"The Navy now believes it has a design that soon will be able to fire 10 times a minute through a barrel capable of lasting 1,000 rounds."
So the barrel lasts just over an hour and a half?
So the barrel lasts just over an hour and a half?
Today's 5" guns have to have their barrel replaced every ~7000 rounds anyway (source: http://www.navweaps.com/Weapons/WNUS_5-62_mk45.htm ).
I suspect the Navy have some records on firing rates achieved in actual battle situations.
The relationship between theoretical firing rate and actual firing rate is often distant. You might find it more useful to read this as a weapon capable of firing not more often than once every six seconds, and having an effective barrel life of 1,000 rounds.
Those 1,000 firings could well be spread over months or years.
Edit: Apologies, basic mistake, mixed up power with energy. Thanks for correcting.
That's not how power works. Power is energy/second, so if one each firing requires 25Mw, firing every round requires 25Mw.
Edit: Although after doing some calculations, firing 1000 shells would require 22 billion joules of energy, which is about the same as the energy released during nuclear fission of three grams of uranium.
Of course, only a small portion of uranium in a reactor core is converted to something else. After that, they replace the fuel as its output drops a bit.
Disclaimer: I don't know enough to check the "grandparent" post's math. I'm assuming the calc is right in that it's the fission energy, and not total destruction of matter E=mc^2 / matter-antimatter style.