The 2-way FEM simulation of the HDR blowdown. The simulation is performed by coupling in the ADINA-FEM code with the potential based fluid and the structure. Here, the structure is non-linear, with sliding contact at the core barrel flange, pre-stressed bolts, and plastic material model, and also the potential based fluid is non-linear because the subsonic variant is used. Hence, the pressure at the break location can be used as boundary condition. The model is initialized to full pressure before the start of the blowdown transient, since the non-linear model requires that all loads are applied simultaneously.