| This thesis has studied the concentration distribution of man-made radionuclide—~3H in the groundwater of 5 kilometers' wide, 10 kilometers downriver around CIAE. The program FEMWATER/FEMWASTE developed by National Oak Ridge Laboratory is used to solve problems. And the parameters of the program are selected based on the local experimental material and responding references. The main equation in FEMWATER is Richards Equation and its modifications. The main solute migration mechanisms in FEMWASTE are convective flow, hydraulics diffusion, molecule diffusion, radioactive decay, adsorption, source-converge, and biological decomposition. During the computation, the mass balance of this zone is added and the penetration problem between several layers of aquifer can also be solved. This program is based on Galerkin finite element method with large flexibility in dealing with problems of time, space, initial conditions, sources and boundaries.On the basis of rectangle partition of this region, one-dimension column penetrate model and two- dimension level model are used to describe the migration of ~3H in the unsaturated and aquifer groundwater. The boundaries and initial conditions are set according to the monitor materials about local hydrological geological condition, water level, concentration and so on. The concentrations of unsaturated and aquifer water are calculated in each time step and locational node, on the hypothesis of ~3H entering into the groundwater in a certain concentration continuously. Then the results of unsaturated water are plotted into penetration curve and distribution curve along depth; the results of the concentration of ~3H in aquifer are plotted into relative concentration isolines figures of this zone. Based on these figures, the migration behavior of ~3H in unsaturated and aquifer is analyzed.The simulation results indicate: the penetration velocity of ~3H is very small, about 0.001m/d. The flow velocity is very uniform in nearly the same direction. A little solute moves up-and-down only on a small layer. The flow field basically points from north to south with a velocity of 1-10 m/d. The water head isolines decline steadily from northwest to southeast.The analysis of the relative-concentration distribution figures of ~3H indicate: the migration of ~3H in unsaturated water can be divided into three stages as time. The first one is penetration, in this stage the concentration declines with the increasing of depth. The ~3H arrives at the bottom of unsaturated zone on the 840th day after the start of calculation. The second one is equilibrium stage, the concentration distribution of ~3H inclines to equilibrium while the difference of concentration in different depth becomes smaller. The third one is accumulation, ~3H accumulates in the bottom of unsaturated zone and the zero-flux boundary condition is not suitable any more.In aquifer, ~3H migrates to downriver of the zone along the water flow, three kinds of source are simulated, which are point source, line source and plane source. Its relative concentration changes obviously in the horizontal direction while vertical direction changes slightly. The reason is that the horizontal diffusion coefficient is much lager than the vertical coefficient. And from the simulation we can see: in the whole zone the migration of ~3H is restricted to the east of Dashi River, and an obvious long and narrow concentration belt appears in the migrating range. The difference among three types of the migration of ~3H is: as a result of different shapes of source, the velocities and ranges are different even when the initial concentrations are the same. unsaturated groundwater; aquifer; FEMWATER/FEMWASTE Program; the relative concentration of ~3H. |
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