Characteristics Of Thermal Stress For A Prfessurizer Surge Line Using Finite Element Modelling

Thermal stratification is phenomenon which occurs when fluids of different temperatures co-exist in the same structure.The fluid with higher temperature is less dense and therefore makes up the upper layer of the flow,similarly the lower part of the fluid resides at the bottom.This can cause significant deformation of the fluid structure due to differential thermal expansion at the top and bottom of structure.In thermal plants pipes are usually constrained and as a result the deformation caused by thermal stratification causes unexpected piping movements,which produce excessive stress at the pipe in axial,circumferential,and radial directions,that may exceed the design limits for fatigue and stressesIn this paper a PWR surge line is analysed using CFD software(ANSYS CFX)and FEM solver,(ANSYS MECHANICAL)first several meshing models of surge line are designed in ICEM software and their performance is tested in a steady state analysis.The mesh which is least sensitive to change is mesh is chosen and the temperature profile is exported to FEM solver.Their Structure analysis code is used to determine the thermal stresses applied on the pipe as well as the response characteristics of the structure.Furthermore the temperature profile of surge line in the in-surge case is also investigated in a transient thermal analysis.The results showed large steady state stress present at the edges of the main pipe and the pressurizer,the consequent deformation to pipe as result to the stress showed large displacement at the centre of the surge line.Also further stress in the transient case when the surge line pipe is being filled with hot water are scheduled to be calculated from the transient temperature profile evaluated in this thesis.