To achieve a safety goal of ensuring at least \(1 \mathrm{mk}\) of prompt subcriticality following a reactivity excursion event, SCRAM rods are inserted in a few seconds in the core. Find the maximum allowed drop time for shut off rods (which have to travel \(3 \mathrm{~m}\) for complete insertion in the core for \(30 \mathrm{mk}\) of worth realized with insertion length) following a reactivity excursion involving average reactivity insertion rate of \(2 \mathrm{mk} / \mathrm{s}\) for a typical pressurized water reactor with delayed neutron fraction of 0.006 . Consider a total delay of \(1.5 \mathrm{~s}\) in initiation of SCRAM.