Determination of Helium in Samples from the Irradiated Fuel Channel Spacers of CANDU Power Reactors by Vacuum Fusion-Mass Spectrometry

Abstract Nickel-based alloys have been important component materials for today’s various types of nuclear power reactors and probably will continue to be in the future; however, neutron radiation can affect the mechanical properties and microstructure of the alloys causing damage to the materials through direct displacement of atoms and void swelling by gas generation from nuclide transmutations. Therefore, detailed understanding about neutron radiation damage through these mechanisms to nickel-based alloys is highly important to better assess the reactor component lifetime. Development of analytical methods capable of accurately measuring the helium content in irradiated and highly radioactive nickel alloy materials is essential for this purpose. This paper describes a vacuum fusion – mass spectrometry (VF-MS) method for determination of helium in irradiated nickel alloys. Based on the helium content and the radioactivity of the materials, helium concentrations of samples as small as 0.003 g have been determined accurately and precisely using this method. Up to 12 samples have been analyzed in one batch of analysis within the safe limits of radiation protection. Key experimental parameters, including fusion flux, fusion time and temperature, and mass spectrometric quantification techniques have been optimized. The VF-MS method was validated by analysing a quality control material and comparing the results with an independent laboratory using a different method, and with the predicted values. This method has been used to analyze specimens obtained from the ex-service fuel channel spacers in CANDU® nuclear reactors. The results agreed well with the calculated values based on the reactor’s operating history.