Synopsis
The significance of the mechanical behaviour and condition of concrete for the stresses and deformations in prestressed concrete reactor pressure vessels is discussed with reference to the loading history. Approximate solution techniques for stress and strain analysis currently in use are described briefly and their relative merits discussed. Earlier work has shown that it is important, when evaluating vessel stresses and deformations occurring over a long period of time, to take into account the effect of previous loadings upon the capacity for creep under subsequent loadings. To determine this effect by simple means, an approximate uniaxial strain response function is used to derive curves from which the transient stress behaviour due to creep in unreinforced and reinforced prestressed concrete structures can be determined. It is deduced that, although bounds on stress can be derived for reactor start-up conditions (an initial elastic solution), andfor long-term reactor operation (a steady-state solution), the creep capacity may not be sufficient for the long-term bound to be approached very closely. If this is not appreciated, an unduly pessimistic view of long-term vessel stresses could be obtained.
