Turning Rocks into Gold (Electric gold, that is)
A miracle of modern alchemy
Energy Potentials in the Universe • Hydrogen fusion (as well as other nuclei) – in our sun and all visible stars
• Uranium fission – on earth – both natural and man-made
• Radioactive decay – energy from our primordial “big bang” via supernovae
• Gravitation – drop a pencil, release some energy. Pick it up, store some energy
Uranium is Natural • Our uranium was created in supernova explosions in space, about 6.5 billion years ago – even before the earth was formed
• It is all around us, in soil and rock and water – mostly in low concentrations – In some areas, uranium has been concentrated by the action of flowing water
• It is part of our natural environment – life on earth evolved in a bath of radiation
Uranium?? • It is radioactive – Uranium-238 decays by alpha particle emission to thorium-234; it eventually transforms into lead-206
• Uranium-238 also splits by spontaneous fission – 2 or 3 neutrons are released by the fission fragments
• The fission and decay of natural uranium release (in the whole earth) about 24 million megawatts – this heats the core of the earth – More than half of all geothermal energy leaving the earth’s surface comes from this radioactive decay
Nuclear Fission • When two light nuclei fuse (join), mass is converted to energy • When a heavy nucleus fissions (splits), mass is converted to energy • When gasoline burns in your car, mass is converted to energy
Per atom, heavy element fission is much more energetic than fusion or chemical burning
What are some uses for Uranium? • We use heat from fission to make steam for a steam turbine – more than half Ontario’s electricity comes from uranium
• We have used it to make nuclear bombs – and nations have formed an international organization (IAEA) to guard against its use for this purpose
• We have used it to make attractive glass – until recently some glass-makers added uranium to glass. Such uses are now banned, to protect our health
• We use it as ballast in B747 aircraft
Energy of Fission • It takes 31 billion fission reactions to release one watt-second (one joule) of energy. – Fission is sustained at a constant rate by neutrons emitted during earlier fissions, in a chain reaction – The fragments (fission products) are at first highly radioactive, then rapidly decay to stable elements – Most of the energy appears as heat in the fuel pellets. It is this energy that we use to boil water at high temperature and pressure
Energy in the atomic nucleus
Thermal energy (fuel)
Boiling
Fission
Conduction
Energy Flows
Thermal energy (water)
Mechanical (turbine)
Losses to environment
Your lights, toaster, stove
Transmission
Induction Electrical (generator)
Energy in the atomic nucleus
Thermal energy (fuel)
Nuclear Fuel (pellet & bundle)
• Uranium dioxide – ceramic, melting point 2800 C – It is slightly radioactive – One pellet releases enough energy to make 2 slices of toast every minute for a year (about 1 million slices)
• Over 6 million fuel pellets are loaded in each reactor, in 5760 fuel bundles – Darlington produces 3522 megawatts of electricity from 4 reactors
• The world’s supply of nuclear fuel is inexhaustible
BEFORE LOADING
• Used fuel decays rapidly at first, then more slowly • The “last nucleus” does not decay for a very long time • Hazard returns to the original level after about 300 years
• This suggests “Put the stuff back where you got it”.
About 300 years
About 7 orders of magnitude
HAZARD OF NUCLEAR FUEL
The Magnitude of the Hazard Varies
USED FUEL COOLDOWN REACTOR OPERATION
Making Electricity • Heat energy is pumped in high pressure water to the boilers • Water is then boiled to produce steam to drive a steam turbine • Induction transforms Thermal energy mechanical energy into (water) electrical energy • Electricity is transmitted to you, the customer, all in about 30 seconds after fission • About 70% of the total fission energy is lost to environment
Mechanical energy (turbine)
Electrical energy (generator)
Fuel -- A Small Part of Electricity Cost* • Today, the uranium price is about $90 per kilogram – At this price we have enough to fuel 6000 thermal reactors for > 40 years – The uranium fuel contribution to electricity price is negligible – If the uranium price were half the price of gold, the price of electricity from thermal reactors would double – If the uranium price were half the price of gold, it would be very profitable to extract uranium from seawater – Seawater is known to contain enough uranium to supply 100% of the world’s energy for 4000 years using thermal reactors or at least 600,000 years using fast reactors – Uranium in seawater is constantly replenished by surface water runoff and by dissolution from the seabed. – Thorium (another potential fuel) is more abundant than uranium in the earth’s crust
* D.Lightfoot et al, “Nuclear Fission Energy is Inexhaustible”, Proc. Climate Change Technology Conference, EIC, Ottawa, May 2006
It’s Not all Sweetness and Light • • • • •
Fission must be controlled at a constant rate High pressure pipes must hold water Heat losses must not damage the environment Radiation must be contained Fission products (the ashes of fission) must be safely stored in the long term • Electricity must be affordable Today, we only use 1% of the energy in the fuel
Used Fuel Hazard vs Time (Another view)
Should we really worry so much about this?
Daily Electricity Demand Frequency Control
Peak Tops
Intermediate - reservoir limited Daily Energy Storage
Nuclear energy supply range
Intermediate Load
Base Load
900
Target 2: 2005 total world energy from nuclear
How Many Power Plants?
800 9000
700
7000
600
Target 1: 2005 world energy supply from nuclear, except for hydro and transportation
6000 500
400
300
200
100
NUCLEAR CAPACITY, GWe
NUCLEAR CAPACITY, EJ PER YEAR
The Problem of Scale
8000
5000
Two hundred 1000 MWe units built each year for 30 years
4000
3000
2000
1000
One ambitious plan (Dr. Yoon Chang, 2006) 1970
2070
17
Nuclear Fuel Pellet, compared with a penny This pellet weigh about 30 grams. A similar pellet, in a CANDU reactor, can produce enough electricity to toast one million slices of bread during its time in the reactor – about one year.
The pellet is made of uranium dioxide. This is a ceramic material similar to that used to make coffee cups.
It is safe to hold now – but it will be intensely radioactive when taken out of the reactor. After 300 years in safe storage, you could once again pick it up safely – but I would wear a glove.
Fuel Pellet, Bundle, and Reactor
CANDU FUEL BUNDLE Here is an old friend of mine holding a CANDU fuel bundle. On average, each bundle releases about 500 kilowatts of heat for one year. This is enough heat to produce electricity for about 25 Ontario homes.
There are 5760 fuel bundles in each Darlington reactor Dr. William Garland, McMaster University
Darlington Nuclear Power Plant Four nuclear reactors, producing 3520 megawatts of electricity.