Reliability of reactor components and systems subject to fatigue and creep

Abstract The operation of nuclear reactors at elevated temperatures involving pressure- and temperature-cycling as well as corrosion and irradiation is associated with the gradual deterioration of the mechanical resistance of their critical components. The rate of deterioration depends not only on the intensity of the loading conditions and the level of the operating variables, but is sensitive to their sequence and interaction. The lack independence that is reflected by the development, under operating conditions, of creep and inelastic cyclic strain, as well by the deterioration of the strength properties accompanying such deformation (creep rupture, fatigue), introduces additional potential failure modes or conditions, consideration of which, in the reliability analysis, shifts the emphasis of this analysis from the catastrophic limiting states of failure under remote extremal conditions, of recurrence periods that are large multiples of the design (service) life of the structural element or system, to states of significant structural failure that seriously affect the operability of the reactor but are repairable, as well as to conditions of relatively minor structural failure of reactor elements during operation that are critical because they might lead to escape of contaminating fission products. After basic consideration of the formulation of structural reliability analysis and risk assessment for major structural failures in nuclear reactor plant systems, a review of the problems of design for creep and fatigue — with interaction between creep and fatigue effects — under reactor operational conditions is given.