模拟内陆核电站氚水排放对微生态系统影响的研究

Developing inland nuclear power is the inevitable choice for China to adjust energy resource structure and expand nuclear power layout. Inland nuclear power plants (INPP) are located near rivers, lakes or reservoirs, downstream sections of which could be drinking water sources. In comparison with coastal NPP, receptor water bodies downstream INPP possess neither a large volume for nuclides dilution nor sufficient diffusion conditions. Therefore the impact of waste water discharge, containing low-level radioactive substances, on the ecology of receptor water has been a complex scientific question and also a social issue with great public concerns. ..Based on the actual state of surface water in China, we propose to construct an experimental, circulating micro-ecosystem to study the ecological effects caused by waste water discharge from INPP to aquatic environment. The micro-system contains producers (five algal species), consumers (four species of aquatic animal), and transformers (microbes), growing in either eutrophicated water-sediment collected from Lake Chao or artificial water with lower level of nutrient and sediment with defined ingredients. Tritiated water (HTO) is used to simulate the NPP waste water, which contains 3H at much higher level than other types of nuclides. Changes of inorganic environment, energy flow, circulation of substances and biotic community structure in the system will be followed for a certain period during which HTO keeps flowing into the non-eutrophicated and/or eutrophicated system. By these data, ecological impacts of 3H to “clean” water body or 3H plus eutrophication will be compared and analyzed, and the connection between biotic effects and chemical properties can be inferred. Results obtained will be valuable for modeling and safety evaluation of INPP waste water discharge, particularly in the circumstance of China. Experience gained from setting up the micro-ecosystem will be helpful in future establishment of experimental systems at larger scale.

发展内陆核电是我国能源结构调整、核电布局拓展的必然选择。内陆核电通常滨河（湖）而建，下游可能是城市饮用水源地。由于没有滨海核电厂址那样大的稀释水量和扩散条件，内陆核电厂低放废液排放对河流、湖泊生态环境的影响是非常复杂的科学问题和公众十分关注的社会问题。项目基于我国地表水实际状况构建天然富营养水和实验室配制水的、包含生产者（五种藻类）、消费者（四种水生动物）和转化者（微生物）的循环微生态系统，利用核分析技术等研究核电厂难以处理、排放量较大的氚水，以及氚水与天然水体富营养因子双重作用对微生态系统无机环境、生物群落的影响，重点研究加氚和富营养因子条件下微生态系统能量流动、物质循环和生物群落消长及演化，探索因子与结果（效应）之间的关系，构建初步的物理模型，为内陆核电站低放废液排放生态安全性评估提供实验数据；同时，项目构建的试验模型将为内陆电站建设较真实的实验生态系统提供借鉴。

为探讨内陆核电站排放量大、难处理的含氚废水对受纳水体生态的潜在影响，项目构建了一种由非生物环境和生物群落组成的水生微生态系统以模拟真实的富营养淡水生态系统，初步研究了低浓度氚水对系统中主要种群的影响，为内陆核电低放废水生态安全性评估提供了新的方法和数据。.项目以实验室配制水、人工沉积物，初级生产者（藻类）、消费者（浮游动物）和实验室土著微生物（分解者）组合构建了两类（7种或4种藻）6种（无动物、含1种或4种浮游动物）共52个独立的0.6L微生态系统，各系统可在室内稳定条件下自我维持60天以上。在包含7种或4种藻类、土著微生物，但无消费者的简单系统中，藻类群体增长呈现典型的适应期、对数增长期、稳定期和衰亡期；细胞个体小的斜生栅藻和小球藻为典型的优势藻。引入浮游动物消费者后，它们对藻类的捕食作用使生产者群体数量迅速下降，反过来造成动物的食物匮乏进而对动物种群的维持造成威胁。系统内氮磷营养盐总量保持稳定，可利用的溶解性营养盐水平初期因藻的吸收利用快速下降至初始浓度的1/6左右，之后维持在该浓度上下区间内波动。系统放大至3L后其基本特征与0.6L系统一致。.利用3L规模的模型，初步研究了0、200Bq/L、5000Bq/L、10000Bq/L浓度的氚水对系统的影响，结果显示优势种小球藻在近60天的观察期内，密度增长受氚水的抑制较为明显；而优势种斜生栅藻密度受大型溞摄食的影响，对氚水的响应难以确定。至实验中后期，中剂量组有20%（1/5个系统）、高剂量组有33.3%（2/6个系统）的系统里的大型溞死亡，这是否与氚的作用相关还需要更多研究。下一步将继续利用该模型扩大氚水的剂量范围进行实验，着重关注不同剂量氚水引起的模拟水生态系统中典型模式生物种群变化特征和DNA损伤效应，为评估核电含氚废水排放对受纳水体生态的影响提供关键数据。