Experimental and numerical study of the dynamics at the fuel rod/spacer grid interface in nuclear reactors

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Flow-Induced Vibrations (FIV) found in the Pressurized Water Reactors (PWR) cause fretting wear on critical fuel assembly components, including fuel rods. Fuel rods are long slender tubes made of Zirconium alloy which contain the nuclear fuel and act as the barrier between nuclear fission products and the external environment. Excessive wear in the fuel rods' surface could break this safety barrier and release fission products into the external environment. Thus understanding this fretting phenomenon and developing methodologies to predict the severity is of critical importance to FIV and fretting experts at Framatome Canada Ltd. As this helps them to ensure not only the safety and performance of the fuel components but also reduce costs in manufacturing the same. Specifically, the fretting wear is attributed to the relative motion between the fuel rod and the support. There is no established methodology to experimentally measure this relative motion between them. An accurate measurement of this phenomenon would help FIV experts in validating their fretting models and accurately predicting the impact of fretting wear on the fuel components. The proposed project pertains to the safety and structural integrity of fuel rods subjected to flow-induced vibrations by developing an innovative test methodology to track the relative displacements of the fuel rods surface (point of contact) and the spacer grid surface (point of contact) and the net force exchange between the two surfaces during flow-induced vibrations of the fuel rod. In addition, a theoretical methodology to describe the evolution of the boundary conditions at the fuel rod-spacer grid interface will be developed to better understand the effect of interface conditions on the structural stability of the fuel rod during its dynamic response when subjected to flow-induced vibrations. The proposed project is a continuation of a number of successful collaborations between McGill and Framatome Canada Ltd. (formerly AREVA NP Canada Ltd.) under the NSERC grants such as NSERC-EG#462720-14, NSERCEGplus#476586-14 and NSERC-CRDPJ #490978-15.