Experimental study and evaluation for the blocking effect of freezing method on nuclide seepage based on multiple indicator testing

The emergency control of nuclear contaminated water leakage using artificial ground freezing (AGF) method has good application prospects, but the actual blocking effect is not ideal at present. To promote the solution of this problem, this paper designed a test system for evaluating the impermeability of freezing method, and it conducted blocking seepage tests with I nuclide solution. Based on the results of multi-parameter monitoring during the test, evaluation indicators, grading criteria, and a risk assessment diagram for blocking nuclear contaminated water with freezing were proposed. Furthermore, the blocking mechanism of freezing method on nuclide seepage was ultimately revealed through the integral calculations of ice volume in frozen wall. The research found that the number of freezing tubes is the main controlling factor determining the critical initial flow rate of frozen wall. The permeability coefficient time-history curve can be used to identify the local melting phenomenon of frozen wall within a certain period. The increase in osmotic pressure difference and the permeability coefficient can compensate for the insensitivity of the temperature field to changes in flow rate. The accelerated growth of ice crystals, driven by the migration and phase transition of capillary-film water from unfrozen pores to macropores under an increased number of freezing tubes and without seepage, is the key factor contributing to the significant improvement in seepage prevention. This study provides effective references for exploring the blocking mechanism of freezing method on nuclear contaminated water, early warning of frozen wall disasters, and optimization of artificial freezing parameters.