Abstract
Energy extraction from nuclear materials produces high-level radioactive waste. In geological nuclear waste storage repositories, the decay of radioactive elements generates heat, exposing the reservoir rocks to high-temperature conditions for long periods. To explore the effects of these conditions, this study examines the ability of granite to resist fracturing after thermal treatment for 10 h, 10 days, 30 days and 60 days. The results show that the fracture toughness of the granite remained basically unchanged for up to 10 days of thermal treatment. After thermal treatment for 60 days, the mode I, mode II and mixed-mode (I + II) fracture toughness decreased by 15.39%, 18.09% and 15.17%, respectively, compared with samples heated for 10 h. The change trends of the ability of granite to resist tensile, shear and mixed (tensile + shear) failure with an increased thermal treatment duration were basically consistent. Moreover, there was little change in its brittle fracturing characteristics with an increase in heating duration. Changes caused to the internal microstructure of the granite by high temperature were ongoing even up to 60 days.
Highlights
With the ongoing depletion of traditional energy sources, the development of nuclear energy has been receiving growing attention
When the temperature duration is 10 days, the fracture toughness of the granite is 1.0386 MPa . m1/2, a very small increase of 2.72% compared with the 10 h temperature duration
Granite samples were thermally treated for different periods (10 h, 10 days, 30 days and 60 days), and the semicircular bend (SCB) method was used to test their mode I, mode II and mixed-mode (I þ II) fracture toughness
Summary
With the ongoing depletion of traditional energy sources, the development of nuclear energy has been receiving growing attention. 500–1000 m canister with HLW underground repository storage, as shown, is one of the most effective methods of disposing of high-level nuclear waste [1]. The rock surrounding such repositories is generally granite. If the effects of long-term exposure to such high temperatures should cause the rock to fail, the nuclear waste will leak, which will cause major pollution in the underground environment. Nasseri et al [6] studied the fracture toughness, elastic wave velocities and microcrack density of Westerly granite, and found that thermal cracking caused a decrease in its mechanical strength and affected its dynamic elastic properties. Zhao et al [9] further showed that the permeability of granite increases significantly when heated above a critical temperature
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