KAFKA: Compartment model for flow dynamics and solute transport in a converging underground waste repository (Kompartimentmodell für die Ausbreitung und die Fluiddynamik in einer konvergierenden Untertageanlage für Abfälle)

KAFKA (Kompartimentmodell für die Ausbreitung und die Fluiddynamik in einer konvergierenden Untertageanlage für Abfälle, compartment model for flow dynamics and solute transport in a converging underground waste repository) is a numerical software package for simulating flow and transport processes in underground salt rock repositories for radioactive waste disposal.

The latest version, KAFKA3, was developed by CSD Engineers AG, Aarau, Switzerland, for the Federal Company for Radioactive Waste Disposal (BGE), Germany, based on in its previous version, KAFKA2. It uses a site-specific structural model representing repository conditions through simplified compartments and solves flow and transport equations using the finite-volume method.

KAFKA accounts for effects such as two-phase gas/liquid flow, density-driven flow, repository flooding, salt rock convergence, mineral transformation, solute transport with sorption, solubility, radioactive decay, as well as gas generation.

Key updates in KAFKA3 include a revised numerical approach, an alternative gas generation model considering water availability, a generalized re-dissolution process for mineral reactions and the consideration of capillary effects. These enhancements improve flexibility for assessing closure measures, emergency scenarios, and long-term safety through deterministic or probabilistic calculations.

In our presentation we detail the design principles, discuss the numerical approach, show verification examples and demonstrate a generic application in combination with probabilistic uncertainty and sensitivity analyses.