Energy and the New Reality, Volume 2:
C-Free Energy Supply
Chapter 8: Nuclear Energy
L. D. Danny Harvey
harvey@geog.utoronto.ca
Publisher: Earthscan, UK
Homepage: www.earthscan.co.uk/?tabid=101808
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Outline
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Basics of nuclear physics
Fuels and reactions inside a nuclear reactor
Types of nuclear power reactors
The nuclear fuel chain
Safety
Nuclear weapons and terrorism risks
Cost
Embodied energy and GHG emissions
Operational constraints
Current capacity, future scenarios
Basics of nuclear energy
physics
Nuclei and isotopes
• A given chemical element has a fixed number of
protons in its nucleus (number of protons =
number of electrons)
• A variable number of neutrons is possible,
resulting in different isotopes of an element
• Protons and neutrons together are called
nucleons
• The number of protons in the nucleus is called
the atomic number, while the number of
nucleons is called the mass number
Superscripts and subscripts in front of the
chemical symbol are used to represent the mass
number and atomic number
In 126C, for example, 12 is the mass number and 6
is the atomic number.
Because the element name and atomic number
are redundant, it is common to just write 12C
instead of 126C.
Forces in a nucleus
• Electric force – repulsion between protons,
varies with 1/distance2
• Nuclear force – attraction between any two
nucleons (even having the same charge), varies
much more strongly with distance (and so is
significant only over a distance ~ diameter of the
nucleus)
• Can overcome the electric repulsive force at
distances comparable to the radius of a nucleus
• Thus, neutrons, by providing extra nuclear
forces, act as a glue holding the protons in the
nucleus together
Neutron:proton ratio and
stability of nuclei
• As atomic number increases, the ratio of
neutrons to protons required for stability of the
nucleus increases
• Nuclei with one or two less or one or two more
neutrons are unstable – they eventually decay
• If a heavy nucleus splits (fissions) into the nuclei
of two lighter elements, it will often have too high
a neutron:proton elements (depending on how
the heavy nucleus splits), so the fission products
will themselves often be unstable
Figure 8.1 Neutron:proton ratios of the elements
140
Number of neutrons
120
Stable nuclei
Unstable nuclei
100
80
neutron:proton = 1.5:1
60
neutron:proton = 1:1
40
20
0
0
10
20
30
40
50
Number of protons
60
70
80
90
Half lives of unstable nuclei
• In a collection of unstable nuclei of a given
isotope, not all the nuclei decay at once
• Rather, it is observed that half of the nuclei
existing at any given time will decay within a
fixed length of time called the half-life
• Thus, if the half life is 10 years and we start off
with 1000 nuclei of a given isotope, there will be
500 left after 10 years, 250 left after 20 years,
125 left after 30 years, and so on
Kinds of particles emitted during the
radioactive decay of an unstable nucleus
• Alpha particles, consisting of 2 protons and 2 neutrons
(as in the nucleus of He)
• Beta particles (electrons or, rarely, positrons)
• Neutrons
When alpha particles are emitted, the nucleus drops down
by two atomic numbers.
When an electron beta particle is emitted, a neutron in the
nucleus turns into a proton, so the nucleus moves up by
one atomic number.
Gamma rays (very short wavelength, energetic
electromagnetic radiation) are emitted when a nucleus
drops from an excited to a ground state (perhaps
following absorption of a neutron)
Fission (splitting) of a nucleus
• Can occur spontaneously (i.e., with no external
stimulus)
• Can also occur as a result of the absorption of a highenergy neutron – such nuclei are said to be fissionable
• Can even occur (with some probability) when a
neutron of arbitrarily low energy strikes the nucleus –
such nuclei are said to fissile
• When fission occurs, additional neutrons are released
that can then sustain a fission chain reaction (and
further neutrons will be released when the fission
products themselves decay)
• Some nuclei can absorb neutrons but without splitting
– such nuclei are said to be fertile
Fuels (or potential fuels) and decay
reactions in a nuclear power reactor
• Uranium (the overwhelmingly used fuel)
• Plutonium (from recycling of spent fuel)
• Thorium (usable in principle, has been
demonstrated in the US)
Natural Uranium
•
•
•
•
0.0055% U-234 (234U)
0.7205% U-235
99.275% U-238
All three isotopes are radioactive but with
extremely long half-lives
Note: The above percentages are in terms of numbers of atoms (atom%). When speaking of
enrichment, percentages are given in terms of mass (mass%). 0.72atom% (U-235)= 0.71mass%.
U-235 is fissile, and a sample reaction is
235U
+ n → 236U → 92Kr + 141Ba + 3n
The fission products (92Kr and 141Ba here) and
neutrons travel at high velocity, adding some of
their kinetic energy to the atoms or molecules of
the material through which they travel, heating it
Note that, in the above, 1 neutron is absorbed and
3 are emitted. If one of the 3 that are emitted is
subsequently absorbed by another 235U, the
reaction will be self sustaining.
Figure 8.2: Fission products of U-235
1.0E+01
1.0E+00
Yield (%)
1.0E-01
1.0E-02
1.0E-03
Stable Elements
Half life > 100 yrs
Half life 1 - 100 yrs
Half life < 1 yr
1.0E-04
1.0E-05
70
80
90
100
110
120
130
Mass number
140
150
160
170
U-238 is fertile, and the reactions that occur are
+ n → 239U → 239Np + ß
239Np → 239Pu + ß
238U
Pu-239 is both fissile and fertile – it can either
absorb another neutron (followed by emission of a
beta particle, just like 238U above), or it can split
into two lighter elements (with a half life of 24,000
years) and emit more neutrons as it splits.
The absorption of a neutron by 238U is the first in a
sequence of transmutation reactions, shown in the
next figure.
Figure 8.3. Transmutation reactions
beginning with U-238.
n
n
Cm-242
Cm-243
Cm-244
n
10.1 hr
16.02 hr
Am-241
n
n
Am-242
14.4 yr
Pu-239
Pu-240
Pu-241
2.355 day
n
Am-243
Am-244
n
Pu-242
n
Np-239
23.5 min
U-238
U-239
n
Source: Modified from Wilson (1996, in The Nuclear Fuel Cycle, From Ore to Waste, Oxford University Press, Oxford )
To sum up, the reactions occurring
inside a nuclear reactor are primarily:
• Absorption of neutrons by 235U, producing 236U
that then fissions and releases further neutrons
• Absorption of some of the above neutrons by
238U, producing 239Np and 239Pu through the
sequential emission of two beta particles
(electrons)
• Transmutation of 239Pu into successively heavier
elements (the transuranic elements) through
absorption of neutrons and emission of beta
particles
Thorium as a fuel
• Thorium is fertile, meaning that it can absorb
neutrons without splitting (like U-238)
• It must be used in combination with U-235 or
P-239, which serves as the neutron source
• The end result is to produce U-233 (which does
not occur naturally), which can be easily
separated from the spent fuel and fed into
another reactor as a fuel in a closed cycle
• This would increase the energy that can be
derived from a tonne of mined U by 85%
compared to the usual once-through use of
uranium
• Significant new technologies would need to be
developed to use the uranium-thorium cycle
Sustaining nuclear
chain reactions
• Neutrons released by fission of U-235 after it
absorbs a neutron move so fast that they have
little chance of being absorbed by another U-235
(at least one neutron must be absorbed to
sustain the process)
• Thus, the neutrons must be slowed down using
a moderator (water, heavy water, or graphite) –
which absorbs energy from the neutrons without
(ideally) absorbing the neutrons
Stabilizing nuclear
chain reactions
• For the reaction not to grow exponentially out of
control, exactly one neutron from each fission of
U-235 must cause another fission
• This ratio is maintained by inserting control rods
between the uranium fuel rods – the more that
are inserted, the more neutrons that are
absorbed before they can cause another fission
Thermal reactors
• Neutrons that have been slowed down with a
moderator are called thermal neutrons, and
reactors using them are called thermal reactors
• Those that use water as a moderator require
that the uranium fuel (which is mostly U-238) be
enriched in the fissile isotope U-235 (from about
0.7% to 3-4%). These are called light-water
reactors
• Reactors that use heavy water as a moderator
(namely, the CANDU reactor) do not require
enriched uranium. These are called heavy-water
reactors.
Fast and fast breeder reactors
• Neutrons that have not been slowed down are
called fast neutrons. They can still be used if the
reactor has a high enough density of fissile
material. This requires fuelling a reactor with U233, U-235, or Pu-239. These reactors are
called fast reactors.
• Pu-239 is a natural choice, since it is produced
anyway in thermal reactors
• If the Pu-239 content exceeds 10-20%, more
Pu-239 will be created through absorption of
neutrons by U-238 than is consumed during the
fission that releases the neutrons, so these
reactors are called fast breeder reactors
Fast and fast breeder reactors
(continued)
• By repeatedly cycling nuclear fuel through fast
breeder reactors, almost all of the U-238 in
uranium (which accounts for > 99% of U) can be
used as a fuel. Otherwise, only the U-235
(0.72%) serves as a fuel
• The problem – Pu is ideal for making nuclear
weapons. Vast amounts (1000s of tonnes) would
need to be separated from spent fuel for
recycling. Only 1-2 kg are needed to make a
crude bomb.
The elements produced with atomic number
beyond uranium are called transuranic elements.
Each of them is unstable and will eventually fission
into lighter elements. Uranium and the transuranic
elements, along with thorium, are referred to as
actinides (they form a special series in the periodic
table after the element actinium)
Measures of nuclear radioactivity
• Becquerel (Bq) – 1 Bq = a rate of one decay per
second
• Curie (Ci) – the rate of decay of one gram of
radium 1 Ci = 3.7 x 1010 Bq
• Gray (J/kg) or rad (100s of erg/gm) – amount of
energy deposited per unit mass of living tissue
• Sievert (Sv) or rem – the energy deposited
(grays or rads) times a factor that accounts for
the different amounts of damage caused by
different kinds of radiation
Sources of nuclear radiation:
• Emission of beta particles during the transmutation
of an actinide to an element with a higher atomic
number (as in Fig. 8.3)
• Emission of neutrons during the fission of an
actinide
• The fission products themselves, which are released
with high velocity and are large, so they are quite
damaging
• Emission of beta particles during the eventual decay
of the fission products themselves
• Emission of alpha and beta particles produced by
four different radioactive decay chains that proceed
spontaneously without the absorption of a neutron
Fission products of concern
• Iodine-131, 8-day half life, becomes
concentrated in milk, absorbed by thyroid gland.
Of greatest concern for first few weeks after a
potential nuclear accident
• Stronium-90, 29-year half life, mimics calcium,
becomes concentrated in bones
• Cesium-137, 30-year half life, 6% of fission
products, mimics potassium, distributed
throughout body
Radioactive decay chains
•
•
•
•
Thorium series (Th-232 to Pb-208)
Uranium series (U-238 to Pb-206)
Actinium series (Pu-239 to Pb-207)
Neptunium series (Pu-241 to Tl-205)
The uranium series is shown in Fig 8.4
Figure 8.4a Uranium series radioactive decay chain
U-238
=4.468 Gy
3
a=12.45x10
Th-234
=24.1 days
12
a=857.0x10
Pa-234m
=1.17 min
15
a=73.99x10
U-234
=244.5 ky
6
a=231.4x10
Th-230
=77 ky
6
a=747.7x10
Ra-226
=1600 yr 9
a=36.62x10
Rn-222
=3.825 days
15
a=5.691x10
Po-218
=3.05 min 1 8
a=10.46x10
Pb-214
=26.8min
18
a=1.213x10
Bi-214
=19.9 min
18
a=1.634x10
Po-214
=164 sec
24
a=30.63x10
Pb-210
=22.3 yr
12
a=2.832x10
Bi-210
=5.01 days
15
a=4.592x10
Po-210
=138 days
12
a=166.3x10
Pb-206
Stable
Figure 8.4b Uranium series radioactive decay chain
242
238
U
238
234
Mass Number
230
226
222
218
214
210
206
206
Pb
202
81
82
83
84
85
86
87
88
Atomic Number
89
90
91
92
93
Figure 8.5 U-238 Series Radiation
350
250
9
Radioactivity (10 Bq)
300
200
Rn-222 to Po-210
150
100
Ra-226
Th-230
50
U-234
U-238
Th-234 + Pa-234
0
103
104
105
106
107
Year
108
109
1010
107
Basis: PWR Spent Fuel
50 MWd/kg HM
4.5% initial enrichment
Total
106
Fission
Products
90
137
Si + Cs
Total
Actinides
Figure 8.6
Sources
of radioactivity
from
spent
LWR fuel
Ci/tHM
105
243
Pu
4
10
238
Pu
Am241
3
10
240
Pu
239
Pu
U238
Chain
Am243
2
10
237
Np
Chain
99
Tc
1
10
1
10
100
1000
10,000
100,000
1 million
Years after Discharge
Source: MIT (2003, The Future of Nuclear Power: An Interdisciplinary MIT Study)
Partial summary so far:
• Heat is produced inside a nuclear reactor from collisions
of energetic particles produced by radioactive decay with
the atoms of the material forming the reactor, or by the
absorption of gamma rays
• The kinds of radioactive decay are
- the lighter nuclei produced by fission of U-235 (the
predominant fissioning material) or by fission of
transuranic elements (produced by neutron absorption)
- beta particles emitted during the decay of transuranic
elements that build up (mostly plutonium)
- beta particles from the decay of the fission products
themselves
- gamma rays emitted following neutron capture by U235, U-238, or the transuranic elements
Once the fuel has been removed from a
nuclear reactor,
• The reactions involving absorption of neutrons by 235U
and 238U largely cease, as does the production of
transuranic elements
• The sources of radioactivity in spent nuclear fuel are
-during the first year, the decay of fission products, with
those having half lives of hours to days
-one year after removal, the radioactivity has dropped to
1.3% of that at the time of removal, and is dominated by
the decay of fission products with half lives of around 30
years (primarily Sr-90 and Cs-137)
- thereafter, the decay of transuranic elements
(especially Am-241, Pu-240 and Pu-239) dominates
(until 100,000 years after removal)
-finally, radioactivity from the U and Np series (which
initially increases over time) dominates
Nuclear Power Plant
Reactor Technologies
Nuclear Reactor Technologies
• Boiling-water reactor (a LWR, thermal reactor)
• Pressurized-water reactor (another LWR,
thermal reactor)
• CANDU HWR (also a thermal reactor)
• High-temperature gas-cooled reactor (HTGR)
Figure 8.7 Overview of nuclear powerplant
technologies
nuclear reactors
thermal neutrons
burners
fast neutrons
burners
breeders
Source: van Leeuwen (2007, Nuclear Power- The Energy Balance, Ceedata Consultancy, Chaarn,
Netherlands, www.stormsmith.nl )
Figure 8.8a Boiling-water light-water reactor
reactor
vessel
turbine
generator
steam
electricity
out
uranium fuel
condenser
control
rods
water
coolant/moderator in
out
cooling water
Source: Wolfson (2003, Nuclear Choices: A Citizen’s Guide to Nuclear Technology, MIT Press, Cambridge)
Figure 8.8b Pressurized-water light-water reactor
control rods
primary loop
secondary loop
turbine
uranium
fuel
electricity
out
generator
condenser
reactor
vessel
pump
out
in
cooling water
Source: Wolfson (2003, Nuclear Choices: A Citizen’s Guide to Nuclear Technology, MIT Press, Cambridge)
Figure 8.8c Liquid-metal fast breeder reactor
heat
exchanger
core:
U-235,
Pu-239
steam
generator
steam to
turbine
liquid
sodium
liquid
sodium
U-238
blanket
pump
pump
water
in
Source: Wolfson (2003, Nuclear Choices: A Citizen’s Guide to Nuclear Technology, MIT Press, Cambridge)
Note:
• The High Temperature Gas-Cooled Reactor (HTGR)
uses uranium enriched to 93% U-235 (making it
weapons-grade fuel), uses He as a coolant, and uses
graphite (which is flammable) as a reactor. It has had
mixed performance but is being reconsidered as a
Generation IV reactor (see next slide).
• The liquid-metal fast breeder reactor uses liquid sodium
as a coolant, but sodium burns spontaneously on contact
with air and reacts violently with water. Several were
built but most have been shut down due to difficulties.
Nuclear technology generations
• Generation I: still a few in operation
• Generation II: accounts for most of today’s reactors,
based on military research of the 1940s and 1950s
• Generation III: about 20 different designs are under
development. Mostly incremental improvements
from Generation II, but can still take decades to
develop
• Generation IV: 6 advanced concepts under
development, most involving a closed cycle with
reprocessing of spent fuel [on site] to separate and
use plutonium. These exist only on paper at present,
and would likely take 2-3 decades to develop.
The Nuclear Fuel Chain
Steps in the Nuclear Fuel Chain
• Mining and milling of primary uranium, production of
tailings waste
• Enrichment of primary uranium, done by converting U to
gaseous form and using centrifuges or membranes
under pressure, creating a stream of depleted uranium
(DU) waste. About 7 kg of natural uranium (0.7% U-235)
are needed to produce 1 kg of U enriched to 3.6% U235, with U-235 depleted to 0.2% in the DU stream
• Use of nuclear fuel (the burn-up is the amount of heat
produced per kg of fuel)
• Possible reprocessing of spent fuel, generating lots of
liquid and gaseous wastes
• Isolation (“disposal”) of spent fuel and/or reprocessing of
wastes
Fuel chain step 1: Separation of
uranium from ores
• Uranium occurs as oxides in uranium ores
• The proportion of uranium ores containing U is
quite small (ranging from 0.03% to 18.0% in
commercial operations, but averaging only
0.2%)
• The mass of ore that must be processed per unit
mass of uranium, and the associated rock
waste, is given by the reciprocal of the ore grade
• Thus, for 0.2% grade ore, 500 tonnes of ore
must be processed to obtain 1 tonne of U
• However, in open-pit mines, up to 40 tonnes of
rock might be excavated per tonne of ore that is
extracted
• The recovered ore is crushed and leached with
sulfuric acid or alkaline fluids in order to
separate out the uranium
• The final product is called yellow-cake (U3O8)
• 85% of the radionuclides in the original ore end
up in the wastes, which are called tailings.
• Management of the tailings (due to their
radioactivity and toxicity) will need to continue
essentially forever (several 100,000 years)
Figure 8.9: World uranium extraction techniques in 2007
Heap leaching
2%
Co-product mining
8%
Other
0%
Open pit mining
24%
In situ leaching
28%
Underground
mining
38%
Source: NEA/IAEA (2008, Uranium 2007: Resources, Production and Demand, OECD Publishing, Paris)
Figure 8.10: Yellowcake – U3O8, produced from milling of
the U ore followed by leaching from the crushed ore.
Source: www.wise-uranium.org
Fuel chain step 2: Enrichment of
uranium in U-235
• Light-water reactors require the uranium fuel to
be enriched in U-235 (from 0.7% in natural
uranium to 3-5%)
• This requires converting the uranium to a
gaseous form (UF6), and using either gaseous
diffusion through membranes under pressure, or
centrifuges, to create 2 streams – one enriched
in U-235 and the other depleted in U-235
• The depleted uranium has to be stored
somewhere essentially forever
Figure 8.11 Waste canisters containing depleted uranium,
produced during the enrichment of natural uranium in U-235
Source: www.wise-uranium.org
Fuel chain step 3: Use of U fuel
• The various high-energy particles produced from
the radioactive decay of the fuel (along with
some gamma radiation) impart kinetic energy at
the molecular scale to the surrounding materials
through collisions with the atoms of the
surrounding materials – that is, they heat it up
• The amount of heat produced per unit mass of
fuel is called the fuel burn-up.
• Burn-ups have increased from about 20 GWd
(gigawatt-days) per tonne in the 1970s to an
average today of 45 GWd/t in BWRs and 50
GWd/t in PWRs
• Electricity production per tonne of fuel is given
by the burn-up times the thermal efficiency of the
steam turbine
• Higher burn-ups require the use of more
enriched uranium and use of a greater fraction
of the U-235 that is in the original fuel
• Increasing the U-235 enrichment from 4.5% to
8.3% would double the burn-up from 40 GWd/t
to 80 GWd/t, reduce the consumption of uranium
ores by 7%, reduce the mass of spent fuel by
50%, and increase the concentration of
radionuclides in the spent fuel (increasing the
heat production per unit mass)
Fuel Chain Step 4: Optional
Reprocessing of spent fuel
• Recycle into a LWR
• Recycle into a HWR
• Recycle into fast reactors or fast breeder
reactors
Spent reactor fuel contains
• Most of the original U-238 and perhaps 20% of
the original U-235 (the U-235 may have gone
from an enriched concentration of 4% down to
0.8%)
• Fission products
• Plutonium and minor actinides (such as Np-237,
Am-241 & Am-243, Cm-242 to Cm-248, and Cf249 to Cf-252)
30kg, FP
1kg, Tu
9kg, Put
8kg, U-235
U-235 31kg
U-238
969kg
U-238
952kg
FRESH FUEL
(3.1% ENRICHMENT)
SPENT FUEL
(33,000 MWd/t)
1 TONNE
OF FUEL
Figure 8.12
Composition
of fresh and
spent
nuclear
fuel
Source: Albright and Feiveson (1988, Annual Review of Energy 13, 239–265)
Reprocessing
• Reprocessing requires separating the U-235 and
Pu-239 (which can be used as a fuel) from the
spent fuel
• This is done by dissolving the spent fuel in a
strong acid
• The fission products and minor actinides are not
useful as a fuel, and are highly radioactive, so
they must be removed and stored in containers
that are actively cooled
Reprocessed Fuel
• Consists of mixtures of oxides of U-235 and Pu,
accounting for about 4.5% of the total if fed to
LWRs, along with natural or depleted uranium
(from previous enrichment activities)
• It is therefore called Mixed Oxide (MOX) fuel
• About 5-6 kg of spent fuel must be processed to
make 1 kg of MOX
Reprocessed Fuel (continued)
• There will be a deficit in U-235 in the MOX,
which can be made up either by adding Pu from
dismantled nuclear weapons (thereby providing
a way of getting rid of Pu if and as the world
disarms), or by using the spent fuel from more
than one LWR to provide the fuel for the
equivalent of one LWR running on 100%
reprocessed fuel
• In practice, a LWR would take only 1/3 MOX and
2/3 fresh fuel
• The net result is that using reprocessed fuel in
LWRs extends the uranium supply by 20-25%
Other reprocessing options:
• Use spent LWR fuel directly in a CANDU HWR
• Recycle in a fast reactor that is designed to
exactly consume the amount of Pu and other
transuranic elements produced from a LWR,
leaving only the fission products (all of which
have half lives of 30 years or less)
• Recycle in a fast breeder reactor, having a net
production of Pu (from U-238) that can be fed as
fuel to other reactors
Status of Reprocessing Today
• US reprocessing shut down due to concerns about
proliferation of nuclear weapons, especially after
India made a bomb from extracted Pu in 1974
• Japanese reprocessing shut down in 1995 after a
severe sodium fire; might be restarted
• UK reprocessing shut down in 2005 after discovery
of leakage of spent fuel dissolved in acid
• France (1700 t/yr), Russia (400 t/yr), and India (275
t/yr) are the major reprocessors today
• Other countries (including the US) had been
reconsidering
• Only 27 GW of nuclear plants out of 369 GW
worldwide use some reprocessed fuel (1/3 of their
total, so they are equivalent to 9 GW out of 369
running on 100% reprocessed fuel)
Fuel Chain Step 5: Decommissioning
of nuclear powerplants
This involves:
• Removal of the spent fuel
• Cleaning and decontaminating the plant as
thoroughly as possible
• Altering the ventilation system
• Removing all ancillary equipment and buildings
• Dismantling or reducing in size and removing
the remaining plant parts
Decommissioning is rendered difficult and expensive
because many of the plant materials will have been
rendered radioactive during the operation of the plant. The
radioactivity comes from activation products – nonradioactive isotopes in the plant materials that are turned
into radio-active isotopes through the absorption of
neutrons. Examples include Ca-41 and Cl-36 produced
from Ca-40 and Cl35 in concrete and steel.
Due to this radio-activity, the no-longer used plant must site
idle for some time (up to 135 years allowed in the UK, up to
60 years in the US) before
decommissioning begins. In Japan, idled plants must be
decommissioned within 10 years of shutting down.
Fuel Chain Step 6: Isolation
(“disposal”) of nuclear waste
Categories of nuclear waste
• High level – spent fuel, liquid wastes from
production and possible later reprocessing of
spent fuel, solids into which such liquid wastes
have been converted
• Transuranic or intermediate-level wastes,
produced during processing of spent fuel
• Low-level waste, produced during most steps of
the nuclear fuel chain
Isolation Options
• Reprocessing – using cycles designed to
consume Pu-235 and other long-lived
transuranic elements, leaving shorter-lived
radioisotopes
• Deep geological disposal – concerns about
groundwater as climate changes
• Transmutation – exceeding complex
Geological repositories rely on one of two kinds of
barriers to prevent spread of radio-nuclides:
• Geological barriers – as in the proposed and then withdrawn
and maybe re-instated Yucca Mountain site in Nevada (the
assumption had been that there would never be groundwater
flow through the site during the next 1 million years)
• Engineered barriers, as in the Finnish and Swedish proposals
The Swedish proposal requires
• a 25 t cast-iron canister for every 2 t of waste
• a 5-cm thick copper cladding around each canister
• Placement of canistors 500 m below ground, packed with
bentonite (a swelling clay)
Uranium Mine
Figure 8.13.
Waste flow
associated
with 1 GWyr of
electricity
production,
assuming:
108411.3 tU ore
(216.8 tU)
Uranium Mill
244.9 tU3O8
108,000 t mill tailings
(207.6 tU)
Conversion Plant
305.5 tUF6
542,000 t waste rock
145 t solid waste
3
1343 m liquid waste
(206.6 tU)
Enrichment Plant
5:1 waste rock/ore ratio,
0.2% grade,
38.0 t enriched UF
(25.7 tU)
enrichment
Fuel Fabrication
to 3.6%,
Plant
42 GWd/tU burnup
267.6 t depleted UF6
(180.9 tU)
6
28.8 tUO2
3
12.7 m solid waste
288.7 m3 liquid waste
(25.4 tU)
Nuclear Power
Plant
1 GW-yr of
electricity
28.8 t spent fuel
Nuclear fuel chain: alternative
chains with some recycling
Figure 8.14a Nuclear fuel once-through LWR chains
Option 1a, Low Burnup: 50 GWd/t, n=0.33
Option 1b, High Burnup: 100 GWd/t, n=0.33
Source: MIT (2003, The Future of Nuclear Power: An Interdisciplinary MIT Study)
386,000 t natural U
286,000 t natural U
29864 t spent fuel,
50 GWd/tHM burnup
14932 t spent fuel,
100 GWd/tHM
27893 t/yr U (93.4%)
13055 t/yr U (87.43%)
1538 t/yr FP (5.15%)
1538 t/yr FP (10.30%)
397 t/yr Pu (1.33%)
294 t/yr Pu (1.97%)
36 t/yr MA (0.12%)
45 t/yr MA (0.30%)
Figure 8.14b Nuclear fuel chain Option 2, recycling of Pu from spent
fuel and use of depleted U in a LWR with 50 GWd/t burnup, n = 0.33
Pu: 233 t/yr
Source: MIT (2003, The Future of Nuclear Power: An Interdisciplinary MIT Study)
Figure 8.14c Nuclear fuel chain Option 3, LWR with 50 GWd/t burnup,
CF=0.9, n=0.33; and FR with 120 GWd/t burnup, CF=0.9, n=0.44
Source: MIT (2003, The Future of Nuclear Power: An Interdisciplinary MIT Study)
Safety Issues
•
•
•
•
Routine operation of nuclear power plants
Terrorist attacks on nuclear power plant
Military strikes on nuclear power plants
Accidents at reprocessing plants (several have
already occurred, and we’re hardly doing any
reprocessing)
Nuclear weapons proliferation
issues
There is concern both about more states acquiring
nuclear weapons, and about sub-national or
terrorist groups getting enough materials to make
a crude nuclear bomb.
There are two distinct points of risk
• Enrichment of U-235 for power generation – 2/3
of the effort require to make bomb-grade
uranium (90% U-235) already has to be
expended just to make reactor-grade uranium
(3.5% U-235)
• Separation of Pu from spent fuel (which is highly
radioactive and thereby inhibits handling),
thereby making it relatively safe and easy to use
Figure 8.15: Effort (represented by Separative Work
Units) to enrich uranium in U-235
Separative Work Units per kg of U-235
300
Reactor
grade
250
200
Cd=0.002
150
Cd=0.003
100
Bomb grade
50
0
0.0
0.2
0.4
0.6
U-235 Fraction
0.8
1.0
Cost of nuclear electricity
Factors contributing to the cost
of nuclear electricity
•
•
•
•
Capital cost
Capacity factor
Fuel cost
Decommissioning and long-term isolation of
nuclear wastes
Capital Cost
• Big unknown for complicated, new technologies,
especially if not mass produced (such as
Generation III or IV nuclear reactors)
• Early (2000-2005) estimates of future
construction costs clustered around $2000/kW
• Many recent reactors have cost $3000-4000/kW
• Some analysts have projected costs of $600010000/kW
Figure 8.16 Capital cost of nuclear power plants
12000
Overnight Capital Cost ($/kW)
10000
Wall Street &
Independent
Analysts
8000
6000
Completed Nuclear
Reactors
Utilities
4000
Early Vendors,
Government &
Academics
2000
0
1970
1975
1980
1985
1990
1995
2000
2005
Year
Source: Cooper (2009, Institute for Energy and the Environment, Vermont Law School)
2010
Note: The preceding slide gives “overnight”
capital costs. These costs
• Do not include interest that accrues during the
construction period (which can be up to 10 years)
• Do not include inflation of component costs during the
construction period (which have tended to exceed the
general rate of inflation)
• Do not include additional utility costs, such as the cost of
upgrading the grid to accept a large new source of power
Rather, overnight costs are the costs for the powerplant
alone if everything could be bought at once and the plant
could be constructed overnight. Final costs are typically
50-75% greater than the overnight cost, but have been
as high as double the overnight cost.
Fuel costs
• Fuel is a very small contributor to the overall
cost of nuclear electricity, and the cost of
uranium itself is a small factor in the overall fuel
cost
• Thus, the price of uranium can increase greatly
(due to future scarcity) with little impact on the
overall cost of nuclear energy (but increased
uranium cost would make more uranium
economically available)
Decommissioning and long-term
isolation costs
• These are likely to significantly increase the
overall cost of nuclear electricity
• Most current assessments seem to vastly
underestimate these costs
• In any case, there are very few firm data
available
Figure 8.17: Estimated cost of decommissioning
graphite-moderated nuclear power plants in the UK
Estimated Decommissioning Cost ($/kW)
12000
10000
8000
6000
4000
2000
0
0
200
400
600
800
Powerplant Size (MW)
1000
1200
Figure 8.18 Cost of nuclear energy
0.30
Cost of electricity (2008$/kWh)
0.25
Wall Street &
Independent
Analysts
0.20
0.15
Completed Nuclear
Reactors
Utilities
0.10
Early Venders,
Government &
Academics
0.05
0.00
1970
1975
1980
1985
1990
1995
2000
2005
Year
Source: Cooper (2009, Institute for Energy and the Environment, Vermont Law School)
2010
Note: The preceding costs assume essentially
zero insurance and liability costs compared to the
potential cost of a nuclear accident. This is
because no private investors would be prepared to
accept the risk, and no insurance companying
would be prepared to sell insurance, if the nuclear
power plant operators would be financially
responsible for the majority of the potential
damage in the event of a serious accident.
EROEI and GHG Emissions
Figure 8.19 Fraction of uranium recovered from ore
as a function of the ore grade
Source: van Leeuwen (2007, Nuclear Power- The Energy Balance, Ceedata Consultancy, Chaarn,
Netherlands, www.stormsmith.nl )
Supplemental
figure: The
Escondida
copper mine
in Chile.
Source: van Leeuwen (2007,
Nuclear Power - The Energy
Balance, Ceedata Consultancy,
Chaarn, Netherlands,
www.stormsmith.nl )
Figure 8.20 Cross section of the proposed
open-pit Olympic uranium mine
h1
h2
h3
Source: van Leeuwen (2007, Nuclear Power- The Energy Balance, Ceedata Consultancy, Chaarn,
Netherlands, www.stormsmith.nl )
Energy Inputs Related
to Nuclear Energy
• Energy is required to make all of the materials
that go into a nuclear powerplant (cement, steel,
copper, aluminum especially)
• Energy is also used during mining and milling of
uranium ores, during the enrichment process,
during the operation of the nuclear power plant,
and later during decommissioning, possible
reprocessing of spent fuel, excavation of the
longterm repository for nuclear wastes, and
packaging of the wastes
Energy Return Over Energy Invested
(EROEI)
• The EROEI can be computed based on the ratio of all
the electrical energy generated to all secondary
energy inputs (fuels and electricity)
• Alternatively, it can be based on the primary energy
saved when nuclear electricity is produced (assuming
that fossil fuel electricity generated at 40% efficiency is
displaced) and the total primary energy inputs
• The effective efficiency in using fuels can be computed
as the net electricity production (electricity produced
minus all electricity inputs) divided by the fuel primary
energy
• The EROEI and effective efficiency drop sharply as
the ore grade decreases from 0.1% to 0.01%.
Figure 8.21 Published estimates of the amount of energy
required to construct a 1 GW nuclear powerplant
40
Construction Energy (PJ)
44, 81, 107, 269
30
Based on input-output analysis
Based on economy-wide AEI
Based on process analysis
20
10
0
LWR
BWR
PWR
HTGR
HTR
Type of Reactor
AEI=average energy intensity (KJ/$)
FBR
HWR
AGR
Figure 8.22 Energy use over the 40-year life of a 1-GW
LWR nuclear powerplant with a capacity factor of 0.87
1000
Handling overburden, 1.35 x ore mass
MMR, underground mine
Lifetime Energy Use (PJ)
800
Spent fuel
Decommissioning
Waste operations
600
Fuel production & reactor operations
Construction of reactor
400
200
0
1
0.5
0.15
0.1
0.06
0.05
Ore Grade (%U3O8)
0.04
0.03
0.02
0.01
24
1200
20
1000
16
800
12
600
8
Fuel efficiency, Underground mine
Fuel efficiency, Open-pit mine
EROEI, Underground mine
EROEI, Open-pit mine
EROEI, ISL - Low energy estimate
EROEI, ISL - High energy estimate
4
0
1
0.1
Ore Grade (%)
400
200
0
0.01
Fuel Efficiency (%)
Lifetime EROEI
Figure 8.23 EROEI based on secondary energy for the nuclear
powerplant featured in Fig. 8.22 (left scale) and fuel efficiency (net
electrical energy generated divided by fossil fuel use) (right scale). Note:
the present world average grade of ore is about 0.2%
GHG Emissions
• Wide range of estimates
• Middle value is about 1/3 that of a state-of-art
the natural gas combined cycle powerplant (at
60% efficiency)
• Would increase with a decrease in the average
grade of the ore being mined (due to greater
energy use during mining and milling operations)
Nuclear Energy Today
Figure 8.24 Nuclear Share of Electricity
France
Lithuania
Slovak Republic
Belgium
Switzerland
Ukraine
Bulgaria
Armenia
Slovenia
South Korea
Hungary
Switzerland
Germany
Czech Republic
Japan
Finland
Spain
USA
UK
Russia
Canada
0
10
20
30
40
50
Percent
Source: www.iaea.org/programmes/a2/index.html
60
70
80
90
Figure 8.25 Growth in nuclear energy
TWh/yr Electricity Generation
2500
2000
Asia Pacific
Africa
FSU
Europe
S & C America
North America
1500
1000
500
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
Figure 8.26 Nuclear powerplant capacity factors
100
90
80
Capacity Factor
70
60
50
40
30
20
10
20
05
20
03
20
01
19
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
19
77
19
75
19
73
19
71
0
Source: WEC (2007, 2007 Survey of Energy Resources, World Energy Council, London)
Figure 8.27 Nuclear reactor ages
35
Number of Reactors
30
25
20
15
10
5
0
0
5
10
15
20
25
30
Age (Years)
Source: Data from www.iaea.org/programmes/a2/index.html
35
40
45
Figure 8.28 World Uranium Resources
Other
11.5%
Ukraine
3.6%
Australia
22.7%
Niger
5.0%
Namibia
5.0%
Brazil
5.1%
Kazakhstan
14.9%
USA
6.2%
Canada
7.9%
South Africa
8.0%
Russia
10.0%
Potential Future Contribution
of Nuclear Energy
Maintaining existing capacity
• As of April 2007, 114 out of 436 nuclear power
reactors in the world were more than 30 years
old
• Assuming the normal reactor lifetime of 40
years, 114 new reactors will be needed during
the next 10 years, or an average of one every 5
weeks – just to maintain the existing capacity
• The following decade, a new reactor would be
needed every 22 days on average just to
maintain the existing capacity
Limits on expansion
• To maintain a nuclear fleet with 1000 GW capacity
(about 25% of current total world electrical capacity
but almost 3 times the 2007 nuclear capacity of 369
GW) would generate 20,000 tonnes of spent fuel per
year (assuming a 90% capacity factor and burn-up
of 50 GWd/t), or 10,000 tonnes of spent fuel per
year (if a 100 GWd/t burn-up is achieved).
• This would require the establishment of a new
Yucca Mountain scale waste repository every 3.5 to
7 years, or
• Reprocessing would require 6-12 times the current
French reprocessing capacity (1700 t/yr).
• Included in this would be production of 195-264
tonnes of Pu per year
Resource Constraints
• Its hard to say how much uranium might become
available with large increases in the price of uranium
(due to scarcity)
• However, in the absence of reprocessing and use of fast
breeder reactors (which pose enormous terrorism risks
in today’s world), the supply would likely not be adequate
for more than 100 years (and possibly much less), given
a fleet of 1000 GW.
• As lower grades of uranium ore are exploited, the energy
cost associated with extracting and processing the ore
would rise sharply (at present the nuclear lifecycle GHG
emissions are about 1/3 that of a natural gas powerplant
at 60% efficiency)
Figure 8.29 Distribution of “identified” uranium
resources with respect to the ore grade
Mass of Uranium (kt)
2000
1600
Total
1200
800
Soft or mixed
400
0
100
10
1
0.1
0.01
Ore grade (% U3O8)
Source: van Leeuwen (2007, Nuclear Power- The Energy Balance, Ceedata Consultancy, Chaarn,
Netherlands, www.stormsmith.nl )
Figure 8.30 Cost of uranium vs the grade of
ore supplying the uranium
Source: van Leeuwen (2007, Nuclear Power- The Energy Balance, Ceedata Consultancy, Chaarn,
Netherlands, www.stormsmith.nl )
Concluding Thoughts
Given that nuclear energy could supply 25% of our
electricity needs for at most 100 years, after which
we’ll have to find alternatives anyway, and that the
next 100,000 years or more of generations will be
burdened with dangerous wastes, can we ethically
justify such a short fling with nuclear energy now?
In any case, it is not possible to ramp up nuclear
energy fast enough to make a noticeable
difference to our GHG emissions before 2050.
This is not soon enough – large reductions are
needed during the next 30 years in order to
significantly reduce the risk of or extent of the
foreseeable global ecological catastrophe