[en] A three-dimensional finite element analysis of the stresses in the upper part of a PWR vessel would represent a formidable task. Thus, it is of common practice to carry out a separate analysis of the various items (flanges, nozzles, head...) and to use approximate modelling techniques to reduce the computational effort. By doing this, it is not possible to assess the stress concentration effects and to appreciate the interaction between two elements. The need for more complete studies is evident in order to provide guidelines for the methods commonly used in stress reports. A comprehensive study of the pressure induced stresses in the upper half of a 3-loop PWR vessel was undertaken to satisfy this need by using an epoxy 0.1 scale model. With this model it is possible to represent the six nozzles, the two flanges, the spherical head, the studs and the holes in the flange and in the head. Prestressing in the studs is obtained through the use of helicoidal springs. The experimental technique is the so-called 'frozen stress' method. The results are compared with those of a three-dimensional finite element analysis of the head submitted to the combined action of pressure and stud reaction in order to make an assessment of the computational stress intensification effects near the holes. (Auth.)