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 Harveyharvey@geog.utoronto.ca

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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

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 10 20 30 40 50 60 70 80 90

Number of protons

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-

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

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

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

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

Ra-226 =1600 yra=36.62x10

Rn-222 =3.825 daysa=5.691x10

Po-218 =3.05 mina=10.46x10

Pb-214 =26.8mina=1.213x10

Bi-214 =19.9 mina=1.634x10

Po-214 =164 seca=30.63x10

Pb-210 =22.3 yra=2.832x10

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

81 82 83 84 85 86 87 88 89 90 91 92 93

Atomic Number

Figure 8.5 U-238 Series Radiation

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

FissionProducts

TotalActinides

1 10 100 1000 10,000 100,000 1 million

Si + Cs90 137

UChain

NpChain

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

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

primary loop

cooling waterin out

secondary loop turbineelectricityout

generator

condenser

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

• 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

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

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

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

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

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

0.0 0.2 0.4 0.6 0.8 1.0

U-235 Fraction

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)

1970 1975 1980 1985 1990 1995 2000 2005 2010

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

0 200 400 600 800 1000 1200

Powerplant Size (MW)

Figure 8.18 Cost of nuclear energy

1970 1975 1980 1985 1990 1995 2000 2005 2010

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

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

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

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

1 0.5 0.15 0.1 0.06 0.05 0.04 0.03 0.02 0.01

Ore Grade (%U3O8)

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%

0.010.11

Ore Grade (%)

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

Finland

Russia

Canada

Percent

Source: www.iaea.org/programmes/a2/index.html

Figure 8.25 Growth in nuclear energy

1965 1970 1975 1980 1985 1990 1995 2000 2005

nAsia PacificAfricaFSUEuropeS & C AmericaNorth America

Figure 8.26 Nuclear powerplant capacity factors

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 40 45

Age (Years)

Source: Data from www.iaea.org/programmes/a2/index.html

Figure 8.28 World Uranium Resources

Australia22.7%

Kazakhstan14.9%

Russia10.0%South Africa

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

0.010.1110100

Ore grade (% U3O8)

Soft or mixed

Figure 8.30 Cost of uranium vs the grade of ore supplying the uranium

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

Energy and the New Reality, Volume 2: C-Free Energy Supply Chapter 8: Nuclear Energy L. D. Danny...

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