Calculation of the effects of fuel pellet fragment axial relocation on the peak clad temperature during a loss-of-coolant accident in a pressurized water reactor

During a hypothetical large loss of coolant accident in a Pressurised Water Reactor the potential exists for the fuel cladding to strain and rupture. There is some experimental evidence which suggests that axial movement of the pellet stack may occur during the transient upon burst of the cladding. An assessment of the likelihood of fuel fragment relocation has been completed using data from a wide variety of experimental facilities. This assessment has also determined an appropriate value of the density of fuel fragments within the burst cladding which has been used in the BART code to determine the potential effect of this relocation on calculated clad temperatures. The BART calculations indicate that the likely effect of fragment relocation is modest in terms of the maximum clad temperature at the burst location and very small with respect to calculated peak clad temperatures. (author)