Assessment of residual stresses on U10Mo alloy based monolithic mini-plates during Hot Isostatic Pressing

This article presents an assessment of the residual stresses in U–10 wt.% Mo (U10Mo) alloy based monolithic fuel plates and the elasto-plastic response to thermo-mechanical processing. Monolithic, plate-type fuel is a new fuel form being developed for research and test reactors to achieve higher uranium densities within the reactor core to allow the use of low-enriched uranium fuel in high-performance reactors. Understanding of the three-dimensional residual stress field is important for understanding the in-reactor performance of these plate-type fuels. To define fuel-cladding stress–strain characteristics, a thermo-mechanical finite element model was developed. During fuel plate fabrication, the hot pressing temperature approaches the melting temperature of the cladding, so that temperature dependent material properties were incorporated to improve the accuracy of the model. By using elasto-thermo-plastic material models, it was determined that the cladding material (Al6061-O) is subjected to tensile stresses that exceed its proportional limits. The fuel foil is subject to compressive stresses and remains below yield. The residual stresses in the plates are significant, and therefore, should not be neglected. In particular, the simulations indicate the presence of high stress gradients at the fuel/cladding interface, thus emphasizing the need for a high quality bond.

► Residual stresses dominate the overall performance of mini-plates.
► Thermo-elasto-plastic material model with thermal creep was formulated.
► Fuel foil is exposed to compression, while cladding is exposed to tensile field.
► Even though fuel stays below its yield limit, cladding material exhibits plasticity.
► Thermal creep has negligible effect on residual stresses for 4.8 °C/min.