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Nuclear EnergyNuclear Energy
Mechanical Engineering 496ALT
Alternative Energy
Larry Caretto
February 19 and 23, 2009
Read chapter 8 in text for tonight and next Tuesday.
Midterm exam, Thursday, February 26, will be like homework; it will include a mix of problems and essay questions. The exam will be open book and notes. It will cover up to and including material on electricity generation in the March 17 lecture and the March 24 homework.
Read chapter 8 for the March 3 lecture which is an overview of renewable energy technologies.
2
Main Ideas
- Current and projected use
- Basic physics
- Nuclear electricity generation methods
- Regulation of nuclear energy
- Nuclear safety
- Nuclear waste disposal
- Fusion Energy and Prospects for the
future
Nuclear energy now accounts for a significant fraction of electrical energy produced in the world. In France, the vast majority of electrical energy is produced by nuclear power. Since the accidents at Three Mile Island and Chernobyl there has been an increased public concern about the risks of nuclear energy. In addition, the costs of nuclear power are now higher than other power generation methods.
Recently there has been an increased interest in nuclear generation. In the deregulated power market several older nuclear power plants have been recently sold at a significantly higher price than their previous sale. Increasing concerns about global warming caused by emissions of CO 2 from combustion of fossil fuels have increased the attractiveness of nuclear power.
These notes present an overview of nuclear power generation starting from the basic physics, leading through nuclear plant designs and regulations of nuclear power.
Finally we will discuss the prospects for fusion power and some of the current thinking about the future of nuclear power generation in the US and in the world.
4
Organizations
- Nuclear Regulatory Commission (NRC)
- US agency responsible for nuclear power
plant operations and regulations
- International Atomic Energy Authority
- The IAEA describes itself as the “world's
nuclear inspectorate” to prevent nuclear
proliferation and illegal nuclear use
- US Department of Energy Nuclear
Energy Program for nuclear R & D
Web sites for organizations on chart:
NRC: http://www.nrc.gov/
IAEA: http://www.iaea.org/
DOE/nuclear: http://www.doe.gov/energysources/nuclear.htm
Other organizations and web sites:
The NEI (Nuclear Energy Institute) is an organization of companies involved in the production of nuclear energy including plant operators, construction companies, uranium miners, etc. (http://www.nei.org/)
The WNA (World Nuclear Association) is another organization of companies engaged in all aspects of nuclear energy. (http://www.world-nuclear.org/)
The uranium information center of the Australian Uranium Association (http://www.uic.com.au/) is a useful site for information on uranium production and mining.
The American Nuclear Society (ANS) is the society for working professionals in the field of atomic energy. They have a web site for public information on nuclear issues: http://www.ans.org/pi/
The Federation of Atomic Scientists (http://www.fas.org/nuke/) is an international association of scientists concerned about weapons of mass destruction. Their site has good information on the interactions between nuclear power and potential nuclear proliferation.
5
IAEA Nuclear Forecast
Reference: http://www.iaea.org/OurWork/ST/NE/Pess/RDS1.shtml
Chart taken from power point presentation downloaded from web site.
The forecast is for a general downturn (or nearly constant level) in the percentage of electricity coming from nuclear energy in regions that already have large amounts. Regions with small amounts re forecast to increase.
These forecasts are consistent with the data on nuclear power plants under construction, ordered or planned, and proposed shown on the next chart.
Niger 225,000 5%
Russian Fed. 172,000 4%
World total 4,743,
USA 342,000 7%
World %
Resources
(Tonnes U)
Country
Other 699,000 14%
Brazil 279,000 6%
Namibia 282,000 6%
South Africa 341,000 7%
Canada 444,000 9%
Kazakhstan 816,000 17%
Australia 1,143,000 24%
Reference: http://www.uic.com.au/nip75.htm accessed February 24, 2008
As noted on the previous page for the web site has now been discontinued.
The web sites notes that the data were based on sources (OECD, NEA, and IAEA, Uranium 2005: Resources, Production and Demand ) available on January 1, 2005. The cost of the uranium up to US$130/kg. However, recent US prices have been about $22 to $33 per kg over the last ten years. (EIA web site on uranium cost data, http://www.eia.doe.gov/cneaf/nuclear/umar/summarytable1.html, accessed February 24, 2008.
Current usage is about 68,000 tonnes per year. The current resources are enough to last for about 70 years.
Other countries listed on the web site, but excluded from the table on the chart and their data are:
Uzbekistan 116,000 2%
Ukraine 90,000 2%
Jordan 79,000 2%
India 67,000 1%
China 60,000 1%
All others 287,000 6%
8
Reasonably
Assured Resources
(RAR) of Uranium
Reference: http://www.uic.com.au/nip75.htm accessed February 24, 2008
As noted previously, this web site is no longer operative.
The term reasonably assures resources sounds close to what would be called reserves. They are known and economical to recover at a certain price. (In this case the price may be slightly higher than the current market price, so they are not truly reserves.)
This chart shows that increasing the market price from $40/kg to $80/kg does not make a large increase in the available resources.
Here are some conversion factors: 1 mass unit of U 3 O 8 contains 0. mass units of uranium (with normal isotopic composition).
A cost of $100 per kg U is the same as $84.80 per kg U 3 O 8 , $45.36 per lb U, or $38.46 per lb U 3 O 8.
10
World Nuclear Power Plants
Reference: http://www.insc.anl.gov/pwrmaps/map/world_map.php accessed February 24, 2008 This is from the web site of the International nuclear Safety Center, which is operated by Argonne National Laboratory for the US Department of Energy. The following information about California nuclear power plants would normally begin on the next notes page. Diablo Canyon San Luis Obispo County, California. Construction of the units may have been the longest in U.S. history at 15 and 16 years due to regulatory concern for its ability to withstand seismic activity. Cooling water for the units is obtained from the Pacific Ocean. Operator: Pacific Gas & Electric Company Owner: PG&E Corp. (100.0%) Reactor Supplier: Westinghouse Corporation Unit 1: 1,073 net MWe PWR Date of Operation: November 1984 License Expiration Date: 09/22/2021 2001: 9.47 billion kWh Average Capacity Factor: 100.8% Unit 2 Capacity: 1,087 net MWe PWR Date of Operation: August 1985 License Expiration Date: 04/26/2025 2001: 8.61 billion kWh 2001 Average Capacity Factor: 90.4%
San Onofre 3-unit site near San Clemente. Unit 1, shutdown in 1992, was a first generation Westinghouse commercial unit that operated for 25 years.
Units 2 & 3 Operator: Southern California Edison Co. Owners: Edison International (75.1%); San Diego Gas & Electric Co. (20%); Anaheim Public Utilities Dept. (3.2%); Riverside Utiltities Dept. (1.8%) Reactor Supplier: Combustion Engineering, Inc. Unit 2 capacity: 1,070 net MWe PWR Date of Operation: September 1982 License Expiration Date: 10/18/2022 2001: 9.49 billion kWh Average Capacity Factor: 101.3% Unit 3 Capacity: 1,080 net MWe PWR Date of Operation: September 1983 License Expiration Date: 10/18/2022 2001: 5.65 billion kWh a verage Capacity Factor: 59.7%
11
US and Canada Plant Sites
http://www.insc.anl.gov/pwrmaps/map/united_states.html (accessed on February 24, 2008) is the source for this map and information below and on the previous notes page for California reactors. Humboldt Bay 3 in Eureka is 63 MW(e) BWR that operated from 1963 to 1976 is permanently shut down. Rancho Seco in Clay Station (near Sacramento), PWR 913 MW(e). operated from April 1975 to June 1989. The location near San Francisco is called Vallecitos; this was a 5 MW experimental boiling water reactor that General Electric operated from 1957 to 1963. (Information downloaded from files.asme.org/ASMEORG/Communities/History/Landmarks/5654.pdf on February 16, 2009.)
The Palo Verde plant in Arizona has three PWRs each rated at 1,243 MW(e). This is the largest nuclear facility in the US. Operator: Arizona Nuclear Power Project Owners: Arizona Public Service Co. (29.1%); Salt River Project Agricultural Improvement & Power District (17.5%); Southern California Edison Co. (15.8%); El Paso Electric Co. (15.8%); Public Service Co. of New Mexico (10.2%); Southern California Public Power Authority (5.9%); Los Angeles Department of Water & Power (5.7%) Reactor Supplier: Combustion Engineering, Inc.
Unit 1 in 2001: 9.46 billion kWh 2001 Average Capacity Factor: 86.9%
Unit 2 in 2001: 9.98 billion kWh 2001 Average Capacity Factor: 91.6%
Unit 2 in 2001: 9.29 billion kWh 2001 Average Capacity Factor: 85.0%
Data on San Onofre and Diablo Canyon are on the notes page for the previous chart.
13
Basic Physics
- Einstein: Δe = Δmc 2
- 235 U + n → 144 Ba + 89 Kr + 3n + 177MeV
- Nuclear energy units
- 1 atomic mass unit =1.660 538 73x10 -27^ kg
- 1 eV = 1.602 176 462x10 -19^ J
- Energy comparison
- 235 U fission = 7.3x10^13 J/kg
- Carbon combustion = 3.3x10 7 J/kg
Einstein’s formula e = mc^2 can better be written in terms of Δe and Δm. It is the change in mass in a nuclear reaction that produces a certain amount of energy. Atomic masses are measured in terms of the atomic mass unit or amu. One amu is exactly 1/12 the mass of a C^12 atom. (Recall that the atomic mass system is defined such that the atomic weight of of C 12 is exactly 12; one amu is approximately the mass of a proton or the mass of a neutron.) Since 12 grams of C 12 is exactly one mol with Avogadro's number (6.02214199x10^23 ) of atoms, one atom of C 12 has a mass of 12g/(6.02214199x10^23 ). So the amu is1/12th^ of this mass or 1.66053873x10- (^27) kg.
The energy unit of electron-volts is the energy generated when one electron moves through an electric field of one volt. The change on an electron is 1.602176462x10-19^ coulombs, and one coulomb-volt = 1 joule. (Recall that 1 ampere = 1 coulomb/s and the product of amps and volts is watts or joule- seconds.) Thus the energy in one eV is 1.602176462x10-19^ J. The speed of light is 299,792,458 m/s, so the annihilation of 1 emu of mass produces (1.66053873x10-27^ kg) * (299,792,458 m/s)^2 =1.49241778308056x10-10^ J = 931495084.5 eV = 931.4950845 MeV. In the fission of 235 U into 144 Ba and (^89) Kr, the mass difference is 0.19 amu producing the energy shown.
In this reaction the energy release per unit mass of 235 U is 177 MeV / 235.04394 amu; this is equivalent to 7.3x10^13 J/kg compared to 3.3x10 7 J/kg for carbon combustion.
14
Mass Defect
• Isotopic mass, M, less than mass of
constituents
• Difference is binding energy
• D = Z(mp + m e ) + (A – Z)mn – M
• Where D = mass defect, mp , me , and m n
are masses of proton, electron and
neutron, Z = protons, A – Z = neutrons
• Binding energy, BE = Dc 2
M in this chart is the mass of the nucleus with Z protons and A – Z neutrons. M may be measured in any consistent mass units, amu, kg, etc.
The concept of a mass defect recognizes that the binding energy of the nucleus, BE, can be written in terms of this mass defect using Einsein’s formula that Δe = Δmc 2. In this case the energy change is the binding energy, BE, and the mass change is Δm; this gives the equation that BE = Dc 2. From the conversion factors on the previous chart, a mass defect of 1 amu is equivalent to a binding energy of 931.4950845 MeV.
With the units of amu, the mass of one atom or molecule is just the atomic or molecular weight expressed in amu. For example the mass of 235 U is 235.04394 amu. The mass of a neutron is 1.008665 amu; the masses of a proton and an electron are 1.007276 amu and 0.000549 amu, respectively.
The binding energy is commonly expressed as the average binding energy, ABE, is the binding energy, BI, divided by the total “nucleons”, A, which is the sum of protons and neutrons. The equation for the average binding energy is simply the equation on the chart divided by A.
The binding energy is the energy produced in a hypothetical reaction where the all the protons and all the neutrons which are initially assumed to exist as free particles combine to form the particular isotope.
A
M
m
A
Z
m m
A
Z
ABE p n ⎟ n −
16
Nuclear Radiation
- Spontaneous decay of nuclei can yield
other nuclei and radiation
- Alpha particles 239 Pu → 235 U + α(^4 He)
- Beta particles 90 Sr → 90 Y + β(^0 e)
- Gamma radiation 60 Co → 60 Co+ γ
- The α, β, and γ radiation have different
energy levels that affects their impact
- Major concern: health effects of radiation
In addition to nuclear fusion and fission, we can have a series of other nuclear reactions. In these reactions different kinds of radiation are released. Note that beta radiation, although it is equivalent to an electron, comes from the nucleus, not from the outer shell of the atom. Release of an electron from a nucleus with Z protons and A – Z neutrons increases the number of protons by one and decreases the number of neutrons by one. Decreasing the number of protons changes the chemical identity of the nucleus. Thus the beta decay of strontiun-90 into yttirium comes because the number of protons in the nucleus has increased from 38 to 39.
Gamma radiation is high energy electromagnetic radiation. The wavelength region for gamma rays is between 10 -10^ and 10 -12^ meters. Gamma radiation does not change the chemical identity of the atom.
An alpha particle is a helium nucleus; release of an alpha particle does change the chemical identity of the atom.
In a nuclear reaction a complex series of changes can occur. Not only does the basic fission reaction take place, but products from the original fission, called daughter products can under go other reactions. The complexity of the reaction schemes produces a large amount of different isotopes, with varying degrees of radioactivity in the spent fuel from the nuclear reactor.
17
Chain Reactions
- 235 U + n → 144 Ba + 89 Kr + 3n + 177MeV
- Product neutrons, called fast neutrons,
have MeV range energies
- Slow or thermal neutrons energies are
in the eV range
- In a nuclear reactor the fast neutrons
may be moderated into slow neutrons
The equation at the top of the page is taken from a previous slide. It shows the basic notion of a chain reaction. The reaction not only produces energy, but it also produces additional neutrons to carry on the reaction.
Some of the neutrons may be absorbed and some may leave the reactor. A critical mass is one in which the chair reaction can be sustained.
Additional reactions can take place in a nuclear reactor from the product neutrons. One of these is the production of plutonium-239 by the reaction of a neutron with U- 238 that is usually present. Here is the sequence that produces plutonium (^238) U + n → 239 U + γ
(^239) U → β + 239 Np
(^239) Np → β + 239 Pu
The first reaction in this sequence changes the number of neutrons in the nucleus, but it does not change the number of protons; thus we still have element the element with 92 protons in the nucleus, uranium. In the second reaction, the 239 U releases an electron from the nucleus. This does not affect the total number of nucleons in the nucleus; instead it converts a neutron to a proton. We thus have 93 protons in the nucleus so we have formed element 93 which is called neptunium. The neptunium then undergoes a subsequent beta decay with the same effect. The number of protons in the nucleus is increases giving element 94 which is Plutonium.
Plutonium is the main element used in nuclear weapons. The design of nuclear reactors depends on their purpose. Reactors to produce nuclear weapons are designed to produce significant amounts of plutonium. Civilian reactors are designed to avoid the production of plutonium.
19
Radiation Measurements
- Units for rate of decay
- becquerel (Bq) = 1 disintegration per sec
- curie (Cu) – older unit; 1 Cu = 3.72x10 10 Bq
- Units for energy deposited in matter
- 1 gray (Gy) = 1 J/kg in water
- 1 roentgen (R) = .008 J/kg in air (approx)
- 1 rad =.01 Gy (radiation absorbed dose)
The curie is defined as the amount of radiation from one gram of radium. Thus one gram of radium has 3.72x10 10 disintegrations per second.
The gray is defined as the amount of energy absorbed in water, where water is used as a surrogate for human tissue. The gray is really trying to measure the amount of energy absorbed in human tissue.
The roentgen (R) is a measure of radiation intensity of X-rays or gamma rays. It is formally defined as the radiation intensity required to produce and ionization charge of 0.000258 coulombs per kilogram of air. It is one of the standard units for radiation dosimitry, but is not applicable to alpha, beta, or other particle emission and does not accurately predict the tissue effects of gamma rays of extremely high energies. The roentgen has mainly been used for calibration of X-ray machines. (Quoted from http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html.)
20
Biological Effectiveness
- The sievert (Sv) is the new measure of
effective radiation dose
- Replaces the former unit of rem (roentgen
equivalent man)
- Biological equivalence coefficient, Q,
accounts for different radiation effects
- 1 rad delivers Q rem
- 1 Gy delivers Q Sv
There are two approaches to defining standards. The first uses direct measures of the radiation in terms of grays (or the older units of rads). The other uses the notion of biological effective dose described here. Again, there is a new unit, the sievert, and an old unit, the rem. The conversion between these two is the same as the conversion between grays and rads:
1 gray = 100 rads or 1 rad = 0.01 gray
1 sieverts = 100 rem or 1 rem = 0.01 sievert
The Q factor is not constant. For alpha particles it is about 20. For X-rays it is defined to be one.
Although the sievert is now the preferred unit for radiation exposures, there is still a large amount of data in rems and, more commonly, millirems.
