Some Aspects of Inclusion of Loading History in the Fracture Strength Analysis of Reactor Pressure Vessels Under Thermal Shock Conditions.

The paper addresses some aspects of inclusion of loading history in the fracture strength analysis of reactor pressure vessels under thermal shock conditions. The strength assessment of a reactor pressure vessel and its lifetime extension are shown to essentially depend on reliability of results of elastic-plastic modeling of stress-strain kinetics and determination of design values of the fracture mechanics parameters. The present findings of the finite-element analysis demonstrate that the loading history must be taken into account in the determination of the temperature dependence of stress intensity factor for a postulated specified crack. It is shown that, in the fracture toughness analysis of a reactor pressure vessel, the temperature dependence of the stress intensity factor has to be derived from the results of the analysis of kinetics and mode of loading of metal at the crack tip under thermal shock conditions. For construction of the above dependence, we proposed approach, which accounts for the active loading and unloading processes occurring in the metal in the crack front vicinity. Incorporation of the loading history into the analysis of the temperature dependence of the stress intensity factor using the proposed approach forcan permit revealing some additional margin of strength during the substantiation of lifetime extension for a reactor pressure vessel under thermal shock conditions. [ABSTRACT FROM AUTHOR]