An Approach for Assessing Fuel Assembly’s Structural Integrity Under In-Core Operating Conditions Using Finite Element Method

This paper describes the development and application of a single fuel assembly (FA) finite element analysis (FEA) model that can be used to assess and predict the structural behavior of FA during its entire life at early design stage. This model includes all structural components of a FA and has been validated under laboratory test conditions, including spacer grid test under axial load, skeleton test under axial and lateral load, FA test under axial and lateral load, as well as the fuel rod drag test. The model is then applied to an example FA design by predicting the FA’s in-core behavior, including its growth characteristics due to irradiation, and irradiation-induce creep and hydrogen absorption; effect of spring force relaxation of structural spacer grids; effect of holddown spring force increase with growth; effect of different amounts of initial FA bow and bowed shapes; FA distortion evolution vs. burnup history; and stress and deformation of various structural components. It demonstrates that this approach can be used to assess fuel assembly’s structural behavior under various operating conditions at early design stage.