Advancements in immobilization of cesium and strontium radionuclides in cementitious wasteforms—a review

The safe and secure encapsulation or immobilization of nuclear waste, particularly low to intermediate-level waste (accounting for ∼97% of the total volume of nuclear waste), has been a significant concern. Consequently, numerous studies have been conducted on various materials such as ordinary Portland cement-based, bitumen, and ceramics for the purpose of waste encapsulation/immobilization. However, these studies generally offer a broad overview of materials performance without focusing on specific radioisotopes of concern. Cesium (Cs) and strontium (Sr) are important radioactive nuclides to consider for encapsulation, but the existing studies on immobilizing these elements are fragmented and lack a comprehensive understanding. This critical review article offers a thorough qualitative and quantitative analysis to uncover the primary trends/knowledge gaps within the field. It comprehensively delves into waste classifications/management and leaching assessments, followed by an exploration of the immobilization performance and durability issues of various traditional and advanced cementitious materials including low-temperature chemically bonded ceramics such as alkali-activated matrices and Mg‒K phosphates for the immobilization of Cs and Sr. Furthermore, the review article provides fresh insights and perspectives, including recommendations for improvements, novel technologies, and future trends in this domain

Energy analysis of brittle fracture and its application to zirconium-oxide ceramics

The most useful properties of ceramics (high temperature strength, chemical inertness and hardness at low density) are accompanied by brittleness. This is still the main factor limiting widespread application of ceramic materials. In the present thesis an energy approach to fracture of ceramics was undertaken and refined to account for a nonelastic behaviour of these materials. A chevron-notched (CN) four-point bend specimen was recognized as effective experimental arrangement for room and elevated temperature tests. Consequently, a number of theoretical studies of the specimen's performance were undertaken. Modelling of the variation of the strain energy release rate with the crack extension revealed that the subcritical crack growth in a CN specimen causes dependence of the measured fracture parameters on the experimental procedure (stressing rate, stiffness of the testing system, crack length). It appears that, as complete fracture is approached (i.e. 100% of the specimen's cross-section), the measured work-of-fracture approaches that required for crack initiation. An electrical potential drop technique for crack length measurement in the CN specimen was developed for elevated temperatures fracture studies in the ionically conducting zirconium oxide ceramics. The resistance-to-fracture versus crack extension was determined for a range of temperatures (25 to 1300℃) for stabilized zirconias and their HfO₂ solid solutions and with second phase p-Al₂O₃ particles dispersed in them. The room temperature results agreed with the literature data and model predictions. Above 1000℃ an energy input of ⁻1 J/m² is required to drive the crack through zirconium oxide ceramics. Viscoelastic effects and crack interaction with p-Al₂O₃ particles result in a total fracture energy dissipation two orders of magnitude higher.Doctor of Philosophy (PhD