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(Updated August 2010)
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largest submarines are the 26,500 tonne Russian Typhoon-class, powered by twin 190 MWt PWR reactors, though these were superseded by the 24,000 t Oscar-II class (eg Kursk) with the same power plant.
The safety record of the US nuclear navy is excellent, this being attributed to a high level of standardisation in naval power plants and their maintenance, and the high quality of the Navy's training program. However, 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 Russia's third generation of marine PWRs in the late 1970s safety and reliability had become a high priority.
Nuclear Naval Fleets
Russia built 248 nuclear submarines and five naval surface vessels (plus 9 icebreakers) powered by 468 reactors between 1950 and 2003, and was then operating about 60 nuclear naval vessels.
At the end of the Cold War, in 1989, there were over 400 nuclear-powered submarines operational or being built. At least 300 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 understood to be about 120, including new ones commissioned. India launched its first in 2009, Arihant, based on the Russian Akula-1 class, with a single 85 MWt PWR. (It is also leasing a 12,770 tonne Russian Akula-II class nuclear attack submarine for ten years.)
* In 2007 Russia had about 40 retired subs from its Pacific fleet alone awaiting scrapping. In November 2008 it was reported that Russia intended to scrap all decommissioned nuclear submarines by 2012, the total being more than 200 of the 250 built to date. Most Northern Fleet submarines had been dismantled at Severodvinsk, and most remaining to be scrapped were with the Pacific Fleet.
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 seven nuclear icebreakers and a nuclear freighter in service.
The US Navy has accumulated over 5500 reactor years of accident-free experience, and operates more than 80 nuclear-powered ships (with 103 reactors as of early 2005). Russia has logged 6000 nautical reactor years.
Russia has announced that it will build eight new nuclear submarines to carry strategic missiles in its plan to 2015.
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, to year-round.
The icebreaker Lenin was the world's first nuclear-powered surface vessel (20,000 dwt), commissioned in 1959. It remained in service for 30 years to 1989, being retired due to the hull being worn thin from ice friction. It initially had three 90 MWt OK-150 reactors, but these were badly damaged during refueling in 1965 and 1967. In 1970 they were replaced by two 171 MWt OK-900 reactors providing steam for turbines which generated electricity to deliver 34 MW at the propellers.
It led to a series of larger icebreakers, the six 23,500 dwt Arktika-class, launched from 1975. These powerful vessels have two 171 MWt OK-900 reactors delivering 54 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. Rossija, Sovetskiy Soyuz and Yamal were in service towards the end of 2008, with Sibir decommissioned and Arktika retired in October 2008.
The seventh and largest Arktika class icebreaker - 50 Years of Victory (50 Let Pobedy) - was built by the Baltic shipyard at St Petersburg and after delays during construction it entered service in 2007 (twelve years later than the 50-year anniversary of 1945 it was to commemorate). It is 25,800 dwt, 160 m long and 20m wide, and is designed to break through ice up to 2.8 metres thick. Its performance in service has been impressive.
For use in shallow waters such as estuaries and rivers, two shallow-draft Taymyr-class icebreakers of 18,260 dwt with one reactor delivering 35 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 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.
Russian experience with nuclear powered Arctic ships totals about 300 reactor-years in 2009. In 2008 the Arctic fleet was transferred from the Murmansk Shipping Company under the Ministry of Transport to Atomflot, under Rosatom.
Nuclear propulsion systems
Naval reactors (with the exception of the ill-fated Russian Alfa class described below) have been pressurised water types, which differ from commercial reactors producing electricity in that:
* An IAEA Tecdoc reports discharge assay of early submarine used fuel reprocessed at Mayak being 17% U-235.
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.
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, US, and British navies rely on steam turbine propulsion, the French and Chinese in submarines 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. A new Russian test-bed submarine is diesel-powered but has a very small nuclear reactor for auxiliary power.
The Russian Alfa-class submarines had a single liquid metal cooled reactor (LMR) of 155 MWt and using very highly enriched uranium - 90% enriched U-Be fuel. 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.
The US Navy's second nuclear submarine had a sodium-cooled power plant (S2G). The USS Seawolf, SSN-575, operated for nearly two years 1957-58 with this. The intermediate-spectrum reactor raised its incoming coolant temperature over ten times as much as the Nautilus' water-cooled plant, providing superheated steam, and it offered an outlet temperature of 454°C, compared with the Nautilus’ 305°C. It was highly efficient, but offsetting this, the plant had serious operational disadvantages. Large electric heaters were required to keep the plant warm when the reactor was down to avoid the sodium freezing. The biggest problem was that the sodium became highly radioactive, with a half-life of 15 hours, so that the whole reactor system had to be more heavily shielded than a water-cooled plant, and the reactor compartment couldn’t be entered for many days after shutdown. The reactor was replaced with a PWR type (S2Wa) similar to Nautilus.
Reactor power ranges from 10 MWt (in a prototype) up to 200 MWt in the larger submarines and 300 MWt in surface ships such as the Kirov-class battle cruisers.
The smallest nuclear submarines are the French Rubis-class attack subs (2600 dwt) in service since 1983, and these have a 48 MW integrated PWR reactor from Technicatome which is variously reported as needing no refuelling for 30 years, or requiring refuelling every seven years. The French aircraft carrier Charles de Gaulle (38,000 dwt), commissioned in 2000, has two K15 integrated PWR units driving 61 MW Alstom turbines and the system can provide 5 years running at 25 knots before refuelling. The Le Triomphant class of ballistic missile submarines (12,640 dwt - the last launched in 2008) uses these K15 naval PWRs of 150 MWt and 32 shaft MW. The Barracuda class (4765 dwt) attack submarines, will have hybrid propulsion: electric for normal use and pump-jet for higher speeds. Areva TA (formerly Technicatome) will provide six reactors apparently of only 50 MWt and based on the K15 for the Barracuda submarines, the first to be commissioned in 2017. As noted above, they will use low-enriched fuel.
French integrated PWR system for submarine(steam generator within reactor pressure vessel)
British Vanguard class ballistic missile submarines of 15,800 t have a single PWR2 reactor with two steam turbines driving a single pump jet of 20.5 MW. New versions of this with "Core H" will require no refuelling over the life of the vessel*. UK Astute class attack subs of 7800t have a modified PWR2 reactor driving two steam turbines and a single pump jet variously reported as 11.5 or 20.5 MW, and are being commissioned from 2010. Russia's 19,400 tonne Oscar-II class has two 190 MWt reactors with steam turbines delivering 73 MW, and its 12,700 tonne Akula-II class has a single 190 MWt unit powering a 32 MW steam turbine.
* Rolls Royce claims that the Core H PWR2 has six times the (undisclosed) power of its original PWR1 and runs four times as long. The Core H is Rolls Royce's sixth-generation submarine reactor core.
Russia's large Arktika class icebreakers use two OK-900A (essentially KLT-40) nuclear reactors of 171 MW each with 241 or 274 fuel assemblies of 45-75% enriched fuel and 3-4 year refuelling interval. They drive steam turbines and each produces up to 33 MW at the propellers, though overall power is 54 MW. The two Tamyr class icebreakers have a single 171 MW KLT-40 reactor giving 35 MW propulsive power. Sevmorput uses one 135 MW KLT-40 unit producing 32.5 MW propulsive, and all those use 90% enriched fuel. (The now-retired Lenin's first OK-150 reactors used 5% enriched fuel but were replaced by OK-900 units with 45-75% enriched fuel.) Most of the Arktika-class vessels have had operating life extensions based on engineering knowledge built up from experience with Arktika itself. It was originally designed for 100,000 hours of reactor life, but this was extended first to 150,000 hours, then to 175,000 hours. In practice this equated to a lifespan of eight extra years of operation on top of the design period of 25. In that time, Arkitka covered more than 1 million nautical miles.
For the next generation of Russian icebreakers, integrated light water reactor designs are being investigated possibly to replace the conventional PWR. OKBM Afrikantov is developing a new icebreaker reactor – RITM-200 – to replace the current KLT reactors. This is an integral 210 MWt, 55 MWe PWR with inherent safety features. The first icebreaker to be equipped with this is due to start construction in 2010. For floating nuclear power plants (see below) a single RITM-200 would replace twin KLT-40S (but yield less power).
India's Arihant (6000 dwt) has an 85 MWe PWR using 40% enriched uranium driving a 35 MW steam turbine.
Brazil's navy is proposing to build an 11 MW prototype reactor by 2014 to operate for about eight years, with a view to a full-sized version using low-enriched uranium being in a submarine to be launched in 2021.
Dismantling decommissioned 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 (the rest being recycled normally). In Russia the whole vessels, or the sealed reactor sections, sometimes remain stored afloat indefinitely, though western-funded programs are addressing this and all decommissioned submarines are due to be dismantled by 2012. In 2009 Rosatom said that by late 2010, 191 out of 198 decommissioned Russian submarines would be dismantled.
Marine reactors used for power supply, Floating Nuclear Power Plants
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.
Between 1967 and 1976 an ex-army US Liberty ship of about 12,000 tonnes built in 1945, the Sturgis (but renamed SS Green Port) functioned as a Floating Nuclear Power Plant, designation MH-1A, moored on Gatun Lake, Panama Canal Zone. It had a 45 MWt/ 10 MWe (net) PWR which provided power to the Canal Zone.
Russia has under construction at St Petersburg the first of a series of floating power plants for their northern and far eastern territories. Two OKBM KLT-40S reactors derived from those in icebreakers, but with low-enriched fuel (less than 20% U-235), will be mounted on a 21,500 tonne, 144 m long barge. Refuelling interval is 3-4 years on site, and at the end of a 12-year operating cycle the whole plant is returned to a shipyard for a 2-year overhaul and storage of used fuel, before being returned to service. See also Russia paper.
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 powered ships, it is likely that there will be renewed interest in marine nuclear propulsion.
The head of the large Chinese shipping company Cosco suggested in December 2009 that container ships should be powered by nuclear reactors in order to reduce greenhouse gas emissions from shipping. He said that Cosco is in talks with China's nuclear authority to develop nuclear powered freight vessels.
Nuclear power seems most immediately promising for the following:
Sources:Jane's Fighting Ships, 1999-2000 edition;J Simpson 1995, Nuclear Power from Underseas to Outer Space, American Nuclear SocietyThe Safety of Nuclear Powered Ships, 1992 Report of NZ Special Committee on Nuclear PropulsionBellona 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.