Next, the iteration stability of the GENESIS code for the highly voided condition, which would appear in a severe accident (e.g., design extension) conditions, is discussed.
Use of the effective diffusion coefficient and the artificial grid diffusion coefficients are found to be effective to stabilize the acceleration calculation in highly voided conditions.
The model includes a micro macro void nucleation condition, the initial penny shape nature of the voids, and the growth and coalescence regimes.
A parametric study on the ductility in uniaxial tension of materials with penny shape voids demonstrates the complex couplings existing between the void nucleation condition, the state of hardening, the strain hardening capacity and the particle volume fraction.
As for a natural circulation flow response, it is clarified that the response is strongly influenced by the effect of two-phase pressure loss owing to a high void fraction condition.
In order to obtain a more reasonable description of the actual engineering condition, the voids were considered as prolate ellipsoidal, and the influences of the instantaneous void shape changing, stress state and deformation history were taken into account for the void evolution.
Considering this effect in the iterative model significantly improved the predictions for large liquid slug void fraction conditions.
This operation recasts the flux into a Riemann space which is used directly to remove any incoming information, and thus satisfy void boundary conditions.
Both, benefits and limitations of the existent experimental approaches and their usefulness for model development and validation at these high void fraction conditions are discussed.
CTF uses a two-fluid, three-field representation of the two-phase flow, which makes it capable of modeling the high-void flow conditions expected in BWR operation.
