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The Promise and Problems of Nuclear Energy II

Energy and the Environment

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Summary

• History of Nuclear Energy• Radioactivity• Nuclear Reactors• Boiling Water Reactor• Fuel Cycle• Uranium Resources• Environmental and Safety Aspects of Nuclear

Energy• Chernobyl Disaster• Nuclear Weapons• Storage of High-Level Radioactive Waste• Cost of Nuclear Power• Nuclear Fusion as a Energy Source• Controlled Thermonuclear Reactions• A Fusion Reactor

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Review of Fission• 235U will undergo spontaneous fission if a neutron

happens by, resulting in:– two sizable nuclear fragments flying out– a few extra neutrons– gamma rays from excited states of daughter nuclei– energetic electrons from beta-decay of daughters

• The net result: lots of banging around– generates heat locally (kinetic energy of tiny

particles)– for every gram of 235U, get 65 billion Joules, or about

16 million Calories– compare to gasoline at roughly 10 Calories per gram

a tank of gas could be replaced by a 1-mm pellet of 235U!!

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Enrichment

• Natural uranium is 99.27% 238U, and only 0.72% 235U– 238U is not fissile, and absorbs wandering

neutrons• In order for nuclear reaction to self-sustain, must

enrich fraction of 235U to 3–5%– interestingly, it was so 3 billion years ago– now probability of wandering neutron hitting

235U is sufficiently high to keep reaction crawling forward

• Enrichment is hard to do: a huge technical roadblock to nuclear ambitions

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iClicker Question

• Which is closest to the half-life of a neutron?– A 5 minutes– B 10 minutes– C 15 minutes– D 20 minutes– E 30 minutes

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iClicker Question

• Which is closest to the half-life of a neutron?– A 5 minutes– B 10 minutes– C 15 minutes– D 20 minutes– E 30 minutes

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iClicker Question

• What is the force that keeps the nucleus together?– A weak force– B strong force– C electromagnetic force– D gravitational force

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iClicker Question

• What is the force that keeps the nucleus together?– A weak force– B strong force– C electromagnetic force– D gravitational force

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iClicker Question

• A neutron decays. It has no electric charge. If a proton (positively charged) is left behind, what other particle must come out if the net charge is conserved?

– A No other particles are needed.– B A negatively charged particle must emerge

as well.– C A positively charged particle must emerge

as well.– D Another charge will come out, but it could

be either positively charged or negatively charged.

– E Neutrons cannot exist individually.

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iClicker Question

• A neutron decays. It has no electric charge. If a proton (positively charged) is left behind, what other particle must come out if the net charge is conserved?

– A No other particles are needed.– B A negatively charged particle must emerge

as well.– C A positively charged particle must emerge

as well.– D Another charge will come out, but it could

be either positively charged or negatively charged.

– E Neutrons cannot exist individually.

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iClicker Question

• How many neutrons in U-235?

– A 141– B 142– C 143– D 144– E 145

U23592

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iClicker Question

• How many neutrons in U-235?

– A 141– B 142– C 143– D 144– E 145

U23592

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iClicker Question

• How many neutrons in Pu-239?

– A 141– B 142– C 143– D 144– E 145

Pu23994

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iClicker Question

• How many neutrons in Pu-239?

– A 141– B 142– C 143– D 144– E 145

Pu23994

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iClicker Question

• If a substance has a half-life of 30 years, how much will be left after 90 years?– A one-half– B one-third– C one-fourth– D one-sixth– E one-eighth

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iClicker Question

• If a substance has a half-life of 30 years, how much will be left after 90 years?– A one-half– B one-third– C one-fourth– D one-sixth– E one-eighth

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iClicker Question

• If one of the neutrons in carbon-14 (carbon has 6 protons) decays into a proton, what nucleus is left?– A carbon-13, with 6 protons, 7 neutrons– B carbon-14, with 7 protons, 7 neutrons– C boron-14, with 5 protons, 9 neutrons– D nitrogen-14, with 7 protons, 7

neutrons– E nitrogen-15, with 7 protons, 8

neutrons

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iClicker Question

• If one of the neutrons in carbon-14 (carbon has 6 protons) decays into a proton, what nucleus is left?– A carbon-13, with 6 protons, 7 neutrons– B carbon-14, with 7 protons, 7 neutrons– C boron-14, with 5 protons, 9 neutrons– D nitrogen-14, with 7 protons, 7

neutrons– E nitrogen-15, with 7 protons, 8

neutrons

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iClicker Question

• Basically, what is the nature of the alpha particle?– A an electron– B a proton– C a helium nucleus– D a uranium nucleus– E an iron nucleus

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iClicker Question

• Basically, what is the nature of the alpha particle?– A an electron– B a proton– C a helium nucleus– D a uranium nucleus– E an iron nucleus

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iClicker Question

• Basically, what is the nature of the beta particle?– A an electron– B a proton– C a helium nucleus– D a uranium nucleus– E an iron nucleus

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iClicker Question

• Basically, what is the nature of the beta particle?– A an electron– B a proton– C a helium nucleus– D a uranium nucleus– E an iron nucleus

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Brief History of Nuclear Power

1938– Scientists study Uranium nucleus1941 – Manhattan Project begins1942 – Controlled nuclear chain reaction1945 – U.S. uses two atomic bombs on

Japan1949 – Soviets develop atomic bomb1952 – U.S. tests hydrogen bomb1955 – First U.S. nuclear submarine

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“Atoms for Peace”

Program to justify nuclear technology

Proposals for power, canal-building, exports

First commercial power plant, Illinois 1960

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Emissions Free

• Nuclear energy annually prevents– 5.1 million tons of sulfur– 2.4 million tons of nitrogen oxide– 164 metric tons of carbon

• Nuclear often pitted against fossil fuels– Some coal contains radioactivity– Nuclear plants have released low-level

radiation

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Early knowledge of risks

• 1964 Atomic Energy Commission report on possible reactor accident

– 45,000 dead– 100,000 injured– $17 billion in damages– Area the size of Pennsylvania

contaminated

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States with nuclear power plant(s)

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Nuclear power around the globe

• 17% of world’s electricity from nuclear power – U.S. about 20% (2nd largest source)

• 431 nuclear plants in 31 countries – 103 of them in the U.S.– Built none since 1970s– U.S. firms have exported nukes.– Push from Bush/Obama for new nukes.

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Countries Generating Most Nuclear Power

Country Total MW

USA 99,784

France 58,493

Japan 38,875

Germany 22,657

Russia 19,843

Canada 15,755

Ukraine 12,679

United Kingdom 11,720

Sweden 10,002

South Korea 8,170

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Nuclear Fuel Cycle

• Uranium mining and milling• Conversion and enrichment• Fuel rod fabrication• POWER REACTOR• Reprocessing, or• Radioactive waste disposal

– Low-level in commercial facilities– High level at plants or underground

repository

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iClicker Question

• About what percentage of U.S. electricity is derived from nuclear power?– A 10– B 20– C 30– D 40– E 50

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iClicker Question

• About what percentage of U.S. electricity is derived from nuclear power?– A 10– B 20– C 30– D 40– E 50

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iClicker Question

• Which of the following countries has the highest percentage of electricity generated by nuclear power?– A United States– B United Kingdom (Great Britain)– C Japan– D France– E Russia

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iClicker Question

• Which of the following countries has the highest percentage of electricity generated by nuclear power?– A United States– B United Kingdom (Great Britain)– C Japan– D France– E Russia

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Front end: Uranium mining and milling

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Uranium tailingsand radon gas

Deaths of Navajominers since 1950s

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Radioactivity Basics

Radioactivity – The spontaneous nuclear transformation of an unstable atom that often results in the release of radiation, also referred to as disintegration or decay.

Units

Curie (Ci) the activity in one standard gram of Radium = 3.7 x 1010 disintegrations per second

Becquerel (Bq) 1 disintegration per second – International Units (SI)

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Radioactivity Basics

Radiation – Energy in transit in the form of electromagnetic waves (gamma-γ or x-ray), or high speed particles ( alpha-α, beta-β, neutron-η, etc.)

Ionizing Radiation – Radiation with sufficient energy to remove electrons during interaction with an atom, causing it to become charged or ionized.

– Can be produced by radioactive decay or by accelerating charged particles across an electric potential.

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Radioactivity Basics

Roentgen R the unit of exposure to Ionizing Radiation. The amount of γ or x-ray radiation required to produce 1.0 electrostatic unit of charge in 1.0 cubic centimeter of dry air.

Rad the unit of absorbed dose. Equal to 100 ergs per gram of any material from any radiation.

SI unit = Gray1 Gray = 100 rads

REM the unit of absorbed dose equivalent. The energy absorbed by the body based on the damaging effect for the type of radiation.

REM =Rad x Quality Factor SI unit = Sievert

1 Sv = 100 Rem

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iClicker Question

• Which of the following describes the Roentgen?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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iClicker Question

• Which of the following describes the Roentgen?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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iClicker Question

• Which of the following describes the RAD?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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iClicker Question

• Which of the following describes the RAD?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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iClicker Question

• Which of the following describes the REM?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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iClicker Question

• Which of the following describes the REM?– A the unit of absorbed dose equivalent.– B the unit of absorbed dose.– C the unit of exposure to ionizing radiation– D all of the above– E none of the above

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ALARA

A philosophy, necessary to maintain personnel exposure or the release of radioactivity to the environment well below applicable limits by means of a good radiation protection plan, through education, administrative controls and safe lab practices.

As Low As Reasonably Achievable

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ALARA Principles

Distance• Inverse Square Law

– radiation intensity is inversely proportional to the square of the distance from the source

– Use remote handling tools, or work at arms length

– Maximize distance from source of radiation

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ALARA Principles

Shielding• Any material between

a source of radiation and personnel will attenuate some of the energy, and reduce exposure

• Select proper shielding material for type of radiation, use less dense material for β’s, to minimize Bremsstrahlung (braking) radiation

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Background RadiationBackground Radiation

• Natural Sources (300 mREM): "Natural" background radiation consists of radiation from cosmic radiation, terrestrial radiation, internal radionuclides, and inhaled radon.

• Occupational Sources (0.9 mREM): According to NCRP Report No. 93, the average dose for workers that were actually exposed to radiation in 1980 was approximately 230 mREM.

• The Nuclear Fuel Cycle (0.05 mREM): Each step in the nuclear fuel cycle can produce radioactive effluents in the air or water.

• Consumer Products (5-13 mREM): The estimated annual dose from some commonly-used consumer products such as cigarettes (1.5 pack/day, 8,000 mREM) and smoke detectors (1 mREM) contribute to total annual dose.

• Miscellaneous Environmental Sources (0.6 mREM): A few environmental sources of background radiation are not included in the above categories.

• Medical Sources (53 mREM): The two contributors to the radiation dose from medical sources are diagnostic x-rays and nuclear medicine. Of the estimated 53 mREM dose received annually, approximately 39 mREM comes from diagnostic x-rays.

Below are estimates of natural and man-made background radiation at sea level at middle latitudes. The total averages 400 – 500 mREM/yr

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Metric Conversions• 1 rem = 0.01 Sv = 10 mSv • 1 mrem = 0.00001 Sv = 0.01 mSv =

10 μSv • 1 Sv = 100 rem = 100,000 mrem (or

millirem) • 1 mSv = 100 mrem = 0.1 rem• 1 μSv = 0.1 mrem

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Maximum Permissible Dose Equivalents for Radiation Maximum Permissible Dose Equivalents for Radiation WorkersWorkers

Avg dose/ week (rem)

Max 13 week dose (rem)

Max yearly dose (rem)

Max lifetime dosea (rem)

Radiation controlled areas:

Whole body, gonads, blood-forming organs, and lens of eye

0.1 3 5 5(N - 18)d

Skin of whole body – 10 30 –

Hands and forearms, head neck, feet, and ankles

– 25 75 –

Environs:

Any part of body .01 – 0.5 –

Notes: Avg week dose is for design purposes only1 REM assumed = 1 RNote a: N = age in yearsFor minors, dose limits are 10% of adult limits and radiation work is not permittedSource: National Bureau of Standards Handbook 59 (1958) with addendums.

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Occupational ExposureOccupational Exposure• In terms of absolute energy content, 1

RAD is not a lot (i.e., ~ 0.01 joule absorbed/kg).

• The main risks associated exposure to analytical X-rays are– High Intensity Exposures: Skin

burns and lesions and possible damage to eye tissue

– Long-term chronic Exposures: Possible chromosomal damage and long term risk of skin cancer

• Goal of all Radiation Safety practice is ALARA – As Low as Reasonably Achievable

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Long-term Effects of Radiation ExposureLong-term Effects of Radiation ExposureLong-term effects are usually related to increased risk of cancer,

summarized in the table below:

Disease Additional Cases per 100,000 (with one-time 10 REM dose) *

Adult leukemia 95

Cancer of digestive system

230

Cancer of respiratory system

170* Source: Biological Effects of Ionizing Radiation V (BEIR V) Committee

Radiation-induced life shortening (supported by animal experiments) suggests accelerated aging may result in the loss of a few days of life as a result of each REM of exposure

Genetic Effects of radiation fall into two general categories– Effect on individuals: Can change DNA and create mutation but

long term effects not well understood. Biological repair mechanisms may reduce importance.

– Effect of offspring: Exposure to a fetus in utero can have profound effects on developing organs resulting in severe birth defects. For this reason pregnant women should avoid any non-background exposures

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Bioeffects on Surface tissuesBioeffects on Surface tissues

• Because of the low energy (~8 keV for Cu) of analytical x-rays, most energy will be absorbed by skin or other exposed tissue

• The threshold of skin damage is usually around 300 R resulting in reddening of the skin (erythema)

• Longer exposures can produce more intense erythema (i.e., “sunburn”) and temporary hair loss

• Eye tissue is particularly sensitive – if working where diffracted beams could be present, eye protection should be worn

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Uranium Enrichment

• U-235 – Fissionable at 3%– Weapons grade at 90%

• U-238 – More stable

• Plutonium-239 – Created from U-238; highly radioactive

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Radioactivity of Plutonium

• Life span at least – 240,000 years

• Compare to– Last Ice Age glaciation

10,000 years ago– Neanderthal Man died out

30,000 years ago

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• Largest industrial users of water, electricity– Paducah, KY, Oak Ridge, TN, Portsmouth,

OH

• Cancers and leukemia among workers– Fires and mass exposure.– Karen Silkwood at Oklahoma fabrication

plant.

• Risk of theft of bomb material.

Risks of Enrichment andFuel Fabrication

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Nuclear Fission Reactors

• Nuclear fission is used simply as a heat source to run a heat engine

• By controlling the chain reaction, can maintain hot source for periods greater than a year

• Heat is used to boil water• Steam turns a turbine, which turns a

generator• Efficiency limited by familiar Carnot efficiency:

= (Th - Tc)/Th (about 30–40%, typically)

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Nuclear Plant Layout

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The Core of the Reactor

not shown arethe control rodsthat absorbneutrons andthereby keep theprocess fromrunning away

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Fuel Packaging

• Want to be able to surround uranium with fluid to carry away heat

– lots of surface area is good• Also need to slow down

neutrons– water is good for this

• So uranium is packaged in long rods, bundled into assemblies

• Rods contain uranium enriched to ~3% 235U

• Need roughly 100 tons per year for a 1 GW plant

• Uranium stays in three years, 1/3 cycled yearly

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Control Rod Action

• Basic Concept– need exactly one excess

neutron per fission event to find another 235U

• Inserting a neutron absorber into the core removes neutrons from the pool

• Pulling out rod makes more neutrons available

• Emergency procedure is to drop all control rods at once

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California Nuclear Plant at San Onofre

• 10 miles south of San Clemente

• Easily visible from I-5• 2 reactors brought online

in 1983, 1984– older decommissioned

reactor retired in 1992 after 25 years of service

• 1.1 GW each• PWR (Pressurized Water

Reactor) type• No cooling towers

– the ocean is used

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The relative cost of nuclear power

safety regulations tend to drive cost

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Sidebar Regarding Nuclear Bombs

• Since neutrons initiate fission, and each fission creates more neutrons, there is potential for a chain reaction

• Have to have enough fissile material around to intercept liberated neutrons

• Critical mass for 235U is about 15 kg– for 239Pu it’s about 5 kg– need highly enriched (about 90% 235U for uranium

bomb)• Bomb is relatively simple

– separate two sub-critical masses and just put them next to each other when you want them to explode!

– difficulty is in enriching natural uranium to mostly 235U

68From: National Institutes of Health

Sources of Radiation Exposure

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Useful Radiation Effects INuclear Power

Nuclear fission for electricityThermoelectric for spacecraft

Medical:Diagnostic scans, tracersCancer radiation treatmentPlutonium powered pacemakerMedical, dental sterilization

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Useful Radiation Effects IIPolymer cross-linking

Shrink tubing (e.g., turkey wrapping)Ultra-strong materials (e.g., Kevlar)Tires (replaces vulcanization)Flooring

Food irradiationSterilization of meatDe-infestation of grain and spicesIncrease shelf life (e.g., fruits, veggies)

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The “radura” symbol on foodstuffs

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Useful Radiation Effects III

Sterilization of food for• hospitals and space travel

Radioactive datingInsect controlSemiconductor dopingTesting of space-hardened computer technologyEnvironmental studies in

• air purity, global warming, ozone

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The finite uranium resource

• Uranium cost is about $23/kg– about 1% of cost of nuclear power– more expensive to get as we deplete the

easy spots• Estimated 3 million tons available at cost less

than $230/kg• Need 200 tons per GW-yr• Now have 100 GW of nuclear power generation

– about 100 plants @ 1 GW each• 3 million tons will last 150 years at present rate

– only 30 years if nuclear replaced all electricity production

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Breeder Reactors

• The finite resource problem goes away under a breeder reactor program

• Neutrons can attach to the non-fissile 238U to become 239U– beta-decays into 239Np with half-life of 24

minutes– 239Np beta-decays into 239Pu with half-life of 2.4

days– now have another fission-able nuclide– about 1/3 of energy in normal reactors ends up

coming from 239Pu• Reactors can be designed to “breed” 239Pu in a

better-than-break-even way

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Breeders, continued

• Could use breeders to convert all available 238U into 239Pu– all the while getting electrical power out

• Now 30 year resource is 140 times as much (not restricted to 0.7% of natural uranium), or 4200 yr

• Technological hurdle: need liquid sodium or other molten metal to be the coolant– but four are running in the world

• Enough 239Pu falling into the wrong hands spells:– BOOM!!

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Reactor Risks• Once a vigorous program in the U.S.

– in France 80% of electricity is nuclear

• No new orders for reactors in U.S. since late 70’s– aftershock of Three-Mile Island

• Reactor failure modes:– criticality accident: runaway chain reaction

meltdown– loss of cooling: not runaway, but overheats

meltdown– steam or chemical explosions are not ruled out

meltdown– N.B. reactors are incapable of nuclear explosion

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Risk Assessment

• Extensive studies by agencies like the NRC• 1975 report concluded that:

– loss-of-cooling probability was 1/2000 per reactor year

– significant release of radioactivity 1/1,000,000 per RY

– chance of killing 100 people in an accident about the same as killing 100 people by a falling meteor

• 1990 NRC report accounts for external disasters (fire, earthquake, etc.)

– large release probability 1/250,000 per RY– 109 reactors, each 30 year lifetime 1% chance

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Close to home: Three Mile Island

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The Three-Mile Island Accident, 1979

• The worst nuclear reactor accident in U.S. history• Loss-of-cooling accident in six-month-old plant• Combination of human and mechanical errors• Severe damage to core

– but containment vessel held• No major release of radioactive material to

environment• Less than 1 mrem to nearby population

– less than 100 mrem to on-site personnel– compare to 300 mrem yearly dose

• Instilled fear in American public, fueled by movies like The China Syndrome

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Health around TMI• In 1979, hundreds of people reported nausea,

vomiting, hair loss, and skin rashes. Many pets were reported dead or showed signs of radiation

• Lung cancer, and leukemia rates increased 2 to 10 times in areas within 10 miles downwind

• Farmers received severe monetary losses due to deformities in livestock and crops after the disaster that are still occurring today.

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Plants near TMI

-lack of chlorophyll -deformed leaf patterns -thick, flat, hollow stems -missing reproductive parts -abnormally large

TMI dandelion leaf at right

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Animals Nearby TMI

• Many insects disappeared for years.

– Bumble bees, carpenter bees, certain type caterpillars, or daddy-long-leg spiders

– Pheasants and hop toads have disappeared.

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The Chernobyl Disaster

• Disregard of safety standards plus unstable design led to disaster

• Chernobyl was a boiling-water, graphite-moderated design– unlike any in the USA– used for 239Pu weapons production– frequent exchange of rods to harvest Pu meant

lack of containment vessel like the ones in USA– positive-feedback effect

It gets too hot, it runs hotter runaway possible

– once runaway, control rods ineffective

86

Chernobyl, continued

• On April 25, 1986, operators decided to do an “experiment” as the reactor was powering down for routine maintenance– disabled emergency cooling system!!!– withdrew control rods completely!!!– powered off cooling pumps!!!– reactor went out of control, caused steam

explosion that ripped open the reactor– many fires, exposed core, major

radioactive release

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Chernobyl after-effects

• Total of 100 million people exposed (135,000 lived within 30 km) to radioactivity much above natural levels

• Expect from 25,000 to 50,000 cancer deaths as a result– compared to 20 million total worldwide

from other causes– 20,000,000 becomes 20,050,000 (hard to

notice…– …unless you’re one of those 50,000

• 31 died from acute radiation exposure at site– 200 got acute radiation sickness

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Fallout from Chernobyl

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400 million people exposed in 20 countries

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Radiation and Health• Health effects as a result of radiation

exposure:-increased likelihood of cancer-birth defects including long limbs,

brain damage, conjoined stillborn twins-reduced immunity-genetic damage

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“It Can’t Happen Here”

• Soviet reaction to Three-Mile Island, 1979– Blamed on Capitalism and

pressurized-water reactor design• U.S. reaction to Chernobyl, 1986

– Blamed on Communism and graphite reactor design

• No technology 100% safe– Three-Mile Island bubble almost burst

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iClicker Question 

Consider all of the people throughout history who have been exposed to man-made nuclear radiation, such as Hiroshima and Nagasaki, Chernobyl, Three Mile Island, nuclear bomb tests, accidental spills, etc.

Which number most nearly approximates how many children conceived and born later to these people suffered genetic damage due to a parent’s exposure, excluding exposure during pregnancy?

A. ~ millionsB. ~ thousandsC. ~ hundredsD. ~ zero

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iClicker Question 

Consider all of the people throughout history who have been exposed to man-made nuclear radiation, such as Hiroshima and Nagasaki, Chernobyl, Three Mile Island, nuclear bomb tests, accidental spills, etc.

Which number most nearly approximates how many children conceived and born later to these people suffered genetic damage due to a parent’s exposure, excluding exposure during pregnancy?

A. ~ millionsB. ~ thousandsC. ~ hundredsD. ~ zero

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Nuclear Proliferation

• The presence of nuclear reactors means there will be plutonium in the world

– and enriched uranium• If the world goes to large-scale nuclear power

production (especially breeder programs), it will be easy to divert Pu into nefarious purposes

• But other techniques for enriching uranium may become easy/economical

– and therefore the terrorist’s top choice• Should the U.S. abandon nuclear energy for this reason?

– perhaps a bigger concern is all the weapons-grade Pu already stockpiled in the U.S. and former U.S.S.R.

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Nuclear Waste• Each reactor has storage pool, meant as temporary

holding place– originally thought to be 150 days– 40 years and counting

• Variety of radioactive products, with a wide range of half-lives

– 1GW plant waste is 70 MCi after one year; 14 MCi after 10 years; 1.4 MCi after 100 years; 0.002 MCi after 100,000 years

– 1 Ci (Curie) is 37 billion radioactive decays per second

97

Storage Solutions

• No failsafe storage solution yet developed• EPA demands less than 1000 premature

cancer deaths over 10,000 years!!– hard to design and account for all contingencies

• USA proposed site at Yucca Mountain, NV– Good and bad choice

geologically: cracks and questionable stability

98

Burial Issues• Radioactive emissions themselves are not radioactive

– just light, electrons/positrons and helium nuclei– but they are ionizing: they rip apart

atoms/molecules they encounter• Absorb emissions in concrete/earth and no effect on

biology– so burial is good solution

• Problem is the patience of time– half lives can be long– geography, water table changes– nature always outlasts human structures– imagine building something to last 10,000 years!!

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Yucca Mountai

n

100

Transportation risks

• Uranium oxide spills

• Fuel rod spills (WI 1981)

• Radioactive waste risks

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Transport to Yucca Mountain

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Kyshtym waste disaster, 1957

– Explosion at Soviet weapons factory forces evacuation of over 10,000 people in Ural Mts.

– Area size of Rhode Island still uninhabited; thousands of cancers reported

Orphans

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Risk of terrorism(new challenge to industry)

9/11 jetpassed nearIndian Point

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iClicker QuestionSuppose that all of the electrical energy for the world for the next 500 years were obtained from nuclear reactors. Further suppose that all of the nuclear waste from these reactors were dissolved and spread uniformly throughout the oceans of the world.

Which statement is true:

A. The oceans would be a vast wasteland, unable to support life.

B. Much death and damage to ocean life would be caused.

C. Any effect would be so small that it would be virtually impossible to see.

106

iClicker QuestionSuppose that all of the electrical energy for the world for the next 500 years were obtained from nuclear reactors. Further suppose that all of the nuclear waste from these reactors were dissolved and spread uniformly throughout the oceans of the world.

Which statement is true:

A. The oceans would be a vast wasteland, unable to support life.

B. Much death and damage to ocean life would be caused.

C. Any effect would be so small that it would be virtually impossible to see.

107

Fusion: The big nuclear hope

• Rather than rip nuclei apart, how about putting them together?

• Iron is most tightly bound nucleus• Can take loosely bound light nucleiand build them into more tightly boundnuclei, releasing energy• Huge gain in energy going from protons(1H) to helium (4He).• It’s how our sun gets its energy• Much higher energy content than fission

proton

dueterium

tritium

alpha (4He)

108

Thermonuclear Fusion in the Sun

• Sun is 16 million degrees Celsius in center• Enough energy to ram protons together

(despite mutual repulsion) and make deuterium, then helium

• Reaction per mole ~20 million times more energetic than chemical reactions, in general

4 protons:mass = 4.029

4He nucleus:mass = 4.0015

neutrinos, photons (gamma rays)

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E=mc2 balance sheets

• Helium nucleus is lighter than the four protons!• Mass difference is 4.029 – 4.0015 = 0.0276 a.m.u.

– 0.7% of mass disappears, transforming to energy– 1 a.m.u. (atomic mass unit) is 1.660510-27 kg– difference of 4.5810-29 kg– multiply by c2 to get 4.1210-12 J– 1 mole (6.0221023 particles) of protons 2.51012 J– typical chemical reactions are 100–200 kJ/mole– nuclear fusion is ~20 million times more potent

stuff!– works out to 150 million Calories per gram

compare to 16 million Cal/g uranium, 10 Cal/g gasoline

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Artificial Fusion• 15 million degrees in Sun’s center is just enough to keep the

process going– but Sun is huge, so it seems prodigious

• In laboratory, need higher temperatures still to get worthwhile rate of fusion events

– like 100 million degrees• Bottleneck in process is the reaction:

1H + 1H 2H + e+ + (or proton-proton deuteron)• Better to start with deuterium plus tritium

– 2H and 3H, sometimes called 2D and 3T– but give up some energy: starting higher on binding energy

graph• Then:

2H + 3H 4He + n + 17.6 MeV (leads to 81 MCal/g)

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Deuterium everywhere• Natural hydrogen is 0.0115% deuterium

– Lots of hydrogen in sea water (H2O)• Total U.S. energy budget (100 QBtu = 1020 J per

year) covered by sea water contained in cubic volume 170 meters on a side– corresponds to 0.15 cubic meters per second– about 1,000 showers at two gallons per

minute– about one-millionth of rainfall amount on U.S.– ~4 gallons per person per year

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Tritium Nowhere• Tritium is unstable, with half-life of 12.32 years

– thus none naturally available• Can make it by bombarding 6Li with neutrons

– extra n in D-T reaction can be used for this, if reaction core is surrounded by “lithium blanket”

• Lithium on land in U.S. would limit D-T to a hundred years or so– maybe a few thousand if we get lithium from

ocean• D-D reaction requires higher temperature, but

could be sustained for many millennia

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By-products?• Not like radioactive fission products• Building stable nuclei (like 4He)• Tritium is only radioactive substance

– energy is low, half-life short: not much worry here

• Extra neutrons can tag onto local metal nuclei (in surrounding structure) and become radioactive– but this is a small effect, especially compared

to fission

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Why don’t we embrace fusion?

• A huge technological challenge• Always 20 years from fruition

– must confine plasma at 50 million degrees 100 million degrees for D-D reaction

– all the while providing fuel flow, heat extraction, tritium supply, etc.

– hurdles in plasma dynamics: turbulence, etc.

• Still pursued, but with decreased enthusiasm, increased skepticism– but payoff is huge: clean, unlimited energy

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Fusion Successes?• Fusion has been accomplished in labs, in big

plasma machines called Tokamaks– got ~6 MW out of Princeton Tokamak in 1993– but put ~12 MW into it to sustain reaction

• Hydrogen bomb also employs fusion– fission bomb (e.g., 239Pu) used to generate

extreme temperatures and pressures necessary for fusion

– LiD (lithium-deuteride) placed in bomb– fission neutrons convert lithium to tritium– tritium fuses with deuterium

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Other Forms of Nuclear Power?

• Three main nuclear power reaction types– Radioactive Decay

Atomic Batteries Passive beta decay collectors

Radioisotope thermoelectric generators Passive application of Peltier and

Seebeck effects– Nuclear Fusion

Already discussed– Nuclear Fission

Already discussed

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Passive Radioactive Decay

• Radioisotope Thermoelectric Generator– Obtains power from passive radioactive

decays– Utilized in satellites and space probes– Seebeck/Peltier effect

Junction of two dissimilar metals at different temperatures create a current

– Fuel Long half life, low shielding (beta decay) Plutonium 238 most common

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Discovered by Thomas Johann Seebeck in 1821.He accidentally found that a voltage existed between two ends of a metal bar when a temperature gradient existed within the bar.

The Peltier/Seebeck EffectBy Jacob McKenzie, Ty Nowotny, Colin Neunuebel

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The Seebeck Effect

A temperature difference causes diffusion of electrons from the hot side to the cold side of a conductor. The motion of electrons creates an electrical current. The voltage is proportional to the temperature difference as governed by: V=α(Th-Tc) where α is the Seebeck coefficient of the couple

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History of Peltier devices

The Peltier effect is named after Jean Charles Peltier (1785-1845) who first observed it in 1834. The Peltier effect had no practical use for over 100 years until dissimilar metal devices were replaced with semiconductor Peltiers which could produce much larger thermal gradients.Peltier Cooler - produce a temperature gradient that is proportional to an applied current

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Peltier Effect With Dissimilar Metals

At the junction of two dissimilar metals the energy level of conducting electrons is forced to increase or decrease. A decrease in the energy level emits thermal energy, while an increase will absorb thermal energy from its surroundings. The temperature gradient for dissimilar metals is very small.

The figure of merit is a measure ofthermoelectric efficiency.

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Sidebar: Semiconductor Peltier

Bismuth-Telluride n and p blocksAn electric current forces electrons in n type and holes in p type away from each other on the cold side and towards each other on the hot side.The holes and electrons pull thermal energy from where they are heading away from each other and deliver it to where they meet.

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Sample PeltierTemperature Gradient

Temperature Gradient as a Function of Voltage

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00

Voltage, V

Tem

pe

ratu

re,

C Voltage vsTemp Diff

Cold vs V

Hot vs V

Carnot Efficiency

Nc @ 12v:=1-Tc/Th

=1-283.6/342.3=17.1%

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Applications

Deep space probesMicroprocessor coolingLaser diode temperature stabilizationTemperature regulated flight suits Air conditioning in submarinesPortable DC refrigeratorsAutomotive seat cooling/heating

Radioisotopic Thermoelectric Generator

(RTG)

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RTG Pros and ConsPros

Solid state (no moving parts)No maintenance Long service lifetime

– Relatively constant power production– Solar Panels not neededCons

Good for low electrical power requirementsInefficient compared to phase change cooling

– Decays over time– Requires shielding– Radioactive waste

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Fukushima Nuclear Power Plant

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Wikipedia Reports on Disaster at Fukushima

“An earthquake categorized as 9.0 on the moment magnitude scale occurred on 11 March 2011, at 14:46 Japan Standard Time (JST) off the northeast coast of Japan. On that day, reactor units 1, 2, and 3 were operating, but units 4, 5, and 6 had already been shut down for periodic inspection. When the earthquake was detected, units 1, 2 and 3 underwent an automatic shutdown (called scram).“After the reactors shut down, electricity generation stopped. Normally the plant could use the external electrical supply to power cooling and control systems, but the earthquake had caused major damage to the power grid. Emergency diesel generators started correctly but stopped abruptly at 15:41, ending all AC power supply to the reactors. The plant was protected by a sea wall, but tsunami water which followed after the earthquake topped this sea wall, flooding the low lying generator building…“After the failure of the diesels, emergency power for control systems was supplied by batteries that would last about eight hours. Batteries from other nuclear plants were sent to the site and mobile generators arrived within 13 hours, but work to connect portable generating equipment to power water pumps was still continuing as of 15:04 on 12 March. Generators would normally be connected through switching equipment in a basement area of the buildings, but this basement area had been flooded by the tsunami.”

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Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company

The 10 member, government-appointed panel included scholars, journalists, lawyers and engineers, was supported by public prosecutors and government experts and released its final, 448-pages investigation report on 23 July 2012. The panel interviewed 772 people, including plant workers, government officials and evacuees, for a total of nearly 1,479 hearing hours. Its report was the fourth investigation into the crisis after the earlier release of a Diet study, a private report by journalists and academics as well as an investigation by TEPCO. The panel said the government and TEPCO failed to prevent the disaster not because a large tsunami was unanticipated, but because they were reluctant to invest time, effort and money in protecting against a natural disaster considered unlikely. "The utility and regulatory bodies were overly confident that events beyond the scope of their assumptions would not occur… and were not aware that measures to avoid the worst situation were actually full of holes," the government panel said in its final report. The panel's report faulted an inadequate legal system for nuclear crisis management, a crisis-command disarray caused by the government and Tepco, and possible excess meddling on the part of the prime minister's office in the early stage of the crisis. The panel concluded that a culture of complacency about nuclear safety and poor crisis management led to the nuclear disaster.