Abstract
The paper investigates the long-term durability of concrete barriers in contact with a cementitious wasteform designed to immobilize low-activity nuclear waste. The high-pH pore solution of the wasteform contains high concentration level of sulfate, nitrate, nitrite and alkalis. The multilayer concrete/wasteform system was modeled using a multiionic reactive transport model accounting for coupling between species, dissolution/ precipitation reactions, and feedback effect. One of the primary objectives was to investigate the risk associated with the presence of sulfate in the wasteform on the durability of concrete. Simulation results showed that formation of expansive phases, such as gypsum and ettringite, into the concrete barrier was not extensive. Based on those results, it was not possible to conclude that concrete would be severely damaged, even after 5,000 years. Lab work was performed to provide data to validate the modeling results. Paste samples were immersed in sulfate contact solutions and analyzed to measure the impact of the aggressive environment on the material. The results obtained so far tend to confirm the numerical simulations.
Highlights
Concrete barriers are viewed as a potential solution to store contaminated wasteform resulting from nuclear energy production processes
The paper presented the results of a study dedicated to the long-term performance of concrete barriers used in the context of nuclear waste storage
The work focused on the case of a cementitious wasteform immobilizing low-activity solutions and placed in direct contact with concrete
Summary
Concrete barriers are viewed as a potential solution to store contaminated wasteform resulting from nuclear energy production processes. In this context, concrete is expected to act as a contaminant barrier for extended period of time. Wasteform in direct contact with concrete can compromise the integrity of the barrier due to the potentially high concentration of deleterious ionic species it contains. The multiionic transport model considers electrical coupling between the species, chemical activity effects due to high concentration levels, and the impact of temperature variations. The model was used to simulate the transport of species from the pore solution of a wasteform material through a concrete barrier in order to estimate the long-
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