[en] A discussion is given on the safety issues for the pressure circuit components of the proposed Sizewell B nuclear power station. The detail of the evidence concentrates on the reactor pressure vessel itself, as the principal example of a component whose failure is considered incredible. The general background to construction and operation of pressurized plant is described. A description of the form of the vessel and its role is given. Each of the factors which lead to confidence in the integrity of the vessel is then considered. (U.K.)