Abstract
Pellet relocation is estimated as a function of irradiation history. Fuel fracture at BOL causes an ‘initial relocation’, whereby the fragments are displaced towards the canning. If columnar grain growth does not take place, the pellet remains cracked into pie shaped pieces without circumferential fractures; pellet diameter is stably increased by a term independent on linear power. If columnar grain growth occurs, cracks are filled in the restructured zone and, during a shut-down, circumferential cracks appear. The internal void volume is partially filled during up-ramps so that the relocation is an inverse function of linear power. Cracks healing, causing a void volume to be transferred inwards, produces a ‘time dependent relocation’, related to reactor cycling; as exposure proceeds, the pellet approaches a limiting diameter. The semiempirical model was derived from in-pile temperature measurements at low burn-up and BWR Garigliano rods PIE at high burn-up. A proper choice of literature data was also considered in comparing the parameters with experimental points.
Published Version
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