Experimental Study Of Water Flow In Capillary Barrier Of Nuclear Waste Repository Cover

In the modern world, the lack of energy sources such as coal, petroleum, natural gas becomes serious gradually, all the country in the world have to confront the energy crisis, so nuclear energy will get more and more attention from them. Nuclear energy will get sweeping development as a well developing Energy Substitute. But as the widely use of nuclear energy, there will be more and more nuclear waste. So how to dispose nuclear waste safely will be the focus of the people.Nuclear waste is often disposed by the method of geological disposal at the present time. First, Processing,then put it in waste repository isolating from external environment, avoiding the water infiltration into the nuclear waste repository to the best of its ability. Cover of low-andintermediate level radioactive waste disposal in near-surface facilities is a useful barrier. One important section, consisting of a coarser soil layer usnderlying a finer soil layer, called capillary barrier. Such a configuration is, in reference to the mechanism of capillary tension that limits water's downward movement from a finer soil into a coarser soil, causing temporary water storage in the upper soil layer, if the fine-coarse interface is sloped, water in the fine layer can also drain laterally. This paper presents the systemic research of capillary barrier effect, taking infiltration rate,inclination of slope and thickness of coarser soil into account.To study its performance of the capillary barrier consisting of fine-over-coarse quartz sand layers, it is subjected to different infiltration rates simulating different rainfall in an infiltration box apparatus under unsaturated condition. The barrier was subjected to several infiltration rate of 5,10,15,20 mm/day, successively .Through quantificationally measurement of the diversion water, we can conclude that the bigger the infiltration rate is, the more the penetration water is ,the less diversion water is, the weaker the capillary barrier is, under certain condition of invariable thickness.The impact of coarse layer thickness on the capillary barrier is investigated .The tests are carried on different thickness of coarse quartz sand ,ranging from 1mm to 30mm in a given infiltration rate. The results indicate that the diversion water becomes larger with the increasing of thickness of coarse layer, confirming the positive effect of bigger thickness of coarse layer on reducing penetration water. The increasing the angle of slope also helps to strengthen the capillary barrier effect.While quantificationally measureing the diversion water, the matric suction of different locations in and around the capillary barrier are also measured, which has layed the foundation for the exploring the multiplex effect on the capillary barrier, provided the reference for the design of cover in nuclear waste disposal.