Home' Baird Maritime : November 2011 Contents The nuclear debate polarises opinion. When you ask educated,
professional groups whether we should become more reliant on
nuclear power, 30-40 percent are positive. When you ask the
same group if they would be prepared to take their family on
holiday on a nuclear-powered cruise ship, the number drops
below 10 percent.
Perceptions and fear of the unknown loom large in the nuclear
debate. The Fukushima Daiichi crisis has done much to reverse a
slow thawing of opinion, leaving politicians scrambling to appease
voters with nuclear abolition.
However, perceptions and attitudes to risk change. Early motor
cars were preceded by a man walking with a red flag to warn
people. Even though road accident fatalities persist, the man and
the flag are long gone. We have learned to live with the risk.
For the maritime sector, compliance with IMO emissions
regulations bears down on owners and operators, adding to costs at
a time of vessel oversupply and faltering economic recovery.
Emissions legislation has triggered an emergent market for small
LNG-bunkered vessels that meet the regulations. However, the
question is "who blinks first?" Ship-owners will not convert to
LNG until there are sufficient LNG bunker ports in the right
locations. Ports will hesitate to provide LNG infrastructure until a
guaranteed market exists.
Nuclear propulsion meets these challenges in one stroke. There
are effectively zero emissions, and with refuelling intervals up to
ten years, minimal port dependency. Nuclear also offers an
increasingly competitive cost profile as fossil fuels become more
expensive. Nuclear propulsion deserves another look.
Nuclear shipping to date
The world's first nuclear surface vessel was 'Lenin', a
20,000DWT Soviet icebreaker commissioned in 1959. She
remained in service till 1989 and was only retired because the hull
was worn thin by ice friction. The first nuclear-propelled merchant
ship, the USA's passenger/cargo vessel 'Savannah', entered service
in 1962 and could travel 480,000 kilometres without refuelling.
Arguably the most successful nuclear merchant ship was
Germany's 'Otto Hahn'. A cargo ship and research facility, she was
launched in 1964 and refuelled in 1972, sailing over 650,000
nautical miles. For economic reasons, diesel propulsion was
installed in 1979, but her ten years under nuclear propulsion saw
no technical problems.
Today, the only commercial nuclear vessels in operation
are Russian icebreakers. All others are military vessels,
To date, the maritime nuclear propulsion unit of choice has been
the pressurised water reactor (PWR). Water is heated to 315°C and
pressurised up to 155 bar via nuclear fission in a strong reactor
containment structure. The pressurised water a secondary
independent water circuit, generating steam that drives a turbine,
which can be coupled to the prop shaft or used to generate electricity.
PWRs are stable due to their tendency to produce less power as
temperatures increase. However, the post-shutdown period of one
to three years requires cooling. It was this cooling that failed at
Fukushima, with high temperatures separating water into
hydrogen and oxygen, resulting in explosions. High pressures in
the primary water circuit require robust containment, adding to
build and operating costs.
New technologies are being developed, such as the uranium
nitride nuclear battery, currently being developed by Hyperion
at Los Alamos Laboratories in the USA. The battery measures 1.5
by 2.5 metres, and weighs around 50 tonnes. With a sealed
core and ten-year service life, such units would be easy to
remove and replace. The battery is fuelled by uranium -- but
there are better alternatives.
Thorium can generate significantly larger amounts of energy
than uranium, can be used in existing reactors without conversion
or enrichment, cannot be used as bomb material or cause a
meltdown, and produces waste that can be recycled as fuel. Spent
thorium fuel is radiotoxic for decades rather than millennia.
Thorium exists as a by-product of rare earths and is found
in greater abundance and higher concentrations than
uranium, making it cheaper and less environmentally damaging
to mine. The primary locations of thorium reserves are Australia,
India, Norway, the USA and Canada, improving supply security
Research is underway to commercialise thorium fuels. The
USA is funding research for a destroyer-sized thorium reactor in
2010, and India is developing a 300MW prototype of a thorium-
based advanced heavy water reactor (AHWR). India plans to meet
30 percent of electricity demand through thorium-based reactors
November 2011 BAIRD MARITIME
Marine Pressurised Water Reactor
NUCLEAR PROPULSION I
ADVANCES IN MARINE ENGINES AND PROPULSION SYSTEMS
WORTH ANOTHER LOOK?
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