Influence of protecting gel film on oxidation of zirconium alloys

Thin oxide layers of Zr1Nb and Zry-4S on tubes, used for fuel cladding in light water reactors, which had been protected by thin gel films, were compared with oxide layers on unprotected specimens of the same kind, grown together in two batches in water at 360 °C for 21 and 42 days, respectively. The analysis of the I–V characteristics at constant temperatures up to 180 °C showed a strong decreasing resistivity with oxidation time of the gel-protected layers of the Zry-4S specimens, with indication of an energy dependent trap distribution, although the gel and the oxide alone showed evidence of single, but different, energy traps. The changes are believed to be due to diffusion of different trap centers in both directions. The Zr1Nb specimens retained their single energy trap behaviour also in the combination with the protecting gel film and resistivity dropping with increasing oxidation time.