In order to clarify the mechanism of PCMI failure for high burnup fuels, we investigated the influence of the hydride morphology in the inner region of hydride rim ("region M") on the through-wall crack propagation by using samples prepared from several kinds of hydrogen-charged unirradiated cladding tubes with a precrack on their outer surface. The samples were fractured using a PCM-simulating EDC test apparatus. The sum of the length of all hydrides per unit area (H_(L1)) and the radial component of the length of all hydrides per unit area (H_(L2)) were evaluated in region M of each sample quantitatively. While the strains at failure of SR and CW samples tended to decrease linearly with increasing H_(L1), those of RX samples tended to decrease linearly with increasing H_(L2). It is considered that the hydride morphology in region M is one of the factors which influence the crack propagation through fuel cladding wall by PCMI during RIA.
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