Monday, August 08, 2011

Civilian Marine Nuclear Propulsion

The 22,000 tonne US-built NS Savannah, was commissioned in 1962. It had a 74 MWt reactor delivering 16.4 MW to the propeller.

The 1960s era US civilian nuclear power vessel, Savannah, functioned as both a cargo and a passenger ship.
For a few brief years during the Kennedy and Johnson administrations, the vessel was a nautical superstar, touring the world as an ambassador for the peaceful use of nuclear energy and playing host to royalty. In May 1964, it drew more than 13,000 visitors during a call here.

...Still owned and maintained by the Federal Maritime Administration and regulated by the Nuclear Regulatory Commission, the ship is occasionally opened to visitors. Groups can arrange tours by request, as long as they don't expect too much in the way of air conditioning, elevators or other modern comforts. _LATimes

The German-built 15,000 tonne Otto Hahn cargo ship and research facility sailed some 650,000 nautical miles on 126 voyages in 10 years without any technical problems. It had a 36 MWt reactor delivering 8 MW to the propeller.
The 8000 tonne Japanese Mutsu was the third civil vessel, put into service in 1970. It had a 36 MWt reactor delivering 8 MW to the propeller. It was dogged by technical and political problems and was an embarrassing failure. These three vessels used reactors with low-enriched uranium fuel (3.7 - 4.4% U-235).

In 1988 the NS Sevmorput was commissioned in Russia, mainly to serve northern Siberian ports. It is a 61,900 tonne 260 m long LASH-carrier (taking lighters to ports with shallow water) and container ship with ice-breaking bow. It is powered by the same KLT-40 reactor as used in larger icebreakers, delivering 32.5 propeller MW from the 135 MWt reactor, and it needed refuelling only once to 2003.

A more powerful Russian icebreaker of 110 MW net and 55,600 dwt is planned, with further dual-draught ones of 32,400 dwt and 60 MW power at propellers. The first of these third-generation icebreakers is expected to be finished in 2015 at a cost of RUB 17 billion. _WorldNuclearNews
The Russians are devoting a good deal of effort to the development of a floating nuclear infrastructure that can be used to develop rich Arctic energy resources. To this point, no other nation's industries are as devoted to the development of non-military nuclear marine propulsion.

The world's naval forces have a good safety record with regard to nuclear marine propulsion. More from Rod Adams:
No Western nuclear ship has been lost because of a power failure.

Nuclear propulsion is clean. A nuclear engine can push a sealed submarine for months at a time without affecting the atmosphere in the ship.

Nuclear engines can be very powerful for a given total propulsion plant weight. Though the exact numbers are classified, it is obvious that an engine that can drive an 80,000 ton aircraft carrier at 35 knots into the wind while launching aircraft with steam driven catapults has a significant power capacity.

Based on the amount of payload on nuclear carriers compared to fossil fuel driven carriers, the nuclear engines require less space and weight than the oil fired steam turbines that they replaced.

Purely on capability, nuclear power is worth a look. Cost is a hurdle, however, since aircraft carriers and large submarines are several billion dollar machines. _RodAdams
High cost is a problem for civilian applications, and the highly-enriched nature of the fuel used in marine reactors could also be a problem.
they deliver a lot of power from a very small volume and therefore run on highly-enriched uranium (>20% U-235, originally c 97% but apparently now 93% in latest US submarines, c 20-25% in some western vessels, 20% in the first and second generation Russian reactors (1957-81)*, then 45% in 3rd generation Russian units, 40% in India's Arihant)

...The long core life is enabled by the relatively high enrichment of the uranium and by incorporating a "burnable poison" such as gadolinium - which is progressively depleted as fission products and actinides accumulate. These accumulating poisons would normally cause reduced fuel efficiency, but the two effects cancel one another out.

However, the enrichment level for newer French naval fuel has been dropped to 7.5% U-235, the fuel being known as 'caramel', which needs to be changed every ten years or so. This avoids the need for a specific military enrichment line, and some reactors will be smaller versions of those on the Charles de Gaulle. In 2006 the Defence Ministry announced that Barracuda class subs would use fuel with "civilian enrichment, identical to that of EdF power plants," which may be an exaggeration but certainly marks a major change there. _NWN
The French use of 7.5% U-235 is a promising development, which could help open the way to easier approval for civilian marine reactors.

Another promising trend for civilian nuclear marine power is the development of factory-built and transportable small modular reactors (SMRs), which are being designed to provide power anywhere between 25 MW and 250 MW. Many of these smaller designs could be fitted onto a large ship, perhaps in multiple-reactor configurations.

One other application for civilian nuclear marine propulsion which should be mentioned, is the civilian seastead. A seastead is a permanent floating workplace and residence for large numbers of people. Well designed seasteads could float the open oceans, performing many jobs which require long periods of time offshore. Nuclear power is a natural fit for such floating cities.

Most naval reactors can go 10 years or more without re-fueling. This is a definite advantage for extended cruises. And nuclear fuel is relatively inexpensive, in comparison with fossil fuel costs. It is the up-front costs for nuclear power which represent the greatest expense. And those up-front costs represent enormous opportunities to the innovative engineer.

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