The Effect of Air Fraction in Steam on the Embrittlement of Zry-4 Fuel Cladding Oxidized at 1273-1573 K

This paper deals with the effect of air fraction in steam on the embrittlement of Zry-4 nuclear fuel cladding tubes exposed under steam-air atmospheres (air fractions of 10-100%) in the temperature range of 1273-1573 K. Ring compression tests were carried out in order to evaluate the embrittlement of fuel cladding. Furthermore, the microhardness of prior beta-phase was measured and fractured surfaces were observed under scanning electron microscopy. The degree of the embrittlement is discussed against the results of metallographic and hydrogen analyses. The microstructure and the hydrogen pickup were substantially affected by nitride formation. Accelerated oxidation kinetics enhanced shrinking of the prior beta-region. The enhanced hydrogen absorption resulted in the increased microhardness of prior beta-phase. The degree of the fuel cladding embrittlement, expressed by the plastic strain at failure and the maximum load, correlated well with the microhardness and the thickness of prior beta-phase.