Oceanic Radionuclide Transfer Model for an Emergency Countermeasure for Nuclear Accidents

（1）利用三维水流模型分析了假想事故后北冰洋放射性物质浓度的分布。在核素扩散模型中，考虑了物质之间的吸附和解吸作用（清除作用）以及海水与沉积物之间的相互作用（3层模型），以提高剂量估算的准确性。根据核素（Pu-239和Cs-137）释放情景，对局部地区（喀拉海和巴伦支海）和整个北冰洋进行了分析。在浓度分析中，考察了3个参数（分配系数、颗粒沉降速率和55浓度）对海水和沉积物中核素浓度的影响。三个参数越大，海水中钚-239浓度越大，而铯-137浓度对参数的依赖性越小。两种核素的最大浓度都是在与空气接触的颗粒层中检测到的。 关于我们 在释放后100年和1000年，这两种核素在局部地区和整个北冰洋的分布情况截然不同：90%的Pu-239保留在沉积物中，60%至80%的Cs-137保留在海水中，其余保留在沉积物中。(2)In为了研究悬浮固体的物理化学性质，这被认为是发挥作用的过程中的放射性核素转移到海底沉积物，元素分析进行了PIXE方法。在茨木县Nakaminato采集的海水样品中，无论海水中生物活动的季节性变化如何，主要元素的浓度全年保持相当稳定。此外，从高知县室户近海表层和深层以及青森县周边3个海域采集的样品中，悬浮固体的元素组成几乎相同。从这些结果可以确认，悬浮固体的元素组成不因海域和季节而变化，吸附能力取决于海水中的浓度。(3)We利用IAEA和摩纳哥海洋实验室在2003年摩纳哥事故后收集的Cs-137数据，验证了2003年开发的预测Cs-137在海洋生物中垂直迁移的三维动态模型。少

(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