In all three joint research projects several codes have been used to calculate smart K_d‑values as function of relevant environmental parameters (e.g. DIC, pH, Ca, etc.) and to apply these smart K_d-values in transport models that cover large areas and long time periods. We distinguish two related, but still different applications of the concept:

• On the one hand we are able to make statements on the sensitivity and uncertainty of K_d‑values,
• on the other hand we use smart K_d-values for transport simulations.

The interconnection of all codes, i.e. their application and the fundamental strategy of the coupling procedure is described in Fig. 1 and here. A brief description of the flow and transport code d³f++ and PHAST is provided, whereas all other codes are referenced by their respective original web pages and manuals. PHAST plays a special role insofar that it is only used for internal verification calculations.

• d³f++ is a computer code for efficient modelling of density-driven groundwater flow and transport over very long time frames in large model areas.
• PHAST, a program for simulating groundwater flow, solute transport, and multicomponent geochemical reactions (download).
• PHREEQC (Parkhurst and Appelo, 2013) is used for modeling speciation patterns of the investigated radionuclides including their sorption onto mineral phases (download).
• UCODE (Poeter et al., 2014) is used as data processor/interface. The main input file of UCODE controls the input parameters which have to be varied in PHREEQC: It defines which models to execute, which parameters to substitute, and how to extract the requested PHREEQC-computed output values. Furthermore, it is used to derive and assess suface complexation parameters (e.g. surface complexation constants (logK values)) from experimental data (download).
• SimLab is used for sensitivity and uncertainty analysis (SA/UA) of the smart K_d‑values. The code provides, in contrast to UCODE (where local SA/UA algorithms are incorporated), also methods for Global Sensitivity Analysis. This code is developed by the EU Joint Research Center (JRC) in Ispra/Italy and is available here.

Fig. 1: Flowchart of the coupled codes PHREEQC, UCODE and SIMLAB.