Semipermeability of concrete for hazardous waste containment

Abstract

Low-level waste is stored in multilayer, overlapping barrier systems for long-term containment, which serve as the primary barrier against leakage. Reinforced concrete is typically used as the container material for radioactive wastes, making the material properties paramount for contaminant control. Strength, density, corrosion resistance and permeability are regulated. This study examined the physico-chemical properties of high-density, lower-permeability concrete for potential to hyperfiltrate chloride solutions (185 and 345 parts per million) under relatively low hydraulic head, similar to encasement. Four hyperfiltration experiments were conducted on intact concrete discs, two experiments for each solution at hydrostatic heads of 0·5 and 1·0 m. Chloride concentrations measured within the experimental cells showed an increase ranging from 126% to 152%. Reflection coefficients ranged from 0·15 to 0·19, suggesting that low-permeability concrete discs exhibit measurable solute rejection capabilities. External chloride penetration may initially be hampered. However, once steady state had been established and salt penetrated at a fixed rate, the concentration polarization layer (CPL) provided a source for continued penetration. With the CPL adjacent to a container, corrosion may accelerate in the reinforcing rebar due to the high chloride concentration and chemical gradient within the pores. The application of electro-osmotic pulses can reverse chloride intrusion.

Editorial

“…In the last paper, Hart et al (2016) examined the physico-chemical properties of high-density concrete in order to evaluate its use in low-level radioactive wastes containers. These radioactive waste barrier systems have the aim of preventing the ingress of groundwater into waste and also of retarding or temporarily mitigating the migration of radionuclides from the waste to the surrounding environment.…”

“…However, the osmotic behaviour of concrete barriers also leads to the formation of a polarisation layer, adjacent to the high pressure side of the barrier, which can cause rapid deterioration of the leading edge-reinforcing members due to their greater exposure to chloride, sulfate and other ionic solutes. Laboratory tests conducted by Hart et al (2016) to investigate the ability of high-density/low-permeability concrete to hyperfiltrate chloride solutions show that, once steady state conditions have been established, diffusion, driven by the high gradient that occurs due to the formation of the polarization layer, can determine the penetration of salt into the barrier and the consequent corrosion of the reinforcing rebar.…”