Study On Migration Behavior Of Plutonium In Nuclear Waste Disposal Engineered Barrier

Due to the long half-life and high toxicity,²³⁹Pu is a critical nuclide in radioactive waste,and plays an important role in the safety assessment of geological disposal of radioactive waste.Based on the concept of multiple barrier design,a nuclear waste disposal engineered barrier was selected as the research object,and PHREEQC was applied to calculate the speciation and solubility of Plutonium in the water environment of the engineeried barrier,The TOUGH2 is used to analyze the migration behavior of Plutonium in the disposal cell,the radioactivity distribution of Plutonium at different time in disposal cell was obtained,which reveals the quantitative migration of Plutonium in engineeried barrier.The results show that:?1?More than 99% of Plutonium exist as the Pu?OH?4 and the solubility of Plutonium about 1.0×10-9 mol/kgw in aqueous of the disposal engineered barrier.?2?PH and Eh are the main factors influencing the speciation and solubility of Plutonium.speciation and solubility of Plutonium will not change significantly in the process of fracture water penetrating the barrier.The water environment condition of the engineered barrier is conducive to the release and migration of Plutonium.?3?Considering the migration process of Plutonium in the disposal cell under both normal and extreme scenario,the penetration concentration and rate of Plutonium in the normal scene reached the peak in about 100,000 years,and in the extreme scenario,the peak appeared in advance to 50,000 years;The maximum concentration of Plutonium in disposal cell was reduced by four orders of magnitude under two scenarios,and most of the Plutonium was retained in the engineered barrier,the engineered barrier can block Plutonium migration to the environment effectively.?4?Permeability and partition coefficient are the key parameters in the model.The sensitivity of the partition coefficient is higher than the sensitivity of the permeability.Enhance the adsorption of nuclides and reduce the permeability of the engineering materials can improve the engineered barrier blocking performance of the radionuclide.This study established numerical simulation method of migration of radionuclides and revealed the migration law of Plutonium in engineered barrier,The results can be applied to the optimal design of engineered barrier and provide the basis for safety assessment of disposal repository.