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Originally Posted by Chas H
Don't ships use a BWR?
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No, at least our nuclear powered naval ships use PWR's - Pressurized Water Reactors. You have a separate loop that circulates water thru the reactor to a steam generator, where it circulates thru tubes and boils water on the opposite side of a physical boundary - the steam generated on the opposite side powers the steam plant. All the radioactive crap is kept inside the primary "loop" that circulates between the reactor and "primary" side of the steam generator - the steam generated on the "secondary" side of the generator and the entire steam plant is kept "clean".
Much easier to do emergency cooling with this type of plant - all you have to do is vent steam from the secondary side of the steam generators, to atmosphere if need be with no problem since the steam is as "clean" as that from a coal fired plant - and also easier to get makeup water into the generator since the steam pressure inside them is at least an order of magnitude lower than inside the primary reactor loop.
In a BWR, the steam is boiled off from the reactor itself and directly piped to the steam plant - such that the entire setup is potentially contaminated - and you just can't casually vent steam to atmosphere for emergency cooling purposes, for rather obvious reasons.