Calculation of SIFs for semi-elliptical surface cracks in U-shaped bellows expansion joints of Es-Salam research reactor vessel

Abstract

Expansion joint (EJ) of Es-Salam research reactor (RR) vessel as an element for deformation compensating is subjected to the axial load due to thermal expansion and often work under hostile environment (corrosion, radioactivity, etc.). As some local regions with high elastoplastic strain of bellows type EJ undergo cyclic loadings caused by startup and shutdown and changeable operating conditions of RR, they can be ruptured by crack growth. Therefore, it is necessary to evaluate the influence of cracks to structural integrity of EJ of Es-Salam RR vessel. The fracture criterions as stress intensity factor (SIF) or J-integral (JI) are used to evaluate the resistance to fracture of the constructions with cracks. The SIF is a parameter, which is used to estimate a material resistance to brittle fracture.In the present study the problem of calculation of the SIF of semi-elliptical crack (SEC) located in the stress concentration areas of EJ installed between the lower barrel and the upper barrel of a RR pressure vessel is numerically solved by advanced global-local finite element (FE) analysis. The crack locations are considered at the intersection of the various parts that construct the EJ. The modeling details and methodology, employed in the analysis, are extensively discussed and the numerical approach is proven to be efficient for the SIFs calculation of EJ semi-elliptical cracks. The proposed methodology using software ANSYS was validated by applying the analytical methods (according ASME requirement and R6 method) and also a finite element method but using software ABAQUS. It was received that SIF data are in close agreement. It was demonstrated that applied methodology for modeling of the SIF can be used.