某核电厂近岸海域放射性核素迁移特征探讨

Study on Radionuclide Migration in Near-shore Waters Around a Coastal Nuclear Power Plant

滨海核电厂运行时会有少量的放射性核素通过液态途径进入海洋环境中,在掌握其海域水动力环境的基础上,开展放射性核素迁移研究具有重要意义。基于某核电站近岸海域的水下地形和水文条件,通过潮位、流速、流向的率定,构建水动力环境模型,模拟研究区的潮流运动过程和特征,为放射性核素迁移扩散提供基本流场背景。以核素131I为例,采用恒定速率1Bq/L活度浓度持续排放,用实测两个半月潮模拟核素迁移过程,分析放射性核素131I在该海域的时间和空间分布规律。结果表明：1）随着时间推移,核素逐渐向外海域扩散,但扩散速度较慢;随着距离增大,海域中核素活度浓度呈几何倍数快速下降;厂址东北方向岸边核素活度浓度较高,在一个月后逐步达到稳定,约比排放活度浓度低两个数量级。2）涨潮时核素活度浓度范围较小,落潮时核素活度浓度范围快速扩大,相同核素活度浓度面积为涨潮时的2～3倍。3）排放初期,各处核素活度浓度均随时间迅速增加,随后趋于稳定;不同位置的活度浓度随着潮汐交替涨落,不断波动,涨潮时活度浓度较低,落潮时活度浓度较高;不同位置的平均活度浓度随着潮汐交替涨落,不断波动,大潮期间活度浓度较高,小潮期间活度浓度快速降低。

A very small amount of radioactive nuclides will be discharged to marine environment through fluid as coastal nuclear power plant（NPP）is running.Potential risk of marine environmental pollution by radioactive material leakage might exist,so it is very important to comprehensively understand the hydrodynamic environment of coastal NPP.Based on bathymetry and hydrographic conditions around a NPP,hydrodynamic numerical model is used to simulate tidal processes and related characteristics.With 131 I used as a tracer and a constant discharge,temporal variation and spatial distribution of radionuclide are analyzed with two and a half month simulation of tide and nuclide migration processes.Results show that 1）the radionuclide diffuses to open water gradually at first,but nuclide concentration reduces in geometric multiples as distance increases;the nuclide concentration to the northeast of the site is high,then gradually reaches a stable state a month later,and its concentration is about two orders lower than the source discharge concentration;2）the nuclide diffusion area is small at high tide,but expands quickly at low tide and its diffusion area is about 2to 3times of that at high tide;3）during early discharge period,nuclide concentration increases quickly almost everywhere,then tends to be stable;the nuclide concentration varies with tidal fluctuation,and is lower at high tide but higher at low tide;The average concentration is higher at spring tide,and lower at neap tide.