most reliable factor that controlled the process of self-purification of Baltic Sea water appeared to be the mean annual value of radionuclide concentration. Pronounced divergences were obtained between the measured and calculated mean annual concentrations of 137Cs and 90Sr in surface waters of the Baltic Sea in 1989-2001. These divergences are explained by potential influence of waters from the Gulf of Bothnia and by other additional supplies of radionuclides to marine environment, which were not included into mathematical models.

Iridium concentrations and abundances of meteoritic ejecta from the Eltanin impact in sediment cores from POLARSTERN cruise ANT-XII/4

The abundances of meteoritic ejecta from the Eltanin asteroid impact have been examined in seven sediment cores recovered by the FS Polarstern during expedition ANT XII/4 using elemental concentrations of iridium and weights of coarse (>500 ?m) ejecta debris. Three cores with well-preserved impact deposits, PS2704-1, PS2708-1, and PS2709-1, each contain Ir and ejecta fluences similar to those found previously in USNS Eltanin core E13-4. Small Ir anomalies and traces of ejecta were found in cores PS2706-1 and PS2710-1, but since these cores lack well-defined deposits, these are considered to be reworked and not representative of the fallout. No evidence of ejecta was found in cores PS2702-1 and PS2705-1. These results confirm earlier speculation that the Eltanin impact resulted in deposits of ejecta with up to 1 g/cm**2 of debris over a wide area of the ocean floor. However, there are still large uncertainties over the actual regional or global extent of this unique sediment deposit.

Radionuclide measurements in sediments and water of the Kara Sea

In this report, the results of a 2000-2001 radiogeoecological investigation are presented for the region of the Ob and Yenisei estuaries and the adjacent Kara Sea. In order to study the behaviour and migration of Cs, Sr and Pu radionuclides in a river - sea system experimental research on the distribution of these radionuclides in the water column and surface sediments has been carried out. In addition, the role of suspended and dissolved organic matter on the behaviour of radionuclides in water solutions has been studied. The 137Cs and 239,240Pu concentrations in the upper 0-2cm layer of the sediments varied between 1,4 and 50,0 Bq/kg, with a mean of 12,4 Bq/kg, and between 0,065-1,96 Bq/kg, with a mean of 0,62 Bq/kg, respectively. There is a direct relationship of a specific radioactivity of 137Cs and 239,240Pu in the sediments and the content of clay fraction. The 137Cs, 90Sr and 239,240Pu concentrations in the water samples varied between 0,4 and 7,0 Bq/m**3 (mean of 3,6 Bq/m**3), 0,4 and 9,7 Bq/m**3 (mean of 3,3 Bq/m**3), and 0,01-0,3 Bq/m**3 (mean of 0,02 Bq/m**3), respectively. In the water samples the concentration of the water-soluble species l37Cs increases with increasing salinity, whereas the concentration of the 90Sr-radionuclide decreases with increasing salinity. This may be related to the physico-chemical behaviour of these radionuclides in water solutions and the influence of several sources on radioactive pollution in this basin. In sea water the suspended matter may absorb up to 10% 137Cs, 90Sr and 239,240Pu, in river water samples these values may reach 15-30%. More than 50% 90Sr and 239,240Pu is able to form complexes with dissolved organic matter. This effect is smaller in saline water. The comparison of the data of 137Cs radioactivity in the surface sediments in 1995 and 2000-2001 showed that the level of radioactivity has decreased.