3D-non-linear dynamic analysis of PWR reactor vessel internal with SYSTUS - formulation of a new friction element

A 3D structural dynamic analysis of PWR internals, and vessel under a loss of coolant accident loading (LOCA) has been performed with FRAMATOME's FEM code 'SYSTUS'. The structural response is computed by using the non linear modal superposition method. It consists of analysing a highly non-linear system including unidirectional impacts, concentric impacts and friction elements. (45 geometric non-linearities). A COULOMB friction element has been developped to take into account the relative behaviour between rods and the frame of fuel assemblies. The theoretical description of friction element is described in annex. Friction modelization has a high level influence on results because of the important mass of rods (1/3 of reactor). Extension to a 3D modal gives a more realistic motion of internals and vessel. Results show a good agreement with a previous 2D calculation using direct integration method. (orig.)