The safe geological disposal of low- and intermediate-level radioactive waste relies on a passive multi-barrier system. This paper presents the provisional Swiss design for the low- and intermediate-level waste (L/ILW) emplacement caverns and their expected evolution. In the current design, containers are stacked within the L/ILW disposal caverns, and the remaining void space is backfilled with a porous mortar. Because cementitious materials are used in large quantities, they largely determine the geochemical conditions in the L/ILW near field. A key property of these cementitious materials is their ability to maintain a high-pH porewater environment. Such conditions limit the degradation of organic materials and suppress microbial activity. They also promote the passivation of metal surfaces, resulting in slow corrosion rates and consequently reduced gas generation. The chemical evolution of the near field is strongly coupled to the repository’s saturation history, as water is required for chemical reactions such as for the corrosion of metals, degradation of organic matter or pozzolanic reactions. Given the low permeability of Opalinus Clay, water availability in the caverns is limited, and partially saturated conditions are expected to persist for several hundreds of thousands of years. These conditions help maintain elevated pH levels, particularly in the unsaturated regions of the emplacement caverns. The substantial presence of cementitious materials also enhances the retention and slow release of radionuclides from the L/ILW near field into the host rock, once the waste packages breach. As a result, the L/ILW near field contributes to key safety functions, including immobilization, retention, and controlled release of radionuclides, as well as ensuring compatibility among repository components. The properties and long-term behaviour of these components are sufficiently well understood to allow a robust description of their evolution over extended timescales, supporting the demonstration of their barrier function and long-term performance.