What sort of diesel generators are the ones that are fitted as backup in nuclear submarines?
these are standard marine type diesel generator with turbo charging and snorkeling attachment used to charge up the batteries when nuclear reactors are not operational
They are used both to provide provide propulsive power during cruise (though the batteries ) as well as keep the coolant pumps of the reactor running to remove the core decay heat even when the reactor have been shut down . The radioactive decay of the reactor core takes palce all the time and this heat unless removed can lead to generation of local hot spots and may lead to reactor melt down .
The amount of nuclear fuel used depends on the type of fuel and type of submarine and of course reactor design itself . As a rule attack subs consume more fuel power ton of displaced weight than missile subs like ohio or typhoon
normally 7 -10% fuel rods are taken out every 3 years and new rods placed in its place .The rods nearest or forming the core get used up most so they are taken out and next layer of rods moved forward by one turn forward . Usaly the rods are arranged in concentric hexagons around the reactor core .
So a very rough guess for a 6000 ton attack sub like our ATV we may have to replace 300 -500 kg of enriched uranium rods (35% uranium)
during tri yearly refurbishment cycles .The burnt rods will be taken out -plutonium extracted and dumped in some safe place
Just my guess -nothing more nothing less
