Modeling steel corrosion failure in reinforced concrete canisters (RMCCs) containing low-level radioactive waste (LLRW)

Sablan, Gregory Anthony
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The disposal of radioactive waste of all types and levels is of great concern today. Radioactive waste disposal itself is not new—procedures for its handling, safeguards, regulation, and implementation from the creation of waste to its final disposition continue to develop. Technologies spanning the last six decades enable the storage of hazardous materials over the long-term. Long-term disposal in the United States however, only applies to Low-Level Radioactive Waste (LLRW). Currently, legislation does not permit the final disposal of any other types of waste. Because LLRW is the only form of radioactive waste that is disposed of today, the precautions and conditions for setting it to its “final resting place” are important matters. At the Federal Waste Disposal Facility located in Andrews, Texas, LLRW is stored in what are called Reinforced Modular Concrete Containers (RMCCs) and are intended for final disposal deep underground. These RMCCs are initially checked for structural integrity to handle significant loading. While these RMCCs are designed to remain structurally sound under these loads, these concrete structures are susceptible to corrosion because of its steel reinforcement. When corrosion at the steel occurs, the RMCC will inevitably fail. The service life of the RMCC studied is calculated to be at least 300 years under ideal conditions. However, the design does not inherently consider the effects of corrosive elements that may be present in LLRW. This thesis provides a predictive model of the service life of the RMCC under the failure mechanism of steel corrosion by chlorides. Chloride concentrations in the LLRW will eventually make contact with the RMCC’s walls and will diffuse through concrete’s relatively porous network. Varying the mix designs between different cementitious materials, its water-to-cement (w/c) ratio, temperatures, and chloride exposure are critical to maintaining the RMCC’s service life. It shows that less supplementary cementitious materials, a higher w/c ratio, higher temperatures, and higher chloride concentrations lower the container’s time to failure. This information is critical to subcontractor construction of the RMCCs and confirms its suitability for long-term disposal of LLRW.