Impact of reactivity excursions

From the above considerations it is apparent that fast hybrid reactors have more favourable neutronic characteristics than do thermal reactors. Practi­cally it seems difficult to design a hybrid thermal reactor with keff larger than 0.95 for the U-Pu cycle and 0.92 for the Th-U cycle. The corresponding values for fast reactors would be 0.99 and 0.98 respectively.

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