Investigation of fracture behavior of these fuel clad tubes in nuclear reactors is of utmost importance to the designers and plant operators in order to ensure the maximum residence time of the fuel bundles inside the reactor core as well as to ensure minimal activity during operation and refueling activities. Fracture behavior of these tubes need to be evaluated using axially-cracked non-standard specimens directly machined from the fuel-clad tubes. In this work, a conical mandrel with 4 degree taper angle was used to open the crack in a test setup known as Internal Conical Mandrel technique.
The crack extension was measured with camera and image analysis procedure. Fuel-clad specimens with different initial crack lengths (i.e., a/W ratio from 0.1 to 0.5) were tested and the loaddisplacement response were obtained from the experiments. It was observed that for same applied displacement, specimens with smaller initial crack lengths absorb more energy due to extensive plastic deformation. The total energy absorbed vs. crack extension curves were however observed to be nearly independent of the a/W ratios of the specimens. This may be attributed to the dependence of ductile crack growth on the formation of an intense localized plastic deformation zone ahead of the crack-tip, which is independent of the remaining ligament.

Keywords: Non-standard fracture specimen, Internal conical mandrel technique, Fuel-clad fracture behavior, Zirconium alloys, Pressurized heavy water reactor.