Neutron radiography and tomography applied to fuel degradation during ramp tests and loss of coolant accident tests in a research reactor

• Neutron radiography by utilizing the SART method gives good results for interpretation of LOCA experiments even when relative few neutron projections (sample rotations) are acquired from irradiated test rods.
• Neutron radiography is an excellent non-destructive technique utilized on irradiated fuel rods for interpretation of test results obtained in a test reactor, e.g. secondary fuel degradation tests, reactor power ramp testing, etc.
• Neutron radiography film methods give good spatial resolution (i.e. 40–50 μm) of fuel rod radiographs.
• Neutron radiography applied on re-fabricated rods (already irradiated) is a very useful method applied under fabrication of high burn-up rods for LOCA experiments.

Neutron radiography (NR) is performed at the Institute for Energy Technology (IFE) in Norway since the late 1970s. The application of the non-destructive method was to acquire post-irradiation examination (PIE) data (e.g. fuel integrity and hydrogen up-take in cladding) from safety and integrity tests of nuclear fuels performed under the Organization for Economic Co-operation and Development (OECD) Halden Reactor Project (HRP). The method was later applied under re-fabrication and instrumentation operations of experimental nuclear fuel rods prior to testing in Halden Boiling Water Reactor (HBWR), and for a variety of PIE projects, e.g. reactor power ramp testing, PCI failure detection and fuel degradation experiments. Neutron radiography has also proved to be a very useful tool for examination of nuclear fuels irradiated in the Loss-of-Coolant Accident (LOCA) experimental series initiated in the early 2000s. Neutron tomography data is acquired while an increased international focus arose on fuel fragmentation, fuel relocation and fuel dispersal processes that occur during the LOCA events for high burn-up nuclear fuels. Hydrogen up-take of the fuel cladding, fuel pellet-clad bonding condition, fuel fragmentation, particle size distributions, and other features obtained from neutron tomography data are quite relevant for reactor core safety impact study of LOCA events simulated in the HBWR. Neutron tomography studies of LOCA tested fuel were done in cooperation with the SCK·CEN institute in Mol, Belgium, and the University of Antwerp in Belgium. It’s interesting to observe that the image reconstruction results obtained from the SART method are quite good regarding the relatively few sample rotations utilized under acquisition of neutron radiography projections in the tomography studies of the LOCA examination.