Conventional Liquid Effluents Of Nuclear Power Plants In The Study Of The Migration Of Radionuclides In Coastal Waters

Nuclear energy is a kind of clean energy.The development and utilization of nuclear energy conforms to the trend of China's energy transition.The development of nuclear power can also help carbon peak and carbon neutrality.In recent years,China has accelerated the pace of nuclear power construction.However,radioactive materials produced by the operation of nuclear power plants may have an impact on the environment.At present,all the nuclear power plants in operation in China are coastal nuclear power plants.The radioactive liquid effluent is discharged into the nearby seawater for dilution.The study of the migration of radionuclides in the liquid effluent in the seawater is of great significance to the operation safety and environmental impact assessment of the power station.Taking an AP1000 nuclear power plant as an example,the characteristics of the migration and diffusion of radionuclides in the ocean and the changes in the concentration of liquid effluent under normal operating conditions of the power plant are studied,and the effects of decay,biological concentration,suspended solids adsorption,and atmospheric deposition on the concentration of marine nuclides are studied in detail.The influence of,reveals the temporal and spatial distribution of 3H,137Cs,131I,90Sr in seawater during the discharge phase and the discharge completion phase.The calculation results show:(1)The effect of decay on 131I is obvious and cannot be ignored;it takes several years to several decades for the suspended matter to have a significant effect on the concentration of nuclides;the effect of atmospheric deposition of nuclides caused by gaseous effluents on the concentration of seawater nuclides Can be ignored(2)During the discharge stage,the nuclides mainly migrate and diffuse in the direction of coastal currents,and they are mainly distributed within 1 m near the discharge outlet.Within 6m of the discharge port,the 3H concentration is 9-10 orders of magnitude higher than the background.90Sr is reduced to the surface water concentration level around the power station at 0.2 m away from the discharge port,and it is equivalent to the Yellow Sea background level at 0.4 m;131I concentration Both are lower than the prescribed upper limit of open-air water sources;the concentration of 137Cs at 6 m is 2 orders of magnitude higher than the background level.(3)During the discharge completion stage,the 3H concentration of stations 1 to 4#is much higher than the background level,and after 20 days of discharge,the concentration of 3H is 4 orders of magnitude higher than the background level.The peak values of 137Cs and 90Sr are lower than the background level by 1 to 2,4 to 5,respectively,131I The peak value is 5 to 6 orders of magnitude lower than the upper limit of the open water source requirement;after 1 d and 10 d of discharge,the concentration distribution of nuclide within 1 km and 5 km is as follows:The concentration of nuclide is the highest at the source point,and the concentration of the nuclide is the highest at the source point.The points are symmetrically distributed with the center.After 1 day of discharge,the concentrations of 137Cs and 90Sr were 1,4 orders of magnitude lower than the Yellow Sea background level,and after 10 days,they were 3 to 6 orders of magnitude lower than the Yellow Sea background level.After 1 d,since the initial emission of 131I was higher than that of 137Cs,its concentration was also slightly higher than that of 137Cs.After 10 d,due to decay,the concentration of 131I was slightly lower than that of 137Cs.Through the analysis of the results,the migration mechanism of radionuclides in the liquid effluent under different time spans was revealed.In the process of short-term migration,the concentration of nuclide is mainly affected by the source term,ocean current transport,and 131I decay.In the long-term migration process,the concentration of nuclide is mainly affected by the source term,ocean current transport,suspended solids adsorption,3H decay,90Sr decay,137Cs decay,and the degree of influence of each factor decreases in turn.