Some calculations of the power to initiate melting in fast reactor fuel pins

The methods employed in calculating the linear rating at which the onset of centre melting in fast reactor fuel pins are described. These are then applied to a number of MTR experiments on both pelletted and vibro compacted fuel pins in which power to melt values were obtained; satisfactory agreement between the calculated and experimental values was achieved. Further calculations that are relevant to fuel pin design are reported. In the case of vibro compacted fuel pins containing a mixture of 800 and 80 μm diameter mixed oxide microspheres, the effects of sphere size, filling gas composition and localised preferential movement of the fines component on power to melt values are considered. In the case of pelletted fuel statistical variations in the power to melt of pins contained in a subassembly, due to the observed variability in pin manufacture, are assessed. In some more general analytical treatments, the effect of uncertainties in the values of the various items of input data on the accuracy of the resulting power to melt figures is discussed; also the effect on the power to melt of re-distributing voidage between the fuel and fuel-clad gap is considered. (author)