High resolution neutron imaging of spent fuel cladding sections

At the Paul Scherrer Institute (PSI) in Switzerland the spallation neutron source, SINQ, is operated mainly for research with thermal and cold neutrons. At SINQ a neutron microscope is installed, with one of the highest spatial resolutions for neutron imaging world-wide and being the only instrument of this performance with regular access for the scientific community. The set-up of the high performance neutron-sensitive scintillator was developed in house; the nominal pixel size of acquired images can be routinely as low as 1.3 pm. Neutron imaging has become an important tool to investigate hydrogen distribution and quantification in zirconium alloy components. While zirconium has a very high neutron transmission, hydrogen strongly scatters neutrons. Thus, local hydrogen concentrations can experimentally be identified and quantified. In the present work, besides hydrogen distributions for Zry-4 tube samples without and with a liner (so-called duplex cladding), the hydrogen distribution profiles and quantification also in spent fuel cladding sections have been revealed along the radial direction. The hydrogen and hydrides quantification in spent fuel claddings is crucial to evaluate the potential risk for their integrity. In this contribution, we show that high resolution neutron imaging promises to reveal hydrogen concentrations also in irradiated claddings. In the case of testing active samples, questions arise concerning safety, the sample handling, radiation protection as well as the interdependencies between sample transfer cask, shielding, and beam line set-up and detector geometry