[en] The state of the art in the technology of pressure vessels and piping of the primary cooling circuit of nuclear steam supply systems is discussed. Design and analysis are considered in the frame of the two types of nuclear reactor retained in France (PWR and the pool type LMFBR). Designing nuclear pressure vessels asks for some more specific Codes and Standards than for conventional vessels, and the stress analysis complementing by a direct comparison between operating loads and failure loads is a mandatory practice in France. As for pool type LMFBR, the structural problems of the nuclear vessel are essentially due to component shape, small thickness, and large stress range