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Stator insulations comprised of mica-filled epoxy glass composite materials are of paramount importance for the reliability of high-voltage rotating machines. The present work deals with the fracture mechanical characterization of the winding insulation under conditions of monotonic and cyclic loading. The identification and quantification of the weak interfaces in the material that will most likely result in the initiation and propagation of defects are investigated in detail. Material specimens are processed from insulation tapes, and tests are conducted under mode I, mode II and mixed mode (Fixed Ratio Mixed Mode) loading to characterize the weak interface. The influence of resin content on the strength of the weak interface is also investigated. The results give an indication of the delamination mechanism and a measure of the critical energy release rate in the insulation materials.

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Study of thermal hydraulics of a hexagonal sub-assembly is essential to ensure safe operation of liquid metal cooled fast reactors. Identifying the dryout location in fuel sub-assembly (FSA) is a precursor to the determination of safe Critical Heat Flux (CHF) margins. In this study, a sub-channel analysis code coupled with a film thickness model is employed to predict the CHF location in a hexagonal sub-assembly. A simple post-CHF heat transfer model is proposed and validated against the experimental data. The nature of flow resistance changes and operating conditions would significantly influence the occurrence of CHF. To this end, the effect of blockage (0.0 ≤ b ≤ 0.3) and axial power distribution (APD) on CHF is systematically investigated in a hexagonal sub-assembly. It was observed that, the presence of blockage causes coolant flow maldistribution which results in an early occurrence of CHF for higher mass flux (G > 1500 kgm−2s−1) and lower inlet subcooling (ΔTsub ≤ 30 K) conditions for b = 0.3. Furthermore, a comparative study of uniform and sinusoidal heat flux distributions are performed. It was noticed that sinusoidal APD causes early occurrence of CHF compared to uniform APD.