PSI - Issue 60

Keshav Mohta et al. / Procedia Structural Integrity 60 (2024) 402–410 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. Radial forces on a typical outer fuel pin under constant flow and pulsating flow conditions

3.2. Finite Element Analysis- Evaluation of Contact Forces and Sliding Displacement Detailed 3D transient dynamic FE analysis was carried out to assess the contact forces and sliding time histories at the bearing pad locations. One bundle length section of PT (fresh condition- no sag or diametrical creep) was modeled and surface to surface contact was defined between bearing pads and PT (Fig. 6.). Equivalent flexural rigidity of fuel pin was evaluated from a separate analysis and was assigned to the fuel pins modeled using beam elements. Modal analysis of fuel bundle was carried out using the developed FE model and good agreement with the observations from sine sweep experiment was found indicating appropriate modeling of the mass and stiffness properties of fuel bundle. Transient hydrodynamic forces acting on the fuel pins, as obtained from the CFD analysis, were applied to the respective fuel pins.

(a)

(b)

Fig. 6. (a) FE model of Fuel Bundle and PT with contacts defined; (b) nomenclature used

From FE analysis results, it was observed that the bottom four bearing pads of fuel bundle at each end come into contact with the PT. The contact force and relative sliding for BP12 (see Fig. 6), as obtained from FEA, are plotted in Fig. 7. It may be noted that the 150 Hz frequency response is evident in contact force time history. While the average contact force at the bearing pad locations does not change much, range is higher in case of pressure pulsation.