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PostPosted: Feb 09, 2014 10:41 am 
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E Ireland wrote:
If fuel costs for the reactor are essentially zero the only thing that matters is capital cost.

At which point they will want to go as fast as possible so they can make more trips.

IN other words, 35 knots.


Reactor systems are much more expensive than combustion engines, so the higher power needed for high speed does cost you in terms of capital cost... on the other hand there is the economy of scale which is strong with reactors especially upgrading from a tiny to a small reactor size.

Whatever size is installed though, like you say they will likely run at full throttle all the time with cheap nuclear fuel, plus a nuclear reactor is easier to operate in a constant power mode.


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PostPosted: Feb 09, 2014 3:58 pm 
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Cyril R wrote:
E Ireland wrote:
If fuel costs for the reactor are essentially zero the only thing that matters is capital cost.

At which point they will want to go as fast as possible so they can make more trips.

IN other words, 35 knots.


Reactor systems are much more expensive than combustion engines, so the higher power needed for high speed does cost you in terms of capital cost... on the other hand there is the economy of scale which is strong with reactors especially upgrading from a tiny to a small reactor size.

Whatever size is installed though, like you say they will likely run at full throttle all the time with cheap nuclear fuel, plus a nuclear reactor is easier to operate in a constant power mode.


ICE engines are cheap, but the fuel isn't. And we're assuming oil won't jump to US$ 150-200.

BTW, very large ships aren't built to be able to go that fast, there are structural issues. A ship that only have enough HP to go at 21kts, can't go 35kts without some fatigue issues. Those ships have weight and balance issues similar to a very large aircraft. And if you go very fast, then you'd stay 80% of the time at port (diminishing returns). For instance, I mentioned ore carying ships because my dad was a port manager and I got to visit one of those many times (it was the largest ore/gain ship in the world, Berg Stahl, that was 1988, even in a slow 13kts cruise it spent 15 days travelling each way for 5 days loading or unloading, so 2/3 at sea for 1/3 at port, you double the speed and you're only increasing it's productivity by 1/3, so doubling again makes no sense, but for a ship that did Brazil to China or Japan it would make more sense, since it's a journey 4x longer, they are way too big for the Panama Canal).

All of this assumes current LWR costs. Forget about civilian LWR ships. LFTRs need to cost half as much, by standardizing on a single size if at all possible (say 500MWt / 250MWe, maybe a smaller 100MWt / 50MWe, but it would be better if it could be the same reactor with just less nuclear fuel or some very minor changes), and concentrating on economies of scale and factory production. We fall to the trap of trying to optimize the technical performance of the reactor at the expense of standardization.

Without a scale of at least 100 reactors per year, nuclear will never replace huge ICE engines. Has to be the exact same reactor that would be used on land. Ships sail at least 50% of the time, day and night, so their fuel costs are very high that with an expensive enough oil it would make sense to go nuclear.

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PostPosted: Feb 16, 2014 5:37 am 
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Large ships are sometime maneuvered by diesel powered harbor tugs. Nuclear powered towboats could be used on open seas to conserve diesel or other fuel on long trips. Additional payload equivalent to reduced fuel requirement could also be carried. For ships with electric propulsion, they could act as external power plants. This would correspond to electric locomotives on trains, driven by nuclear electric power.
The carriers could be standardized to convenient easily maneuvered size and economy exercised by towing/powering several with one tow/power boat like railway wagons.


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PostPosted: Feb 17, 2014 9:00 am 
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jagdish wrote:
Large ships are sometime maneuvered by diesel powered harbor tugs. Nuclear powered towboats could be used on open seas to conserve diesel or other fuel on long trips. Additional payload equivalent to reduced fuel requirement could also be carried. For ships with electric propulsion, they could act as external power plants. This would correspond to electric locomotives on trains, driven by nuclear electric power.
The carriers could be standardized to convenient easily maneuvered size and economy exercised by towing/powering several with one tow/power boat like railway wagons.


You don't want to cross the Atlantic in a little tug ship. Specially in the winter.
The tug idea isn't a bad one, since it would have a much higher utilization level, but it would only be acceptable for a very limited set of routes. It would also help contain the radiation BS that would come with such an idea. The tugs could be kept a minimum say two miles from shore. With diesel tugs taking the cargo from port to handoff to nuclear tugs.
Maybe this model could evolve to tugs + barges, with a tug pulling multiple barges chained, allowing setups like three barges leave Boston, exchange two in NYC, exchange two in Philly, and so on. Like its done on trains.
But connecting and disconnecting stuff at sea, doesn't sound like an easy thing. I just don't know.

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PostPosted: Feb 18, 2014 4:18 am 
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Perhaps something similar to stern barge lifting cargo ships, have a lift/crane on the stern of a cargo ship for a nominally floating power barge (standard unit size barge with electrical power offload, and maybe some self powered electric thrusters, plus small diesel backup). The cargo ship would also have a nominal backup diesel for minimal forward propulsion on it's electric drivetrain. The assumption is the cargo ship will be handled by tugs near port (once you get to megasized Panamax and above that's reasonable), but the primary powerplant is divorced from the running gear. Easy enough to demo with a diesel or gas turbine demo power barge. That russian nuclear power barge is basically setting up the underlying barge class for ship type certification, and stern lift cargo barge type ships are a well understood design. The only pain is doing the power barge pickup/lift offshore (beyond the 12 mile limit) for jurisdictions that dislike the power barge getting close.

Other option is something like a semisubmersible Dockwise ship or LPD with a stern wet deck/dock to lift the power barge from below rather than lift from above via crane rig.


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PostPosted: Feb 18, 2014 9:36 am 
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Personally I like the idea of making the power module submersible and docking it up from below.

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PostPosted: Feb 20, 2014 3:14 am 
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KitemanSA wrote:
Personally I like the idea of making the power module submersible and docking it up from below.


Nothing wrong with that, and potential dual use as a fixed undersea nuke powerplant for semi-permanent offshore emplacement (established site with subsea power cables and transformers, but the modules are retrieved for refueling, much like that DCNS concept.

Submersible also means it can do the equivalent of a moonpool entry into the underside of a ship. I guess this would be similar to how some new FPSO ships connect to their moored turrets?

The underlying problem of open ocean pickup under poor weather conditions doesn't really go away though even with a submersible barge. There is the additional issue of enough depth in local waters to support entry from the underside. The littoral waters around some ports may simply be insufficient to come up from underneath. Perhaps the equivalent of a stern opening connected to a long divot or tunnel in the bottom of the ship, allowing a long submarine style cylindrical vessel to dock from the rear might fix the depth issue, but then changes the docking problem to "threading a needle"...


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PostPosted: Feb 20, 2014 11:03 am 
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How about a simple power cable between the nuclear power station and the ship with electric motors?
The nuclear power station could still be submersible so that in the event of extreme ocean conditions where the ships will sink the nuclear power station could go down where things are calmer.


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PostPosted: Feb 21, 2014 2:58 am 
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A number of interesting suggestions have come up, most of which could be workable. In my opinion, however, there are two very workable arrangements for nuclear power unit separate from the main carrier.
1. Main propulsion arrangement in the towboat towing a raft with limited maneuverability. The carriers concentrate on payload.
2. Main propulsion of electric type on the ship with the nuclear boat as a towed power station. In this case both the cable and hawser has to be carried on the towed power station.
Stability in rough weather may be important for both in either case.


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