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Energy Systems & Climate Change
Thus. 5 Nov. 2009
Ch.7: Nuclear
Dr. E.J. Zita (& Cheri Lucas Jennings)[email protected]
http://academic.evergreen.edu/curricular/energy/0910/home.htm
What’s happening today: • Questions? Announcements?• Ch.7: Nuclear• Brief Reports at 2:30
• 3:15 Seminar – finishing McKibben
Responses due this week to Brief Reports:
Percent of electricity from nuclear
Nuclear-generating capacity
Fundamental Forces
Gravity Electromagnetism Nuclear
Unification
http://abyss.uoregon.edu/~js/cosmo/lectures/lec20.html
Discovery of the atomic nucleus1909 Rutherford
Nuclear strong force (vs. electric)
Isotopes 238
235
99.3
0.7
U
U
Isotopes
Same number of protons = same chemistry
p nprotons Element
Solve for m2
Nuclear binding energy
Nuclear binding energy
E=mc2
Fission → radioactive wasteFusion is safe, but works only in stars, so far
Magnetic confinement fusion
E=mc2: The nuclear difference
Nuclear energy ~ 10 million x chemical energy
1 truckload Uranium/yr ~ 100 trainloads coal/wk
E=mc2 really only applies to mass-energy transformations (not stretched rubber bands…)
Nuclear Fusion in the Sun: 4H He + m
Fusion: 4H He + m
Nuclear fission
Heavy, unstable nuclei can fall apart naturally.
Throwing neutrons at them can make them split faster:
Neutron-induced fission (Lise Meitner)
Discovery of fission1938 Hahn + Strassmann Meitner + Frisch
Nuclear chain reaction:critical mass ~ 30 lb for U235 ~ 30 tonnes coal
Controlled fission reaction: Moderator keeps neutron multiplication factor = 1
Moderator slows neutrons so they can fission U. Fast neutrons can’t do the job. Removal of graphite rods stops fission.
Atomic mass
Ex.7.5 showed that using a 5 kW electric dryer (powered by a 33% efficient nuclear plant) for an hour produces
N=1.2x1018 nuclei of 239Pu (plutonium).
Mass per nucleon = mn = 1.67 x 10-27 kg
The mass of each 239Pu nucleus = m = 239 mn = _____
Total 239Pu mass produced = M = N m = ______
Nuclear reactors
Light-Water reactors (LWR) need enriched U235
(ordinary water steam turbine electricity)
•Boiling-water reactor (simple, 1/3 of LWRs)
•Pressurized-water reactor (primary doesn’t boil)Pro: Safety: loss of coolant = loss of moderatorCon: difficult to refuel
CANDU (Deuterated, or heavy water + natural U238)•Continuous refueling capability, easy to steal
More Nuclear reactors
Graphite moderatorPro: continuous refueling capabilityCon: loss of coolant ≠ loss of moderatorChernobyl
HTGR (High Temperature Gas-cooled Reactor)Pro: high safetyCon: low performance
Breeder reactors: first discuss beta decay…
Beta decay (weak force)
n p + e- + neutrino
14 146 7C N e neutrino
Breeder reactors
Rare U235 is fissile when hit with neutronsCommon U238 can transmute Pu contributes to fission power generation in old U reactors
Breeder reactors
Pro: * use up common U238* operate at higher temperature (efficiency)
Con: • higher temperature, higher risk of nuclear accident• Liquid sodium coolant – flammable with air contact• Plutonium = potent bomb fuel• Critical mass ~ 5 kg (see Example 7.5)
Even France only uses one breeder.
Plutonium reprocessing(Union of Concerned Scientists: www.ucsusa.org)
• Reprocessing would increase the risk of nuclear terrorism• Reprocessing would increase the ease of nuclear proliferation• Reprocessing would hurt U.S. nuclear waste management efforts• Reprocessing would be very expensive
Advanced reactor designs
Standard LWR: coolant = moderatorAdvanced LWR: passive safety featuresStandardized design – easier to buildMaximum nuclear efficiency: 36%
Advanced HTGR: pebble-bed reactorpebbled fuel
He gas coolant heat exchanger turbineCould burn Pu from old nuclear weaponsDesign efficiency 50% (not yet operational)
Nuclear power plants
Pressure vessel limits Thigh and efficiencyOtherwise, much like other power plants
Radioactivity
Gamma rays: very high energy photons – zero mass (produced by excited nuclei)
Alpha particles: very high mass (Helium nuclei) can have high or low kinetic energyIf they penetrate matter, can do great damage.Most dangerous if ingested.
Beta particles: electrons (or anti-electrons)Can have high or low kinetic energyCan slightly penetrate matter. (weak force)
Alpha decayAlpha particle = helium nucleus
4 4 42 2 2
nn nucleons nucleonspp protons protonsHe Element X He
Radioactivity
Gamma decay
Alpha decay
C14 from cosmic rays
Cosmic rays excite N14 → decays to C14
Solar max: magnetic solar wind sweeps away cosmic rays → less *N14 → less C14
http://www.nuclearonline.org/newsletter/Oct05.htm
Lower recent C14 /C12 from fossil fuel burning
Evidence of anthropogenic source for greenhouse gases
Little Ice Age: low solar magnetic activity more cosmic rays and C14
Nuclear Policy• High subsidies supported growth in industry in
decades past• Safety regulations plus major cost and schedule
overruns made nuclear start-ups increasingly diffiult
• 1979 Three Mile Island accident “seriously damaged public confidence in nuclear power”
• US nuclear in decline – no new plants in 30 years
• 1986 Chernobyl near-meltdown, major irradiation of local area, contamination spreading to lesser extent throughout USSR, Europe, Asia. Undetermined # of lives lost
Radioactive decay: =decay rate
N N t
dN Ndt
dNdt
N
0
0
0
ln
( )
t
t
Nt
N
Ne
N
N t N e
0 0
N t
N t
N N t
dN Ndt
dNdt
N
dNdt
N
Half-life = T1/2
1 2
1 2
0
01 2
00
( )
( )2
21
2
t
T
T
N t N e
NN T
NN e
e
1 2
1 2
1
1 2
1 2
1ln ln 2 ln2
ln 2 ln
ln 2
T
T
e
e T
T
Half-life
Solve for n and then t…
Measuring radiation
Bequerel = 1 decay per second: but what kind of decay? How much energy?Curie = radioactivity of 1 g of 226Ra
Consider effects on biological tissue:Rad = 0.01 J of radiation absorbed by 1 kg
Also consider what kind of particles – alpha, beta, gamma? Most useful measure:Sv = Sievert = dose (in rad) * quality factor (QF)
Radiation quality factor (QF)
Higher QF = more dangerous radiation
Type QF
X and gamma rays ~ 1
Beta ~ 1
Fast protons 1
Slow neutrons ~ 3
Fast neutrons up to 10
Alpha particles and up to 20
heavy ions
Chernobyl: how many deaths?
http://www.nirs.org/reactorwatch/accidents/accidentshome.htm
http://www.nirs.org/ch20/index.htm
How many accidents unreported?
http://www.iht.com/articles/2007/03/15/business/nuke.php
More Nuclear PolicyAdvocates call for nuclear renaissance
because:• Technology is well-established• We know it can produce high-density electric
power• Since we are not willing to give up quality of life
dependent on high-density power, nuclear and hydro are the only current options
• Hydro is essentially fully developed in countries like the US, and has ecological costs of its own
• Vitrification can address waste issues
Waste disposal: Yucca Mountain?
http://library.thinkquest.org/17940/texts/nuclear_waste_storage/nuclear_waste_storage.html
Waste disposal: Vitrification?
http://picturethis.pnl.gov/PictureT.nsf/All/3U2S5D?opendocumenthttp://environment.pnl.gov/brochures/WTP.pdf
UCS on nuclear
1. Need cheap, effective solutions to GW quickly
2. Nuclear power is not the “silver bullet”
3. Rapid major expansion of nuclear is not feasible
4. Nuclear security is a major concern
5. Research should continue, especially on nuclear waste issues
UCS: Nuclear is not the solution to GW
http://www.ucsusa.org/global_warming/solutions/nuclear-power-and-climate.html
Brief Reports
Please get / put homework from/on the front table
Break…
Seminar on last half of McKibben