Oceanic Radionuclide Transfer Model for an Emergency Countermeasure for Nuclear Accidents

点击翻译按钮获取中文摘要

(1)Distribution of radioactive substance concentrations in the Arctic Ocean after a hypothetical accident was analyzed by means of a 3-dimensional flow model. In nuclide dispersion model, adsorption and desorption between substances (the scavenging effect) and interactions between seawater and sediments (the 3-layer model) were taken into consideration in order to improve accuracy of the dosage estimate. Based on nuclide (Pu-239 and Cs-137) release scenarios, local areas (the Kara and Barents Seas) and the whole Arctic Ocean were subjected to analysis. In concentration analysis, effects of 3 parameters (distribution coefficient, settling rate of particles and 55 concentration) on nuclide concentrations in seawater and sediment were examined. The greater the three parameters, the greater were Pu-239 concentrations in seawater, while Cs-137 concentrations were less dependent on the parameters. For both nuclides the maximum concentrations were detected in the particle layer in contact wit … More h seawater.Contrasting distributions of the two nuclides were demonstrated at the time of 100 years and 1000 years after the release, for the local area and the whole Arctic Oceans, respectively : while 90% of Pu-239 was retained in the sediment, 60 to 80% of Cs-137 remained in seawater, the rest being retained in the sediment.(2)In order to examine physicochemical properties of suspended solids, which is considered to play a role in the processes of radionuclide transfer to seabed sediment, the element analysis was conducted by means of the PIXE method. In seawater samples taken at Nakaminato, Ibaraki Prefecture, concentrations of main elements remained fairly constant throughout the year, irrespective of the seasonal changes of biological activities in seawater. Moreover, element compositions of suspended solids were nearly identical among samples taken from the surface and deep layer off Muroto, Kochi Prefecture, and those collected from 3 sea areas surrounding Aomori Prefecture, From these results it was confirmed that element compositions of suspended solids did not vary by sea area and season of the year, and that the adsorption capacity was dependent on their concentration in seawater.(3)We compiled data concerning radionuclide transfer to biota, and examined a model describing a vertical transfer of nuclides through the planktonic ecosystem.Using Cs-I 37 data, which was collected off Monaco by IAEA and Monaco Marine Laboratory after the Chernobuyl accident, we verified our dynamic 3-dimensional model for predicting Cs-137 in marine organisms which was developed in the fiscal 2003. Less