[en] The hydrogen uptake rates reported for zirconium alloys in BWRs, PWRs, HWRs and various experimental in-reactor loops have been surveyed. The scatter in the data is large and arises from a variety of sources: variability in material properties; variations in temperature, irradiation flux, and water chemistry at different points in the reactor; and a lack of accurate knowledge of the sources of hydrogen which ends up in the zirconium-alloy cladding. An attempt has been made to assess the significance of these sources of variability in order to estimate the baseline for hydrogen uptake from the outside of good-quality cladding under normal BWR operating conditions. The probable effect of continuous hydrogen injection on this baseline has been estimated. It is concluded that severe localized hydrogen uptake, which might lead to hydride blisters is very improbable, but that an increase in the uniform rate of hydrogen absorption at the outside of the cladding may be expected