Simulation of heat transfer in measurements of thermal gap conductance by laser flash method
Thermal gap conductance between the cladding/fuel capsule gap plays an important role to heat transfer analysis in nuclear reactor operations. It consists of the conductance of the gas in the gap, and the additional interface thermal resistance which is quantified by a temperature jump distance. The temperature jump distance for He on Zircoloy cladding and UO2 may be as large as 10 microns, at the same level of the gap distance. There are several theoretical models that calculate the temperature jump distance, but their predictions vary in a wide range, requiring further validation by experiments. The most recent experiments were carried out in 1979, and the laser flash method was applied to measure thermal conductance of the gap between Zircoloy-4 and UO2 created by three spacers. However, this experimental study fails to correct the models mainly because of high uncertainties in the experimental results. This study investigates experimental designs of the laser flash method in measurements of thermal gap conductance. Heat transfer is simulated through the gap which is formed by four spacers between two sample discs. In order to diminish heat shunt across spacers, the grooves may be added along the rims of the rear disc or both discs. The results show that heat shunt effect is significant for wide gaps but can be greatly reduced by grooves on both discs. Grooves on the rear disc as exploited in 1979 experiments overestimate the predictions by up to 30%, becoming one significant design flaw.
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zhuorui song (POC,Primary Presenter), Utah state university, email@example.com;