Effect of hydrogen content on the embrittlement of ZR alloys

An experimental series has been carried out in the KFKI Atomic Energy Research Institute in order to clear up the role of oxidation and H uptake in the Zr cladding embrittlement process. Russian E110 type Zr1%Nb and Zircaloy-4 cladding were used and the differences between the two alloys were also examined. The sample preparation covered the following cases: Oxidation in steam, Oxidation in Ar+O2 atmosphere, Hydrogenisation of as received and oxidised in Ar+O2 atmosphere samples. The oxidation in Ar+O2 and later hydrogenisation possible to produce samples with well characterised H and O content. The hydrogen content of samples oxidised in steam was determined after mechanical testing using high temperature desorption. The results of the experiments provided detailed information on the effect of H and O content of the embrittlement of Zr alloys. The most important conclusions were the following: Hydrogen seems to play a more important role in embrittlement of Zr alloys than oxygen. The Zry-4 samples becomes brittle at lower H content than the Zr1%Nb. Under steam oxidation conditions the Zr1%Nb alloy takes up much more H than the Zry-4 and it resulted in earlier embrittlement. This explains the observed difference in ring compression tests with E110 (Zr1%Nb) and Zry-4 claddings. (author)