Cold neutron prompt gamma activation analysis, a non-destructive technique for hydrogen level assessment in zirconium alloys

We propose a novel use of a non-destructive technique to quantitatively assess hydrogen concentration in zirconium alloys. The technique, called Cold Neutron Prompt Gamma Activation Analysis (CNPGAA), is based on measuring prompt gamma rays following the absorption of cold neutrons, and comparing the rate of detection of characteristic hydrogen gamma rays to that of gamma rays from matrix atoms. Because the emission is prompt, this method has to be performed in close proximity to a neutron source such as the one at the National Institute of Technology (NIST) Center for Neutron Research. Determination shown here to be simple and accurate, matching the results given by usual destructive techniques such as Vacuum Hot Extraction (VHE), with a precision of ±2 mg kg−1 (or wt ppm). Very low levels of hydrogen (as low as 5 mg kg−1 (wt ppm)) can be detected. Also, it is demonstrated that CNPGAA can be applied sequentially on an individual corrosion coupon during autoclave testing, to measure a gradually increasing hydrogen concentration. Thus, this technique can replace destructive techniques performed on “sister” samples thereby reducing experimental uncertainties.

► Cold Neutron Prompt Gamma Activation Analysis has been performed to detect hydrogen in various Zr alloys.
► CNPGAA is non-destructive and can precisely detect low levels of hydrogen (as low as 5 wt ppm).
► Hydrogen pick-up fraction of ZIRLO samples has been investigated using CNPGAA and Vacuum hot Extraction.
► It is shown that the hydrogen pick-up fraction undergoes significant increase slightly before the weight gain transition.