Current Understanding and Modeling of The Aging of Cementitious Waste Forms—A Hanford Site Perspective

Cementitious waste forms, or waste forms produced in ambient conditions (termed grout in the U.S.) play a crucial role in nuclear waste management strategies. These waste forms allow for incorporation of a number of different waste types (e.g., solids, liquids), overcome volatility challenges, provide low-cost production methods and allow the tailoring of final waste form properties through formulation design. With the hydration or polymeric reactions that make up this class of waste forms the matrix continues to age and evolve with time. Depending on the disposal site location for a cementitious waste form, being able to track and predict these evolutions is crucial to evaluating the waste form performance within the disposal facility in a performance assessment. A wide range of mechanisms and processes are possible for cementitious waste forms and the dominant and passive ones change with the disposal environment As such, site- and material-specific R&D is required to provide a technical underpinning to support long-term disposal modeling. This presentation will cover recent efforts at the U.S. Department of Energy Hanford site to further both the understanding of key mechanisms and processes to cementitious waste form aging at the site (e.g., oxidation, carbonation, Ca leaching) and approaches to capture these processes in long-term models. Several multi-institute reviews in the U.S. have highlighted a need to update and harmonize the modeling approach for grout materials at the Hanford Site to account for time-dependent processes (e.g., carbonation) that control bulk mechanisms (e.g., cracking). This presentation will also cover an overview of a U.S. Department of Energy Office of Environmental Management project using a multi-organization expert team to produce conceptual models for grout aging at Hanford that can be applied in PAs using a <i>Hanford Grout Modeling Framework</i>.