Proposal of new Oβ oxidation criterion for new types of the Zr1Nb alloy of fuel claddings

This paper deals with oxygen concentration measurements and mechanical testing of nonirradiated modified E110 nuclear fuel cladding tubes exposed to low- and high-temperature steam environment. The oxygen concentrations were measured in the prior β-phase region using two experimental methods (SIMS and TEA). The results of both techniques were compared with satisfactory agreement. Then ring compression tests (RCT) and fractographic analyses of failed ring specimens followed. By correlating the oxygen concentration results with the results of RCT, the oxygen concentration threshold of the β-phase embrittlement has been assessed (Cβ,threshold = 0.38 wt%). The tubes exceeding this oxygen concentration in the β-phase may become brittle. The threshold was compared with the results of other authors with satisfactory agreement. Eventually, the kinetics of the oxygen uptake in the prior β-phase has been assessed based on the SIMS and TEA results: Cβ = 128 × exp(−10,875/T) × t1/3. By implementing the oxygen concentration threshold into the kinetics equation, the new oxidation criterion Oβ has been determined and compared to the conventional 17% ECR criterion and the empirical criterion K.

► Oxygen concentrations inside oxidized fuel claddings were measured.
► The oxygen concentration threshold of the β-phase embrittlement has been assessed.
► The kinetics of the oxygen uptake in β-Zr has been determined.
► The new oxidation criterion Oβ has been proposed.