Transcript Turning Rocks into Gold - Canadian Nuclear Society

Turning Rocks into Gold
(Electric gold, that is)
A miracle of modern alchemy
Presented at Seminar on Canada’s Nuclear Technology
University of Ontario institute of Technology
October 15, 2009
Potential Energy in the Universe
• Hydrogen fusion (as well as other nuclei)
– in our sun and all visible stars
• Uranium fission
– 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 (that energy came from the sun via your food)
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, thorium
and potassium releases (in the whole earth) about
38 million megawatts
– This radioactivity heats the core of the earth
• geothermal energy leaving the earth’s surface comes almost
entirely from this radioactive decay
The First Fission Reactors
(1.7 Billion years ago in Gabon, West Africa – 15 discovered)
Uranium-Bearing
Zone
Water
Cross section of Geological Strata
Water
Nuclear Fission
• When two light nuclei fuse (join), mass is converted to
energy
• This happens in the sun
• When a heavy nucleus fissions (splits), mass is
converted to energy
• This happens in a nuclear reactor
• When gasoline burns, mass is converted to energy
• This happens in your car’s engine
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 a strong international
organization (IAEA) to guard against use for weapons
• 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 could be called “Femtopower” a nucleus is very
small
– uranium nucleus diameter is 16 femtometers (10-15 meters)
• It takes 31 billion fission reactions to release one wattsecond (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
Potential Energy
in the atomic
nucleus
Thermal energy
(fuel)
Boiling
Fission
Conduction
Energy Flows
Thermal energy
(water)
Mechanical
Energy (turbine)
Losses to
environment
Your lights,
toaster, stove
Transmission
Induction
Electrical energy
(generator)
Energy in the
atomic
nucleus
Thermal energy
(fuel)
Nuclear Fuel
(pellet)
• Uranium dioxide – ceramic, melting point 2800 C
– It is slightly radioactive
– One fuel 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
Darlington reactor, in 5760 fuel bundles
– Darlington produces 3524 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
• Radioactive hazard returns
to the original level after
about 300 years
About 300 years
About 7-8 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 mechanical
Thermal energy
energy into electrical energy
(water)
• Electricity is transmitted to you,
the customer, all within less than
30 seconds after fission
• About 70% of the total fission
energy is lost to the environment
Mechanical energy
(turbine)
Electrical energy
(generator)
Nuclear Reactor Designs
• Most of today’s Nuclear Plants (436) use Water Reactors
– Pressurized water reactor (PWR)
– Boiling water reactor (BWR)
– Pressurized heavy water reactor (PHWR)
• These designs are being modified as technology improves
– Under construction: 50
– On order or planned: 137
– Proposed: 295
• Future designs are known as “Generation 3 or 4”
– Some of these power plants will use fast reactors (FBR)
A Canadian Dream for the Future
Around the year 2100?
U
U/Th
CANDU
CANDU
PWR
BWR
Oxide Fabrication
Plant
Fresh
Fuel
Fresh
Fuel
U238
CANDU
CANDU
CANDU
PHWR
DUPIC Plant
Pu
REPROC. +
FAB.
PLANT
FBR
FBR
Waste
U + Pu + f.p.
Disposal
Fission
products
Storage
Reprocessing
Plant
Storing Electricity? – Transform It!
Frequency
Control
Peak
Tops
Intermediate - reservoir limited
Daily Energy
Storage
Nuclear energy
supply range
Intermediate
Load
Base Load
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
As market price increases the amount of “ore” (at a lower grade) increases
The uranium fuel contribution to electricity cost is negligible today
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 (PWR, BWR, PHWR) or at least
600,000 years using fast reactors (FBR)
– Thorium (another potential fuel) is more abundant than uranium in the
earth’s crust
* D.Lightfoot et al, “Nuclear Fission Energy is Inexhaustible”, Proceedings of the first Climate
Change Technology Conference, Engineering Institute of Canada, 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
Nuclear Energy is:
Available
Safe
Inexhaustible