Flow and heat transfer characteristics in plate-type fuel channels after formation of blisters on fuel elements

Due to the special structure, the plate-type fuel element possesses a unique failure mode, i.e. blistering. Blistering is a kind of plastic deformation, induced by thermal stress and pressure of gaseous fission products at the interface of fuel meat and cladding. A blistering cladding surface will alter the flow channel shape and thus affect the flow and heat transfer characteristics in a fuel assembly. The influence is significant because the parallel channels are closed and narrow. In this study, three plates and channels were modeled to represent parallel channels in a fuel assembly. Two kinds of blisters were considered, namely round blister and pillow-like blister. Six cases with various blistering distribution were simulated to investigate its influence on pressure drop, mass flow distribution, and fuel temperature. The turbulent model and mesh condition were carefully chosen and validated. Detailed flow structures were visualized and their relations with flow and heat transfer characteristics were analyzed. Results show that multiple blisters can induce the flow distribution factor to exceed the design threshold value. A single blister, due to the large thermal resistance of gaseous fission products, can cause a relatively high maximum temperature in the fuel plate and lead to additional structure rupture. Multiple blisters' influence on fuel temperature is independent and similar with that of a single blister. Larger blisters lead to higher maximum fuel meat temperature and therefore are more dangerous. (C) 2019 Elsevier Ltd. All rights reserved.