Energy, Nuclear & Sustainable Power: Rhodri Owen, Horizon Nuclear Power
NUCLEAR POWER PLANT.pptx
Transcript of NUCLEAR POWER PLANT.pptx
NUCLEAR POWER
PLANTProf Ir Dr. Ab Saman b. Abd Kader, PEng, MIEM,MCIT
Faculty of Mechanical Engineering,UTM
INTRODUCTION
Nuclear powered ships are becoming increasingly popular in advancingship technology.
Previous drawbacks for using nuclear power centred mainly around theinherent safety concerns for the crew; installation, maintenance anddisposal costs and the exceptionally high standards required forcomponent manufacturing and quality assurance.
These hurdles are slowly being overcome as more funds are beingallocated to social security and defense worldwide and as a greaterdemand is being placed on sustained performance efficiency in navalships.
Of course this does not mean to say that nuclear ships were not aroundin the earlier days.
Shown below is the picture of a nuclear ship which was taken nearly 4decades ago and shows a ship named "Otto Hahn" which was a
HOW DOES A NUCLEAR POWER PLANT ON
SHIP WORK
The energy generating house or propulsion plant of a nuclear powered
ship utilizes a nuclear reactor to generate heat.
The heat is generated within the nuclear reactor as a result of the
fissioning of the nuclear fuel.
Lead shields are placed around the reactor as a preventive measure
against the radiation produced from the fissioning process.
The nuclear propulsion plant operates as a pressurized water reactor
design containing both a primary and secondary system.
Primary sys tem : This is where water is circulated through the reactor,
piping loops, pumps and steam generators. As the heat transferred from
the reactor to the water is done at such a high pressure, it does not boil.
Instead, the water is pumped from the steam generator back to the
reactor for re-heating.
Secondary system: Steam which is produced at the
steam generators supply the energy required to drive the turbine
generators. The turbine generators then cause the propeller to rotate
thereby causing thrust and a forward motion to the ship.
Turbine generators are also utilized in supplying the ship with electricity.
Once the steam has passed through the turbines, it is cooled and
condensed into water and then fed back to the steam generators by the
feed pumps.
As can be noted, both the primary and secondary systems involve the
recirculation and renewal of water.
A TYPICAL NUCLEAR SHIP ARRANGEMENT
The above mentioned theory is generic in nature and good enough togive you a broad idea what a nuclear powered ship consists of.
In this section we will take a look at a specific arrangement of a nuclearship with the help of a diagram.
As you can see in the picture below the diagram is fairly self explanatoryand the nuclear components are shown on the left hand side of thediagram and the steam generation system which ultimately drives thepropeller shaft on the right hand side.
The nuclear reactor produces heat which is used to generate steam andthat steam in turn in used to provide motive power for turbines.
Of course this arrangement might vary in different kinds of ships but isgood enough to explain the overall idea.
INDEPENDENCE
The functionality of the propulsion plant does not require oxygen thereby
allowing the ship to operate independently from any external
atmospheric requirements.
Ship maneuvering and continuosuly changing operating performance
requirements dictate highly irregular power demands.
As can be imagined, the quality, strength and durability of component
parts are of crucial importance to ensure sustained durability under such
harsh conditions.
One should bear in mind that the internals of a nuclear reactor remain
inaccessible for inspection or replacement for an extensive period of
time.
FULL STEAM AHEAD FOR NUCLEAR
SHIPPING
Preparations are under way for nuclear reactors to
make a major comeback in commercial shipping.
Although shipping is already highly energy efficient, pressure has
come on the industry to lower emissions.
There is the potential for market-based measures for
controlling carbon dioxide emissions, while the entry into force of
strict International Maritime Organisation controls in 2020 provides a
firm deadline against which the industry can weigh the benefits of a
range of technology enhancements and fuel options.
But with no clear technological fix to lower emissions using
traditional diesel or LPG fuels, nuclear energy is emerging as a
practical option.
This trend has been developing quickly in recent years and the recentannouncement of a major joint research project on the topic is the mostsignificant to date.
Marine and energy consultants BMT Group and Enterprises Shipping andTrading have joined with start-up small reactor firm Hyperion and Lloyd'sRegister to "investigate the practical maritime applications for small modularreactors."
"We will see nuclear ships on specific trade routes sooner than manypeople currently anticipate," said Lloyd's Register CEO Richard Sadler.
The organisation has been an independent service provider to the shippingindustry for 250 years.
In response to its members' interest in nuclear propulsion Lloyd's Registerhas recently rewritten its 'rules' for nuclear ships, which concern theintegration of a reactor certified by a land-based regulator with the rest ofthe ship.
A draft of the rules was put before Lloyd's technical committee two weeksago and this represents a further step towards an international regulatoryre ime to ensure worldwide safet in a otential nuclear shi in sector.
Vince Jenkins of Lloyd's Register told World Nuclear News: "National
maritime regulators have little nuclear capability, so land based nuclear
regulators will be needed in support.
Since there are no internationally traded nuclear powered merchant
vessels today, our nuclear powered ship rules have suggested a
framework which may allow nuclear powered shipping to operate.
Within this suggested framework, we have developed the area where it
is felt that a ship classification society can add value and confidence to
the safety of nuclear powered vessels, the integration of the reactor
plant into the ship.“
The new program of joint research is meant to produce "a concept
tanker ship design based on conventional and modular concepts," said
Lloyd's.
It noted that "Special attention will be paid to analysis of a vessel's
lifecycle cost as well as to hull-form designs and structural layout,
"
Nuclear power looked set for a maritime role in the 1960s thanks to early
vessels like the Savannah and Otto Hahn,
although in the end the Savannah worked for only ten years and
the Otto Hahn was repowered with diesel engines after nine years.
The Japanese-built Mutsuoperated from 1970 until 1992 but none of
these ships was a commercial success.
A notable exception has been the icebreaker fleet that works Russia's
trade routes in the Arctic Ocean.
These vessels number only seven, but one is a cargo vessel and small
reactors of the same type are currently being fitted to the Akademik
Lomonosov , the world's first floating nuclear power plant, set for
deployment in Russia's far east.
Nevertheless, there remain about 200 small reactors at sea in militaryfleets but this technology cannot easily be transferred to the civil sectordue to the requirement of using low-enriched uranium (LEU).
In the military sector of recognised nuclear weapons states, high-enriched uranium allows more compact reactor designs with weight andcontrollability benefits.
The reactor of the Hyperion system uses LEU and measures about 1.5metres by 2.5 metres.
It would produce about 70 MWt - enough for about 25 MWe forpropulsion.
Its 'battery' design simplifies refuelling to a swap-out operation every 8-10 years with the possibility of managed lease arrangements similar toaircraft engines.
However, incorporation of any reactor in a ship would require extensive
radiation shielding, consideration of impact protection.
A step change in crew training would be required and there is a strong
case for crew to be supplied by reactor vendors.
Similar to nuclear power on land, the additional capital cost of nuclear
compared to fossil fuels is a significant obstacle despite the fact that
savings on fuel and potential emissions charges would make nuclear
economic in the long run.
One of the most effective ways for a diesel-powered vessel to save fuel
and emissions is to travel more slowly and avoiding this practical
constraint could make nuclear vessels particularly attractive for certain
cargoes and routes.
INTRODUCTION TO SHIPS POWERED BY
NUCLEAR ENERGY
The warships of many of the world’s navies are powered by nuclearenergy, normally provided by a Pressurized Water Reactor. (PWR)
The heat generated in nuclear reactors is used to raise steam to drivesteam turbines.
The turbine can either drive the ship’s shafts through a gearbox, or usethe electrical power to drive the propeller shaft.
Large submarines use nuclear energy because of its high power outputcoupled with the length of time between refueling.
These submarines are able to cruise around under the world’s oceanswithout surfacing for many months.
Other naval ships such as cruisers and aircraft carriers are also poweredby nuclear energy.
The use of nuclear energy to power merchant navy ships has not proven
very successful, with only a handful being built with nuclear reactors.
However there are numerous icebreakers operating in the Arctic using
nuclear energy because of the high power output required to break
through ice sometimes over a meter thick.
This is another article on the series of Nuclear Energy.
This covers the use of nuclear energy to power warships and
submarines.
We shall examine the nuclear fuel enrichment required, the operation of
the shipboard power plant, and the different methods of using this power
to drive the propeller shafts.
We begin with a quick overview of nuclear energy, moving on to its
application in powering the world’s warships and submarines.
NUCLEAR ENERGY OVERVIEW
Nuclear energy relies on the reactions of enriched uranium.
In a PWR, the enriched uranium is placed in fuel rods which are bundledtogether to form the fuel assembly.
The fuel assembly is placed in the core of the reactor where the reactionstake place.
The speed and reactions are controlled by control rods and a moderator.
In the core, uranium atoms are bombarded with free neutrons producingimmense heat.
This heat is transferred by a cooling medium to a heat exchanger whereprocess water is converted to dry high pressure steam.
The steam is then used to drive a steam turbine, as in a normal steam plant.
SHIPBOARD NUCLEAR REACTOR
OPERATION
The operation of a nuclear reactor to raise steam outlined above is
similar to a shipboard one. The main differences being as follows,
Type of Fuel Used
As we have seen the normal fuel used in the reactor is enriched uranium
known as UO2, however the fuel used by the PWR for ships propulsion
has a different form.
This fuel is still uranium based but alloyed with different percentages of
aluminum or zirconium.
Fuel Enrichment
The UO2 fuel is normally enriched with 3-5% of U235.
The uranium alloy has been enriched to contain up to 90% U235, but is
normally used at between 45-75% U235 enrichment in PWR for ships
propulsion.
Internal Neutron Shield
The internal neutron shield is designed to contain the aggressive
neutrons movement occurring within the narrow compact pressure
vessel containing the reactor core.
The neutron shield is fabricated from a high mass/density material which
provides a good source of neutron absorption.
This prolongs the reactors core life by preventing the embrittlement of
the steel of the pressure vessel, with some reactors being designed to
last between 40 and 50 years.
The Plant’s Compactness
The shipboard nuclear reactor is very compact compared to the normal
power plant reactor.
This compact plant is normally about 4m high with a diameter of 2m.
This makes these plants particularly suitable for submarines, where
space is at a premium
Power output
The power output from ships nuclear energy plants ranges from 200MWt
for submarine propulsion to 300MWt for larger warships such as aircraft
carriers.
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