Actually, the most critical decay attribute for the operation of Naval pressurized water nuclear reactors is the decay rate of the Delayed Neutron Precursors - those fission products that decay and emit a neutron shortly after the fission. Without that extremely stable decay, the reactor's criticality would not be controlable.
Anyway, what boat is he on? I hope you get to do a "Father's Cruise" at some point (if they still do those.) My Dad thought it was one of the neatest things he had ever done.
Haven't got that yet. He's on the Olympia. She just got a reactor replacement and major overhaul. He stationed at Pearl, but I got a call from him a few days ago from San Diego, and they were getting ready to leave there for Alaska and then parts unknown.