Author: Michal Balatka,¹⁾ Jiří Maryška, Andrea Kobík Valihorová

Institute of Mechatronics and Computer Engineering (MTI)
Faculty of Mechatronics, Informatics and Interdisciplinary Studies (FM)
Technical University of Liberec (TUL)

EBscape is a software tool for simulating the escape of radionuclides from a disposal package containing spent nuclear fuel (SNF) through a bentonite buffer and a rock layer in a deep geological repository.

The simulation includes:

• radioactive decay of isotopes,
• failure of the disposal package (hereafter also referred to as the “container”),
• degradation of fuel rods,
• dissolution of radionuclides,
• diffusion and sorption of radionuclides in the bentonite (buffer) and the surrounding rock.

Simulation results can be visualized using the OUTIMEPLOT application.

The domain of the task includes engineered barriers for SNF disposal from nuclear power plants and the surrounding rock, where radionuclides can migrate by diffusion only (not advection).

Model domain and dimensionality:

• Container (0D model)
• Bentonite buffer (radial 1D model)
• Surrounding rock (radial 1D model)

EBscape uses a two-phase fuel degradation model:

1. Dry phase: No water is present in the container; only radioactive decay of intact SNF takes place.
2. Wet phase: The container is instantly flooded with water, triggering:
   1. Dissolution of the instantly released fraction (IRF),
   2. Degradation of intact SNF (fuel rods) into degraded SNF (“sand”),
   3. Dissolution of the degraded SNF,
   4. Migration of radionuclides through the bentonite buffer (diffusion, linear sorption).

Unless radioactive decay is explicitly disabled, it continues throughout the simulation.
Intact SNF does not dissolve; it only degrades. Only degraded SNF dissolves.

EBscape does not model the gradual corrosion of the container over time, as it focuses on long-term evolution.

Each simulation scenario is configured using an input file in YAML format, containing the following sections:

• simulation_params – basic simulation parameters (time steps, number of iterations, included processes),
• output – output data specification (output interval, selected quantities, CSV format),
• container – disposal container parameters (dimensions, fuel degradation, transition to wet phase),
• bentonite – properties of the bentonite buffer (thickness, density, diffusion coefficients),
• granite_layer – definition of the rock layer, if active as a transport medium,
• isotopes – list of isotopes, their half-lives, diffusion, and sorption properties.

Example configuration file

Outputs are generated in CSV format. They contain a time series of radionuclide concentrations at different points in the system:

1. In the container – amount of fuel and its dissolved fraction,
2. In the bentonite – diffusion and sorption of radionuclides,
3. In the rock – cumulative outflow of radionuclides from the bentonite.

Output example