PSI - Issue 60

R.P. Pandey et al. / Procedia Structural Integrity 60 (2024) 324–334 R.P. Pandey/ StructuralIntegrity Procedia 00 (2023) 000 – 000

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represents the pull-out strength of the joint as different temperatures. It may be noted that the pull-out strength of the joint is 680 kN at room temperature (27 o C) and it reduces to 475 kN at operating temperature of 300 o C (approximately). At 627 o C (severe accident regime), it can reduce to below 100 kN. This data is important in order to study the progress of channel disassembly during postulated severe accidents in PHWRs.

Fig. 12: Load-displacement data as obtained during pull-out process of pressure tube from the PT-EF rolled joint at different temperature. The maximum load signifies the pull-out strength of the joint.

6. Conclusions In this work, 3D finite element simulation of the rolling process between the Zr2.5Nb pressure tube and end-fitting of 220 MWe Indian PHWR has been carried out in order to evaluate the residual stress distribution at different regions and its effect of pull-out strength of the joint at different temperatures. The following conclusions can be derived from the work presented in this paper.  The residual stresses are generates due to the difference in nature of deformation of pressure tube (which is being plastically rolled) and the end-fitting, which mainly remains in elastic state due to its large thickness.  After retrieval of the roller, the stresses in the pressure tube is overall compressive in nature, whereas the end fitting retains the tensile residual stress.  The pattern of residual stress changes significantly due to presence of grooves and the flow of pressure tube material into the grooved region of the end-fitting during the rolling process, effectively locking the tube with tube end-fitting.  The stresses change to tensile in nature near the grooved edges, which are contact with pressure tube and these are significant from point of view of structural integrity of the pressure tube.  The pull-out strength signifies the maximum load in the load-displacement data as obtained during axial pulling of the pressure tube from the locked grooves of end-fitting and it decreases significantly at higher temperatures.  The data of residual stress and pull-out strength at different temperature are important to study progression of channel disassembly during postulated severe accidents in Indian PHWRs. References Abselesalam U.A, Dokainish M.A., 1993. Tube-to-tubesheet joints: A review and finite element analysis. In: International conference on expanded and rolled joint technology, (Toronto, Ontario: September 13-14, 1993), Canada: Canadian Nuclear Society, C73-C96. Alexouli, D., Bøjesen D., Bøystrup L.R., Klose C.R., Nikolov G.N., 2017. Parameter study and a numerical model of mechanical roller expansion of tube-tubesheet joint, In: Proceedings of the fifth student symposium on mechanical and manufacturing engineering, Wisconsin, USA. Al-Aboodi M.N., Shuaib A.Y., and Al-Anizi S.S., 2006. FEA of the effects of initial tube-tubesheet clearance, wall reduction and material strain hardening on rolled joint strength. Proceedings of the ASME 2006 Pressure Vessels and Piping: Volume 3: Design and analysis, (Vancouver, BC, Canada: ASME 2006 PVP, ICPVT-11, July 23 – 27, 2006), NewYork: American Society ofMechanical Engineers, pp. 267-273.