The Marines do not know squat about running commercial nuclear plants and it usually takes the Navy boys a few years to adjust properly from the government to the commercial world. probably 60-70%, if not more, of the management and at least 40-50% of the engineering/technical staff at US commercial nuclear plants are ex Navy already.
We don't need Marines for security at them either. Nukes are very hard targets. If you don't believe me, go try breaking into one.