Structural integrity assessment and stress measurement of CHASNUPP-1 fuel assembly skeleton

A fuel assembly (FA) structure without fuel rods is called FA skeleton which is a long and flexible structure. This study has been made in an attempt to find the structural integrity of the Chashma Nuclear Power Plant-1 (CHASNUPP-1) FA Skeleton at room temperature in air. Non-linear buckling analysis has been performed using ANSYS 13.0, in-order to determine the buckling behavior of the FA skeleton as well as the location/values of the maximum stress intensity and stresses developed in axial direction under applied compression load of 4900 N. The finite element (FE) model of spacer grids, guide thimbles with dash-pots & flow holes, in addition to spot welds between spacer grids and guide thimbles, has been developed using Shell 181 element. The FA skeleton is a non-straight structure. Its actual behavior of the geometry is non-linear. The value of the perturbation force is related to the geometry of the model and/or the tolerance defined for the geometry. Therefore, a sensitivity study has been made to determine the appropriate value of an arbitrary perturbation load. been observed that FA skeleton deformation values obtained through FE Analysis & Experiment (Technical Report, 1994a,b) under applied compression load are comparable and show linear behaviors. Therefore, it is confirmed that buckling of FA skeleton will not occur at the specified load. Moreover, the values of stresses obtained at different locations of the guide thimbles are also comparable with the stress values of the experiment determined at the same locations through strain gauges. the results of both studies (analytical & experimental) are comparable, therefore, validation of the FE methodology is confirmed. The SINT and stresses are less than the design stress limit of the materials used for the grid (ASTM, 2013) and the guide thimble (ASTM, 2012). Therefore, the structural integrity criterion of CHASNUPP-1 FA Skeleton is fulfilled safely.