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During the operation of underground repository of high-level radioactive waste, the highly alkaline solution generated by groundwater corroding lining concrete will diffuse into the bentonite buffer barrier, resulting in the degradation of barrier property. The KOH solution with different pH values was used to simulate the alkaline solution, and a one-year contact diffusion test at room temperature was conducted. Then, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) were performed to investigate the effect of slow diffusion on the mineralogy of bentonite. The XRF test results show that when the pH of KOH solution was greater than 12.6, the content of silicon began to decrease, that is, montmorillonite, quartz, cristobalite and other Si-containing minerals in bentonite were dissolved. At the same time, the content of K increased, indicating that the bentonite had an ion exchange reaction with the alkaline solution, a large amount of K+ ions in the solution entered the montmorillonite crystal layer. The XRD test results show that the 001 peak of montmorillonite mineral started to shift to the right at pH=12.6, the peak widths widened, and the peak intensity reduced considerably. When the pH>13, the crystal interlayer space decreased from 1.385 3 nm (13.853 Å) to 1.221 0 nm (12.210 Å), indicating that the crystal layer of montmorillonite was compressed. With the increase of the pH value, the content of minerals such as montmorillonite and quartz decreased significantly, and the contents of illite, clinoptilolite and feldspar minerals increased slightly. The SEM test results show that part of the montmorillonite crystal layer overlapped with the pH of the solution increasing, and then some cracks and holes were generated. As a result, the cracks can accelerate the dissolution of montmorillonite. In the one-year contact diffusion test, the diffusion depth of the KOH solution with pH=13.8 exceeded 7.5 mm, and the newly formed illite crystallites were observed on the contact surface between the alkaline solution and the bentonite. It is confirmed that the strong alkaline solution will cause montmorillonite dissolution and illitization.

Due to their strong polarity, phenolic compounds cannot be directly determined by Gas Chromatography-Mass Spectrometry. Derivatization can reduce the strength of the polarity of phenols, and improve the detection sensitivity. However, the traditional derivative steps are tedious, with many interference factors and complex operations. By applying improvements to the traditional pretreatment method, phenols in groundwater were measured through solid-phase membrane extraction combined with Ultrasonic Derivatization-Negative Chemical Ionization Mass Spectrometry. The membrane was transferred into a derivative bottle after extraction, and then the elution and derivatization were processed simultaneously using ultrasound. The solution was determined by Gas Chromatography-Negative Chemical Ionization Mass Spectrometry directly. By determining the spiked samples at different concentration levels, the recoveries of the method for target components are in the range of 70%-90%, the detection limits are 0.25-0.35 μg/L and relative standard deviations (RSD) are less than 10%. The proposed method simplifies the traditional tedious steps by using 2 mL acetone for elution and derivation. All target objectives have good recoveries. Due to conducting the elution and derivation processes in an airtight environment, less interference factors were introduced without the problem of secondary pollution, and consequently the data were more reliable.