Nuclear marine propulsion is propulsion of a ship powered by a
nuclear reactor.
Naval nuclear propulsion is propulsion that specifically refers to naval warships (see
Nuclear navy).
A nuclear fuel element for the cargo ship
NS Savannah. The element contains four bundles of 41 fuel rods. The uranium oxide is enriched to 4.2 and 4.6 percent of U-235
Power plants
Naval
reactors are of the
pressurized water type which differ from commercial reactors producing
electricity in that:
- they have a high power density in a small volume; some run on low-enriched uranium (requiring frequent refuelings), others run on highly enriched uranium (>20% U-235, varying from over 96% in U.S. submarines (They do not need to be refueled as often and are quieter in operation from smaller core) to between 30–40% in Russian submarines to lower levels in some others),
- the fuel is not UO2 (uranium oxide) but a metal-zirconium alloy (circa 15% U with 93% enrichment, or more U with lower enrichment),
The long core life is enabled by the relatively high enrichment of the
uranium and by incorporating a "burnable
poison" in the cores which is progressively depleted as
fission products and
minor actinides accumulate, leading to reduced
fuel efficiency. The two effects cancel each other out. One of the technical difficulties is the creation of a fuel which will tolerate the very large amount of radiation damage. It is known that during use the properties of
nuclear fuel change; it is quite possible for fuel to
crack and for
fission gas bubbles to form.
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.)
Reactor sizes range up to 55
MW in the larger submarines and surface ships. The French s have a 48 MW reactor which needs no refueling for 30 years.
The
Russian,
U.S. and
British navies rely on
steam turbine propulsion, while the French and Chinese use the turbine to generate electricity for propulsion (
turbo-electric propulsion). Most Russian submarines as well as most American aircraft carriers since
CVN-65 are powered by two reactors (although
Enterprise has eight). U.S., British, French and Chinese submarines are powered by one.
Decommissioning nuclear-powered submarines has become a major task for US and Russian navies. After defuelling, U.S. practice is to cut the reactor section from the vessel for disposal in shallow land burial as low-level waste (see the
Ship-Submarine recycling program). In Russia, the whole vessels, or the sealed reactor sections, typically remain stored afloat, although a new facility near Sayda Bay is beginning to provide storage in a concrete-floored facility on land for some submarines in the Far North.
Russia is well advanced with plans to build a
floating nuclear power plant for their far eastern territories. The design has two 35 MW units based on the
KLT-40 reactor used in
icebreakers (with refueling every four years). Some Russian naval vessels have been used to supply electricity for domestic and industrial use in remote far eastern and Siberian towns.
History
Under the direction of
Admiral Hyman G. Rickover, the design, development and production of nuclear marine propulsion plants started in the
USA in the 1940s, with the first test reactor being started up in 1953. The first nuclear-powered submarine,
USS Nautilus (SSN-571), put to sea in 1955. Much of the early development work on naval reactors was done at the
Naval Reactor Facility on the campus of the
Idaho National Laboratory.
This marked the transition of submarines from slow underwater vessels to warships capable of sustaining 20-25
knots (37-46
km/h) submerged for many weeks.
Nautilus led to the parallel development of further s, powered by single reactors, and a cruiser,
USS Long Beach (CGN-9), in 1961, powered by two reactors. The aircraft carrier
USS Enterprise, commissioned in 1962, was powered by eight reactor units in 1960.
Enterprise remains in service.
By 1962 the
United States Navy had 26 nuclear submarines operational and 30 under construction. Nuclear power had revolutionized the Navy. The technology was shared with the
United Kingdom, while
French,
Soviet,
Indian and
Chinese developments proceeded separately.
After the
Skate-class vessels, reactor development proceeded and in the USA a single series of standardized designs was built by both
Westinghouse and
General Electric, one reactor powering each vessel.
Rolls Royce built similar units for
Royal Navy submarines and then developed the design further to the PWR-2 (
pressurized water reactor).
The largest nuclear submarines ever built are the 26,500 tonne Russian .
Civil vessels
Development of
nuclear merchant ships began in the 1950s, but has not generally been commercially successful. The US-built
NS Savannah, was commissioned in 1962 and decommissioned eight years later. It was a technical success, but not economically viable. The German-built
Otto Hahn cargo ship and research facility sailed some on 126 voyages in 10 years without any technical problems. However, it proved too expensive to operate and was converted to diesel. The Japanese
Mutsu was the third civil vessel. It was dogged by technical and political problems and was an embarrassing failure. All three vessels used reactors with low-enriched uranium fuel.
The fourth nuclear merchant ship,
Sevmorput, operates successfully in the specialised environment of the
Northern Sea Route. Recently there has been renewed interest in nuclear propulsion, and some proposals have been drafted. For example, the cargo coaster is a new design for a nuclear cargo ship. Using the new
micro nuclear reactors, other existing cargo ships could potentially be converted to nuclear propulsion as well.
Nuclear propulsion has proven both technically and economically feasible for
nuclear powered icebreakers in the
Soviet Arctic. The power levels and energy required for icebreaking, coupled with refueling difficulties for other types of vessels, are significant factors. The
Soviet icebreaker Lenin was the world's first nuclear-powered surface vessel and remained in service for 30 years (new reactors were fitted in 1970). It led to a series of larger icebreakers, the 23,500
ton , launched from 1975. These vessels have two reactors and are used in deep Arctic waters.
NS Arktika was the first surface vessel to reach the
North Pole.
For use in shallow waters such as estuaries and rivers, shallow-draft
Taymyr class icebreakers with one reactor are being 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.
Naval nuclear accidents
United States
Both sank for reasons unrelated to their reactor plants and still lie on the
Atlantic sea floor.
Russian or Soviet
- K-159 (radioactive discharge) (sank recently, 9 killed)
- K-219 (sank after collision, 6 killed)
- K-429 (sank twice, 16 killed)
While not all of these were reactor accidents, they have a major impact on nuclear marine propulsion and the global politics because they happened to nuclear vessels. Many of these accidents resulted in the sinking of the boat containing
nuclear weapons on board, which remain there to this day.
See also
