Groundwater Environmental Impact Assessment Of The Radioactive Contamination In Offshore NPP

Compared with the coastal site,the hydrogeological conditions of the offshore nuclear power plant is complex.Once the radioactive waste or substance leaks occur,the radionuclides are likely to migrate along with the movement of groundwater,pollut the groundwater environment and threaten the public health and safety around the site.The groundwater environmental impact assessment of the radioactive contamination in offshore NPP will help improve the acceptability and credibility of NPP site selection and evaluation,provide the basis for the environmental impact assessment and safety analysis work of the nuclear power plant,provide the supportment for the offshore nuclear power plant license application and construction.In this paper,Hebei Haixing nuclear power plant is a typical offshore nuclear power plant,the comprehensive use of water chemical analysis,hydrogen and oxygen isotope tracer,analytical screening and numerical simulation,research the hypothetical accident and source terms of the groundwater radioactive contamination,analyze the hydrogeological conditions,explore the groundwater circulation rule,reveal the characteristics of the radionuclide migration in groundwater,predict and evaluate the impact of the NPP radioactive contamination leakage on the groundwater environment under the hypothetical accident.The engineering analysis of the AP1000 unit shows that the rupture accident of the temporary storage tank of the radioactive waste liquid system is enveloping,which can be used as a hypothetical accident condition for the groundwater environmental impact assessment of the radioactive contamination,and the source term of the accident is all kinds of nuclides in the radioactive liquid of the temporary storage tank.The analysis of hydrogeological mapping,drilling,field test and laboratory test results of the hydrogeology investigation shows that the groundwater in the study area exist in silty clay and silty sand of the marine and terrestrial interactive deposit in Quaternary Holocene,Pleistocene and clay rock in Neogene,which can be divided into the aquifer I groundwater,aquifer II groundwater,aquifer ? groundwater and aquifer ? groundwater from top to bottom.The groundwater in aquifer I group is the shallow groundwater,which belongs to pore phreatic water in loose rock mass.It is widely distributed,and the depth of the water level is shallow and changes with the seasons.The groundwater in other aquifer belongs to the deep groundwater.The total dissoloved solid of the shallow groundwater and aquifer II deep groundwater were higher,which belongs to salt water,and Cl-Na(K)water chemistry type.The total dissoloved solid of aquifer ? and ? groundwater is low,which belongs to the brackish water,and HCO3·Cl-Na(K)water chemistry type.There are differences in hydrogen and oxygen stable isotopes in different layers of groundwater,and the overall performance is gradually poor with the increase of depth.The analysis of groundwater circulation characteristics by dynamic observation,water chemical analysis and isotope screening show that the shallow groundwater recharge by the atmospheric precipitation and surface water,such as Yangcheng reservoir,Yangcheng wetland and Yangcheng hondo,shrimp pond and salt field,runoff from the southwest to the northeast,influx to Zhang Wei New river,Xuan Hui river in East and west sides,and the Yangcheng ditch in center,drain out of the study area in the Northeast boundary eventually,and the hydraulic connectio between the shallow groundwater and deep groundwatern is weak.The radionuclide migration features is the radionuclide migrate to the northwest after enter in the shallow groundwater under the influence of the groundwater flow general trend and Yangcheng hondo recharge,and then into the Yangcheng ditch.Based on the analytical mathematical model,the results of nuclide screening analysis show that only the year committed effective dose of H-3 which is not adsorbed is greater than the evaluation acceptance criterion,and the other nuclides are negligible.The numerical prediction and evaluation by the groundwater numerical simulation software GMS showe that H-3 migrated to Yangcheng ditch after 25 years and reached the peak value in 65 years,and the total effective dose of public intake is less than 0.1m Sv,which satisfies WHO groundwater quality standard.Under the hypothetical accident,the groundwater environmental impact assessment results of radioactive nuclide leak contamination meet the requirements of the evaluation criteria,and will not have adverse effects on the environment.