So they designed the AZ-5 system to only gradually reduce the reactor’s power to zero. Rather than dedicated emergency motors, the system was driven by the same electric servos that moved the manual reactor control rods, used by the operators to manage reactor power during normal operation. Starting from their fully withdrawn position above the reactor, it would take between eighteen and twenty-one seconds for the AZ-5 rods to descend completely into the core; the designers hoped that the rods’ slow speed would be compensated for by their great number. But eighteen seconds is a long time in
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