REACTIVITY FEEDBACK EVALUATION OF MATERIAL RELOCATIONS IN THE CABRI-1EXPERIMENTS 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 tog ether with fuel reactivity worth distributions from SNR-300 to estimat e the reactivity effect which these motions would have if they occurre d in SNR-300 at the same relative distance to the peak power point as in Cabri. The procedure for the reactivity evaluation is outlined. Thi s includes the assumptions made for fuel mass conservation. The result s show that the initial fuel motion yields always negative reactivitie s. They also document the mechanism for a temporary reactivity increas e by in-pin fuel flow in some transient overpower tests. This mechanis m never dominates, however, because material accumulates always suffic iently above the peak power point. Thus, the late autocatalytic amplif ications of voiding induced power excursions by compactive in-pin fuel flow that had been simulated in bounding loss of flow analyses for SN R-300 have no basis at all when considering the results from the Cabri -1 experiments.