open access

https://hdl.handle.net/2115/73039

Modelling Long-Term Durability Performance of Cementitious Materials under Sodium Sulphate Interaction

英語

radioactive waste disposal

2018-12

MDPI

Applied sciences

8(12)

2597

Cementitious materials are one of the essential components for low- and intermediate-level waste disposal sites. Low-level nuclear waste from power plants consists of highly concentrated (similar to 25 wt %) Na2SO4, and the wastes are solidified with cementitious materials. Degradation of cementitious materials that result from chemical and physical sulphate attack is a major concern in the safety of the waste disposal. In this study, hydration and reactive transport models, developed in previous works by the authors, were applied with Pitzer interactions coefficients to evaluate the long-term performance of Port-land cement (PC) solidified with high concentration of Na2SO4. Expansive sulphate-bearing products of ettringite and mirabilite were formed and filled the pores in the hydrating PC with 25% of Na2SO4 by weight, but they were destabilised as temperature increased. Influence of Na2SO4 concentration and temperature on mineralogical changes is discussed. The simulation results from the reactive-transport model showed that the degradation of solidified Na2SO4 waste by cementitious materials exposed to 10% Na2SO4 for 1000 years is due to dissolution of mirabilite and secondary formation of ettringite, but not Na2SO4 crystallisation. The phases and porosity became stable close to exposure surface after 10 years, although the deterioration progressed from the surface to core with exposure time.

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© 2018 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/).

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