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Gap Gas Model

The gap gas model handles the evolution of gap volume, pressure, temperature and composition. The specific gapGas model

The gap gas model type can be selected with the gapGas keyword in the main dictionary of OFFBEAT (i.e. the solverDict dictionary, located in the constant folder).

Warning

In the gapGas model the gap volumes typically refer to the portion of the rod actually modeled i the geometry. To illustrate this, let us consider a rod plenum volume of 36 cm3. If the rod is reproduced with a 2-degree wedge mesh, the plenum volume in the model is:

\[ V_{model plenum} = \frac{2}{360}\cdot\frac{36}{1e6} m^3 = 2 \cdot 10^{-07} m^3 \]

For TRISO fuels, let us consider a full sphere gap of 36 cm3. If the sphere is reproduced with a 2-degree wedge mesh (in 1D), its fraction compared with the whole sphere is

\[ fraction = \frac{(2\pi/180)^2}{4\pi}=9.696273622\cdot10^{-5} \]

So the gap volume in this TRISO model is

\[ V_{model} = 36\cdot10^{-6}\cdot9.696273622\cdot10^{-5} m^3 = 3.49\cdot10^{-9} m^3 \]

Classes

Currently OFFBEAT supports the following gap gas models:

  • none - This model neglects the presence of a gap gas model. This is the default choice in OFFBEAT if the user does not specify the gapGas model in the solverDict..
  • FRAPCON - This model takes into account the evolution of the gap and plenum volume, pressure and temperature. The calculation of the gap gas properties is mostly derived from FRAPCON.
  • TRISO - Similar to the previous model but applied to TRISO buffer-to-IPyC gap.