[en] In a containment composed of a concrete structure with a steel liner plate attached to its interior face, the liner's function is to isolate the containment atmosphere from the environment, even in case the concrete is cracked. To perform this function the liner must be absolutely leak-tight. The response to Earthquake ground motion is found by representing the containment as a distributed mass beam, and considering only the first vibrational mode. Depending on the extent of cracking, the response will be between that of a shear beam and that of a cantilever beam. The stresses at any point are found then from internal forces, as a combination of the stresses from a shell model (with mainly membrane action) and the stresses from a beam model, in which horizontal planes remain plane. The resulting stresses and strains in the liner reveal that although the liner might yield under very high ground accelerations, its high ductility will prevent it from tearing. As the average performance of the liner will be satisfactory, we next seek potential localized weak points in it. We identify the seam welds between adjacent liner panels as such points, and weld defects as potential crack initiators. Statistics concerning the size and frequency of occurrence of weld defects in structures similar to the liner plate are used. Assuming that the provisions of the ASME-ACI code, regarding sampling and radiographe examination of welds, are applied, we find the frequency of occurrence of various sizes of defects after examination and the cold-pressure-test