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Comment by krschultz | Hacker News Reader

Even the US Navy is backing away from nuclear power. They only build nuclear powered aircraft carriers and submarines. They used to build nuclear powered cruisers.

It is more expensive to build, to maintain, to break down at the end, and to train the many crews that will serve over the ship's lifetime.

Only when you absolutely need a nuclear reactor does it make sense to absorb that expense.

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That makes no sense-a nuclear powered carrier that doesn't require underway replenishment, would be much more capable if its escorts also didn't require conventional oil fueling.

If the US had continued to build nuclear powered surface ships through the end of the cold war, then it probably wouldn't be so expensive-economies of scale, plus you'd still have the infrastructure and training pipeline there.

Carrier attack groups have a refueling ship along with all the cruisers/attack ships. It probably makes sense, just going by the size differences the carrier would use more conventional fuel than all of its escorts combined, so having the carrier be nuclear powered doubles your range.

> That makes no sense-a nuclear powered carrier that doesn't require underway replenishment, would be much more capable if its escorts also didn't require conventional oil fueling.

The battle group still needs underway replenishment for food, ammunition, avgas, maintenance materials, and all the other various and sundry items required to keep ships functioning. Fuel isn't that big a deal when combined with all of these other items.

Also, nuclear reactors were replaced with gas turbines in surface ships. Nuclear is attractive versus the older oil-fired boilers. Large gas turbines changed the calculus. The steaming range of cruisers and destroyers with gas turbine power plants is excellent, hence the reason fuel is not a big deal to add to all the other stuff that needs to be provided for the battle group.

Lack of qualified operators is real operational problem.

Majoring in physics pretty much guaranteed you a NROTC scholarship, if you wanted one, back when I was in undergrad. Around a third of my cohort (and the ones graduating immediately before and after mine) were in NROTC, and every last one of them was earmarked for the nuclear program when they finished school.

I'd speculate that the Navy simply doesn't have enough personnel to put a nuclear drive-train on every cruiser, much less the entire fleet.

Edit: grammar

Edit2: Also, keep in mind that aircraft don't run on uranium. A carrier group needs tanker replenishment anyway, so switching to nuclear ship propulsion doesn't save you from needing to worry about the logistics of transporting large volumes of flammable liquid to the group.

What I was always told when I worked as a nuclear power operator in the Navy is that it's not so much that the people could not be found and trained, it was that on anything smaller than a carrier the engine room crew ended up being half the crew of the ship. The larger engine room crew size necessitated designing the entire ship around a larger ship crew, which introduces a whole lot of other logistical and practical concerns.

If I remember correctly, nuclear power also gives an aircraft carrier the speed to create more wind over the flight deck to help in aircraft operations.

It also makes it easy to generate steam for the catapults.

True. Interesting to note, though, that steam catapult's days are numbered: https://en.wikipedia.org/wiki/Aircraft_catapult#Future

The reason the Navy has moved away from Nuclear for cruisers is that nukes do not like their load to be highly variable. Cruisers, by their very nature want to throttle up and down very quickly. Carriers and subs, on the other hand, transition from full throttle to idle very infrequently.

Worst case scenario, what could happen if the nuclear reactor failed or was damaged in some way?

I see the benefits, but attaching them en-masse to various classes of warships seems like a recipe for disaster if war does actually break out.

In a war where significant numbers of aircraft carriers are being blown up the environmental damage from this is probably among the least of our concerns.

The bottom of the ocean is generally a very good 'containment system'. That's not to say there won't be environmental damage, but we do have some examples to go off of to indicate how much.

http://en.wikipedia.org/wiki/USS_Thresher_(SSN-593)

http://en.wikipedia.org/wiki/List_of_sunken_nuclear_submarin...

Not to mention all the sunken Soviet/Russian submarines (most of which have two nuclear reactors instead of one).

None of these examples were worst case scenario. How well does the ocean absorbs the ionizing radiation from a meltdown or some other extreme event? Would part of the ocean's water become radioactive and spread through currents? Are the oceans so voluminous that the effect would be only a minor increase in radiation levels?

The Fukushima Daiichi nuclear disaster gives a good approximation of what that would look like. "Pretty well", "yes, but well below what's considered safe limits", "yes, detectable but minor."

Well the mantle of the Earth (including its radioactive components that power plate tectonics) is literally pouring forth into the depths of the Atlantic Ocean (in the valleys of the mid-Atlantic Ridge) and that seems to have not caused noticeable calamities... which is because yes, the ocean really is that voluminous.

As it turns out the ocean is also really good at both shielding radiation (water is what the nuclear experts use in large amounts, after all) and diluting radioactive contaminants, if it came to that, until the radionuclides themselves decay away and become stable.

Additionally it's not as if radioactivity is infectious or permanent. If something is radioactive here and I move it over there, it can't be radioactive in both places, which is why dilution is so effective.

http://en.wikipedia.org/wiki/Bioaccumulation

You seem to imply that I haven't heard of this. Does this contradict anything I said and if so, how?

Before you answer, you might want to compare "biological half-life" with "radiological half-life" (as they are usually far different), and why the same issue of bioaccumulation has noted caused famine from hazardous materials that we know to have been dumped into the ocean in orders of magnitude much larger quantities. How many oil spills have fisheries survived in general?

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