GOTHIC is an advanced code for thermal-hydraulic flow simulation in nuclear reactor containments and other confinements. Battelle Europe has participated in the development and verification of the code over a number of years.

Described are blind and open posttest calculations of the Heiss Dampf Reaktor hydrogen-mixing experiments E11.2 and E11.4 in comparison with measured data.

Caused by a miscalibration of steam source flow rates and neglect of the heat sink capability of the instrumentation cooling lines, the pressure, temperature, and steam concentrations were drastically overpredicted by the blind predictions and are quantitatively not comparable to experimental data.

The following conclusions can be drawn from the parametric open posttest calculations:

1. Scenarios with homogeneous containment atmosphere (like E11.4) can be simulated accurately with lumped-parameter models.

2. The lumped-parameter method is seemingly not fully qualified to predict the hydrogen distribution in a stratified containment atmosphere (like E11.2).

3. Improved predictive quality may require the application of distributed parameter models.