近岸海域“水气耦合”下氚的水体弥散模型及特性研究

Most of the nuclear facilities in operation and planning are distributed in the eastern coastal areas of China. Both nuclear power plant (NPP) and future fusion power plant (FPP) would bring tritium effluents which might produce radiation detriment to the aquatic organisms and humans. Compared with the other radionuclides, special characteristics of tritium dispersion in coastal waters are shown as follows: (1) dry and wet deposition of air tritium (from the gaseous discharge or evaporation) on the water underlying surface; (2) evaporation of tritium into the air from the water; (3) infiltration of tritium into the deeper layer from the bottom mud; (4) biological metabolism of tritium. In light of the above, this project aims to perform the studying of tritium dispersion modeling and characteristics in coastal waters with the consideration of air-water coupling. On the one hand, the features and model of dry and wet deposition of air tritium on the water underlying surface will be studied by designing a small scale experiment. On the other hand, the tritium dispersion model will be developed by introduce the tritium characteristics such as deposition and evaporation to the basic 3-D diffusion equation. Through the computational fluid dynamics (CFD) simulation, the relations between tritium discharge and dynamic tritium concentration in the aquatic environment are expected to be found. After finishing the project, a model and series of strategy suggestions will be proposed for tritium discharge of nuclear facilities in China, which are significant to the safety operation of coastal nuclear facilities and future nuclear reactors in the floating platform.

我国在运及规划的核设施主要分布在东部沿海区域，而现有核电厂和未来聚变电站都无法避免含氚流出物的排放，氚进入水体可能会对水体生物、乃至人体产生辐射危害。相比其他放射性核素，氚的水体弥散过程具有以下特性：（1）“水体下垫面”的干、湿沉降特性（空气氚来自核设施气态释放或水体蒸发）；（2）伴随水体的蒸发作用；（3）通过底泥的下渗作用；（4）生物代谢作用。鉴于上述特点，本项目提出开展近岸海域“水气耦合”下氚的水体弥散模型及特性研究。一方面，通过实验设计，研究空气氚（HTO）在水体下垫面的干、湿沉降特性及模型；另一方面，基于三维扩散方程，引入上述氚特性的修正，构建模型，通过计算流体力学（CFD）模拟，获得液态含氚流出物的水体弥散特性，明确不同水体区域受放射性污染的规律。通过本项目研究，试图为我国液态氚排放提供模型与策略建议，对保障我国沿海核设施及近期提出的近海核动力浮动平台等的安全运行都具有重要意义。

氚是核能利用中向环境排放活度最大的放射性核素，分为气载和液态排放两种途径。本项目主要关注通过液态排放或大气沉降进入水体氚的行为，采用数值模拟和实验方法研究了近岸海域“水气耦合”下氚的水体弥散模型及特性，主要包括两项研究内容：（1）针对蒸汽氚在水体下垫面的干湿沉降特性及模型研究，A、建立了数值模型，分别采用单相组分输运模型和两相颗粒流动模型研究了大气中蒸汽氚和液滴氚的沉降特性，获得了多因素影响下的沉降速度；B、研制了实验平台，实验平台可产生自主可控的载带气温度、湿度和风速，用重水蒸汽和液滴替代蒸汽氚和液滴氚作为示踪物，通过蒸汽发生器或高压喷嘴实现源项控制，获得了空气-水体两相传质数据。（2）针对蒸发等因素下氚的水体弥散模型及特性研究，A、以我国氚排放量最大核电基地的受纳水体“杭州湾”、内陆水库为例，建立了欧拉数值模型，研究了潮汐作用下近岸海域和水库氚的水体弥散规律，并评估了氚蒸发通量对沿岸居民的辐射剂量，与鱼虾等食入剂量水平进行了对比分析；B、以我国氚排放量最大核电基地为例，基于水分运移和溶质运移模型，结合动态边界条件、动态源项和衰减因素等，建立了包气带氚行为数值模型，研究了包气带氚的动态分布特性，获得了动态蒸发、下渗及生物吸收率等数据。通过本项目执行，研制了实验平台，获得了氚沉降速度、动态蒸发率、下渗率、生物吸收率等关键数据，建立了动边界驱动下的数值模型，为含氚流出物的排放及辐射影响提供了理论依据和技术支撑。项目执行期间，研究成果在国内权威期刊《中国科学：技术科学》和TOP期刊Renewable & Sustainable Energy Reviews、Journal of Hazardous Materials、Journal of Hydrology、Chemosphere等发表期刊论文6篇，在ICONE2022和中国核工业教育学会首届学术年会发表国际和国内学术会议论文2篇，在国际国内会议开展主题、口头报告7次，获优秀学术会议论文奖或优秀报告奖4次，培养在读博士、硕士研究生3人。