The aim of this work is to study the Leak Tightness of the closure systems of nuclear pressure equipment during all situations including in-service operating, emergency and accidental conditions. The analysis is performed using a complete 3-dimensional finite element model of the closure system including : the studs, the gasket, the contacts between the gasket and their seating surfaces (contact elements), the nuts, the cover, the part of the shell on which the opening is located and the tightening preload of the studs. It comprises 2 main phases:

(a) Using the 3D model, with non linear internal parameters converted in appropriate linear that allows performing linear analyses, we select, with respect to leaktightness, the most critical thermal and pressure transient among a large amount of transient. This selected transient presents the weakest compressing force between the gasket and its seating surfaces, which is the selection criterion.

(b) Then, using the 3D model we perform a full non-linear analysis of the selected transient, taking into account the non linearity of the contacts as well as the non linearity of the gaskets and the tightening preload of the studs.

Thus for this transient, we obtain the history of the compressive forces on the gasket and particularly the history of the metal-metal contact for the gaskets multi-ring type (metallic-graphite-metallic) and we can check if compressive forces remain effective.

An important consequence is the re-calculation of the tightening preload applied to the studs if the intensity of the metal-metal contact is not sufficient.

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