ENVM558

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ENV-M558 Contemporary Issues in Climate Change
and Energy 2008
14. NUCLEAR POWER
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NUCLEAR POWER

• Background Introduction
• Nature of Radioactivity
• Structure of the Atom
• Radioactive Emissions
• Half Life of Elements
• Fission
• Fusion
• Chain Reactions
• Fertile Materials
• Fission Reactors
• Nuclear Fuel Cycle
• Fusion Reactors

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(No Transcript)
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Historic and Future Demand for Electricity
Business as usual
Energy Efficient Future ?
Number of households will rise by 17.5 by 2025
and consumption per household must fall by this
amount just to remain static
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Electricity Options for the Future
Energy Efficiency consumption capped at 420
TWh by 2010 But 68 growth in gas demand
(compared to 2002) Business as Usual 257
increase in gas consumption ( compared to 2002)
The Gas Scenario Assumes all new non-renewable
generation is from gas. Replacements for ageing
plant Additions to deal with demand
changes Assumes 10.4 renewables by 2010
25 renewables by 2025
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Alternative Electricity Options for the Future

• 25 Renewables by 2025
• 20000 MW Wind
• 16000 MW Other Renewables inc. Tidal, hydro,
  biomass etc.

Energy Efficiency Scenario Other Options Some
New Nuclear needed by 2025 if CO2 levels are to
fall significantly and excessive gas demand is to
be avoided
Business as Usual Scenario New Nuclear is
required even to reduce back to 1990 levels
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NUCLEAR POWER

• Background Introduction
• Nature of Radioactivity
• Structure of the Atom
• Radioactive Emissions
• Half Life of Elements
• Fission
• Fusion
• Chain Reactions
• Fertile Materials
• Fission Reactors
• Nuclear Fuel Cycle
• Fusion Reactors

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NATURE OF RADIOACTIVITY (1)

• Structure of Atoms.
• Matter is composed of atoms which consist
  primarily of a nucleus of
• positively charged PROTONS
• and (electrically neutral) NEUTRONS.
• The nucleus is surrounded by a cloud of
  negatively charged ELECTRONS which balance the
  charge from the PROTONS.
• PROTONS and NEUTRONS have approximately the same
  mass
• ELECTRONS are about 0.0005 times the mass of the
  PROTON.
• A NUCLEON refers to either a PROTON or a NEUTRON

Lithium Atom 3 Protons 4 Neutrons
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NATURE OF RADIOACTIVITY (2)

• Structure of Atoms.
• Elements are characterized by the number of
  PROTONS present
• HYDROGEN nucleus has 1 PROTON
• HELIUM has 2 PROTONS
• OXYGEN has 8 PROTONS
• URANIUM has 92 PROTONS.
• Number of PROTONS is the ATOMIC NUMBER (Z)
• N denotes the number of NEUTRONS.
• The number of neutrons present in any element
  varies.
• 3 isotopes of hydrogen all with 1 PROTON-
• HYDROGEN itself with NO NEUTRONS
• DEUTERIUM (heavy hydrogen) with 1 NEUTRON
• TRITIUM with 2 NEUTRONS.
• only TRITIUM is radioactive.
• Elements up to Z 82 (Lead) have at least one
  isotope which is stable

Symbol D Symbol T
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NATURE OF RADIOACTIVITY (3)

• Structure of Atoms.
• URANIUM has two main ISOTOPES
• 235U which is present in concentrations of
  0.7 in naturally occurring URANIUM
• 238U which is 99.3 of naturally occurring
  URANIUM.
• Some Nuclear Reactors use Uranium at the
  naturally occurring concentration of 0.7
• Most require some enrichment to around 2.5 - 5
• Enrichment is energy intensive if using gas
  diffusion technology, but relatively efficient
  with centrifuge technology.
• Some demonstration reactors use enrichment at
  around 93.

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NATURE OF RADIOACTIVITY (4)

• Structure of Atoms.
• Protons have strong nuclear forces to overcome
  the strong repulsive forces from the charges on
  them. This is the energy released in nuclear
  reactions

Stable elements plot close to blue line.
Those isotopes plotting away from line are
unstable. For elements above Lead (Z 82),
there are no stable isotopes.
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NATURE OF RADIOACTIVITY (5)

• Radioactive emissions.
• FOUR types of radiation-
• 1) ALPHA particles (?)
• large particles consisting of 2 PROTONS and 2
  NEUTRONS
• the nucleus of a HELIUM atom.
• 2) BETA particles (ß) which are ELECTRONS
• 3) GAMMA - RAYS. (?)
• Arise when the kinetic energy of Alpha and Beta
  particles is lost passing through the electron
  clouds of atoms. Some energy is used to break
  chemical bonds while some is converted into GAMMA
  -RAYS.
• 4) X - RAYS.
• Alpha and Beta particles, and gamma-rays may
  temporarily dislodge ELECTRONS from their normal
  orbits. As the electrons jump back they emit
  X-Rays which are characteristic of the element
  which has been excited.

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NATURE OF RADIOACTIVITY (6)
? ß ?
? - particles are stopped by a thin sheet of
paper ß particles are stopped by 3mm
aluminium ? - rays CANNOT be stopped they can
be attenuated to safe limits using thick Lead
and/or concrete
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NATURE OF RADIOACTIVITY (7)

• Radioactive emissions.
• UNSTABLE nuclei emit Alpha or Beta particles
• If an ALPHA particle is emitted, the new element
  will have an ATOMIC NUMBER two less than the
  original.

• If an ELECTRON is emitted as a result of a
  NEUTRON transmuting into a PROTON, an isotope of
  the element ONE HIGHER in the PERIODIC TABLE will
  result.

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NATURE OF RADIOACTIVITY (8)

• Radioactive emissions.
• 235U consisting of 92 PROTONS and 143 NEUTRONS is
  one of SIX isotopes of URANIUM
• decays as follows-

• Thereafter the ACTINIUM - 227 decays by further
  alpha and beta particle emissions to LEAD - 207
  (207Pb) which is stable.
• Two other naturally occurring radioactive decay
  series exist. One beginning with 238U, and the
  other with 232Th.
• Both also decay to stable (but different)
  isotopes of LEAD.

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NATURE OF RADIOACTIVITY (9)

• HALF LIFE.
• Time taken for half the remaining atoms of an
  element to undergo their first decay e.g-
• 238U 4.5 billion years
• 235U 0.7 billion years
• 232Th 14 billion years
• All of the daughter products in the respective
  decay series have much shorter half - lives some
  as short as 10-7 seconds.
• When 10 half-lives have expired,
• the remaining number of atoms is less than 0.1
  of the original.
• 20 half lives
• the remaining number of atoms is less than one
  millionth of the original

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NATURE OF RADIOACTIVITY (10)

• HALF LIFE.
• From a radiological hazard point of view
• short half lives - up to say 6 months have
  intense radiation, but
• decay quite rapidly. Krypton-87 (half life 1.8
  hours)- emitted from some gas cooled reactors -
  the radioactivity after 1 day is insignificant.
• For long half lives - the radiation doses are
  small, and also of little consequence
• For intermediate half lives - these are the
  problem - e.g. Strontium -90
• has a half life of about 30 years which means it
  has a relatively high radiation, and does not
  decay that quickly.
• Radiation decreases to 30 over 90 years

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NATURE OF RADIOACTIVITY (11) Fission
Some very heavy UNSTABLE elements exhibit FISSION
e.g. 235U
235U
93Rb

• This reaction is one of several which might
  take place. In some cases, 3 daughter products
  are produced.

140Cs
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NATURE OF RADIOACTIVITY (12)

• FISSION
• Nucleus breaks down into two or three fragments
  accompanied by a few free neutrons and the
  release of very large quantities of energy.
• Free neutrons are available for further FISSION
  reactions
• Fragments from the fission process usually have
  an atomic mass number (i.e. NZ) close to that of
  iron.
• Elements which undergo FISSION following capture
  of a neutron such as URANIUM - 235 are known as
  FISSILE.
• Diagrams of Atomic Mass Number against binding
  energy per NUCLEON enable amount of energy
  produced in a fission reaction to be estimated.
• All Nuclear Power Plants currently exploit
  FISSION reactions,
• FISSION of 1 kg of URANIUM produces as much
  energy as burning 3000 tonnes of coal.

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NATURE OF RADIOACTIVITY (13) Fusion
Fusion of light elements e.g. DEUTERIUM and
TRITIUM produces even greater quantities of
energy per nucleon are released.
Deuterium Tritium fusion
Tritium
Deuterium
(3.5 MeV)
(14.1 MeV)
In each reaction 17.6 MeV is liberated or 2.8
picoJoules (2.8 10-15J)
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NATURE OF RADIOACTIVITY (14) Binding Energy
1 MeV per nucleon is equivalent to 96.5 TJ per kg
Redrawn from 6th report on Environmental
Pollution Cmnd. 6618 - 1976

• The energy released per nucleon in fusion
  reaction is much greater than the
• corresponding fission reaction.
• 2) In fission there is no single fission product
  but a broad range as indicated.

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NATURE OF RADIOACTIVITY (15) Fusion

• Developments at the JET facility in Oxfordshire
  have achieved the break even point.
• Next facility (ITER) will be built in Cadarache
  in France.
• Commercial deployment of fusion from about 2040
  onwards
• One or two demonstration commercial reactors in
  2030s perhaps
• No radioactive waste from fuel
• Limited radioactivity in power plant itself
• 8 litres of tap water sufficient for all energy
  needs of one individual for whole of life at a
  consumption rate comparable to that in UK.
• Sufficient resources for 1 10 million years

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NATURE OF RADIOACTIVITY (16) Chain Reactions
Fast Neutrons are unsuitable for sustaining
further reactions
fast neutron
235U
Slow neutron
235U
fast neutron
Slow neutron
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NATURE OF RADIOACTIVITY (17)

• CHAIN REACTIONS
• FISSION of URANIUM - 235 yields 2 - 3 free
  neutrons.
• If exactly ONE of these triggers a further
  FISSION, then a chain reaction occurs, and
  continuous power can be generated.
• UNLESS DESIGNED CAREFULLY, THE FREE NEUTRONS WILL
  BE LOST AND THE CHAIN REACTION WILL STOP.
• IF MORE THAN ONE NEUTRON CREATES A NEW FISSION
  THE REACTION WOULD BE SUPER-CRITICAL
• (or in layman's terms a bomb would have been
  created).

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NATURE OF RADIOACTIVITY (18)

• CHAIN REACTIONS
• IT IS VERY DIFFICULT TO SUSTAIN A CHAIN REACTION,
  
• Most Neutrons are moving too fast
• TO CREATE A BOMB, THE URANIUM - 235 MUST BE
  HIGHLY ENRICHED gt 93,
• Normal Uranium is only 0.7 U235
• Material must be LARGER THAN A CRITICAL SIZE
  and SHAPE OTHERWISE NEUTRONS ARE LOST.
• Atomic Bombs are made by using conventional
  explosive to bring two sub-critical masses of
  FISSILE material together for sufficient time for
  a SUPER-CRITICAL reaction to take place.
• NUCLEAR POWER PLANTS CANNOT EXPLODE LIKE AN
  ATOMIC BOMB.

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NATURE OF RADIOACTIVITY (19)

• FERTILE MATERIALS
• Some elements like URANIUM - 238 are not FISSILE,
  but can transmute-

fast neutron
238U
239U
239Np
239Pu
239Np Neptunium - 239
239Pu Plutonium - 239
239U Uranium - 239
238U Uranium - 238
PLUTONIUM - 239 is FISSILE and may be used in
place of URANIUM - 235. Materials which can be
converted into FISSILE materials are FERTILE.
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NATURE OF RADIOACTIVITY (20)

• FERTILE MATERIALS
• URANIUM - 238 is FERTILE as is THORIUM - 232
  which can be transmuted into URANIUM - 233.
• Naturally occurring URANIUM consists of 99.3
  238U which is FERTILE and NOT FISSILE, and 0.7
  of 235U which is FISSILE. Normal reactors
  primarily use the FISSILE properties of 235U.
• In natural form, URANIUM CANNOT sustain a chain
  reaction free neutrons are travelling fast to
  successfully cause another FISSION, or are lost
  to the surrounds.
• MODERATORS are thus needed to slow down/and or
  reflect the neutrons in a normal FISSION REACTOR.
• The Resource Base of 235U is only decades
• But using a Breeder Reactor Plutonium can be
  produced from non-fissile 238U producing 239Pu
  and extending the resource bas by a factor of 50
  

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NATURE OF RADIOACTIVITY (21) Chain Reactions
Sustaining a reaction in a Nuclear Power Station
Fast Neutrons are unsuitable for sustaining
further reactions
fast neutron
235U
Slow neutron
fast neutron
235U
fast neutron
Slow neutron
Insert a moderator to slow down neutrons
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NUCLEAR POWER

• Background Introduction
• Nature of Radioactivity
• Fission Reactors
• General Introduction
• MAGNOX Reactors
• AGR Reactors
• CANDU Reactors
• PWRs
• BWRs
• RMBK/ LWGRs
• FBRs
• Generation 3 Reactors
• Generation 3 Reactors
• Nuclear Fuel Cycle
• Fusion Reactors

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FISSION REACTORS (1)

• FISSION REACTORS CONSIST OF-
• i) a FISSILE component in the fuel
• ii) a MODERATOR
• iii) a COOLANT to take the heat to its
  point of use.
• The fuel elements vary between different Reactors
• Some reactors use unenriched URANIUM
• i.e. the 235U in fuel elements is at 0.7 of fuel
• e.g. MAGNOX and CANDU reactors,
• ADVANCED GAS COOLED REACTOR (AGR) uses 2.5 2.8
  enrichment
• PRESSURISED WATER REACTOR (PWR) and BOILING WATER
  REACTOR (BWR) use around 3.5 4 enrichment.
• RMBK (Russian Rector of Chernobyl fame) uses 2
  enrichment
• Some experimental reactors - e.g. High
  Temperature Reactors (HTR) use highly enriched
  URANIUM (gt90) i.e. weapons grade.

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FISSION REACTORS (2) Fuel Elements
PWR fuel assembly UO2 pellets loaded into fuel
pins of zirconium each 3 m long in bundles of
200
AGR fuel assembly UO2 pellets loaded into fuel
pins of stainless steel each 1 m long in
bundles of 36. Whole assembly in a graphite
cylinder
Magnox fuel rod Natural Uranium metal bar approx
35mm diameter and 1m long in a fuel cladding made
of MagNox.
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FISSION REACTORS (3)

• No need for the extensive coal handling plant.
• In the UK, all the nuclear power stations are
  sited on the coast so there is no need for
  cooling towers.
• Land area required is smaller than for coal fired
  plant.
• In most reactors there are three fluid circuits-
• 1) The reactor coolant circuit
• 2) The steam cycle
• 3) The cooling water cycle.
• ONLY the REACTOR COOLANT will become radioactive
• The cooling water is passed through the station
  at a rate of tens of millions of litres of water
  and hour, and the outlet temperature is raised
  by around 10oC.

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FISSION REACTORS (4)

• REACTOR TYPES summary 1
• MAGNOX - Original British Design named after the
  magnesium alloy used as fuel cladding. Four
  reactors of this type were built in France, One
  in each of Italy, Spain and Japan. 26 units were
  built in UK.
• They are only in use now in UK. On December
  31st 2006, Sizewell A, Dungeness A closed after
  40 years of operation leaving only Wylfa and
  Oldbury both with two reactors each operating.
  All other units are being decommissioned
• AGR - ADVANCED GAS COOLED REACTOR - solely
  British design. 14 units are in use. The
  original demonstration Windscale AGR is now being
  decommissioned. The last two stations Heysham
  II and Torness (both with two reactors), were
  constructed to time and have operated to
  expectations.

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FISSION REACTORS (5)

• REACTOR TYPES - summary
• SGHWR - STEAM GENERATING HEAVY WATER REACTOR -
  originally a British Design which is a hybrid
  between the CANDU and BWR reactors.
• PWR - Originally an American design of
  PRESSURIZED WATER REACTOR (also known as a Light
  Water Reactor LWR). Now most common reactor.-
• BWR - BOILING WATER REACTOR - a
  derivative of the PWR in which the coolant is
  allowed to boil in the reactor itself. Second
  most common reactor in use.
• RMBK - LIGHT WATER GRAPHITE MODERATING
  REACTOR (LWGR)- a design unique to the USSR
  which figured in the CHERNOBYL incident. 16
  units still in operation in Russian and Lithuania
  with 9 shut down.

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FISSION REACTORS (5)

• REACTOR TYPES - summary
• CANDU - A reactor named initially after
  CANadian DeUterium moderated reactor (hence
  CANDU), alternatively known as PHWR
  (pressurized heavy water reactor). 41 currently
  in use.
• HTGR - HIGH TEMPERATURE GRAPHITE
  REACTOR - an experimental reactor. The original
  HTR in the UK started decommissioning in 1975.
  The new Pebble Bed Modulating Reactor (PBMR) is a
  development of this and promoted as a 3
  Generation Reactor by South Africa.
• FBR - FAST BREEDER REACTOR - unlike
  all previous reactors, this reactor 'breeds'
  PLUTONIUM from FERTILE 238U to operate, and in so
  doing extends resource base of URANIUM over 50
  times. Mostly experimental at moment with
  FRANCE, W. GERMANY and UK, Russia and JAPAN
  having experimented with them.

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MAGNOX REACTORS (also known as GCR)

• ADVANTAGES-
• LOW POWER DENSITY - 1 MW/m3. Thus very slow
  rise in temperature in fault conditions.
• UNENRICHED FUEL
• GASEOUS COOLANT
• ON LOAD REFUELLING
• MINIMAL CONTAMINATION FROM BURST FUEL CANS
• VERTICAL CONTROL RODS - fall by gravity in case
  of emergency.

• FUEL TYPE - unenriched URANIUM METAL clad in
  Magnesium alloy
• MODERATOR - GRAPHITE
• COOLANT - CARBON DIOXIDE
• DIRECT RANKINE CYCLE
• - no superheat or reheat efficiency 20 to
  28.

• DISADVANTAGES-
• CANNOT LOAD FOLLOW Xe poisoning
• OPERATING TEMPERATURE LIMITED TO ABOUT 250oC -
  360oC limiting CARNOT EFFICIENCY to 40 - 50,
  and practical efficiency to 28-30.
• LOW BURN-UP - (about 400 TJ per tonne)
• EXTERNAL BOILERS ON EARLY DESIGNS.

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ADVANCED GAS COOLED REACTORS (AGR)

• ADVANTAGES-
• MODEST POWER DENSITY - 5 MW/m3. slow rise in
  temperature in fault conditions.
• GASEOUS COOLANT (40- 45 BAR cf 160 bar for PWR)
• ON LOAD REFUELLING under part load
• MINIMAL CONTAMINATION FROM BURST FUEL CANS
• RELATIVELY HIGH THERMODYNAMIC EFFICIENCY 40
• VERTICAL CONTROL RODS - fall by gravity in case
  of emergency.

• FUEL TYPE - enriched URANIUM OXIDE - 2.3 clad
  in stainless steel
• MODERATOR - GRAPHITE
• COOLANT - CARBON DIOXIDE
• SUPERHEATED RANKINE CYCLE (with reheat) -
  efficiency 39 - 41

• DISADVANTAGES-
• MODERATE LOAD FOLLOWING CHARACTERISTICS
• SOME FUEL ENRICHMENT NEEDED. - 2.3

• OTHER FACTORS-
• MODERATE FUEL BURN-UP - 1800TJ/tonne (c.f.
  400TJ/tonne for MAGNOX, 2900TJ/tonne for PWR).
• SINGLE PRESSURE VESSEL with pres-stressed
  concrete walls 6m thick. Pre-stressing tendons
  can be replaced if necessary.

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CANDU REACTOR (PHWR)

• ADVANTAGES-
• MODEST POWER DENSITY - 11 MW/m3.
• HEAVY WATER COOLANT - low neutron absorber hence
  no need for enrichment.
• ON LOAD REFUELLING - and very efficient indeed
  permits high load factors.
• MINIMAL CONTAMINATION from burst fuel can -
  defective units can be removed without shutting
  down reactor.
• MODULAR - can be made to almost any size

• FUEL TYPE - unenriched URANIUM OXIDE clad in
  Zircaloy
• MODERATOR - HEAVY WATER COOLANT - HEAVY
  WATER

• DISADVANTAGES-
• POOR LOAD FOLLOWING CHARACTERISTICS
• CONTROL RODS ARE HORIZONTAL, and therefore cannot
  operate by gravity in fault conditions.
• MAXIMUM EFFICIENCY about 28

• OTHER FACTORS-
• MODERATE FUEL BURN-UP - MODEST FUEL BURN-UP -
  about 1000TJ/tonne
• FACILITIES PROVIDED TO DUMP HEAVY WATER MODERATOR
  from reactor in fault conditions
• MULTIPLE PRESSURE TUBES instead of one pressure
  vessel.

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PRESSURISED WATER REACTORS PWR (WWER)

• ADVANTAGES-
• GOOD LOAD FOLLOWING CHARACTERISTICS - claimed for
  SIZEWELL B. - most PWRs are NOT operated as such.
• HIGH FUEL BURN-UP- about 2900TJ/tonne
• VERTICAL CONTROL RODS - drop by gravity in fault
  conditions.

• FUEL TYPE - 3 4 enriched URANIUM OXIDE clad
  in Zircaloy
• MODERATOR - WATER
• COOLANT - WATER

• DISADVANTAGES-
• ORDINARY WATER as COOLANT - pressure to prevent
  boiling (160 bar). If break occurs then water
  will flash to steam and cooling will be less
  effective.
• ON LOAD REFUELLING NOT POSSIBLE - reactor must be
  shut down.
• SIGNIFICANT CONTAMINATION OF COOLANT CAN ARISE
  FROM BURST FUEL CANS - as defective units cannot
  be removed without shutting down reactor.
• FUEL ENRICHMENT NEEDED. - 3-4.
• MAXIMUM EFFICIENCY 31 - 32
• latest
  designs 34

• OTHER FACTORS-
• LOSS OF COOLANT also means LOSS OF MODERATOR so
  reaction ceases - but residual decay heat can be
  large.
• HIGH POWER DENSITY - 100 MW/m3, and compact.
  Temperature can rise rapidly in fault
  conditions. NEEDS active ECCS.
• SINGLE STEEL PRESSURE VESSEL 200 mm thick.

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BOILING WATER REACTORS BWR

• ADVANTAGES-
• HIGH FUEL BURN-UP- about 2600TJ/tonne
• STEAM PASSED DIRECTLY TO TURBINE therefore no
  heat exchangers needed. BUT SEE DISADVANTAGES..

• FUEL TYPE - 3 enriched URANIUM OXIDE clad in
  Zircaloy
• MODERATOR - WATER
• COOLANT - WATER

• DISADVANTAGES-
• ORDINARY WATER as COOLANT but designed to boil
  pressure 75 bar.
• CONTROL RODS MUST BE DRIVEN UPWARDS - SO NEED
  POWER IN FAULT CONDITIONS. Provision made to
  dump water (moderator in such circumstances).
• ON LOAD REFUELLING NOT POSSIBLE - reactor must be
  shut down.
• SIGNIFICANT CONTAMINATION OF COOLANT CAN ARISE
  FROM BURST FUEL CANS - as defective units cannot
  be removed without shutting down reactor. ALSO IN
  SUCH CIRCUMSTANCES RADIOACTIVE STEAM WILL PASS
  DIRECTLY TO TURBINES.
• FUEL ENRICHMENT NEEDED. - 3.
• MAXIMUM EFFICIENCY 34-35

• OTHER FACTORS-
• LOSS OF COOLANT also means LOSS OF MODERATOR so
  reaction ceases - but residual decay heat can be
  large.
• HIGH POWER DENSITY - 100 MW/m3, and compact.
  Temperature can rise rapidly in fault
  conditions. NEEDS active ECCS.
• SINGLE STEEL PRESSURE VESSEL 200 mm thick.

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RMBK (LWGR) (involved in Chernobyl incident)

• ADVANTAGES-
• ON LOAD REFUELLING
• VERTICAL CONTROL RODS which can drop by GRAVITY
  in fault conditions.
• NO THEY CANNOT!!!!

• FUEL TYPE - 2 enriched URANIUM OXIDE clad in
  Zircaloy
• MODERATOR - GRAPHITE
• COOLANT - WATER

• DISADVANTAGES-
• ORDINARY WATER as COOLANT - flashes to steam in
  fault conditions hindering cooling.
• POSITIVE VOID COEFFICIENT !!! - positive feed
  back possible in some fault conditions -other
  reactors have negative voids coefficient in all
  conditions.
• IF COOLANT IS LOST moderator will keep reaction
  going.
• FUEL ENRICHMENT NEEDED. - 2
• PRIMARY COOLANT passed directly to turbines.
  This coolant can be slightly radioactive.
• MAXIMUM EFFICIENCY 30 ??

• OTHER FACTORS-
• MODERATE FUEL BURN-UP - MODEST FUEL BURN-UP -
  about 1800TJ/tonne
• LOAD FOLLOWING CHARACTERISTICS UNKNOWN
• POWER DENSITY probably MODERATE?
• MULTIPLE PRESSURE TUBES

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FAST BREEDER REACTORS (FBR or LMFBR)

• ADVANTAGES-
• LIQUID METAL COOLANT - at ATMOSPHERIC PRESSURE.
  Will even cool by natural convection in event of
  pump failure.
• BREEDS FISSILE MATERIAL from non-fissile 238U
  increases resource base 50 times.
• HIGH EFFICIENCY ( 40)
• VERTICAL CONTROL RODS drop by GRAVITY in fault
  conditions.

• FUEL TYPE - depleted Uranium or UO2 surround
  PU in centre of core. All elements clad in
  stainless steel.
• MODERATOR - NONE
• COOLANT - LIQUID METAL

• DISADVANTAGES-
• DEPLETED URANIUM FUEL ELEMENTS MUST BE
  REPROCESSED to recover PLUTONIUM and sustain the
  breeding of more plutonium for future use.
  
• CURRENT DESIGNS have SECONDARY SODIUM CIRCUIT
• WATER/SODIM HEAT EXCHANGER. If water and
  sodium mix a significant CHEMICAL explosion may
  occur which might cause damage to reactor itself.

• OTHER FACTORS-
• VERY HIGH POWER DENSITY - 600 MW/m3 but rise in
  temperature in fault conditions limited by
  natural circulation of sodium.

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GENERATION 3 REACTORS the EPR1300

• Schematic of Reactor is very similar to later
  PWRs (SIZEWELL) with 4 Steam Generator Loops.
• Main differences? from earlier designs.
• Output power 1600 MW from a single turbine
• (cf 2 turbines for 1188 MW at Sizewell).
• Each of the safety chains is housed in a separate
  building.

• Efficiency claimed at 37

Construction is under way at Olkiluoto,
Finland. Second order signed for a Reactor at
Flammanville, France on 24th January 2007.
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GENERATION 3 REACTORS the AP1000

• A development from SIZEWELL
• Power Rating comparable with SIZEWELL

• Will two turbines be used ??
• Passive Cooling water tank on top water falls
  by gravity
• Two loops (cf 4 for EPR)
• Significant reduction in components e.g. pumps
  etc.

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GENERATION 3 REACTORS the ACR1000

• A development from CANDU with added safety
  features less Deuterium needed
• Passive emergency cooling as with AP1000

See Video Clip of on-line refuelling
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ESBWR Economically Simple BWR

• A derivative of Boiling Water Reactor which has
  several safety features but which inherently has
  two disadvantages of basic deisgn
• Vertical control rods which must be driven
  upwards
• Steam in turbines can become radioactive

47
GENERATION 3 REACTORS the PBMR

• Pebble Bed Modulating Reactors are a development
  from Gas Cooled Reactors.
• Sand sized pellets of Uranium each coated in
  layers of graphite/silicon carbide and aggregated
  into pebbles 60 mm in diameter.
• Coolant Helium
• Connected directly to closed circuit gas turbine
• Efficiency 39 40, but possibility of CCGT??
• Graphite/silicon carbide effective cladding
  thus very durable to high temperatures

48
GENERATION 3 REACTORS the PBMR

• Unlike other Reactors, the PBMR uses a closed
  circuit high temperature gas turbine operating on
  the Brayston Cycle for Power. This cycle is
  similar to that in a JET engine or the gas
  turbine section of a CCGT.
• Normal cycles exhaust spent gas to atmosphere.
• In this version the helium is in a closed circuit.

PBM Reactor
Combustion Chamber
Open Brayston Cycle
Closed Brayston Cycle
Heat Exchanger
Air In
49
GENERATION 3 REACTORS the PBMR

• Efficiency of around 38 40, but possibility of
  CCGT???
• Helium passes directly from reactor to turbine
• Pebbles are continuously fed into reactor and
  collected.
• Tested for burn up and recycled as appropriate
  typically 6 times

50
ENV-M558 Contemporary Issues in Climate Change
and Energy 2008
NUCLEAR POWER 16. The Nuclear Fuel Cycle
Keith Tovey (???) M.A, PhD, CEng, MICE, CEnv
?.?.???? ?.?, ?-? ??????????? ???? Energy Science
Director CRed Project HSBC Director of Low
Carbon Innovation
51
The NUCLEAR FUEL CYCLE

• TWO OPTIONS AVAILABLE-
• ONCE-THROUGH CYCLE,
• REPROCESSING CYCLE
• CHOICE DEPENDS primarily on-
• REACTOR TYPE IN USE (more or less essential for
  MAGNOX),
• AVAILABILTY OF URANIUM TO COUNTRY IN QUESTION,
• DECISIONS ON THE POSSIBLE USE OF FBRs.
• DECISIONS ON HOW RADIOACTIVE WASTE IS TO BE
  HANDLED.
• Reprocessing leads to much less HIGH LEVEL
  radioactive waste, but more low level
  radioactive waste
• ECONOMIC CONSIDERATIONS done 10 years ago show
  little difference between two types of cycle
  except that for PWRs, ONCE-THROUGH CYCLE appeared
  MARGINALLY more attractive.

52
The NUCLEAR FUEL CYCLE

• NUCLEAR FUEL CYCLE divided into two parts-
• FRONT-END - includes MINING of Uranium Ore,
  EXTRACTION, CONVERSION to "Hex", ENRICHMENT, and
  FUEL FABRICATION.
• BACK-END - includes TRANSPORTATION of SPENT
  FUEL, STORAGE, REPROCESSING, and DISPOSAL.
• NOTE
• Transportation of Fabricated Fuel elements has
  negligible cost as little or no screening is
  necessary.
• Special Provisions are needed for transport of
  spent fuel for both cycles.
• For both ONCE-THROUGH and REPROCESSING CYCLES,
  the FRONT-END is identical. The differences are
  only evident at the BACK- END.

53
Simplified Fuel Cycle for a PWR (1)
REPROCESSING
Once Through
9 kg Plutonium
Storage
UF6
Liquid 5m3
0.96 t Uranium
0.4m3 IL waste
0.7m3 LL waste
0.8m3 IL waste
1500 m3
54
Simplified Fuel Cycle for a PWR (2)

• MINING - ore gt 0.05 by weight of U3O8 to be
  economic.
• Typically at 0.5, 500 tonnes (250 m3) must be
  excavated to produce 1 tonne of U3O8
  ("yellow-cake") which occupies about 0.1 m3.
• URANIUM leached out chemically
• resulting powder contains about 80 yellow-cake.
  The 'tailings' contain the naturally generated
  daughter products.
• PURIFICATION/CONVERSION
• - dissolve 'yellow-cake' in nitric acid and
  conversion to Uranium tetrafluoride (UF4)
• UF4 converted into URANIUM HEXAFLOURIDE (UF6) or
  "HEX" if enrichment is needed.

55
Simplified Fuel Cycle for a PWR Enrichment (1)

• ENRICHMENT.
• proportion of URANIUM - 235 is artificially
  increased.
• GAS DIFFUSION - original method still used in
  FRANCE.
• "HEX" is allowed to diffuse through a membrane
  separating the high and low pressure parts of a
  cell.
• 235U diffuses faster than 238U through this
  membrane.
• Outlet gas from lower pressure is slightly
  enriched in 235U (by a factor of 1.0043) and is
  further enriched in subsequent cells.
• HUNDREDS / THOUSANDS of such cells are required
  in cascade depending on the required enrichment.
  
• Pumping demands are very large as are the cooling
  requirements between stages.

56
Simplified Fuel Cycle for a PWR Enrichment (2)

• ENRICHMENT GAS DIFFUSION.
• Outlet gas from HIGH PRESSURE side is slightly
  depleted URANIUM and is fed back into previous
  cell of sequence.
• AT BACK END, depleted URANIUM contains only 0.2 -
  0.3 235U,
• NOT economic to use this for enrichment.
• This depleted URANIUM is currently stockpiled,
  but could be an extremely value fuel resource
  should we decide to go for the FBR.

57
Simplified Fuel Cycle for a PWR Enrichment (3)

• ENRICHMENT.
• GAS CENTRIFUGE ENRICHEMENT
• similar to the Gas diffusion in that it requires
  many stages.
• "HEX" is spun in a centrifuge, and the slightly
  enriched URANIUM is sucked off near the axis and
  passed to the next stage.
• ENERGY requirements for this process are only
  10 of the GAS DIFFUSION method.
• All UK fuel is now enriched by this process at
  Capenhurst.

58
Simplified Fuel Cycle for a PWR Fuel Fabrication

• FUEL FABRICATION -
• MAGNOX reactors URANIUM metal is machined into
  bars using normal techniques.
• CARE MUST BE TAKEN not to allow water into
  process as this acts as a moderator and might
  cause the fuel element to 'go critical'.
• CARE MUST ALSO BE TAKEN over its CHEMICAL
  TOXICITY although this is not a much a problem as
  PLUTONIUM
• URANIUM METAL bars are about 1m in length and
  about 30 mm in diameter.
• OXIDE Fuels for Other Reactors
• Because of low thermal conductivity of oxides of
  uranium, fuels of this form are made as small
  pellets which are loaded into stainless steel
  cladding in the case of AGRs, and ZIRCALLOY in
  the case of most other reactors.
• TRANSPORT of FUEL Elements
• Little screening is needed as URANIUM is an alpha
  emitter and even a thin layer of paper is
  sufficient to stop such particles.
• No special precaution are needed as even enriched
  fuel is unsuitable for bomb making

59
FISSION REACTORS (2) Fuel Elements
PWR fuel assembly UO2 pellets loaded into fuel
pins of zirconium each 3 m long in bundles of
200
AGR fuel assembly UO2 pellets loaded into fuel
pins of stainless steel each 1 m long in
bundles of 36. Whole assembly in a graphite
cylinder
Magnox fuel rod Natural Uranium metal bar approx
35mm diameter and 1m long in a fuel cladding made
of MAGNOX.
60
Simplified Fuel Cycle for a PWR Fuel Fabrication

• PLUTONIUM
• Fuel fabrication presents much greater problems.
  
• Workers require more shielding from radiation.
• Chemically toxic.
• Metallurgy is complex.
• Can reach criticality on its own WITHOUT a
  MODERATOR.
• Care must be taken in manufacture and ALL
  subsequent storage that the fuel elements are not
  of size and shape which could cause a
  criticality.
• NOTE-
• Transport of PLUTONIUM fuel elements
• a potential hazard, as a crude atomic bomb could
  be made without the need for a large amount of
  energy cf enriched URANIUM.
• DELIBERATE 'spiking' of PLUTONIUM with some
  fission products is considered to make the fuel
  elements very difficult to handle.

61
Simplified Fuel Cycle for a PWR Fuel Fabrication

• 1 tonne of enriched fuel for a PWR produces 1PJ
  of energy.
• 1 tonne of unenriched fuel for a CANDU reactor
  produces about 0.2 PJ.
• However, because of losses, about 20-25 MORE
  ENERGY PER TONNE of MINED URANIUM can be obtained
  with CANDU if the spent fuel is reprocessed.

62
Simplified Fuel Cycle for a PWR BACKEND (1)

• BOTH ONCE-THROUGH and REPROCESSING CYCLES
• SPENT FUEL ELEMENTS from the REACTOR
• FISSION PRODUCTS mostly with SHORT HALF LIVES.
  heat is evolved
• spent fuel elements are normally stored under
  water
• at least in the short term.
• 100 days, the radioactivity reduced to about 25
  of its original value, and after 5 years the
  level will be down to about 1.
• Early reduction comes from the decay of
  radioisotopes such as IODINE - 131 and XENON -
  133 -half-lives (8 days and 1.8 hours
  respectively).
• CAESIUM - 137 decays to only 90 of its initial
  level even after 5 years.
• accounts for less than 0.2 of initial
  radioactive decay, but 15 of the activity after
  5 years.

63
Simplified Fuel Cycle for a PWR BACKEND (1)

• BOTH ONCE-THROUGH and REPROCESSING CYCLES
• SPENT FUEL ELEMENTS stored under 6m of water
• also acts as BIOLOGICAL SHIELD.
• Water may become radioactive from corrosion of
  fuel cladding causing leakage - so water is
  conditioned
• kept at pH of 11 - 12 (i.e. strongly alkaline in
  case of MAGNOX). Other reactor fuel elements do
  not corrode so readily.
• Any radionucleides escaping into the water are
  removed by ION EXCHANGE.
• Subsequent handling depends on whether
  ONCE-THROUGH or REPROCESSING CYCLE is chosen.
• Spent fuel can be stored in dry caverns,
• drying the elements after the initial water
  cooling is a problem.
• Adequate air cooling must be provided, and this
  may make air - radioactive if fuel element
  cladding is defective. WYLFA power station
  stores MAGNOX fuel elements in this form.

64
Simplified Fuel Cycle for a PWR No Reprocessing

• ADVANTAGES-
• NO REPROCESSING needed - therefore much lower
  discharges of low level/intermediate level
  liquid/gaseous waste.
• FUEL CLADDING NOT STRIPPED - therefore less solid
  intermediate waste created. (although sometimes
  it is)
• NO PLUTONIUM in transport so no danger of
  diversion.
• DISADVANTAGES-
• CANNOT RECOVER UNUSED URANIUM - 235, PLUTONIUM OR
  URANIUM - 238. Thus fuel cannot be used again.
• VOLUME OF HIGH LEVEL WASTE MUCH GREATER (5 - 10
  times) than with reprocessing cycle.
• SUPERVISION OF HIGH LEVEL WASTE needed for much
  longer time as encapsulation is more difficult
  than for reprocessing cycle.

65
Simplified Fuel Cycle for a PWR Reprocessing
Cycle (1)

• ADVANTAGES-
• MUCH LESS HIGH LEVEL WASTE - therefore less
  problems with storage
• UNUSED URANIUM - 235, PLUTONIUM AND URANIUM - 238
  can be recovered and used again, or used in a FBR
  thereby increasing resource base 50 fold.
• VITRIFICATION is easier than with spent fuel
  elements. Plant at Sellafield now operational
  although technical problems are preventing
  vitrification at full capcity.
• DISADVANTAGES-
• Greater volumes of both Low Level and
  Intermediate Level Waste are created.
• Historically, routine emissions from reprocessing
  plants have been greater than storage of
  ONCE-THROUGH cycle waste.

66
Simplified Fuel Cycle for a PWR Reprocessing
Cycle (2)

• Dealing with liquid effluents
• At SELLAFIELD the ION EXCHANGE plant
• SIXEP (Site Ion EXchange Plant)
• commissioned in early 1986,
• substantially reduced the radioactive emissions
  in the effluent discharged to Irish Sea since
  that time by a factor of 500 times
• Further improvements with more advance waste
  treatment have now been installed.
• PLUTONIUM is stockpiled or in transport if used
  in FBRs. (although this can be 'spiked').

67
Simplified Fuel Cycle for a PWR Reprocessing
Cycle (3)
The Chemistry
Fuel stored in cooling ponds to allow
further decay

• Pipes in this are of small diameter to prevent
  CRITICALITIES.

68
Waste Disposal An Introduction

• LOW LEVEL WASTE.
• CONTAINS MATERIALS CONTAMINATED WITH
  RADIOISOTOPES
• either very long half lives indeed,
• or VERY SMALL quantities of short lived
  radioisotopes.
• FEW SHIELDING PRECAUTIONS ARE NECESSARY DURING
  TRANSPORTATION.
• PHYSICAL BULK MAY BE LARGE as its volume
  includes items which may have been contaminated
  during routine operations.
• Laboratory Coats, Paper Towels etc.
• Such waste may be generated in HOSPITALS,
  LABORATORIES, NUCLEAR POWER STATIONS, and all
  parts of the FUEL CYCLE.

69
Waste Disposal An Introduction

• OPTIONS FOR DISPOSAL OF LOW LEVEL WASTE.
• BURYING LOW LEVEL WASTE SURROUNDED BY A THICK
  CLAY BLANKET IS A SENSIBLE OPTION.
• If clay is of the SMECTITE type acts as a very
  effective ion exchange barrier which is plastic
  and deforms to any ground movement sealing any
  cracks.
• IN BRITAIN IT IS PROPOSED TO BURY WASTE IN STEEL
  CONTAINERS AND PLACED IN CONCRETE STRUCTURES IN A
  DEEP TRENCH UP TO 10m DEEP WHICH WILL BE
  SURROUNDED BY THE CLAY.
• IN FRANCE, THE CONTAINERS ARE PILED ABOVE GROUND
  AND THEN COVERED BY A THICK LAYER OF CLAY TO FORM
  A TUMULUS.
• Energy Field Courses in 1999 and 2001 visited the
  site at ANDRA near Cherbourg. (Agence National
  de Déchets Radioactive)

70
Waste Disposal An Introduction

• INTERMEDIATE LEVEL WASTE.
• contains HIGHER quantities of SHORT LIVED
  RADIOACTIVE WASTE,
• or MODERATE QUANTITIES OF RADIONUCLEIDES OF
  MODERATE HALF LIFE
• - e.g. 5 YEARS - 10000 YEARS HALF LIFE.
• IN FRANCE SUCH WASTE IS CAST INTO CONCRETE
  MONOLITHIC BLOCKS AND BURIED AT SHALLOW DEPTH.
• IN BRITAIN, it was originally proposed to bury
  similar blocks at the SAME SITES to those used
  for LOW LEVEL WASTE.
• UNSATISFACTORY AS CONFUSION BETWEEN THE TWO TYPES
  OF WASTE WILL OCCUR.
• SEPARATE FACILITIES ARE NOW PROPOSED.

71
Waste Disposal An Introduction

• HIGH LEVEL WASTE.
• At Sellafield, high level waste is now being
  encapsulated and stored on site in specially
  constructed vaults.
• A building about the size of the UEA swimming
  pool house in area and about twice as high houses
  all the high level radioative waste from the UKs
  Civil Nuclear Program with space for
  decommissioning of all final fuel from MAGNOX.
• MOST RADIONUCLEIDES IN THIS CATEGORY HAVE HALF
  LIVES OF UP TO 30 YEARS, and thus ACTIVITY in
  about 700 years will have decayed to around
  natural background radiation level.
• PROPOSALS FOR DISPOSAL INCLUDE
• burial in deep mines in SALT
• burial 1000m BELOW SEA BED and BACKFILLED with
  SMECTITE
• burial under ANTARCTIC ICE SHEET,
• shot INTO SPACE to the sun!

72
Waste Disposal An Introduction

• UK processes waste from Overseas Countries.
• Should we send back exact quantities of each of
• High Level Waste
• Intermediate Level Waste
• Low Level Waste
• Or should we
• Send back same amount of radioactivity
• i.e. a larger amount of a small volume of High
  Level Waste
• and no Intermediate and Low Level Waste?