The Numerical Simulation Study On The Migration Of The Nuclide In The Unsaturated Zone

In recent decades, the nuclear industry has been rapid development, but in the meantime, It also casts a more critical and urgent problems:How could be secure, efficient and economical disposal of nuclear waste. At the present time, People has a relatively mature technology for the safe disposal of the Low-level radioactive nuclear waste. But the high-level waste contains highly toxic because of its long half-life of radioactive nuclides. Now, Deep geological disposal is to be a generally accepted and feasible plan of disposal of the High-level radioactive waste .High-level radioactive waste was buried in hundreds of meters thick of unsaturated zone, and the human environment to a permanent segregated.239Pu is a transuranium nuclide, belong to A high-level waste. Study the migration law of the 239Pu in the unsaturated zone is of great significance.This paper has analyzed the existing research results at home and abroad, Based on the theory of fluid dynamics in porous media and solute transport. Experimental use of KU-PF and the self-developed soil column experiment, mensurated the soil water characteristic parameters of the unsaturated zone. Built a mathematical model of Radionuclide migration in the unsaturated zone. And use the HYDRUS-1D to simulate the migration of the radionuclide in the unsaturated zone.From these work, some conclusion and recognition are achieved:1.Through the laboratory soil column experiment and Ku-pF unsaturated hydraulic conductivity measurement experiment results show that the same disturbed soil samples measured in different scales characteristic parameters of vadose zone water is consistent.2 The study of the migration of nuclide 239Pu is based on the study of the water transport in the unsaturated zone. The study of the water transport offer the soil water characteristic parameters for the study of the nuclide migration. The speed of the migration of nuclide and water is directly proportional. In the drought and thickness unsaturated zone, pore water velocity is small. The order of magnitude about the pore water velocity in the stable time is 10-4 m/d. The so small Pore water velocity Strengthen the role of molecular diffuse. Nuclide migration to the surrounding. In the thickness and less rainfall unsaturated zone, exist a stabilized zone about water movement.3. Comparison of simulation results under three scenarios:The unsaturated zone has a strong retention capacity of nuclide 239Pu, Under the Basic scenario, the concentration peak of nuclide 239Pu did not move down after 20,000 years. The migration velocity of the nuclide 239Pu in the unsaturated zone showed non-uniformity. A small part of the nuclide 239Pu migrate rapidly. The rainfall infiltration is the main factors about the migration of nuclide 239Pu u. If large amount of rainfall infiltration, the speed of the nuclide 239Pu will be faster.4. The simulation results of the Migration about nuclide in the three media are compared: On the same boundary conditions, Water flow in sandy clay is very slow, followed by sandy loam, and fastest in the loamy sand. The speed of the migration of nuclide and water is directly proportional. Sandy clay can remain the nuclide 239Pu strongly, is most suitable for the disposal of nuclide 239Pu, Loamy sand can not used to dispose the nuclide 239Pu.