| 高温碱溶液作用下混合型缓冲回填材料膨胀特性研究 | |
| Alternative Title | Combined Effect of High Temperature and Alkaline Solutions on the Swelling Pressure of Buffer/Backfill Materials for HLW Disposal |
| 季泽 | |
| Subtype | 硕士 |
| Thesis Advisor | 张虎元 |
| 2021-05-23 | |
| Degree Grantor | 兰州大学 |
| Place of Conferral | 兰州 |
| Degree Name | 工学硕士 |
| Degree Discipline | 岩土工程 |
| Keyword | 高放废物处置 混合型缓冲回填材料 膨胀力 温度 KOH溶液 |
| Abstract | 我国的高水平放射性废物处置工作研究自二十世纪八十年代开始，已经取得了长足的进步。缓冲回填材料的研究已经进入现场原位试验的阶段。 当前地下实验室初步工程设计已经完成，场址定位甘肃北山新厂地区，深度为560m，由地面设施和地下设施两部分组成。高放废物处置库采用多重屏障系统。处置库的长期运行过程中，地下水会逐渐将混凝土衬砌溶蚀，溶出物具有高碱性，会侵入缓冲回填屏障中，与缓冲回填材料发生反应。除此之外，高放废物中的放射性核素在衰变的过程中，向周围的缓冲回填屏障辐射热量。高温与碱溶液的共同作用下，缓冲回填材料的膨胀性能会发生劣化，对缓冲回填屏障的长期性能产生不利的影响。 本研究为模拟缓冲回填材料在处置库长期运营过程中所处的高温碱性环境，改装温控式固结仪，以满足对测试时施加温度和化学溶液的要求，并对改装后仪器的进行检测与校准。本试验选择以兰州大学自主研发的混合型缓冲回填材料(70%高庙子膨润土和30%石英砂混合物)为试验对象，设置试验温度为15℃(平均室温)和90℃，以蒸馏水和0.1M、0.3M、1.0M的KOH溶液为孔隙溶液，进行膨胀力试验。借助X射线衍射对试验后的试样的蒙脱石矿物含量进行测量与定量分析，揭示混合型缓冲回填材料膨胀力衰减的机理。主要结论如下： (1) 高温提升了蒸馏水中试样膨胀力发展速率与膨胀力值。最大膨胀力值增大，平均增幅约为13%。 (2) 缓冲回填材料最终膨胀力与KOH溶液浓度呈负相关，与初始干密度呈正相关。溶液浓度增大，特定膨胀时间均减小;最终膨胀力与初始干密度使用 模型拟合效果良好。 (3) 90℃ KOH溶液作用下缓冲回填材料膨胀力随时间发展出现衰退现象，是碱溶液危害膨胀性能的典型特征。 (4)最大膨胀力抑制率 、最大膨胀力丧失率 和最终膨胀力衰减率 ，均与KOH溶液浓度呈正相关，与初始干密度呈负相关。升温效应会弱化膨胀力的抑制和衰减。 (5) XRD测试结果表明：温度的增长对试样中蒙脱石含量的影响较小。90℃ KOH溶液作用后的混合型缓冲回填材料试样中蒙脱石含量下降，对应衍射角增大，蒙脱石含量最大下降了15.3%。增加试验后的试样蒙脱石含量与KOH溶液浓度呈负相关与试样的初始干密度呈正相关。 (6) 高初始干密度的缓冲回填材料较低初始干密度，在高温与碱溶液叠加作用下膨胀力衰减率更小，蒙脱石含量更高。组成的缓冲屏障长期性能更好。 |
| Other Abstract | Since the beginning of the 20th century, Chinese research on the disposal of high-level radioactive waste has made considerable progress. The research of buffer backfill materials has entered the stage of in-situ testing on site. The preliminary engineering design of the current underground laboratory has been completed. The site is located in the Xinchang area of Beishan, Gansu, with a depth of 560m. It consists of two parts: surface facilities and underground facilities. The high-level radioactive waste repository adopts a multi-barrier system. During the long-term operation of the repository, groundwater will gradually dissolve the concrete lining, and the dissolve will be highly alkaline and will invade the buffer backfill barrier and react with the buffer backfill material. In addition, the radionuclides in the high-level waste radiate heat to the surrounding buffer backfill barrier during the decay process. Under the combined action of high temperature and alkaline solution, the swelling performance of the buffer backfill material will be degraded, which will adversely affect the long-term performance of the buffer backfill barrier. In this study, to simulate the high temperature and alkaline environment of the buffer backfill material in the long-term operation of the repository, the swelling pressure test instrument was modified to meet the requirements of the temperature and chemical solution applied during the test, and the modification of the instrument Perform testing and calibration. In this experiment, the mixed buffer backfill material (70% Gaomiaozi bentonite and 30% quartz sand mixture) independently developed by Lanzhou University was selected as the test object, and the test temperature was set to 15℃ (average room temperature) and 90℃, with distilled water and 0.1 M, 0.3M, 1.0M KOH solutions are pore solutions, and the swelling pressure test is carried out. With the help of X-ray diffraction, the mineral composition of the tested sample is measured and quantitatively analyzed, and the mechanism of the attenuation of the swelling pressure of the hybrid buffer backfill material is revealed. The main conclusions are as follows: (1) High temperature increases the development rate and value of the swelling pressure of the sample in distilled water. Under the action of high temperature, the specific swelling time T100, T90, and T50 of the mixed buffer backfill material in distilled water will be reduced by more than 50%;the maximum swelling pressure value will increase, with an average increase of about 13%. (2) The stable swelling pressure of the buffer backfill material is negatively correlated with the KOH solution concentration, and positively correlated with the initial dry density. As the solution concentration increases, the swelling pressure and The maximum swelling force inhibition rate _1, the maximum swelling force loss rate βand the final swelling force attenuation rate γ_1 are all positively correlated with the KOH solution concentration and negatively correlated with the initial dry density. The heating effect will weaken the suppression and attenuation of the expansion force.specific swelling time T100, T90, T50 will decrease;the stable swelling pressure and initial dry density use model fits well. (3) The time-history curve of the swelling pressure of the buffer backfill material changes under the action of the 90℃ KOH solution, which can be divided into two stages: stage I, after the swelling pressure reaches the peak from zero, the swelling pressure caused by the compression effect of the electric double layer at this stage is suppressed. Dominant;Phase II swelling pressure begins to decrease after reaching the peak, and finally reaches a stable state. At this stage, the loss of swelling pressure caused by the chemical effect of montmorillonite dissolution and cation exchange is dominant. The attenuation of the swelling pressure under the action of the KOH solution is composed of these two effects. (4) The maximum swelling force inhibition rate 1, the maximum swelling force loss rate βand the final swelling force attenuation rate γ1 are all positively correlated with the KOH solution concentration and negatively correlated with the initial dry density. The heating effect will weaken the suppression and attenuation of the expansion force. (5) XRD test results show that the increase in temperature has little effect on the content of montmorillonite in the sample. The montmorillonite content in the mixed buffer backfill material sample after the action of 90℃ KOH solution decreased, corresponding to the increase of the diffraction angle, the montmorillonite content decreased by 15.3%. After increasing the test, the montmorillonite content of the sample is negatively correlated with the KOH solution concentration and positively correlated with the initial dry density of the sample. (6) The buffer backfill material with high initial dry density has a lower initial dry density, and the attenuation rate of swelling pressure is smaller under the superposition of high temperature and alkali solution, and the content of montmorillonite is higher. The composed buffer barrier has better long-term performance. |
| Pages | 77 |
| URL | 查看原文 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | https://ir.lzu.edu.cn/handle/262010/462447 |
| Collection | 土木工程与力学学院 |
| Affiliation | 土木工程与力学学院 |
| First Author Affilication | School of Civil Engineering and Mechanics |
| Recommended Citation GB/T 7714 | 季泽. 高温碱溶液作用下混合型缓冲回填材料膨胀特性研究[D]. 兰州. 兰州大学,2021. |
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