Fuel-cladding mechanical interaction in PCI-resistant LWR fuel designs during normal operation and power ramping

The fuel cladding mechanical interaction behavior of developmental fuel rods irradiated in the Halden Boiling Water Reactor was evaluated based primarily on rod elongation measurements made during steadystate and power-ramping irradiation. The developmental fuel rod designs were selected based on attributes that were expected to reduce pellet-cladding interaction (PCI) failures during irradiation. Testing results were compared to a nonpressurized reference design with dished-pellet fuel. For the reference rods, there was a relationship between thermal feedback and fuelcladding mechanical interaction during steady-state irradiation. Significant cladding stresses developed in both the axial and hoop directions in the reference rods during power ramping. During power ramping the general cladding stress distribution in fuel rods with annular fuel pellets was primarily axial while cladding stresses in rods with sphere-pac fuel were mostly in the hoop direction. These results are indicative of superior PCI resistance in the annular pellet fuel rod designs when compared to the reference and sphere-pac rods