(Updated January 2015)
- Nuclear power is particularly suitable for vessels which need to be at sea for long periods without refuelling, or for powerful submarine propulsion.
- Over 140 ships are powered by more than 180 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. So far, exaggerated fears about safety have caused political restriction on port access.
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 remained in service to the end of 2012.
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.
* 1955-66, 1963-92, 1976-2003, 1995 on, according to Bellona.
The largest submarines are the 26,500 tonne (34,000 t submerged) Russian Typhoon-class, powered by twin 190 MWt PWR reactors, though these were superseded by the 24,000 t Oscar-II class (eg Kursk) with the same power plant.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. There were more than 20 radiation fatalities.* Nevertheless, by Russia’s third generation of marine PWRs in the late 1970s safety and reliability had become a high priority. (Apart from reactor accidents, fires and accidents have resulted in the loss of two US and about 4 Soviet submarines, another four of which had fires resulting in loss of life.)
* The K-19 accident at sea in 1961 due to cooling failure in an early PWR resulted in 8 deaths from acute radiation syndrome (ARS) in repairing it (doses 7.5 to 54 Sv) and possibly more later as well as many high doses. The K-27 accident at sea in 1968 also involved coolant failure, this time in an experimental lead-bismuth cooled reactor, and 9 deaths from ARS as well as high exposure by other crew. In 1985 the K-431 was being refuelled in Vladivostok when a criticality occurred causing a major steam explosion which killed 10 workers. Over 200 PBq of fission products was released causing high radiation exposure of about 50 others, including ten with ARS.
Lloyd's Register shows about 200 nuclear reactors at sea, and that some 700 have been used at sea since the 1950s.
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. (Bellona gives 247 subs with 456 reactors 1958-95.) For operational vessels in 1997, Bellona lists 109 Russian submarines (plus 4 naval surface ships) and 108 attack submarines (SSN) and 25 ballistic missile ones apart from Russia.
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. Most or all are fuelled by high-enriched uranium (HEU).
* 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.
India launched its first nuclear submarine in 2009, the 6000 dwt Arihant SSBN, with a single 85 MW PWR fuelled by HEU driving a 70 MW steam turbine. It is reported to have cost US$ 2.9 billion. The INS Aridaman SSBN is under construction at the Ship Building Centre in Visakhapatnam, and due to be launched in 2015. Another SSBN and six nuclear SSNs are planned. India is also leasing an almost-new 7900 dwt (12,770 tonne submerged) Russian Akula-II class nuclear attack submarine for ten years from 2010, at a cost of US$ 650 million: the INS Chakra, formerly Nerpa. It has a single 190 MWt VM-5/ OK-659B PWR driving a 32 MW steam turbine and two 2 MWe turbogenerators.
The USA has the main navy with nuclear-powered aircraft carriers, while both it and Russia have had nuclear-powered cruisers (USA: 9, Russia 4). The USA had built 219 nuclear-powered vessels to mid 2010, and then had five submarines and an aircraft carrier under construction. All US aircraft carriers and submarines are nuclear-powered.
The US Navy has accumulated over 6200 reactor-years of accident-free experience involving 526 nuclear reactor cores over the course of 240 million kilometres, without a single radiological incident, over a period of more than 50 years. It operated 82 nuclear-powered ships (11 aircraft carriers, 71 submarines – 18 SSBN/SSGN, 53 SSN) with 103 reactors as of March 2010. In 2013 it had 10 Nimitz-class carriers in service (CVN 68-77), each designed for 50-year service life with one mid-life refuelling and complex overhaul of their two A4W Westinghouse reactors. The forthcoming Gerald Ford-class (CVN 78 on) will have some 800 fewer crew and two more powerful Bechtel A1B reactors driving four shafts. Late in 2014 the US Navy had 86 nuclear-powered vessels including 75 submarines.
The Russian Navy has logged over 6000 nautical reactor-years. It appears to have eight strategic submarines (SSBN/SSGN) in operation and 13 nuclear-powered attack submarines (SSN), plus some diesel subs. Russia has announced that it will build eight new nuclear SSBN submarines in its plan to 2015. Its only nuclear-powered carrier project was cancelled in 1992. It has one nuclear-powered cruiser in operation and three others being overhauled. In 2012 it announced that its third-generation strategic subs would have extended service lives, from 25 to 35 years.
In 2012 construction of a nuclear-powered deep-sea submersible was announced. This is based on the Oscar-class naval submarine and is apparently designed for research and rescue missions. It will be built by the Sevmash shipyard at Severodvinsk, which builds Russian naval submarines.
China has about 12 nuclear-powered submarines (7 SSN, 4-5 SSBN), and in February 2013 China Shipbuilding Industry Corp received state approval and funding to begin research on core technologies and safety for nuclear-powered ships, with polar vessels being mentioned but aircraft carriers being considered a more likely purpose for the new development. Its first nuclear powered submarine was decommissioned in 2013 after almost 40 years service.
France has a nuclear-powered aircraft carrier and ten nuclear submarines (4 SSBN, 6 Rubis class SSN). The UK has 12 submarines, all nuclear powered (4 SSBN, 8 SSN).
The occupational radiation doses to crew of nuclear vessels in very small. US Naval Reactors’ average annual occupational exposure was 0.06 mSv per person in 2013, and no personnel have exceeded 20 mSv in any year in the 34 years to then. The average occupational exposure of each person monitored at US Naval Reactors' facilities since 1958 is 1.03 mSv per year.
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, with six nuclear icebreakers and a nuclear freighter, 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, and was retired due to the hull being worn thin from ice abrasion. 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. Lenin is now a museum.
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-900A 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 are in service (launched 1985, 1990, 1992 respectively), with Sibir and Arktika decommissioned in 1992 and 2008. Soyuz has been in reserve but is being restored for service from 2017. Nominal service life is 25 years, but Atomflot commissioned a study on Yamal, and confirmed 30-year life for it. Atomflot has a service life extension program to take them up to 175,000 - 200,000 hours. Arktika class are 148 m long and 30 m wide, and designed to break 2 metres of ice.
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 propulsive power is about 54 MW. 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 171 MWt KLT-40M reactor delivering 35 MW propulsive were built in Finland and then fitted with their nuclear steam supply system in Russia. They – Taymyr and Vaygach – are built to conform with international safety standards for nuclear vessels and were launched in 1989 and 1990 respectively. They are 152 m long and 19 m wide, will break 1.77 metres of ice, and are expected to operate for at least 30 years.
Tenders were called for building the first of a new LK-60 series series of Russian icebreakers in mid-2012, and the contract was awarded to Baltijsky Zavod Shipbuilding in St Petersburg. The keel of Arctica was laid in November 2013 and it is to be delivered to Atomflot by the end of 2017 at a cost of RUR 37 billion. A RUR 84.4 billion contract for two more vessels was let in May 2014 to the same shipyard. The LK-60 (project 22220) vessel is to be dual-draught (10.5m with full ballast tanks, minimum 8.55m at 25,540 t), displacing up to 33,530 t, 173 m long, 34 m wide, and designed to break through 3 m thick ice at up to 2 knots. The wider 33 m beam at waterline is to match the 70,000 tonne ships it is designed to clear a path for, though a few of these with reinforced hulls are already using the Northern Sea Route. There is scope for more use: in 2011, 19,000 ships used the Suez Canal and only about 40 traversed the northern route. This increased in 2013 – see below.
The LK-60 will be powered by two RITM-200 reactors of 175 MWt each using low-enriched fuel (<20%), which together deliver 60 MW at the three propellers via twin turbine-generators and three motors. At 65% capacity factor refuelling is every 7-10 years, overhaul at 20 years, service life 40 years. It is designed to operate in the Western Arctic – in the Barents, Pechora and Kara Seas, as well as in shallow water of the Yenissei River and Ob Bay, for year-round pilotage (also as tug) of tankers, dry-cargo ships and vessels with special equipment to mineral resource development sites on the Arctic shelf. The Yamal LNG project is expected to need 200 shipping movements per year from Sabetta at the mouth of the Ob River. The vessel will have a smaller crew than its predecessors – only 62.
In January 2013 Rosatom called for bids to build two more of these universal icebreaker vessels, for delivery in 2019 and 2020, but closing of the tender was delayed to April 2014.
A more powerful Russian LK-110 icebreaker of 110 MW net and 55,600 dwt is planned.
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. The reactor used 4.2% and 4.6% enriched uranium. It was a technical success, but not economically viable. It had a 74 MWt reactor delivering 16.4 MW to the propeller, but the reactor was uprated to 80 MWt in 1964. 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 capable of breaking 1.5 metres of ice. It is powered by a KLT-40 reactor similar to the OK-900As used in larger icebreakers, but with only 135 MWt power delivering 32.5 propeller MW. It needed refuelling only once to 2003. The reactor was to be decommissioned about 2014, but Rosatom has approved overhauling it so that the ship is returned to service in 2016.
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. This is progressively becoming a commercial enterprise, with the 40% state subsidy of RUR 1262 million in 2011 due to phase out in 2014.
In August 2010 two Arktika-class icebreakers escorted the 100,000 dwt tanker Baltika, carrying 70,000 tonnes of gas condensate, from Murmansk to China via the Arctic Northern Sea Route (NSR), saving some 8000 km compared with the Suez Canal route. In November 2012 the Ob River LNG tanker with 150,000 cubic metres of gas as LNG, chartered by Russia's Gazprom, traversed the northern sea route from Norway to Japan accompanied by nuclear-powered icebreakers, the route cutting 20 days off the normal journey and resulting in less loss of cargo. It has a strengthened hull to cope with the Arctic ice. There are plans to ship iron ore and base metals on the northern sea route also.
In 2013 the Atomflot icebreakers supported freight transportation and emergency rescue operations along the Northern Sea Route (NSR), and freezing northern seas and estuaries of rivers. In the framework of the regulated activity paid for as per rates established by the Federal Tariff Service of Russia (FST), 151 steering operations were carried out for ships with cargo and in ballast to and from ports in the aquatic area of the NSR, including steering of ships with cargo for building Sabetta Port of JSC Yamal SPG to Okskaya Bay and steering of a convoy of Navy ships under a contract with the Ministry of Defence. Over the 2013 summer-autumn navigation season, 71 transit steering operations were carried out, including 25 foreign-flag ships. A total of 1,356,000 tonnes of various cargoes was shipped east and west through the aquatic area of the NSR.
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:
- 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 21% to 45% in 3rd generation Russian units (40% in India's Arihant).
- 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 (over 1.5 million kilometres) in most submarines.
- 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.
- There is no soluble boron used in naval reactors (at least US ones).
* 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. Reactors had to be kept running, even in harbour, since the external heating provision did not work. The design was unsuccessful and used in only eight trouble-plagued vessels, which were retired early.
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.
For many years the Los Angeles class submarines formed the backbone of the US SSN (attack) fleet, and 62 were built. They are 6900 dwt submerged, and have a 165 MW GE S6G reactor driving two 26 MW steam turbines. Refueling interval is 30 years. The US Virginia class SSN submarine has pump-jet propulsion built by BAE Systems and is powered by a PWR reactor (GE S9G) which does not need refueling for 33 years. They are about 7900 dwt, and ten were in operation as of late 2013, with more on order.
Unlike PWRs, boiling water reactors (BWRs) circulate water which is radioactive* outside the reactor compartment, and are also considered too noisy for submarine use.
* Radioactivity in the cooling water flowing through the core is mainly the activation product nitrogen-16, formed by neutron capture from oxygen. N-16 has a half-life on only 7 seconds but produces high-energy gamma radiation during decay.
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 two A4W units in US Nimitz class aircraft carriers are unofficially quoted at 104 shaft MW each (USS Enterprise had eight A2W units of 26 shaft MW and was refuelled three times). The Gerald Ford-class carriers have A1B reactors reported to be 240-300 MW each, but running a ship which is entirely electrical, including an electromagnetic aircraft launch system. The reactors are two to three times as powerful as the A4W units in Nimitz-class.
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 (14,335 dwt submerged – the last launched in 2008) uses these K15 naval PWRs of 150 MWt and 32 shaft MW with pump-jet propulsion. 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 (SSBN) of 15,900 dwt submerged 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 7400 dwt submerged have a modified (smaller) PWR2 reactor driving two steam turbines and a single pump jet reported as 11.5 MW, and are being commissioned from 2010. In March 2011 a safety assessment of the PWR2 design was released showing the need for safety improvement, though they have capacity for passive cooling to effect decay heat removal. The PWR3 for the Vanguard replacement will be largely a US design.
* 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.
Since 1959 Russia has used five types of PWRs in its civil; fleet: OK-150 in the Lenin until 1966 (3x90 MW), OK-900 subsequently in the Lenin (2x159 MW), OK-900A in the main Arktika class icebreaker fleet (2x171 MW), KLT-40M in two Tamyr class icebreakers (1x171 MW), and KLT-40 in the Sevmorput (1x135 MW).
Russia's main submarine power plant is the OK-650 PWR. It uses 20-45% enriched fuel to produce 190 MW. The 19,400 tonne Oscar II-class and 34,000 tonne Typhoon-class (NATO name, Akula-class in Russia) ballistic missile subs (SSBN) have two of these reactors with steam turbines together delivering 74 MW, and its new 24,000 t Borei-class ballistic missile sub along with Akula-(Russia: Shchuka-class), Mike- and Sierra-class attack subs (SSN) have a single OK-650 unit powering a 32 MW steam turbine. The Borei-class is the first Russian design to use pump-jet propulsion. (displacements: submerged). A 5th generation naval reactor is reported to be a super-critical type (SCWR) with single steam circuit and expected to run 30 years without refuelling. A full-scale prototype was being tested early in 2013.
Russia's large Arktika class icebreakers use two OK-900A (essentially KLT-40M) 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 propulsive power is about 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 LK-60 generation of Russian icebreakers, OKBM Afrikantov is developing a new reactor – RITM-200 – to replace the current KLT design. Under Project 22220 this is an integral 175 MWt PWR with inherent safety features and using low-enriched uranium fuel. Refueling is every seven years, over a 40-year lifespan. Two reactors drive two turbine generators and then three electric motors powering the propellers, producing 60 MW propulsive power. The first icebreaker to be equipped with these is due to start construction in 2013. For floating nuclear power plants (FNPP, see below) a single RITM-200 would replace twin KLT-40S (but yield less power).
The KLT-40S is a 4-loop version of the icebreaker reactor for floating nuclear power plants which runs on low-enriched uranium (<20%) and has a bigger core (1.3 m high instead of 1.0 m) and shorter refueling interval: 3 to 4.5 years. A variant of this is the KLT-20, specifically designed for FNPP. It is a 2-loop version with same enrichment but 10-year refueling interval.
OKBM has supplied 460 nuclear reactors for the Russian navy, and these have operated more than 6500 reactor-years.
India's Arihant (6000 dwt) has an 85 MWe PWR using 40% enriched uranium driving one or two 35 MW steam turbines. It has 13 fuel assemblies each with 348 fuel rods, and was built indigenously. The reactor went critical in August 2013. A 20 MW prototype unit had operated for several years from 2003.
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 its 6000 tonne, 100 m long SNBR submarine to be launched by 2025.
UK nuclear submarine layout
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 (originally Charles H. Cugle) 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 for nine years at a capacity factor of 54%. The propulsion unit of the original ship was removed and the entire midsection replaced with a 350 t steel containment vessel and concrete collision barriers, making it about 2.5 m wider than the rest of the ship, now essentially a barge. The containment vessel contained not only the reactor unit itself but the primary and secondary coolant circuits and electrical systems for the reactor.
In the 1970s Westinghouse in alliance with Newport News shipyard developed an Offshore Power Systems (OPS) concept, with series production envisaged at Jacksonville, Florida. In 1972 two 1210 MWe units were ordered by utility PSEG for offshore Atlantic City or Brigantine, New Jersey, but the order was cancelled in 1978. By the time NRC approval was granted in 1982 for building up to eight plants, there were no customers and Westinghouse closed down its OPS division. Two blogs here and here on the NRC website describe the saga. Westinghouse and Babcock & Wilcox are reported to be revisiting the concept.
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), are 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 two-year overhaul and storage of used fuel, before being returned to service. See also Russia NP paper.
China has a project with SNERDI in Shanghai designing a CAP-FNPP reactor. This is to be 200 MWt and relatively low-temperature (250°C), so only about 40 MWe with two external steam generators and five-year refueling
With increasing attention being given to greenhouse gas emissions arising from burning fossil fuels for international air and marine transport, particularly dirty bunker fuel for the latter, 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 world's merchant shipping is reported to have a total power capacity of 410 GWt, about one third that of world nuclear power plants.
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 was in talks with China's nuclear authority to develop nuclear powered freight vessels. However, in 2011 Cosco aborted the study after three years, following the Fukushima accident.
In 2010 Babcock International's marine division completed a study on developing a nuclear-powered LNG tanker (which requires considerable auxiliary power as well as propulsion). The study indicated that particular routes and cargoes lent themselves well to the nuclear propulsion option, and that technological advances in reactor design and manufacture had made the option more appealing.
In November 2010 the British maritime classification society Lloyd's Register embarked upon a two-year study with US-based Hyperion Power Generation (now Gen4 Energy), British vessel designer BMT Group, and Greek ship operator Enterprises Shipping and Trading SA "to investigate the practical maritime applications for small modular reactors." The research was to produce a concept tanker-ship design, based on a 70 MWt reactor such as Hyperion's. Hyperion (Gen4 Energy) had a three-year contract with the other parties in the consortium, which planned to have the tanker design certified in as many countries as possible. The project included research on a comprehensive regulatory framework led by the International Maritime Organisation (IMO), and supported by the International Atomic Energy Agency (IAEA) and regulators in countries involved.
In response to its members' interest in nuclear propulsion, Lloyd's Register has rewritten its 'rules' for nuclear ships, which concern the integration of a reactor certified by a land-based regulator with the rest of the ship. The overall rationale of the rule-making process assumes that in contrast to the current marine industry practice where the designer/builder typically demonstrates compliance with regulatory requirements, in the future the nuclear regulators will wish to ensure that it is the operator of the nuclear plant that demonstrates safety in operation, in addition to the safety through design and construction. Nuclear ships are currently the responsibility of their own countries, but none are involved in international trade. Lloyd's Register said it expected to "see nuclear ships on specific trade routes sooner than many people currently anticipate."
In 2014 two papers on commercial nuclear marine propulsion were published* arising from this international industry project led by Lloyd's Register. They review past and recent work in the area of marine nuclear propulsion and describe a preliminary concept design study for a 155,000 dwt Suezmax tanker that is based on a conventional hull form with alternative arrangements for accommodating a 70 MWt nuclear propulsion plant delivering up to 23.5 MW shaft power at maximum continuous rating (average: 9.75 MW). The Gen4Energy power module is considered. This is a small fast-neutron reactor using lead-bismuth eutectic cooling and able to operate for ten full-power years before refueling, and in service last for a 25-year operational life of the vessel. They conclude that the concept is feasible, but further maturity of nuclear technology and the development and harmonisation of the regulatory framework would be necessary before the concept would be viable.
* Hirdaris et al, 2014.
The UN's IMO adopted a code of safety for nuclear merchant ships, Resolution A.491(XII), in 1981, which is still extant and could be updated. Also Lloyd's Register has maintained a set of provisional rules for nuclear-propelled merchant ships, which it has recently revised.
Apart from naval use, where frequency of refueling is a major consideration, nuclear power seems most immediately promising for the following:
- Large bulk carriers that go back and forth constantly on few routes between dedicated ports – eg China to South America and NW Australia. They could be powered by a reactor delivering 100 MW thrust.
- Cruise liners, which have demand curves like a small town. A 70 MWe unit could give base-load and charge batteries, with a smaller diesel unit supplying the peaks. (The largest afloat today – Oasis class, with 100,000 t displacement – has about 60 MW shaft power derived from almost 100 MW total power plant.)
- Nuclear tugs, to take conventional ships across oceans
- Some kinds of bulk shipping, where speed is essential.
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