chemical, biological and environmental engineering other conventional power: nuclear power

Chemical, Biological and Environmental Engineering

Other Conventional Power:Nuclear Power

Advanced Materials and Sustainable Energy LabCBEE

HousekeepingMid-term

– Tuesday 2/8 – Can have one page worth of notes– Cover sheet with useful data/formulae included– AY wrote a summary of the first half / assignment keys 2&3 posted

Assignment 4– Would be good to have worked through prior to mid term– As discussed, HW4 due MONDAY 2/7 @ 5:00 (1700) – Key will be posted at that time (therefore will take no late work)– AY will be available Monday afternoon 1200 – 1700, Tuesday

morning 1000-1200


US Net Generation (GWHr)Conventional

Coal 2,016,456Natural Gas 896,590Other Gases 13,453Petroleum 65,739

Nuclear 806,425

Renewables

Hydroelectric 247,510Pumped Storage -6,896

Wind 34,450

Solar (Th and PV) 612

Wood 39,014Other Biomass 16,525

Geothermal 14,637Total Renewables 105,238

All Sources 4,156,745


Nuclear IntroFundamental concept highlighted by Einstein in 1905

E = mc2

Energy in matter as “binding energy”• Makes mass of heavy isotopes smaller than sum of nucleons• Find released energy by calculating “mass anomaly”

The possibility of harvesting nuclear energy recognized in the 1930s

Drivers: • Obtaining large amounts of energy from small amounts of

matter• No CO2 emissions (but yes, radiological waste produced)


Early discoveriesBequerel 1896: photographic plates “exposed” by

Uranium salts– Identifies radioactivity (similar to “cathode rays”)

Marie and Pierre Curie: Active principle stronger than Uranium– 1898 – Polonium– 1902 – Radium (100 mg from 1000 kg ore…)

Ernst Rutherford: Radioactivity follows zero order kinetics (half life of radioactive materials…)


Early DiscoveriesIrene and Frederic Joliot-Curie, 1932:

Discovery of neutron

Also identified ca. 3 neutrons per 235U fission later

Hahn, Strassman and Meitner, 1938: Artificial fission demonstrated (bombarding U with neutrons led to formation of Ba)

Fermi and Szilard 1942: Self sustaining nuclear chain reaction (part of Manhattan Project)

Nuclear power plants developed for naval propulsion and energy production in 1950s


Nuclear Power PioneersWorld’s first nuclear-powered electric generating plant

was constructed by Soviet Union in 1954 – 5 MW

First US PWR was constructed and placed in service by Westinghouse at Pennsylvania in 1957 – 4 MW

First US BWR was constructed and placed in service by GE at California in 1957 – 5 MW

Most nuclear plants are light water reactors– Pressurized Water Reactor (PWR) – Most Common– Boiling Water Reactor (BWR)


HISTORICAL PERSPECTIVEUS Nuclear plant orders placed annually

1979: Three Mile Island #2


Historical Perspective: Decline Factors

Expansion in US halted in 1970s

Drivers– Overbuilt generation and cheap coal/natural gas– Reduction in load growth rate– Popular objection to nuclear power

• Media: “The China Syndrome” • Reinforced by: Three Mile Island / Chernobyl

(different perceptions for high-consequence, low risk events vs. chronic risk)

• Inherited secretive culture of nuclear energy industry due to association with nuclear weapons programs

• Industry downplayed issues with disposal of high level waste


HISTORICAL PERSPECTIVEThere are 439 nuclear plants in the world

103 of them in 31 US states


HISTORICAL PERSPECTIVE


U.S. Nuclear Plant Capacity Factors

90.5

50

55

60

65

70

75

80

85

90

95

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Capaci

ty F

act

or

(%)

http://www.nei.org/


How it worksElement’s chemical nature determined by the number

of electrons

In a neutral atom, the number of electrons is equal to the number of protons in the nucleus

The repelling positive charge of protons is overcome by “residual nuclear force” from neutrons-Like electrostatic force, but much stronger and shorter range of action

Energy gain due to residual nuclear force interaction leads to mass anomaly


BACKGROUNDThe number of protons in a nucleus determines the

elements (atomic number, Z)

The number of neutrons determines the isotope

Sum of number of protons and neutrons is the “mass number” (A)

• Example– Uranium nucleus has 92 protons

• If it has 143 neutrons, it is Uranium-235 ( )• If it has 146 neutrons, it is Uranium-238 ( )

23592U23892U


BACKGROUND103 named elements in about 1000 isotopes

There are 4 more un-named known elements

Of all identified isotopes, 279 are stable

There are 14 known isotopes of uranium

More than one combination of p and n can be stableSn has 10 stable isotopes (!)

Not all Z can make a stable isotopeTc has no stable isotopes…


FissionUnstable nuclei will eventually decay

But the half life may be longer than the age of the solar system…113Cd half-life is 7.7 x 1015 years

Decay always leads to a more stable isotope and involves emission of disintegration product(s)

Ex:

( a is a 4He nucleus)238 234 492 90 2U Th He


Emitted particles from nuclear decay

Alpha particle: Helium nucleus emitted

Beta particle: electron emitted

Gamma ray: high energy photon

Neutron

Daughter nuclei: large fragments carrying the remainder of mass


TransmutationYou can artificially convert nuclei by

bombarding them with– Neutrons– Protons– Helium nuclei

If you use photons you can change the “nuclear angular momentum” which may cause nucleus to fall apart


Nuclear reactionsA chemical reaction is a reaction which involves

electrons

Nuclear reaction is a reaction which involves the nucleus of an atom

Nuclear reaction produces more energy per atom than chemical reactionsBecause nuclear forces holding the nucleus together are much stronger than the electrostatic forces that are holding electrons


Artificial FissionIn 1938 Hahn and Strassman in Berlin

bombarded a Uranium-235 target with neutrons and demonstrated nuclear fission for the first time


NUCLEAR FISSIONEnormous amounts of energy released as heat

Notice the 3 neutrons releasedCarry some of the excess energy

If you can use neutron to start new nuclear reaction, we have the chain reaction

At a certain capture level we get a self-sustaining chain reaction

Neutrons that have too much energy (are too fast) cannot be captured

Neutrons for reactions need to be slowed (concept of “moderator” invented by Fermi)


Neutron Energy and Moderator1 b

arn

= 1

0-2

8 m

2


CriticalityBasic concept relates to ability to have reaction at

steady state

If a general example reaction is

235U + 0n → 141Ba + 92Kr + 3 0n (+ DH)

One of the terms in “reaction rate” should be neutron concentration…

r=k[235U][0n]


CriticalitySub-critical: • fewer neutrons produced than consumed• reaction dampened

Critical: • as many free neutrons produced as consumed• reaction at steady state

Super-critical: • more free neutrons produced than consumed• reaction accelerating


CriticalityTime dependence of flux for a source-free multiplying medium


Nuclear FuelBohr found that nuclear fission was more likely to

occur in 235U than in 238U

Natural uranium is 0.7% 235U and 99.3% 238U – Separation difficult

The process of “enrichment” was developed to increase concentration of 235U in the mixture

Other common nuclear fuels: 239PU and 232Th


Mining Processes

• World reserves:

3.1 million tU

• Open-pit mining: 30%• Underground mining: 38% (55% in 1990)• In situ leaching (ISL): 21%

Australia30%

Kazakhstan17%

Canada15%

South Africa10%

Namibia8%

Brazil7%

Russia Fed.5%

United States4% Uzbekistan

4%


Milling – Uranium Extraction• Grinding (~100 microns)• Acid (H2SO4) or alkaline (Na2CO3 / NaHCO3) leach

• Solid / liquid separation of slurry • Purification (simple or extensive)• Precipitation – diuranate salt (e.g. Na2U2O7)

• Drying

Uranium oxide concentrate (UOC)

(predominantly U3O8)


Milling – Uranium Conversion

• Dissolving of U3O8 in HNO3

• Calcination (strong heating) → UO3

• Reduction with H2 → UO2

• Hydrofluorination (HF) → UF4

• Fluorination (F2) → UF6

• In most cases, end-use requires conversion to UF6 for enrichment

• Certain reactors (CANDU) can use “natural” UO2


EnrichmentNatural uranium: 235U: 0.7%, 238U: 99.3%

Reactor-grade: 235U increased to 3-5%– Necessary to sustain fission chain reaction

Enrichment Methods– Thermal diffusion (primitive, uses Soret/thermophoretic effect)– Ion/cyclotron resonance (“Caultron” – still used in France)– Gas diffusion (GD, nearly obsolete, uses membranes/ Graham’s Law)– High-speed gas centrifugation (GC, current technology)

• 5% of power requirements for GD– Laser technology (in development, Separation of Ions by Laser

Excitation - SILEX)• Proposed as ca. 1% of GD

Afterward, UF6 converted back to UO2 for mechanical processing (fuel rods)


Nuclear Fuel Cycle

• Uranium Mining and Milling

• Conversion to UF6

• Enrichment• Fuel Fabrication• Power Reactors• Waste repository


Nuclear Fuel Cycle with Reprocessing


FUELFissile material made into pellets by sintering

Oxide – Most reactors use oxide (UO2) fuel elements due to high melting point (melting point of UO2 is 2800oC)

– “UOX” – Uranium oxide– “MOX” – Mixed Oxide (Pu and U oxides mixed together)

Metal – Some reactors use metal/metal alloy fuel elements – Safer due to strongly negative “temperature factor”– E.g., UZrH alloy used in OSU’s TRIGA reactor

“Ceramic” – Non oxide materials like Nitrides and carbides– Even higher melting point– Better thermal conductivity


FUELCm sized pellets are arranged in zirconium alloy tubes to form

fuel rods

Pellets are 1 cm in diameter and 1.5 cm long

Rods arranged in core


Nuclear fuel costs

Cost in $

Natural uranium 75/kg

Conversion 6/kg

Enrichment 140/SWU

Fabrication 175/kg

Back-end 800/kg fuel

Total fuel cycle cost $0.009 /kWh(e)


U.S. Electricity Production Costs 1995-2008, In 2008 cents per kilowatt-hour

Production Costs = Operations and Maintenance Costs + Fuel Costs. Production costs do not include indirect costs and are based on FERC Form 1 filings submitted by regulated utilities. Production costs are modeled for utilities that are not regulated.

Source: Ventyx Velocity SuiteUpdated: 5/09


Fuel breeding232Th + 0n → 233Th → 233Pa + b → 233U + b 238U + 0n → 239U → 239Np + b → 239Pu + b

232Th and 238U are “fertile” nuclei

(can be transmuted to “fissile” nuclei using neutrons)

Fast breeder reactor that creates more fuel than it burns can be designed…

200x 238U and 400x 232Th in earth’s crust than 235U.


Nuclear Power Plants use Rankine Cycle


NUCLEAR POWER PLANT


The CoreReactor core is the portion of the nuclear

reactor which contains the nuclear fuel where the nuclear reaction takes place

The main function of a core is to create an environment which establishes and maintains the nuclear chain reaction

It provides a means for controlling the neutron population and removing the energy released within the core


NUCLEAR POWER PLANT


MODERATORNewly released neutrons after a nuclear fission move

at 300,000 km/sec

“Fast neutrons”

Think of the energy contained as kinetic energy

E=hn=1/2mv2

Slow moving neutrons are much more likely to be absorbed by uranium atoms to cause fission than fast moving neutrons

Moderator is a material which slows down the released neutrons from the fission process


MODERATORNeutrons must be slowed down or “moderated”

to speeds of a few km/sec

“epi-thermal neutrons”

• This is necessary to cause further fission and continue the chain reaction


Common Moderators• Water - H2O

– Light water reactor – Not efficient – it slows neutrons and absorbs them

• Heavy water (D2O) – Heavy water reactor– Efficient – slows neutrons and bounces them back– CANDU (Canada Deuterium Uranium) reactor can use natural/low

enriched Uranium!

• Graphite– RBMK design– Efficient, but graphite (carbon) can burn…


NUCLEAR POWER PLANT


Control Rods• Too many neutrons could lead to runaway reaction

(not a good thing)– Number of neutrons in reactor controlled by absorbing

some

• Made of neutron-absorbing material– Cadmium– Hafnium– Boron

Rods inserted or withdrawn from the core to control rate of reaction


CONTROL ROD


NUCLEAR POWER PLANT


COOLANTLiquid or gas circulating through the core

Carries the heat away from the reactor

It generates steam in the steam generator May not have separate steam and coolant cycles

The most common coolant is pressurized water

Others includeHelium, CO2, molten Na/K, molten Pb/Bi, molten Na2AlF6


• 1000 psi, 285oC

Boiling Water Reactor


Pressurized Water Reactor• 2300 psi, 315oC


CANDU-PHWR


Pressure Tube Graphite moderated R (PTGR)

Note: this is the RBMK reactor design as made famous at Chernoybl


HTGR


STEAM GENERATOR• It is a heat exchanger

• Uses heat from the core which is transported by the coolant

• Produces steam for the turbine


NUCLEAR POWER PLANT


CONTAINMENTThe structure around the reactor core

Protects the core from outside intrusion

More important, protects environment from effects of radiation in case of a malfunction

Typically it is meter thick concrete and steel structure


Containment Structure


SPENT FUEL POOLStores the spent fuel from the nuclear reactor

About 1/4 to 1/3 of the total fuel is removed from the core every 12 to 18 months and replaced with the fresh fuel

Removed fuel rods still generate a heat and radiation

Spent fuel kept in “pool” filled with “poisoned water”

Water that absorbs neutrons

Usually Li/B salts dissolved in water


SPENT FUEL POOL• The spent fuel is typically stored underwater

for 10 to 20 years before being sent for disposal or reprocessing


CATEGORIES OF RADIOACTIVE WASTE

Low Level Radioactive Waste Clothing used by workers, gasses and liquid emitted by reactor

Hospital waste, etc

Stored in metal containers on site, later permanently disposed

Shallow land burial (often incinerated first)

Intermediate Level Radioactive WasteFuel element claddings, materials from reactor decomissioning

Deep burial

High Level Radioactive WasteSpent fuel (fission products and actinides after cooling)

Remainder from reprocessing

Currently disposed at WIPP


Problematic WasteFission Products Actinides

Nuclide Half-life (years) Nuclide Half-life (years)106Ru 1 237 Np 2.1x106

125Sb 2.7 238 Pu 89134Cs 2.1 239 Pu 2.4x104

147Pm 2.6 240 Pu 6.8x103

155Eu 1.8 241 Pu 1390Sr 28.8 242 Pu 3.8x105

137Cs 30 241Am 458151Sm 90 243Am 7.6x103

99Tc 210000 144Cm 18.1


Remaining activity after storage

Activity (Ci) after 10 years 100 years 1000 years

Fission products 300000 3500 15

Actinides 10000 2200 600

Curie (Ci): 37,000,000,000 disintegrations per second (1 gram pure radium)


Nuclear Waste


Radiation UnitsRad: radiation absorbed dose: 0.01 J / kg body tissue

SI unit is Gray (1 rad = 10 mGy)

US customary unit still rad

Rem: roentgen equivalent manThe dose equivalent in rems is numerically equal to the absorbed dose in rads multiplied by modifying factors for each radiation type. Alpha: 1/10

Beta: 1

Gamma: 1

SI unit is Sievert (Sv, 100rem = 1 Sv)


Exposure levels• 500 rem dose fatal to 1/2 of population

• 100 - 200 rem: vomiting, temporary sterility, hair loss, spontaneous abortion, cancer

• 5 rem: maximum allowable sustained exposure

• AY dosimeters from XRD: never greater than 0.5 rem


Exposure Pathways


Effects of Ionizing Radiation

Chemistry in Context, Chapter 7

Ionizing radiation has sufficient energy to knock bound electrons from atom or molecule

Can form highly reactive free radicals with unpaired electrons

E.g., H2O [H2O.] + e-

Rapidly dividing cells are particularly susceptible to damage • Pregnancy…• Used to treat certain cancers and Graves disease

of the thyroid


http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs10bkvsman.htmNCRP Report No. 93 www.epa.gov/rpdweb00/docs/402-f-06-061.pdf

• Natural sources (81%) include radon (55%), external (cosmic, terrestrial), and internal (K-40, C-14, etc.)

• Man-made sources (19%) include medical (diagnostic x-rays- 11%, nuclear medicine- 4%), consumer products, and other (fallout, power plants, air travel, occupational, etc.)

http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs10bkvsman.htm


http://www.epa.gov/rpdweb00/docs/402-f-06-061.pdf


www.epa.gov/rpdweb00/docs/402-k-07-006.pdf

http://www.epa.gov/rpdweb00/docs/402-k-07-006.pdf

http://www.epa.gov/rpdweb00/docs/402-k-07-006.pdf


Effect of Smoking on Radiation Dose

Average annual whole body radiation dose is about 360 mrem

If you smoke, add about 280 mremTobacco contains Pb-210 from fertilizer

Decays to Po-210.

Pb-210 deposits in bones.

Po-210 works on liver, spleen, kidneys


http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm


http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm


Waste…• Fuel reprocessing…

• Geological repositories – Identify solutions that are both safe and publicly acceptable– Use retrievable form, rather than irreversible solution

• Allow adoption a better solution in future– Sweden – site selection for nuclear waste repository– Finland

• Proposal to build repository in cavern near the NPPs at Olkiluoto. • Construction start in 2010, operation about 2020 (parliament approval?)

– “Yucca Mountain”

• Other R&D – reduce actinide generation – transmutation using accelerator driven system

• Change long-lived nuclear waste to low or medium nuclear waste


WIPP?“Waste Isolation Pilot Plant”Waste from research and weapons programsOpen in 1999


Transmutation?Isn’t that what alchemists do?

This is where Actinides (IUPAC: “actinoids”) come from

Example:


Transmutation 238U can be made into fissile 239Pu232Th can be transmuted to 233U

• Fertile material: can be transmuted to fissile material– After 5 years in fast breeder reactor can get enough 239Pu

to fuel another reactor from 238U…– Natural U is 99.3% 238U…– Similar for 232Th, also there’s 4x as much Th as U in the

world…

• Fissile material: actual nuclear fuel


Waste Fuel ReprocessingUREX process (URanium EXtraction)

Dissolve waste fuel in HNO3

Extract with tributylphosphate/alkane mixture

Crash out recovered U using reductant (e.g., NaBH4)

AY worked on e-chem variant of this (used depleted 238U…)

PUREX is a variant – also extracts Pu

Remaining aqueous stuff has actinides, fission products

Dispose by vitrification/synroc

chemical, biological and environmental engineering other conventional power: nuclear power

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