Short-time creep and rupture tests on high burnup fuel rod cladding

Short-time creep and rupture tests were performed to assess the strain potential of cladding of high burnup fuel rods under conditions of dry storage. The tests comprised optimized Zry-4 cladding samples from fuel rods irradiated to burnups of up to 64 MWd/kg U and were carried out at temperatures of 573 and 643 K and at hoop stresses of about 400 and 600 MPa. The applied stresses were chosen to reach about 2% strain within an envisaged testing time of 3–4 days. The tests were followed by a low temperature phase at 423 K and 100 MPa to assess the long-term behaviour of the cladding ductility especially with regard to the higher hydrogen content in the cladding of the high burnup fuel. These tests showed that around 600 K, a uniform plastic strain of at least 2% is reached without cladding failure. The low temperature phase at 423 K for up to 5 days revealed no cladding failure under these conditions of reduced cladding ductility due to the increased hydrogen content.