Sediment inventories radionuclides

Radionuclide loss rates and total sediment inventories... 

The short4ived particle reactive radionuclides of the U/Th series also have enormous potential for tracking particle source and transport in ocean margins. Mass balances comparing inventories in sediments with supply can be used to determine import or export of particles to an area. Such approaches are increasingly important in understanding the fates of particle-reactive contaminants whose sources are often enhanced in the coastal ocean. Studies of especially when supplemented by other... 

By combining the findings of Cacchione, Drake and the results reported here, a coherent model can be proposed to explain the deposition inventory of the radionuclides. The down-canyon current transports large quantities of sediment toward the radioactive waste disposal site at 4000 m. Within the upper canyon, fine material is transported the furthest. Near the mouth of the canyon, sediment erosion of the walls occurs due to the down-canyon currents meeting a proposed opposing on-shore bottom current. The eroded material from the walls is transported and the finer material is deposited in eddies formed where the two currents meet. 

Particle-reactive radionuclides provide a tracer with which to evaluate the net lateral redistribution of sediments. In some cases, inventories or accumulation rates of these nuclides can be compared to their known rate of supply to estimate the net extent of lateral redistribution of sediments. In other cases, inventories (or accumulation rates) of nuclides can be compared among several sites to assess the relative rate of sediment deposition among the sites, even if the rate of supply of the tracer is not known accurately. Inherent in this approach is the assumption that sediments deposited at all of the sites have a uniform initial radionuclide content. Deposition of sediments must be roughly at steady state over the... 

The radionuclide content of the aqueous phase will be a more sensitive indicator of change than the sediment since only a small proportion of the radionuclide inventory is present in solution. Over a three day period, the control batch (Figure 1) showed a 20%... 

On 7 April 1989, a fire broke out in the stem section of the Komsomolets nuclear submarine. The submarine sank to a depth of 1685 m at 73°43T6"N, 13°15 52"E, near the south-west of Bear Island. The site is about 300 nautical miles from the Norwegian coast. The wreck contains one nuclear reactor and two nuclear warheads, one of which was fractured. The radionuclide inventory includes 1.5 PBq Sr, 2 PBq Cs, about 16 TBq " Pu in the two warheads and 5 TBq of actinides in the reactor s core. During June/July 1994, an international expedition to the Komsomolets site at the request of the Russian Federation was organised. The objectives of the scientific cmise on board the R/V Mstislav Keldysh were to close nine door holes, including torpedo tubes, by capping them with titanium metal cover caps, and to sample and monitor for ambient radioactivity. A series of 280-600 1 sea-water samples collected in profile, a suite of surface sediments and cores and various biota samples were returned to lAEA-MEL for analysis. The results showed that a very limited leakage of caesium and tritium had occurred from the submarine. 

Caesium is said to behave conservatively that is, the bulk of the radionuclide inventory is associated with the water phase and so transport processes are dominated by the bulk movement of sea water. Plutonium and americium, on the other hand, behave non-conservatively the bulk of their inventory is associated with sediments and the transport processes affecting sediments are very important to their behaviour. The proportion of each nuclide present in the water column as suspended particulate is a simple function of value and suspended sediment load (Sholkovitz, 1983), as indicated in Table 8.2. Thus, for the full range of sediment loadings, water column inventories of Cs are dominated by... 

The net effect of the above processes is that the bulk of the Cs inventory is transported with water movements with a small fraction being adsorbed to suspended particulate and deposited in bed sediments, whereas a large fraction of the Pu and Am inventory is adsorbed to suspended sediments and deposited in the bed sediments of the eastern Irish Sea. The behaviour of Pu and Am deposited in bed sediments is then determined by the processes of sediment mixing (in which bioturbation is very important), resuspension, and remobilisation of adsorbed radionuclides into the solution phase. 

The intertidal areas on the north-west coast of England and the south-west coast of Scotland also contain significant inventories of radionuclides associated with sediments. Surveys made in the 1980s (Eakins et al., 1988,1990 Garland et al., 1989 Carpenter et al., 1991) have indicated total inventories of 36 TBq of 239,240py 50TBq of Am in the intertidal area between south-west Scotland and the coast of north Wales, as summarised in Table 8.3. 

Kada J, Heit M. 1992. The inventories of anthropogenic lead, zinc, arsenic, cadmium, and the radionuclides cesium-137 and excess lead-210 in lake sediments of the Adirondack region, USA. 

Edgington, D. N., J. Van Klump, . A. Robbins,Y. S. Kusner, V. D. Pampura I. V. Sandimirov, 1991. Sedimentation rates, residence times and radionuclide inventories in Lake Baikal from Cs and... 

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