Upload
albania-energy-association
View
354
Download
3
Embed Size (px)
DESCRIPTION
nuclear power
Citation preview
T. Ferguson, University of Minnesota, Duluth. 2008
Session 10 – Nuclear Power
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
Terminology
• Nucleon• Nuclide• Radionuclide• Isotope• Alpha, Beta, Gamma Rays• Fissionable Material• Fertile Material• Enrichment
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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)
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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)
T. Ferguson, University of Minnesota, Duluth. 2008
Nuclear Fission
Uranium-235 + Neutrons Fission
Energy
Neutrons(about 2.5)
Radioactive fission products
Process repeats
Uranium-235
(scattered)
(absorption & capture)
(absorption &)
T. Ferguson, University of Minnesota, Duluth. 2008
Nuclear Fission
Uranium-235 + Neutrons Fission
Energy
Neutrons(about 2.5)
Radioactive fission products
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
T. Ferguson, University of Minnesota, Duluth. 2008
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>
T. Ferguson, University of Minnesota, Duluth. 2008
Nuclear Fission
Uranium-235 + Neutrons Fission
Energy
Neutrons(about 2.5)
Radioactive fission products
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
T. Ferguson, University of Minnesota, Duluth. 2008
Thermal Nuclear Fissionvs. Fast Fission
Uranium-235 + Neutrons Fission
Energy
Neutrons(about 2.5)
Radioactive fission products
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
T. Ferguson, University of Minnesota, Duluth. 2008
Thermal Fission
From Wikipedia: http://upload.wikimedia.org/wikipedia/commons/7/72/Thermal_reactor_diagram.pngAccessed 2/28/08
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
The Uranium Fuel Cycle- Sources -
Source: International Atomic Energy Agency
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
New Reactor Locations, US
Source: NRC
T. Ferguson, University of Minnesota, Duluth. 2008
T. Ferguson, University of Minnesota, Duluth. 2008
Boiling Water Reactor
Source: US NRC
T. Ferguson, University of Minnesota, Duluth. 2008
Pressurized Water Reactor
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
Nuclear Power Performance
US Reactors Operating:
• Licensed 1968-74: 38 reactors, 6 closed
• Licensed 1975-78: 23 reactors, 3 closed
• Licensed 1979-96: 52 reactors, 0 closed
• 104 reactors in operation
• Only 1 reactor licensed since 1976 is permanently closed (TMI-II)
Source: EIA
T. Ferguson, University of Minnesota, Duluth. 2008
Nuclear Power Performance
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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)
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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
T. Ferguson, University of Minnesota, Duluth. 2008
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