Effect of high temperature steam oxidation on yielding of zircaloy-4 PWR cladding tubes through expandingcopper mandrel test

Abstract

With the Zircaloy-4 tube oxidized in high temperature (1323 K) steam for 5, 10, 30, and 60 minutes, the expanding copper mandrel test was carried out over a temperature range of 673 - 1173 K at $\varepsilon = 3.0\times10^{-5}S^{-1}$. The oxidation parameters (Ki) of present study were linearly proportional to square root of time (Ki = \delta_{Ki}t^{\frac{1}{2}}$) and their rate constants ($\delta_{Ki}$) are 0.281, 2.82, and 2.313 for weight gain and thickness of ZrO2 and $\alpha$ (0) layer, respectively. With the oxide layer thickness (K; expressed in ECR, \%) and the yield stress obtained from the mandrel test, an empirical relation was derived as ($\delta/\alpha)^n = k^m$. exp(Q/RT) with n = 6.9, m = 5.03, $\alpha = 1.2\times 10^{-3}$ Mpa, and Q = 554.2 KJ/mol. This higher activation energy (Q) for plastic deformation at temperature above 1023 K compared with that of as-received and/or other experimental conditions might be due to the structural change and increase in oxygen contents and the deformation mechanism seems to be constant at this temperature range of all oxidation conditions.