[en] Study of plastic failure during LOCA, as carried out by previous investigators, appears to take insufficient account of certain potential mitigating effects associated with the loading condition. The study is aimed at clarifying some of these, such as, (1) the axial non-uniformity of the pressure distribution, (2) the effect of rise time (non-impulsive loading), and (3) elastic unloading (e.g., during an axially traveling wave). The report deals with Phase I of the project. It is found that there is a slight reduction in the fundamental component of the response to the excitation. However, the first harmonic component of the response is not insignificant, and so the hoped-for improvement in the response behavior does not materialize. Study of Phase II of the investigation is about to be started. In the light of recent studies by many workers in the field, Phase III no longer seems to be propitious, and in the conclusions of the report a modification is suggested