Kandala S. Resource of elements of the internal casing devices of the WWER-1000 reactor, taking into account residual welding stresses

In Ukraine, most power units of nuclear power plants of the WWER-1000 type operate in an above-design mode. The substantiation of the extension of the resource of the structural elements of the WWER-1000 reactor, such as the Internal Components (IC), is carried out using calculation methods, and the accuracy of the calculations, in order to correctly estimate the period of safe operation of the power units, must be constantly increased. When extending the service life of the IC, the most difficult and urgent problem is the radiation swelling of structural steel 08H18N10T (AISI 316), from which the structural elements of the IC are made. In particular, due to the degradation of the mechanical properties of the material and progressive deformation, which is mostly caused by radiation swelling and creep. According to regulatory documents and modern concepts of fracture mechanics, when calculating the substantiation of the extension of the resource of the responsible structural elements of the nuclear power plant, it is necessary to take into account the residual stresses associated with the manufacturing technology. Usually, when calculating the substantiation of the life extension of IC, the residual stresses after welding and subsequent heat treatment are not taken into account, as it is considered that their level is quite low and does not affect the stress-strain state (SSS) of the structure as a whole. The relevance of the problem: the baffle and the barrel are elements of the IC that determine and limit the residual resource of the WWER-1000 reactors when the service life is extended. The influence of residual technological stresses on the life of the elements of the IC has not been investigated before. The purpose of the investigate is to carry out a calculated assessment of the kinetics of changes in the clearances between the baffle, barrel and fuel cells, as well as the strength (resistance to brittle failure) of the baffle of the WWER-1000 reactor, taking into account the residual welding stresses to substantiate the extension of the period of safe operation (up to 60 years) under conditions of intense radiation exposure . The object of the investigation is the thermo-deformation technological processes of manufacturing and operation in conditions of intense radiation exposure of structural elements made of austenitic steel 08H18N10T (AISI 316). The subject of the study is the determination of the resource of the baffle and the barrel of the WWER-1000 reactor during long-term operation of up to 60 years under conditions of radiation exposure, taking into account the residual technological stresses after the welding and heat treatment processes associated with the technology of welding and post-weld heat treatment.