模拟深地质处置条件下动力堆高放废液玻璃固化体的浸出行为

    Leaching Behavior of Glasses With High Level Liquid Waste From Power Reactor Under Simulated Deep Geological Disposal Conditions

    • 摘要: 高放废液玻璃固化体处置在深地质介质中,在长时间的存放过程中,地下水会侵蚀玻璃固化体,不仅会改变玻璃固化体的结构,还会导致放射性核素的浸出。本工作以动力堆高放废液玻璃固化体为研究对象,采用静态浸出实验方法,开展了在模拟处置条件下,模拟高放废液玻璃固化体在不同浸泡液(北山地下水与去离子水)和温度(25 ℃与90 ℃)下的浸出行为研究,对玻璃固化体表面形貌及其内部5种元素Si、B、Na、Cs、U的浸出浓度进行分析。结果表明:玻璃网络骨架溶解速率与温度呈现正相关性,浸泡温度为90 ℃时,5种元素的归一化损失量比25 ℃时的提升1~2个数量级,其中Na元素因非桥氧的生成和离子交换作用损失最为显著(90 ℃时高达101 g/cm2量级);X射线衍射(XRD)与扫描电镜-能谱(SEM-EDS)形貌分析结果表明,两种浸泡液下玻璃固化体表面均形成了清晰的侵蚀层,特别是北山地下水中的Mg2+与玻璃浸出液中的组分发生反应生成了硅酸镁(MgSiO3)修复层,使侵蚀层中的硅氧比提升至23.31%,显著延缓了腐蚀速率;经220 nm滤膜过滤后,两种浸出液中并没有稳定胶体形成,核素随胶体共迁移的概率较低。

       

      Abstract: During the disposal process of high-level radioactive waste(HLLW) liquid glass solidified body in deep geological media, groundwater intrusion into protective barriers may expose glass wasteforms to corrosive environments, leading to structural degradation and radionuclide release. This paper systematically investigates the leaching behavior of nuclear waste glass under various simulated disposal conditions. The primary elements analyzed include Si, B, Na, Cs, and U, both on the surface and within the glass matrix. The findings indicate that elevated temperatures accelerate network dissolution by enhancing molecular and ionic mobility, thereby increasing the kinetic energy of water molecules and dissolved ions. When Na+ is added to the glass, the radio of Si to O is reduced, and non-bridging oxygens(NBOs) appear. The emergence of non-bridging oxygens causes the silicate network to fracture, leading to the gradual breakdown of the network structure. The above reasons lead to significant leaching of elements from the bulk glass into the aqueous solution. At temperatures of 25 ℃ and 90 ℃, the particle sizes of the glass wasteform measured in the two leaching liquids were found that after filtration through a 220 nm filter membrane, a large amount of micron-sized precipitate was removed from both leaching solutions, and no stable colloids were formed. This prevents the probability of radionuclides migration in the form of colloids. In 90 ℃ atmospheric environment, corrosion was noted on the surface of the glass solidified bodies immersed in deionized water and Beishan groundwater during the 60-day testing period; however, the morphology and composition of the resulting corrosion layer aredifferent between the two immersion liquids. SEM-EDS and XRD analyses demonstrate that corrosion layers formed on glass surfaces after 60-day immersion at 90 ℃ exhibit distinct morphologies depending on the leaching solution. In Beishan groundwater, the presence of Mg2+ induces the formation of a magnesium silicate(MgSiO3) repair layer, enriching the corrosion layer in Si and O(silicon-oxygen ratio increased to 23.31%) and the repair layer acts as a natural barrier to mitigate further corrosion. In contrast, deionized water immersion results in alumina(Al2O3) impurities and amorphous silica(SiO2) as primary corrosion products. Filtration experiments(220 nm membrane) confirm the absence of stable colloids, indicating negligible colloid-facilitated radionuclide migration. The findings elucidate the synergistic effects of temperature and geochemical conditions on glass durability, highlighting the critical role of Mg2+ in mitigating corrosion through reparative mineralogical phase formation.

       

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