[en] The main conclusions and recommendations of the UKAEA study group on PWR pressure vessel integrity are presented. The present paper summarizes a more comprehensive account of the work of the study group. This document reviewed the material properties and their variation, detailed the various reactor transient conditions and assessed a typical design against the possibilities of ductile and non-ductile failure. Critical crack sizes were assessed for all design conditions and special consideration was given to such reactor fault conditions as loss of coolant and steam-line break. A careful assessment was made of the rate of crack growth to be expected in service due to fatigue and corrosion effects. The role of the cold hydro pressure test in preventing vessels entering service with significant defects was discussed. The quantitative estimation of pressure vessel reliability is a problem in which account must be taken of the various material properties, crack sizes, and their variability. (Auth.)