Energy Systems & Climate Change

Thus. 5 Nov. 2009

Ch.7: Nuclear

Dr. E.J. Zita (& Cheri Lucas Jennings)zita@evergreen.edu

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