兰州大学机构库 >土木工程与力学学院
高放废物缓冲砌块压实性能研究
Alternative TitleResearch on Compacting Properties of Bentonite Buffer Block for HLW Disposal
王学文
Thesis Advisor张虎元
2017-05-05
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword高放废弃物处置 膨润土 缓冲砌块 压实工艺 干密度
Abstract

世界各国普遍认为,深地质处置法能够实现高放射性废弃物与生态环境安全、有效的隔离。我国在缓冲回填材料筛选方面已经开展了较多的研究工作。室内试验使用的试样尺寸较小,试验条件能够得到控制,非常适合于材料筛选、配比优化及室内工程性质试验。在实际处置工程中,缓冲材料采用压实块砌筑法进行施工,需要采用工业化压实设备,批量加工成特定形状和厚度的块体(简称砌块),以期很好地适应处置库封闭需求。大型缓冲砌块材料的尺寸效应较大,必须独立进行研究。

参考国外砌块压制研究成果,兰州大学张虎元研究室提出我国缓冲砌块制备体系,选定扇形砌块基本尺寸,以YHD32-200四柱液压机为原型,设计出1/6型扇形砌块和1/12型扇形砌块压实模具,分别压制1/6(A型)和1/12(B型)型扇形砌块。本研究采用应变(变形)控制方式进行缓冲材料砌块单轴压实试验,设计掺砂率为30%,含水率分别为w=8%、11%、13%、15%、18%、20%,在静力20MPa压实能作用下进行缓冲砌块压实试验。本论文的主要目标是研(开)发膨润土缓冲砌块压实工艺技术;统计分析砌块密度分布的空间离散性。

研究总结出膨润土缓冲砌块压实工艺:1)按照试验计划计算制样所需要的膨润土粉末、干砂以及需要加入水的质量,膨润土与砂的混合湿化过程,采用喷雾加水及搅拌法进行人工混合;混合后的膨润土-砂混合材料装入密封袋中进行保湿养护。2)利用压实系统,压制1/12(B型)扇形砌块:填料时,先将亚克力垫板放入模具底部,然后将混合料填充到模具中,对混合料表面轻微压实、整平,最后将砌块上表面垫板放入模具中;随后,操作压实设备对缓冲材料进行压实。3)压实完成后,利用顶出底板将试样从模具中自动顶出。砌块压实和脱模过程顺利,压实缓冲砌块比较均匀,达到了期望的密度。

当掺砂率为30%时,砌块上表面压实能为20MPa时,大型缓冲砌块最优含水率为12.11%,最大干密度为1.89g/cm3。各砌块不同部位含水率测量数据的标准偏差在0.3-0.8%之间,各砌块密度值的标准偏差在0.02-0.05g/cm3之间,各向异性不明显。综合密度测量试验数据可以看出,压实砌块中干密度分布与初始含水率相关。在较低含水率压实砌块中,从压实端到砌块底部,砌块密度逐渐减小,砌块四周边缘部位密度比砌块中心部位小。随含水率逐渐增大至最优含水率,干密度分布逐渐趋于均匀,达到理想压实效果。在高含水率砌块中,随着距砌块压实面距离的增大,干密度分布表现出先减小后增大的趋势,这与低含水率情形时有较大区别。

Other Abstract

Nowadays, deep geological disposal is accepted to isolate high-level radioactive waste (HLW) from ecosystems safely. Numerous researches have been done in the screening of buffer backfill materials for HLW disposal in China. Laboratory tests use small-sized samples and have controllable test conditions, thus very suitable for the test of material screening, ratio optimization and engineering properties. With respect to the practical disposal project, the buffer barrier is constructed by installing together the compacted blocks, which needs to be prepared by industrial compaction equipment into specific shape and thickness so to meet the storage requirements of the repository. Buffer block material should be studied independently because of its large scale effect.

Based on the related research achievements abroad, Professor Zhang’s research group on HLW disposal in Lanzhou University established a prototype systems for buffer block preparation, mainly including the fundamental dimensions of the fan-shaped buffer block, selection of YHD32-200 four-column hydraulic press machine, and the designing of the compressing molds for 1/6 (A type) and 1/12 (B type) fan-shaped block respectively. In this thesis, the uniaxial compaction test of buffer material blocks is carried out by means of strain (deformation) control method with a sand content of 30% and the moisture content of 8%, 11%, 13%, 15%, 18% and 20%, separately, under a static 20MPa pressure. The main goal of this thesis is to develop the compaction technology of bentonite buffer block and to analyze the density discrete within compacted block.

Compaction process of bentonite buffer blocks can be prepared successfully as followings. 1) Calculate the quality of bentonite powder, dry sand and water required by sample preparation according to the test plan, and mix bentonite, sand and water added by spray-distribution method. Then, bentonite-sand mixture is packed into the sealed pocket for moisture conservation. 2) Press 1/12 (B type) fan-shaped block using compaction system. Firstly, puts the acrylic pad into the mold, then fills the mixture into the mold, flattens the surface of the mixture, and finally place the upper subplate of the block into the mold. Start the equipment to compact the buffer block material. 3) After compaction, push the block out the mold automatically by the system. The compacted buffer block is relatively uniform and achieved the desired density.

When bentonite with a sand ratio of 30% is compacted under 20MPa, the large buffer block is achieved an optimum moisture content of 12.11% and a maximum dry density of 1.89g/cm3. The standard deviation of the measured water content among different parts in the same block is between 0.3-0.8%, and the standard deviation of the density varies between 0.02-0.05g/cm3, indicating that buffer block has no obvious anisotropy. Test date shows that density distribution is related to initial moisture content. In case of a lower moisture content, the density is gradually decreased from the compaction top to the bottom of the block, and the density around the edge of the block is lower than that of the central part. In case that the moisture content is high to about the optimum moisture content, the dry density tends to be well-distributed gradually, thus achieving the desired compaction effect. When initial water content is high, along the compressing direction from the top to the bottom of the block, density distributed in such a tendency that is decreased at first and then increased, which is quite different from that of low initial moisture content.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226436
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
王学文. 高放废物缓冲砌块压实性能研究[D]. 兰州. 兰州大学,2017.
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