More Uranium neededFound this while I was searching for info on Uranium power plants, adds to the number of nuclear reactors in use substantially
Nuclear-powered Ships
Briefing Paper 32
March 2005
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Nuclear power is particularly suitable for vessels which need to be at sea for long periods without refuelling, or for powerful submarine propulsion.
Over 150 ships are powered by more than 220 small nuclear reactors and more than 12,000 reactor years of marine operation has been accumulated.
Most are submarines, but they range from icebreakers to aircraft carriers.
In future, constraints on fossil fuel use in transport may bring marine nuclear propulsion into more widespread use.
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Work on nuclear marine propulsion started in the 1940s, and the first test reactor started up in USA in 1953. The first nuclear-powered submarine, USS Nautilus, put to sea in 1955.
This marked the transition of submarines from slow underwater vessels to warships capable of sustaining 20-25 knots submerged for weeks on end. The submarine had come into its own.
Nautilus led to the parallel development of further (Skate-class) submarines, powered by single pressurised water reactors, and an aircraft carrier, USS Enterprise, powered by eight reactor units in 1960. A cruiser, USS Long Beach, followed in 1961 and was powered by two of these early units. Remarkably, the Enterprise remains in service.
By 1962 the US Navy had 26 nuclear submarines operational and 30 under construction. Nuclear power had revolutionised the Navy.
The technology was shared with Britain, while French, Russian and Chinese developments proceeded separately.
After the Skate-class vessels, reactor development proceeded and in the USA a single series of standardised designs was built by both Westinghouse and GE, one reactor powering each vessel. Rolls Royce built similar units for Royal Navy submarines and then developed the design further to the PWR-2.
Russia developed both PWR and lead-bismuth cooled reactor designs, the latter not persisting. Eventually four generations of submarine PWRs were utilised, the last entering service in 1995 in the Severodvinsk class.
The largest submarines are the 26,500 tonne Russian Typhoon-class, powered by twin 190 MWt PWR reactors, though these were superseded by the 24,000 t Oscar-II class (eg Kursk) with the same power plant.
Compared with the excellent safety record of the US nuclear navy, early Soviet endeavours resulted in a number of serious accidents - five where the reactor was irreparably damaged, and more resulting in radiation leaks. However, by the third generation of marine PWRs in the late 1970s safety had become paramount.
Nuclear Naval Fleets
Russia built 248 nuclear submarines and five naval surface vessels powered by 468 reactors between 1950 and 2003, and was then operating about 60.
At the end of the Cold War, in 1989, there were over 400 nuclear-powered submarines operational or being built. Some 250 of these submarines have now been scrapped and some on order cancelled, due to weapons reduction programs. Russia and USA had over one hundred each in service, with UK and France less than twenty each and China six. The total today is about 160.
The USA has the main navy with nuclear-powered aircraft carriers (11), while both it and Russia have had nuclear-powered cruisers (USA: 9, Russia 4). Russia has eight nuclear icebreakers in service. The US Navy has accumulated over 5500 reactor years of accident-free experience, and operates more than 80 nuclear-powered ships (with 105 reactors as of Aug 2004). Russia has logged 6000 nautical reactor years.
Civil Vessels
Nuclear propulsion has proven technically and economically essential in the Russian Arctic where operating conditions are beyond the capability of conventional icebreakers. The power levels required for breaking ice up to 3 metres thick, coupled with refuelling difficulties for other types of vessels, are significant factors. The nuclear fleet has increased Arctic navigation from 2 to 10 months per year, and in the Western Arctic, year-round.
The icebreaker Lenin was the world's first nuclear-powered surface vessel (20,000 dwt) and remained in service for 30 years, though new reactors were fitted in 1970. It led to a series of larger icebreakers, the six 23,500 dwt Arktika-class, launched from 1975. These powerful vessels have two reactors delivering 56 MW at the propellers and are used in deep Arctic waters. The Arktika was the first surface vessel to reach the North Pole, in 1977.
For use in shallow waters such as estuaries and rivers, two shallow-draft Taymyr-class icebreakers of 18,260 dwt with one reactor delivering 38 MW were built in Finland and then fitted with their nuclear steam supply system in Russia. They are built to conform with international safety standards for nuclear vessels and were launched from 1989.
Development of nuclear merchant ships began in the 1950s but on the whole has not been commercially successful. The 22,000 tonne US-built NS Savannah, was commissioned in 1962 and decommissioned eight years later. It was a technical success, but not economically viable. It had a 74 MWt reactor delivering 16.4 MW to the propeller. 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. However, it proved too expensive to operate and in 1982 it was converted to diesel.
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 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 30 propeller MW from the 135 MWt reactor and it needed refuelling only once to 2003.
Russian experience with nuclear powered Arctic ships totalled 250 reactor-years in 2003. A more powerful 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.
Power plants
Naval reactors (with one exception) have been pressurised water types, which differ from commercial reactors producing electricity in that:
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, and up to 45% in later Russian ones),
the fuel is not UO2 but a uranium-zirconium or uranium-aluminium alloy (c15%U with 93% enrichment, or more U with less - eg 20% - U-235) or a metal-ceramic (Kursk: U-Al zoned 20-45% enriched clad in zircaloy, with c 200kg U-235 in each 200 MW core),
they have long core lives, so that refuelling is needed only after 10 or more years, and new cores are designed to last 50 years in carriers and 30-40 years in submarines (US Virginia class: lifetime),
the design enables a compact pressure vessel while maintaining safety. The Sevmorput pressure vessel for a relatively large marine reactor is 4.6 m high and 1.8 m diameter, enclosing a core 1 m high and 1.2 m diameter.
thermal efficiency is less than in civil nuclear power plants due to the need for flexible power output, and space constraints for the steam system.
The long core life is enabled by the relatively high enrichment of the uranium and by incorporating a "burnable poison" such as gadolinium in the cores which is progressively depleted as fission products and actinides accumulate, leading to reduced fuel efficiency. The two effects cancel one another out.
Long-term integrity of the compact reactor pressure vessel is maintained by providing an internal neutron shield. (This is in contrast to early Soviet civil PWR designs where embrittlement occurs due to neutron bombardment of a very narrow pressure vessel.)
The Russian Alfa-class submarines had a single liquid metal cooled reactor (LMR) of 155 MWt and using very highly enriched uranium. These were very fast, but had operational problems in ensuring that the lead-bismuth coolant did not freeze when the reactor was shut down. The design was unsuccessful and used in only eight trouble-plagued vessels.
Reactor power ranges from 10 MWt (in a prototype) up to 200 MW (thermal) in the larger submarines and 300 MWt in surface ships such as the Kirov-class battle cruisers. The French Rubis-class submarines have a 48 MW reactor which needs no refuelling for 30 years. Russia's Oscar-II class has two 190 MWt reactors.
The Russian, US and British navies rely on steam turbine propulsion, the French and Chinese use the turbine to generate electricity for propulsion. Russian ballistic missile submarines as well as all surface ships since the Enterprise are powered by two reactors. Other submarines (except some Russian attack subs) are powered by one.
The larger Russian icebreakers use two KLT-40 nuclear reactors each with 241 or 274 fuel assemblies of 30-40% enriched fuel and 3-4 year refuelling interval. They drive steam turbines and each produce up to 33 MW (44,000 hp) at the propellers. Sevmorput uses one of the same units, though it is said to use 90% enriched fuel.
For the next generation of Russian icebreakers, integrated light water reactor designs are being investigated possibly to replace the conventional PWR.
click to enlarge
UK nuclear submarine layout
Decommissioning nuclear-powered submarines has become a major task for US and Russian navies. After defuelling, normal practice is to cut the reactor section from the vessel for disposal in shallow land burial as low-level waste. In Russia the whole vessels, or the sealed reactor sections, sometimes remain stored afloat indefinitely.
A marine reactor was used to supply power (1.5 MWe) to a US Antarctic base for ten years to 1972, testing the feasibility of such air-portable units for remote locations. Russia is well advanced with plans to build a floating power plant for their far eastern territories. The design has 2 x 35 MWe units based on the the KLT-40 reactor used in icebreakers (with refuelling every four years).
Future prospects
With increasing attention being given to greenhouse gas emissions arising from burning fossil fuels for international air and marine transport and the excellent safety record of nuclear powered ships, it is quite conceivable that renewed attention will be given to marine nuclear propulsion.
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Sources:
Jane's Fighting Ships, 1999-2000 edition;
ANSTO, Nuclear Services Section;
NucNet news # 294/96
J Simpson 1995, Nuclear Power from Underseas to Outer Space, American Nuclear Society
The Safety of Nuclear Powered Ships, 1992 Report of NZ Special Committee on Nuclear Propulsion
Bellona 1996, The Russian Northern Fleet and Civil Nuclear Powered Vessels (on web)
M B Maerli, in Bull. Atomic Scientists Sep-Oct 2001.
Rawool-Sullivan et al 2002, Technical and proliferation-related aspects of the dismantlement of Russian Alfa-class submarines, Nonproliferation Review, Spring 2002.
Thompson, C 2003, Recovering the Kursk, Nuclear Engineering Int'l, Dec 2003.
Mitenkov F.M. et al 2003, Prospects for using nuclear power systems in commercial ships in Northern Russia, Atomic Energy 94, 4.