Study On The Distribution Of Non-exchangeable Organically Bound Tritium In The Soil Around A Nuclear Facility

With the development of China’s economy and the improvement of people’s living standard,the demand for energy and beautiful environment are increasing.As a clean energy,nuclear energy has received the attention of governments.At present,China has become the country with the largest number of nuclear power plants under construction in the world.In the future,China’s nuclear power generation will occupy a higher proportion of power generation.However,while peaceful use of nuclear energy,more and more people are beginning to pay attention to the environmental impact of radioactive materials.As one of the radionuclides emitted by nuclear power plants,and having similar physical and chemical properties as hydrogen,tritium(T)is extremely easy to enter the ecosystem and threaten human health.When the tritium enter the organic matter to form organically bound tritium(OBT),the biological half-life of OBT is longer and more harmful to humans.The OBT has become one of the hotspots in the tritium research field.Soil is the basis of the ecological cycle of tritium.And the OBT is also an important part of tritium in soil.However,the factors affecting the formation and migration of OBT in soil are too complicated.At present,the study of soil OBT is still a major difficulty in the OBT research field.This study investigated the OBT in surface soil and deep soil at different sampling sites in different sampling years around the nuclear facility(Qinshan Nuclear Power Station).This study first proposed,measured and obtained the distribution of OBT in soil particle size because the formation and migration of OBT in soil is affected by soil microbes,and the distribution of soil microbes is related to soil particle size.The spatial distribution,depth distribution and variation of time of different forms of tritium in soil around the nuclear facility were also obtained.At the same time,according to the correlation analysis of OBT and HTO,soil organic matter content and soil microorganism on different particle sizes,the sources of OBT in the soil were discussed,which laid a foundation for the establishment of the migration and transformation model of OBT in the soil.The tritiated water(HTO)and the non-exchangeable organically bound tritium(NE-OBT)in the soil around the Qinshan Nuclear Power Station have a certain spatial distribution.The higher HTO and NE-OBT activity appear in the sampling sites which are closer to the nuclear power plant,in the main wind direction and without the barrier of the mountain.The HTO in the soil has a depth distribution,but the NE-OBT has no obvious depth distribution.The NE-OBT in soil has a trend to migrate downward gradually with time,and HTO has no obvious trend.For the exchangeable organically bound tritium(E-OBT)in soil,the activity is mostly near the background level,and showing no space and depth distribution.In the particle size distribution,the distribution of NE-OBT in the soil is similar to the distribution of organic carbon and microorganism in the soil.For the source of OBT in the soil,the ratio of OBT/HTO in the soil ranges from 0.08 to 16.27,which is similar to other studies,with the average being greater than 0.7 given by the Canadian Standard Association.Based on the ratios of OBT/HTO in the soil and the correlation between total NE-OBT and total HTO in the soil,the NE-OBT in soil may be related to soil HTO,but not directly related.Through the correlation analysis between NE-OBT and HTO on different soil particle sizes,it is speculated that in the larger soil particle size,the NE-OBT in the soil is related to the HTO in the soil.According to the analysis of the total NE-OBT and the total organic matter content in the soil and the correlation in different soil particle sizes,it is found that the NE-OBT is related to the soil organic matter in the smaller soil particle size.Through the correlation analysis between the total NE-OBT activity and the total amount of different types of microorganisms in the soil,it is found that in the phylum category,the two fungi,Zygomycota and Basidiomycota,have a strong correlation with the total NEOBT in the soil.