模擬用過條件鋯二合金護套在水氣環境之高溫氧化動力學

Oxidation Kinetics Study on the Simulated Spent Fuel Cladding of Zircaloy-2 in High-temperature Vapor

本研究探討用過燃料護套鋯二合金在水氣環境下之高溫氧化行為。為模擬用過燃料護套內部氫化與表面具氧化層之條件，鋯二合金管材經過充氫及預氧化處理，獲得表面形成約30μm厚氧化層，及內部有氫含量100 ppm ~ 1000 ppm範圍條件之模擬試片，以熱重分析儀（TGA）進行500℃~ 800℃水氣條件之氧化實驗。結果顯示模擬條件試片呈現二階段線性氧化速率；初始階段為較低的線性速率，氧化層增加1 ~ 3μm後轉變至第二階段較高的線性速率。試片氫含量對氧化速率常數之效應在初始階段並不明顯，但在轉變後階段則顯現影響氧化速率常數之效應。

The oxidation kinetics of Zircaloy-2 cladding in vapor was investigated to study the oxidation behavior of the spent fuel cladding. To simulate the conditions of spent fuel cladding, hydriding and pre-oxidation of the Zircaloy-2 tube specimens were conducted. The simulated specimens with oxide thickness of 30 μm on the cladding surface and hydrogen contents of 100 ppm ~ 1000 ppm in the cladding were obtained. Oxidation tests in vapor at the temperature ranges of 500 ℃ ~ 800 ℃ were carried out by TGA. The results showed that the simulated specimens revealed two-stage linear oxidation kinetics. At the initial stage, a lower linear rate law was exhibited until 1 ~ 3 μm oxide scale formed and then the transition of oxidation rate occurred. After transition, the oxidation kinetics followed a higher linear rate law. The effect of hydriding on the oxidation rate constant was insignificant for the initial stage oxidation, it was, however, more evident at the stage of post-transition.