Speaker
Description
Crushed Salt is used as a backfill material for closing nuclear waste repositories, with the advantage that this is a residual material of e.g. salt mining. As backfill it has different functions such as mechanical stabilization, heat transport and sealing. Numerical simulations play a crucial role for the long-term assessment of these safety functions and in enhancing our understanding of repository systems. Simulations are instrumental not only in the safety analysis of repositories, but also in aiding the search for suitable repository sites. High-quality constitutive models are indispensable for these simulations, ensuring accurate and reliable results. The visco-plastic material behavior of crushed salt deformation can be decomposed in compaction creep, dislocation creep, fracture and grain rearrangement creep and pressure solution creep [1]. In this contribution, a constitutive model that handles the above-mentioned deformation mechanisms is presented. The underlying mechanisms for creep are derived from the examination of microscale processes within a Representative Volume Element (RVE). Compaction and dislocation creep initially occurs in the grain contact zone, where the applied stress is localized. A high void ratio at the beginning of creep process leads to an increased creep rate. Pressure solution creep is modeled as a diffusion-controlled process in the contact zone. The creep rate is derived from the mass balance of salt ions. The material model is implemented in the Finite Element software JIFEMP and calibrated by an experiment of the KOMPASS II project [2].
[1] Munson, D., \& Dawson, P. (1984). Salt constitutive model using mechanism maps. The Mechanical Behavior of Salt. Proc. Of the First Conf. On Salt, 673–680.
[2] Friedenberg, L., et al. (2024). KOMPASS-II: Compaction of Crushed Salt for Safe Containment - Phase 2. Gesellschaft für Anlagen- und Reaktorsicherheit (GRS).
