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Transcript of Energy and the New Reality, Volume 2: C-Free Energy Supply Chapter 8: Nuclear Energy L. D. Danny...
Energy and the New Reality, Volume 2:
C-Free Energy Supply
Chapter 8: Nuclear Energy
L. D. Danny [email protected]
This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see www.earthscan.co.uk for contact details.
Publisher: Earthscan, UKHomepage: www.earthscan.co.uk/?tabid=101808
Outline
• 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 12
6C.
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
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80 90
Number of protons
Nu
mb
er o
f n
eutr
on
s
Stable nucleiUnstable nuclei
neutron:proton = 1:1
neutron:proton = 1.5:1
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 high-
energy 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-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
70 80 90 100 110 120 130 140 150 160 170
Mass number
Yiel
d (%
)
Stable ElementsHalf life > 100 yrsHalf life 1 - 100 yrsHalf life < 1 yr
U-238 is fertile, and the reactions that occur are
238U + n → 239U → 239Np + ß239Np → 239Pu + ß
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.
Pu-240 Pu-241 Pu-242
n
16.02 hr 10.1 hr
23.5 m in
Cm -243
Am -242 Am -243 Am -244
Cm -244
2.355 day
Np-239
Cm -242
U-239 U-238
Am -241
n
n
n
n
n
n
n n
14.4 yr
Pu-239
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 U-233, 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 Gya=12.45x103
Th-234 =24.1 daysa=857.0x101 2
Pa-234m =1.17 mina=73.99x101 5
U-234 =244.5 kya=231.4x106
Th-230 =77 kya=747.7x10
6
Ra-226 =1600 yra=36.62x10
9
Rn-222 =3.825 daysa=5.691x10
1 5
Po-218 =3.05 mina=10.46x10
1 8
Pb-214 =26.8mina=1.213x10
1 8
Bi-214 =19.9 mina=1.634x10
1 8
Po-214 =164 seca=30.63x10
2 4
Pb-210 =22.3 yra=2.832x10
1 2
Bi-210 =5.01 daysa=4.592x101 5
Po-210 =138 daysa=166.3x101 2
Pb-206Stable
Figure 8.4b Uranium series radioactive decay chain
202
206
210
214
218
222
226
230
234
238
242
81 82 83 84 85 86 87 88 89 90 91 92 93
Atomic Number
Mas
s N
um
ber
206Pb
238U
Figure 8.5 U-238 Series Radiation
0
50
100
150
200
250
300
350
Year
Ra
dio
acti
vity
(10
9 Bq
)
103 104 105 106 107 108 109 1010
U-238 Th-234 + Pa-234
U-234Th-230
Ra-226
Rn-222 to Po-210
Figure 8.6 Sources of radio-activity from spent LWR fuel
Basis: PWR Spent Fuel 50 MWd/kg HM 4.5% initial enrichment
Years after Discharge
Ci/t
HM
107
FissionProducts
TotalActinides
106
105
104
103
102
101
Total
1 10 100 1000 10,000 100,000 1 million
Si + Cs90 137
Pu243
Pu238
Am241
Pu240
Pu239
Am243
Tc99
UChain
238
NpChain
237
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 U-235, 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
therm al neutrons fast neutrons
burners 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
control rods
electricityouturanium fuel
generatorturbine
condenser
steam
cooling water
watercoolant/moderator in out
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
uraniumfuel
reactorvessel
pump
primary loop
cooling waterin out
secondary loop turbineelectricityout
generator
condenser
Source: Wolfson (2003, Nuclear Choices: A Citizen’s Guide to Nuclear Technology, MIT Press, Cambridge)
Figure 8.8c Liquid-metal fast breeder reactor
heatexchanger
liquid sodium
pumppump
core:U-235,Pu-239
U-238blanket
steam to turbine
steamgenerator
waterin
liquid sodium
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% U-235, 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
Open pit mining24%
Underground mining
38%
In situ leaching28%
Co-product mining8%
Heap leaching2%
Other0%
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 Cf-249 to Cf-252)
Figure 8.12 Composition of fresh and
spent nuclear
fuel
U-235 31kg3 0 kg , F P1 kg , Tu9 kg , P u t
8kg, U-235
U-238952kg
U-238969kg
1 TO N N EO F F U E L
F R E S H F U E L(3 .1 % E N R IC H M E N T )
S P E N T F U E L(3 3 ,0 0 0 M W d /t)
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
• 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
This involves:
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 – non-radioactive 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) beforedecommissioning 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)
Figure 8.13. Waste flowassociated with 1 GWyr of electricityproduction,assuming:
5:1 waste rock/ore ratio,0.2% grade, enrichment to 3.6%,42 GWd/tU burnup
Uranium M ine 542,000 t waste rock
108,000 t m ill tailings
145 t solid waste1343 m liquid w aste 3
Uranium M ill
Conversion Plant
108411.3 tU ore (216.8 tU )
244.9 tU O 3 8 (207.6 tU)
305.5 tUF 6 (206.6 tU)
Enrichm ent Plant 267.6 t depleted UF 6
(180.9 tU)
38.0 t enriched UF 6 (25.7 tU)
Fuel Fabrication Plant
12.7 m solid waste 3
288.7 m liquid w aste 3
28.8 tUO 2 (25.4 tU)
Nuclear PowerPlan t
1 GW-yr ofelectricity
28.8 t spent fue l
Nuclear fuel chain: alternative chains with some recycling
Figure 8.14a Nuclear fuel once-through LWR chains
Option 1a, Low Burnup: 50 GW d/t, =0.33n
Option 1b, High Burnup: 100 GW d/t, =0.33n
Source: MIT (2003, The Future of Nuclear Power: An Interdisciplinary MIT Study)
27893 t/yr U (93.4% )
1538 t/yr FP (5.15% )
397 t/yr Pu (1.33% )
36 t/yr MA (0.12% )
13055 t/yr U (87 .43% )
1538 t/yr FP (10.30%)
294 t/y r Pu (1.97% )
45 t/yr MA (0.30%)
29864 t spent fuel, 50 GWd/tHM burnup
14932 t spent fuel,100 GWd/tHM
386,000 t natural U
286,000 t natural U
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
0
50
100
150
200
250
300
0.0 0.2 0.4 0.6 0.8 1.0
U-235 Fraction
Sep
arat
ive
Wo
rk U
nit
s p
er k
g o
f U
-235
Cd=0.003
Cd=0.002
Bomb grade
Reactorgrade
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 $6000-
10000/kW
Figure 8.16 Capital cost of nuclear power plants
Source: Cooper (2009, Institute for Energy and the Environment, Vermont Law School)
0
2000
4000
6000
8000
10000
12000
1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
Ove
rnig
ht
Cap
ital
Co
st (
$/kW
)
Early Vendors,Government &Academics
Utilities
Wall Street &IndependentAnalysts
Completed NuclearReactors
Note: The preceding slide gives “overnight” capital costs. These costs
• Do not include interest that accrues during the construction period (which can be up to 10 years)
• Do not include inflation of component costs during the construction period (which have tended to exceed the general rate of inflation)
• Do not include additional utility costs, such as the cost of upgrading the grid to accept a large new source of power
Rather, overnight costs are the costs for the powerplant alone if everything could be bought at once and the plant could be constructed overnight. Final costs are typically 50-75% greater than the overnight cost, but have been as high as double the overnight cost.
Fuel costs
• Fuel is a very small contributor to the overall cost of nuclear electricity, and the cost of uranium itself is a small factor in the overall fuel cost
• Thus, the price of uranium can increase greatly (due to future scarcity) with little impact on the overall cost of nuclear energy (but increased uranium cost would make more uranium economically available)
Decommissioning and long-term isolation costs
• These are likely to significantly increase the overall cost of nuclear electricity
• Most current assessments seem to vastly underestimate these costs
• In any case, there are very few firm data available
Figure 8.17: Estimated cost of decommissioning graphite-moderated nuclear power plants in the UK
0
2000
4000
6000
8000
10000
12000
0 200 400 600 800 1000 1200
Powerplant Size (MW)
Est
imat
ed
Dec
om
mis
sio
nin
g C
ost
($/
kW)
Figure 8.18 Cost of nuclear energy
0.00
0.05
0.10
0.15
0.20
0.25
0.30
1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
Co
st o
f el
ectr
icit
y (2
008$
/kW
h)
Completed Nuclear Reactors
Early Venders,Government &Academics
Utilities
Wall Street &IndependentAnalysts
Source: Cooper (2009, Institute for Energy and the Environment, Vermont Law School)
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
h 2
h 3
h 1
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
0
10
20
30
40
Co
nst
ruct
ion
En
erg
y (P
J)
Based on input-output analysis
Based on economy-wide AEI
Based on process analysis
LWR BWR PWR HTGR HTR FBR HWR AGR
44, 81, 107, 269
Type of Reactor
AEI=average energy intensity (KJ/$)
Figure 8.22 Energy use over the 40-year life of a 1-GW LWR nuclear powerplant with a capacity factor of 0.87
0
200
400
600
800
1000
1 0.5 0.15 0.1 0.06 0.05 0.04 0.03 0.02 0.01
Ore Grade (%U3O8)
Lif
etim
e E
ner
gy
Use
(P
J)
Handling overburden, 1.35 x ore mass
MMR, underground mine
Spent fuel
Decommissioning
Waste operations
Fuel production & reactor operations
Construction of reactor
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%
0
200
400
600
800
1000
1200
0.010.11
Ore Grade (%)
Lif
etim
e E
RO
EI
0
4
8
12
16
20
24
Fu
el E
ffic
ien
cy (
%)
Fuel efficiency, Underground mineFuel efficiency, Open-pit mineEROEI, Underground mineEROEI, Open-pit mineEROEI, ISL - Low energy estimateEROEI, ISL - High energy estimate
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
0 10 20 30 40 50 60 70 80 90
France
Lithuania
Slovak Republic
Belgium
Switzerland
Ukraine
Bulgaria
Armenia
Slovenia
South Korea
Hungary
Switzerland
Germany
Czech Republic
Japan
Finland
Spain
USA
UK
Russia
Canada
Percent
Source: www.iaea.org/programmes/a2/index.html
Figure 8.25 Growth in nuclear energy
0
500
1000
1500
2000
2500
1965 1970 1975 1980 1985 1990 1995 2000 2005
Year
TW
h/y
r E
lect
rici
ty G
ener
atio
nAsia PacificAfricaFSUEuropeS & C AmericaNorth America
Figure 8.26 Nuclear powerplant capacity factors
0
10
20
30
40
50
60
70
80
90
100
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
Cap
acit
y F
acto
r
Source: WEC (2007, 2007 Survey of Energy Resources, World Energy Council, London)
Figure 8.27 Nuclear reactor ages
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40 45
Age (Years)
Nu
mb
er o
f R
eact
ors
Source: Data from www.iaea.org/programmes/a2/index.html
Figure 8.28 World Uranium Resources
Australia22.7%
Kazakhstan14.9%
Russia10.0%South Africa
8.0%
Canada7.9%
USA6.2%
Brazil5.1%
Namibia5.0%
Niger 5.0%
Ukraine3.6%
Other11.5%
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
0
400
800
1200
1600
2000
0.010.1110100
Ore grade (% U3O8)
Mas
s o
f U
ran
ium
(kt
)
Total
Soft or mixed
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