Reactivity feedback evaluation of material relocations in the Cabri-1 experiments with fuel worth distributions from SNR-300

The fuel relocations from the Cabri-1 experiments with irradiated fuel that had been evaluated from the hodoscope measurements were used together with fuel reactivity worth distributions from SNR-300 to estimate the reactivity effect which these motions would have if they occurred in SNR-300 at the same relative distance to the peak power point as in Cabri. The procedure for the reactivity evaluation is outlined. This includes the assumptions made for fuel mass conservation. The results show that the initial fuel motion yields always negative reactivities. They also document the mechanism for a temporary reactivity increase by in-pin fuel flow in some transient overpower tests. This mechanism never dominates, however, because material accumulates always sufficiently above the peak power point. Thus, the late autocatalytic amplifications of voiding induced power excursions by compactive in-pin fuel flow that had been simulated in bounding loss of flow analyses for SNR-300 have no basis at all when considering the results from the Cabri-1 experiments. (orig.)