| Abstract |
| The oxidation characteristics of Zr-xNb (x=0, 0.2, 1.5, 3.0, 10 wt.%) alloys were investigated in the LOCA temperature ranges of 800 to 1200℃ under the steam condition, using a modified thermo-gravimetric analyzer. In all temperature ranges, the oxidation rate constants of the alloys were controlled by parabolic rate law. The rate constants increased gradually as the Nb contents increased at temperatures below 1000℃. This is the reason why the oxidation reaction of Zr-xNb alloys was enhanced by the formation of Zr (3phase at temperatures of 800 to 1000℃. But the rate constants decreased slowly with increasing the Nb contents at tempeartres above 1000℃. The prior 13-Zr region of Zr-xNb alloys were consisted with an a-Zr(0) phase having grain-boundary shape and a needle-like Widmansta¨tten phase incorporated into the a-Zr(0) phases above 1000℃. And, above 1000℃, the oxides of the ZrxNb alloys were duplex structures, i.e. outer oxide: columnar structure, inner oxide: network structure. The inner network-structured oxides would be caused by the formation of niobium oxides in the oxide and would retard the oxygen diffusion through the oxide. This could result in reducing the rate contants of Zr-xNb alloys in the temperature range of 1000 to 1200℃. (Received April 9, 2004) |
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| Key Words |
| Zirconium alloy, Zr-Nb system, High-temperature oxidation, Steam oxidation, Oxidation kinetics, Oxidation rate constant, Loss-of-coolant accident, LOCA |
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