Nuclear energy is generated by neutron bombardment of certain uranium or thorium
isotopes (nuclides), which causes fission of the atom nucleus, a process which
releases huge amounts of heat that can then be used to make steam and drive
turbines for electricity generation.
Nuclear energy provides 13 % of total electricity generation worldwide. In the U.S. it is
19 %, in Europe 30 % and in France 80 %.
Electricity production by primary source
World total electricity
production = 2.3 TW
(20 000 TWh)
Uranium is mined either in open pit, by
standard underground mining or by in
situ dissolving of the minerals and
pumping the solution to the surface. In
open pit mining, the ore is exposed by
drilling and blasting and then mined by
blasting and excavation. Workers need to
stay in enclosed cabins to limit exposure
to radiation. Water is extensively used to
suppress airborne dust levels and in deep
undergound mines to cool. There is less
waste material removed from underground
mines than open pit mines. However, this
type of mining exposes underground
workers to the high levels of radioactive
radon gas, unless sufficient ventilation is
The naturally occurring oxide forms and not
the uranium metals are used for safety
(the oxide melting point is much higher
than that of the metal and it cannot burn,
being already in the oxidized state).
Before use as fuel uranium is enriched.
Today (2013) 437 nuclear power
reactors are operational in
31 countries. The total identified and
probable (yet undiscovered) uranium
resources are about 15 megaton,
representing a power capacity of 235 TW.
World production is ~60,000 tonnes/year
generating ~380 GWelectric power (~1 TW
primary heat power from the reactors)
Uranium235 (U235) (0.7% of all natural uranium) is used in the conventional
nuclear reactors, called thermal reactors, using slow (low energy) neutrons.
During operation there is both fission and the formation of new isotopes due
to neutron capture, i.e. U236 and U238. Further neutron capture and beta
particle decay generates Plutonium (Pu)239 Pu240 , Pu241, Pu242 and other
transuranic or actinide nuclides. Pu239 and Pu241 are fissile.
Some of the fission products have a high neutron absorption capacity, by
which neutrons are removed from the reactor, making the nuclear reactor
stand still. Typically after 3-5 years the spent fuel has to be removed to a
final repository for storage as waste.
Recycled fuel (MOX): Spent fuel can also be delivered to a nuclear
reprocessing plant where 95% of spent fuel can be recycled to be returned as
fuel (known as ‘mixed oxides’; MOX) in a power plant. MOX is made in the UK
and France, and to a lesser extent in Russia, India and Japan. About 30
thermal reactors in Europe (Belgium, Switzerland, Germany and France) are
using MOX as nuclear fuel. However, in many countries recycling is not done
or prohibited by law to avoid that the Pu is used for nuclear weapon
U238 (99.3% of all natural uranium) is used as fuel in ‘fast breeder reactors’. Fast
(high energy) neutron bombardement of U238 turns this isotope into several
isotopes of plutonium. Two of these, Pu239 and Pu241, then undergo fission to
Whereas water under pressure is the coolant in thermal reactors, liquid metal
(sodium, mercury, lead) is the coolant in fast breeder reactors, as they have a
much higher boiling point than water. The high heat capacity provides thermal
inertia against overheating. The outlet temperature of the reactor is 510–550 °C.
So far, these reactors remain in the R&D phase, except for one in France, one in
Russia and one in Japan. Both China and India are now building fast breeder
In principle these reactors extract almost all of the energy contained in the fuel,
decreasing fuel requirements by a factor of 100 compared to traditional
U235 reactors. Moreover, they utilize uranium at least 60 times more
efficiently than the U235 reactor.
The great advantage of fast reactors is that they permit nuclear fuels to be bred from
almost all the uranium-derived actinides in nuclear waste from conventional
thermal reactors, including depleted uranium samples (remainder uranium after
U235 enrichment), in this way strongly mitigating the actual nuclear waste
A future source of nuclear energy could be
Thorium232. It is used in a
conventional thermal reactor.
Neutrons turn Th232 into U233 and then
cause fission of U233. Th232 is about 3.5
times more common than uranium in
the Earth's crust.
India has looked into this technology,
as it has abundant thorium but little
The thorium reactor makes a closed cycle:
Once started the reactor keeps working
automatically (see Figure)
Coal 24-30 MJ/kg
Natural Gas 38 MJ/m3
Crude Oil 45-46 MJ/kg
Uranium235 - thermal reactor grade 500,000 MJ/kg
Uranium238 – fast breeder grade 86,000,000 MJ/kg
Typical Heat Values of Various Fuels
The great advantage of nuclear energy plants is their very high energy density,
constant power supply, small size of land use for installation and absence of
CO2 emissions (at least after the uranium mining and enrichment phase and
construction of the power plant). Nuclear energy saves the emission of about
2.6 billion tonnes of CO2 each year (compared with about 10 billion tonnes per
year emitted from fossil fuel electricity generation).The Intergovernmental Panel
on Climate Change (IPCC) has recommended nuclear power as a key
greenhouse gas mitigation method that is currently commercially available.
There are serious safety and environmental
concerns with U235 thermal reactor power
Health issues: Because uranium ore emits
radon gas, uranium mining can be a health
hazard, unless adequate ventilation systems
Environmental issues: Nuclear power
plants are almost always built near lakes,
rivers and oceans because running a nuclear
reactor requires a large amount of cooling
water. A typical 1 GW nuclear reactor needs
approximately 1500 m3 per minute and this
warmer water is then discharged back into
the local ecosystem causing adverse effects
for the aquatic life.
Safety: The 1979 accident at Three Mile
Island, the 1986 Chernobyl disaster, the
1995 Monju accident and the recent
Fukushima nuclear disaster in Japan clearly
demonstrated the potential catastrophic
danger of nuclear power plants. This played a
part in stopping new plant
construction in many countries and to shut
down facilities in some others.
Radioactive waste disposal: About 10,000
tonnes of highly radioactive nuclear waste is
stored each year, mainly at individual
reactor sites (over 430 locations around the
world). Of particular concern are
Technetium99 (half-life 220,000 years) and
Iodine129 (half-life 15.7 million years). Other
products are unconverted U235 , plutonium
and curium. About 95% of the depleted
uranium is stored as uranium hexafluoride
(UF6), in steel cylinders in open air close to
enrichment plants. There is no consensus yet
where to safely longterm store nuclear
Misuse of fuel for nuclear weapon
production (from plutonium)
The nuclear power debate
There are multiple organizations which have taken a position on nuclear power – some are proponents,
and some are opponents.
• Friends of the Earth International, a network of environmental organizations in 77 countries.
• Greenpeace International, a non-governmental environmental organization with offices in 41
• Nuclear Information and Resource Service (International)
• World Information Service on Energy (International)
• Sortir du nucléaire (France)
• Pembina Institute (Canada)
• Institute for Energy and Environmental Research (United States)
• Sayonara Nuclear Power Plants (Japan)
• World Nuclear Association, a confederation of companies connected with nuclear power production.
• International Atomic Energy Agency (IAEA)
• Nuclear Energy Institute (United States)
• American Nuclear Society (United States)
• United Kingdom Atomic Energy Authority (United Kingdom)
• EURATOM (Europe)
• Atomic Energy of Canada Limited (Canada)
• Environmentalists for Nuclear Energy (International)
Attempts to mitigate the nuclear radioactive waste problem
• Reprocessing of the spent U235 fuel can potentially recover up to 95% of the
remaining uranium and plutonium which can be reused as fuel (MOX). The
radioactivity left consists largely of short-lived fission products, and its volume is
reduced by 90%. Reprocessing is done in the UK and France, and to a lesser
extent in Russia, India and Japan. However, it is not allowed in the U.S. The
Obama administration has disallowed reprocessing on the basis of nuclear weapon
• The nuclear waste problem can substantially be mitigated in the future by
using fast breeder reactors that almost completely convert the nuclear fuel,
leaving radioactive waste products in much smaller amounts for much shorter
times (a few hundred years).
• Used Thorium fuel also remains radioactive for only a few hundreds of years.
• Fast breeder reactors also offset the present relative shortage of U235.
• However, fast breeder reactors are much more expensive, the fuel needs to be
more enriched, sodium used as a coolant can explode and burns in air and is very
corrosive and nuclear proliferation concerns remain real. Thorium fuel products
are claimed to be more nuclear weapon proliferation-resistant than other fuel
products since Thorium produces fissionable U233 instead of fissionable plutonium. 9
World mine production is about 60,000
tonnes per year, but a lot of the market
is being supplied from secondary
sources such as stockpiles, including
material from dismantled nuclear
weapons. The latter are, however,
Present production of new uranium
fuels cannot follow increasing
demands. Shortage (peak uranium)
is imminent. Read more. In recent
years 40 new nuclear power plants are
being built or planned. With the
presently functioning U235 thermal
reactors at present consumption rates,
the proved resources of U235 in the
Earth crust, will be exhausted in about
60-80 years. Thus, a further
expansion of thermal reactors
On the basis of probability estimates
that more resources will be found – be
It at lower concentration and thus higher cost of mining and with more environmental damage – a
period of 270 years can be covered at best.
Nevertheless several optimistic considerations
have been advanced for nuclear energy use in
If recycling of Pu in spent uranium fuel
becomes more widespread or U238 fast
breeder reactors are used, nuclear energy
could be generated for thousands of years.
If U235 is extracted from phosphate mines
(that are richer in uranium), up to 160,000
years could be covered. However, it is not
shown to be economically feasible yet.
Uranium is present in seawater in amounts of
3.3 parts per billion (4.6 x 109 tonnes – which is
~300 x the conventional reserves) and rivers
bring uranium into the sea at a rate of 3.2 x
104 tonnes per year (~50 % of present
consumption). At present however, extraction
of uranium from the sea has only been tested at
the laboratory scale and is very expensive. Read
However, new methods of affinity adsorption
have recently been developed that may
halve the cost. Read more. See also the
book « The Ultimate Resource 2 ».
Source: OECD, 2006b; OECD, 2006c.
• Direct use of nuclear fission energy is used to drive steam tubines to give
locomotive force in some large ships and in nuclear submarines.
• For small vehicles, however, a small energy carrier is needed. Under high
temperature various procedures exist to create such carriers. Nuclear power
plants produce an excess of heat that can be adopted to make the carrier.
The following procedures are in the research and development phase:
– Generation of syngas (hydrogen + CO mixture) from methane by
steam methane reforming or from coal by coal gasification
– Generation of hydrogen from water by electrolysis at high temperature
(the electrolysis reaction is more efficient at higher temperature) or
from water by thermochemical splitting. Nuclear power plant electricity
can be used during periods of lower electricity needs (off-peak).
– Generation of synthetic fuels from coal, natural gas, oil shale, or
biomass. Since it requires large energy input, excess nuclear heat may
be a welcome opportunity. World commercial synthetic fuels production
capacity was over 240,000 barrels per day (38,000 m3/d) in 2009.