A finite element model of pellet-clad interaction in advanced gas cooled
reactor fuel experiencing extended reduced power operations is
presented. The model considers a 1/8th segment of fuel and overlaying
cladding bonded to it. A radial crack is introduced to the pellet, this is
able to open and close, straining a section of cladding above the crack.
In addition, circumferential cracks in the fuel pellet result in a sliver of
fuel being bonded to the cladding; this sliver of fuel contains hairline
radial cracks, known as ladder cracks, the opening and closing of which
are modelled. Finally, the model predicts the creep strain at the tip of an
incipient crack in the cladding, ahead of the radial crack in the fuel pellet.
Results show that the crack tip creep strain is strongly dependent on the
model of ladder cracking chosen.