Failure mechanism and risk decision-making process of frozen soil wall for blocking nuclear contaminated water leakage: A laboratory study

Abstract

Under the influence of seepage erosion and nuclide decay heat release, the frozen soil wall constructed by artificial ground freezing method (AGF) to prevent nuclear leakage is prone to occur local ablation and impermeability failure. To ensure its long-term safety and effectiveness, this study conducted a series of laboratory tests to assess the blocking effect of frozen wall to nuclide seepage using the designed impermeability test system. After identifying the critical initial state, the failure mechanism under different conditions was revealed, and a risk decision-making process for AGF disposal of nuclear leakage was proposed. The results show that under the condition of environmental temperature increase, the deterioration effect of frozen wall caused by the cessation of freezing tube is more obvious than that of nuclide continuous seepage. Under the coupling effect of environmental temperature rise and seepage, the monitoring index will appear “pseudo normal” phenomenon, and the anti-seepage performance of frozen wall will suddenly fail after a certain time. The critical temperature and the second critical flow rate determine whether ice crystals appear between soil particles and whether the nuclide solution can penetrate into small pores to further accelerate the deterioration of frozen wall, respectively. It is recommended to determine the risk level in the order of frozen wall temperature, osmotic pressure difference, flow rate, and permeability coefficient. If the risk level is at the fourth level, measures such as increasing the number of freezing pipes and rapid cooling should be taken to quickly respond to the emergency.