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首页> 美国政府科技报告 >Buoyancy flow in fractured rock with a salt gradient in the groundwater. A second study of coupled salt and thermal buoyancy
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Buoyancy flow in fractured rock with a salt gradient in the groundwater. A second study of coupled salt and thermal buoyancy

机译：裂隙岩石中的浮力流与地下水中的盐梯度。关于耦合盐和热浮力的第二项研究

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An underground nuclear waste repository produces heat that will induce a buoyancy flow of groundwater in fractures and other permeable regions in the surrounding rock. The radioactive material may then, in case of penetrated canisters, possibly reach the biosphere. Measurements of ground water in crystalline rock show an increasing salt content with depth. The resulting increase of water density counteracts the thermal buoyancy, and it may create a natural barrier for the groundwater flow between the repository and the biosphere. The aim of the study is to analyse this barrier effect and to assess the maximum upward displacement of water starting from the vicinity of the repository. The coupled flow process for groundwater, salt and heat with buoyancy due to temperature and salt concentration differences is studied. The equations have been analysed in great detail, and a numerical model has been developed for the case of groundwater flow in a fracture plane. The largest upward displacement from the repository has been determined with the model for any heat release. Approximate formulas, which are shown to be sufficiently accurate for assessments, have been derived. The main formula concerns the case, when the canisters are stacked on the top of each other in a very deep borehole. There are no restrictions in the position of the fracture plane. The borehole may even lie directly in the fracture plane. We find a strong barrier effect. In a reference case with a salt concentration increase of 2% per km downwards and with 300 canisters placed over a length of 2000 m in the borehole (the total amount of released heat is 0.32 TWh), the largest upward displacement from the top of canisters becomes, according to the formula, 60 m. (Atomindex citation 25:001097)

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