Sample container for high-resolution neutron imaging of spent nuclear fuel cladding sections

In this work, for the first time, high-resolution neutron imaging (true spatial resolution of 13 μm) is used for irradiated nuclear fuel cladding, applying an adapted procedure for transfer, handling, and measurements of highly radioactive samples in combination with the neutron microscope detector at Paul Scherrer Institut. A sample container referred to as an active box for high-resolution neutron imaging of highly active spent nuclear fuel cladding sections was developed. Sections of unirradiated and irradiated cladding of duplex type, having a liner, with hydrogen average concentrations of 420 wppm and 450 wppm were investigated using this device. The irradiated cladding originated from a fuel rod operated for five cycles in a Swiss pressurized water reactor. The irradiated cladding sample was measured inside the active box. Long circumferential hydride accumulations were revealed together with notable hydride precipitation at the liner–substrate interface. Measurements of the unirradiated cladding in air and inside the active box delivered consistent results, confirming the applicability of the developed device for high-resolution neutron imaging.