Determination of low concentrations of hydrogen in zirconium alloys using neutron radiography as a non-destructive technique

Zircon base alloys (Zr) are used in the manufacture of fuel sheaths and structural components of power reactors because of their low neutron absorption. These alloys are susceptible to damage by hydrogen (H) because the concentration of the alloys can be increased locally in response to temperature or stress gradients. This causes a general degradation of its mechanical properties, and can generate a degradation process known as Delayed Hydride Cracking (DHC). H content in zirconium alloys is generally determined by destructive techniques. In this work we determine the H content in the range 0-300 wt ppm with a sensitivity of similar to 5 wt ppm and a spatial resolution of similar to 0.1 mm using neutron radiography as a nondestructive technique. In order to compare the capacity of different neutrography facilities for this type of analysis, the studies were carried out in four laboratories with different characteristics in terms of the flow and the energy distribution of the incident neutrons on the sample, as well as the maximum spatial resolution available in each case (L/D parameter). The facilities were ANTARES in the FRM-II reactor (Germany), Engin-X in the pulsed source ISIS (UK), BOA in the SINQ (Switzerland) sputtering source, and the neutron facility at the Bariloche RA-6 reactor (Argentina). The spatial resolution obtained allows to determine the diffusion coefficient of H in Zr-alloys using samples of 5x10x10 mm(3), approximately.