利用海洋环流模型对¹³⁷Cs和（²³⁹,²⁴⁰）Pu浓度进行数值模拟。

Tsumune Daisuke, Aoyama Michio, Hirose Katsumi

Environmental Science Department, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken 277-1194, Japan.

J Environ Radioact. 2003;69(1-2):61-84. doi: 10.1016/S0265-931X(03)00087-0.

We simulated the spatial distributions and the temporal variations of 137Cs and (239,240)Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and (239,240)Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum (239,240)Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated (239,240)Pu concentrations in surface water could be simulated by considering the scavenging effect.

我们使用美国国家大气研究中心开发的海洋环流模型，模拟了海洋中137Cs和（239,240）Pu浓度的空间分布和时间变化。这些核素因大气核武器试验产生的全球沉降而进入海水。根据全球降水数据以及日本气象研究所和新西兰多个观测点的放射性核素年沉降观测值，估算了全球海洋放射性沉降的分布。全球沉降产生的放射性核素通过平流、扩散和清除作用进行输运，其浓度在海洋中因放射性衰变而降低。我们通过将海水中137Cs和（239,240）Pu的模拟值与日本气象研究所构建的HAM数据库中历史人工放射性核素所含的观测值进行比较，验证了模型计算结果。计算得到的137Cs浓度垂直分布在20世纪60年代至250米深度、70年代至500米深度、80年代至750米深度以及90年代至750米深度与观测剖面吻合良好。然而，与深层观测到的137Cs相比，计算得到的137Cs浓度被低估了。这可能表明137Cs向深水的其他输运过程。可以模拟地表水137Cs浓度的水平分布。进行了数值示踪剂释放实验以解释水平分布模式。对于观测值和计算值，（239,240）Pu浓度最大值层出现在中间深度，这是由颗粒清除作用形成的。通过考虑清除效应，可以模拟计算得到的地表水（239,240）Pu浓度的水平分布。