Download - Session 10 – nuclear power

T. Ferguson, University of Minnesota, Duluth. 2008

Session 10 – Nuclear Power


Session 10 – Nuclear Power

• Recall that nuclear supplies ~ 8 Quads to US annually (8% of total; 20% of electricity)

• Terminology

• Fuels, reserves, wastes

• Energy Release, Efficiencies

• Costs

• Status and Policy


Nuclear PowerBasics

• Nuclear vs. chemical energy• All energy derives from nuclear!• Fission: Splitting heavy atoms• Fusion: Combining lighter atoms• Fissionable isotope captures neutron, yields:

– Unstable isotope– Fragments with high kinetic energy– Neutrons– Beta, gamma, neutrino emissions

• Moderator• Control Rods

Resulting sum of products has slightlyless mass than sumof original reactants


Terminology

• Nucleon• Nuclide• Radionuclide• Isotope• Alpha, Beta, Gamma Rays• Fissionable Material• Fertile Material• Enrichment


Radioactive DecayFission might be best understood by first looking at how the most abundant, naturally occurring isotope of Uranium, U-238, decays:

• First, elements with atomic number above Lead tend to decay• “Decay” implies transitioning to a stable element with

smaller neutron-proton ratio• U-238 has 146 neutrons, for an n/p of 1.587• This neutron ratio is the highest for any natural isotope

U-238 decays by first emitting an alpha particle: 2n + 2p• An alpha particle is identical to the Helium nucleus• So U-238 loses 2n and 2p, reducing it to Thorium-234• But Thorium is also unstable, and emits a

Beta particle: nuclear electron• This, in effect, increases the proton count by 1, forcing

the release of a neutron to keep the nucleon count constant

So, Thorium-234 becomes Protactinium-234 (Z=91),which is also unstable . . . And eventually ends at Pb


Radioactive Decay

Radioactive Half-life: time for half of atoms to decay

If N=number of atoms present, and N0 = number of atoms initially, and

λ = decay rate constant,

Then N = N0 e –λt

Set N=0.5N0 to solve for T1/2

U-238 half-life is 4.5 E 9 years (age of universe)


Radioactive Decay

Radioactive Half-life: time for half of atoms to decay

Radium: Discovered by Curies in 1898, T1/2 of 1600 years, part of U-238 decay chain

Decay rate of 1 gram of Radium is basis for unit of decay, the curie.

So, the curie is a measure of the radioactivity of a material


Radioactive Decay

Derivation of curie:

If N = N0 e –λt, then λ = 0.693/T1/2.

Given T1/2 for Ra-226 = 1600 yrs,λ = 1.375 E -11 sec-1.

To obtain the decay rate, we need the number of atoms in one gram of Ra-226


Radioactive Decay

Ra-226 has atomic weight of about 226, so1 kg-mol = 226 kghas Avogadro’s number of atoms

(6.02 E 26), which becomes N0.1 gram, therefore, contains 2.66 E 21 atoms,

which is NThe decay rate is λN = 3.66 E 10 disintegrations per

second(almost 40 billion events per second)

(The curie is formally 3.7 E 10 disintegrations/s)


Nuclear Fission

Uranium-235 + Neutrons Fission

Energy

Neutrons(about 2.5)

Radioactive fission products

Process repeats

Uranium-235

(scattered)

(absorption & capture)

(absorption &)


Nuclear Fission


Energy

Neutrons(about 2.5)


Process repeats

Uranium-235

3. Critical: Steady rate of chain reaction Subcritical: Decreasing reaction rate Supercritical: Increasing reaction rate

1. Neutrons are the key ingredient

2. If at least oneof these resultsin a second event,a self-sustainingfission chain reactionensues


Quote of the Week

“If we have in the future an accident where the reactors go critical, I would only pray for Miami-Dade County since there is no way to evacuate the population today compared with in 1972, when the reactors were originally permitted," the president Rhonda Roff of an environmental group called "Save It Now, Glades" told AFP.

Comment from article from AFP on Florida’s electrical blackout of 2/26/08

<http://afp.google.com/article/ALeqM5hqzKZYV_FS7JoyYm90kopwwsSKBA>


Nuclear Fission


Energy

Neutrons(about 2.5)


Process repeats

Uranium-235

2. Neutrons:W/O moderator: 2 MeVWith moderator: 1/40 eV

1. Moderator

3. Neutrons start with high energy,but are then thermalized by moderator


Thermal Nuclear Fissionvs. Fast Fission


Energy

Neutrons(about 2.5)


Process repeats

Uranium-235

1. U-235 only natural fuel that workswith thermal neutrons

2. Probability of spontaneous fission of U-235 very, very small (1 per

second, or 200 MeV=3.2E-11 J/s/kg)3. Fission starts with absorption of neutron4. Prob of absorption decreases with neutron

energy (so moderator used in thermal reactors)

5. Fast fission reactors use other fuels able to fission with high energy neutrons


Thermal Fission

From Wikipedia: http://upload.wikimedia.org/wikipedia/commons/7/72/Thermal_reactor_diagram.pngAccessed 2/28/08

http://upload.wikimedia.org/wikipedia/commons/7/72/Thermal_reactor_diagram.png


Energy of Fission

• Fission of U-235 releases about 200 MeV per atom

(recall that 1 electron volt = 1.6 E -19 J,

or 200 MeV = 3.2 E -11 Joules)• Compare to combustion of Carbon with Q=94E6 cal/kg-mol

4.1 eV per atom• 50 million times more energy on atom-atom basis• 2.5 million times more energy on weight basis• Instead of 3 million tons of coal per year for 1000 MW plant,

nuclear fission would require 1.2 tons of U-235


PWR Fuel Assembly

From http://www.mnf.co.jp/pages2/pwr2.htm. Accessed 2/28/08; and instructor notes

Sample PWR Fuel Assembly

•Array of 14X14 rods

•179 fuel rods

•16 control rods - ganged

•1 instrumentation rod

•Assembly is 7” X 7”, 12 ft tall

Fuel: U-235 enriched from natural concentration of 0.71% to a few %

Fission of U-238 possible only with fast neutrons

http://www.mnf.co.jp/pages2/pwr2.htm


The Uranium Fuel Cycle- Sources -

Source: International Atomic Energy Agency


Fuel CycleAnnual mass flows for 1000 MWe LWR

Ore86,000 tons

U3O8 solid162 tons

UF6 gas203 tons

Enriched UF6

53 tons

UO2 Fuel36 tons

ReactorSpent Fuel36 tons

Low Level Waste50 tons

Reprocessing(UK, France)

Storage(US)

Adapted from Tester, et al, Sustainable Energy. Figure 8.6


Reactor Designs

Designs Currently in Operation (Generation II)• PWR – Pressurized Water Reactor

(Westinghouse)• BWR – Boiling Water Reactor (GE)• GCR – Gas Cooled Reactor • LMFBR – Liquid Metal Fast Breeder Reactor• PHWR – Pressurized Heavy Water Reactor• RBMK – Similar to BWR


New Reactor Designs

Designs Submitted in Recent Applications (Generation III and III+):– AP1000 (Westinghouse) (6 COLs)1

– EPR (Areva) (3)– ESBWR (GE) (5)– ABWR (GE) (1)– US-APWR (Mitsubishi) (1)

1Combined Licenses, as of 10/21/08. Covers 25 new units


New Reactor Locations, US

Source: NRC


Boiling Water Reactor

Source: US NRC


Pressurized Water Reactor


Nuclear Power Performance

• Water in liquid state limited to 705 °F• Reactors (PWR, BWR) limited to η<30%• (70% waste heat)/(30% useful) =

2 1/3 units of waste heat per useful unit- must be dissipated in condenser

• Fossil Fuel: η=40%, or 1.5 units waste/useful

• Hence, difference in cooling tower size



US Reactors Operating:

• Licensed 1968-74: 38 reactors, 6 closed



• 104 reactors in operation

• Only 1 reactor licensed since 1976 is permanently closed (TMI-II)

Source: EIA



US Nuclear Plant Capacity Factors• 1980: 56%• 1990: 66%• 2000: 88%• 2002: 90%• 2007: 91.8%

• Capacity constant since 1990, but . . .• Energy produced increased by 33%

Source: EIA


Costs

• Average Operating Expenses, 2001– Nuclear: 1.8 cents/kWh (1/4 is fuel)

– Fossil: 2.3 cents (3/4 is fuel)

– Hydro 1.0 cents (no fuel cost)

– Other Fossil: 5.0 cents (80% is fuel)

• Fuel: $1787/kg UO2 (1/2007)– For 45,000 MWd/t burn-up: 360,000 kWh/kg, or $0.005/kWh

• Capital: $1000/kW in Czech Republic

$2500/kW in Japan

(Compare to $1000-1500 for coal, $500-1000 for gas,

and $1000-1500 for wind; 2005 numbers)

Source: EIA, Electric Power Annual 2000; Australian Uranium Association


Costs

Cost Projections for 2010 with 10% discount rate (capital becomes 70% of energy cost):

Nuclear Gas CoalUSA 4.65 c/kWh 3.65 4.90France 3.93 4.42 4.30Japan 6.86 6.91 6.38Canada 3.71 4.12 4.36Korea 3.38 2.71 4.94Czech Rep. 3.17 3.71 5.46

US 2003 cents/kWh; 40 year lifetime; 85% capacity factor

Source: OECD/IEA NEA 2005/Australian Uranium Association


Major US Nuclear Plant Operators

• Exelon 17,000 MW 17%

• Entergy 9,000 MW 9%

• Duke 7,000 MW 7%

• TVA 6,700 MW 7%

• NMC 1,689 MW 2%

(figures are approximate)

Sources: EIA, Wikipedia.org/wiki/nuclear_management_corporation (accessed 3/10/08)


US Nuclear Power Policy

Energy Policy Act of 2005– Price-Anderson Act extended to 2026 ($10B)– Cost overrun support for up to 6 new plants– First 6000 MW: PTC of 1.8 cents/kWh

Nuclear Power 2010 Program, of 2002– Joint gov’t/industry effort to build adv. Plants– 3 consortia have received grants– Applications have been submitted

Source: DOE


US Nuclear Power PolicyA Renaissance?

After nearly 30 years, the first applications to the NRC for Combined Construction and Operating Licenses:– 9/2007: South Texas Project: GE ABWR’s– 11/2007: TVA in Alabama: Westinghouse

AP1000 PWR’s– 5 18 other sites

Source: NRC


Global Nuclear Power Policy

• Canada: will maintain current fleet• Mexico: Planning another 8 reactors• UK: Undecided• Russia: Planning another 27 reactors• China: Planning another 25• India: Planning another 15• Pakistan: Planning another 2• Japan: Planning another 12• Norway/Sweden/Finland: maybe/no/yes• Germany: Phase out by 2020• Italy: Shuttered; moratorium• Brazil: Planning another 7 reactors

Source: Wikipedia

Download - Session 10 – nuclear power

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