In all three joint research projects several codes have been used to calculate smart Kd‑values as function of relevant environmental parameters (e.g. DIC, pH, Ca, etc.) and to apply these smart Kd-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 Kd‑values,
- on the other hand we use smart Kd-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 Kd‑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.