Strength problems of reactor steel pressure vessel of large dimensions

The production of an operationally reliable pressure vessel for the reactor is one of the difficult tasks encountered in many projects of large nuclear power stations. These steel vessels have large dimensions (diameters from 3 m to 8 m) and a comparatively high internal pressure so that the basic wall thickness is sometimes amounting to several tens of centimetres. According to the type of nuclear reactor it is possible to divide the pressure vessels in the bodies working at high temperature (>250°C) and low temperature (<250°C). This paper concerns the second group of vessels, where it is not necessary to consider the creep of metals. In particular, the effect of size on quasi-brittle strength of pressure vessel steel and the effect of pulsating loads on the strength of vessels are discussed. It is emphasized, that the selection of materials, shape and size of large welded reactor pressure vessels only on the basic of standard tests of mechanical properties of materials performed with small test specimens is completely inadequate. Special attention is called to the great importance of the size factor.