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The Promise and Problems of Nuclear Energy II

Lecture #13HNRS 228Energy and the Environment

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Chapter 6 Summary Again

• 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

• 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

• 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

• 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

• 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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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 reporton possible reactor accident

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

contaminated18

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 (Wisconsin as

leader). – U.S. firms have exported nukes.– Push from Bush/Obama for new nukes.

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Countries Generating Most Nuclear Power

8,170South Korea10,002Sweden11,720United Kingdom12,679Ukraine15,755Canada19,843Russia22,657Germany38,875Japan58,493France99,784USA

Total MWCountry

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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

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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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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.

UnitsCurie (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 BasicsRadiation – 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 BasicsRoentgen 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 FactorSI unit = Sievert1 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

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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

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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

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ALARAA 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 PrinciplesShielding• 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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Maximum Permissible Dose Equivalents for Radiation WorkersMaximum Permissible Dose Equivalents for Radiation Workers

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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LongLong--term Effects of Radiation Exposureterm 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 95Cancer 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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BioeffectsBioeffects on Surface tissueson 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 of least 240,000 years

Last Ice Age glaciationwas 10,000 years ago

Neanderthal Man died out30,000 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

• Simple 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:

– it’s got the ocean for that

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The relative cost of nuclear power

safety regulations tend to drive cost52

Aside on 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 dirt-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

53From: 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.”

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Useful Radiation Effects IIIAbsolute sterilization of food:

hospitals and space travelRadioactive datingInsect controlSemiconductor dopingTesting of space computer technologyEnvironmental studies:

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• As we go for more, it’s more expensive to get

– depleted the easy spots• 3 million tons available at cost < $230/kg• Need 200 tons per GW-yr• Now have 100 GW of nuclear power generation

– in 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 60

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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.

– still so in France: 80% of their electricity is nuclear• No new orders for reactors in U.S. since late 70’s

– not coincidentally on the heels of Three-Mile Island• Failure modes:

– criticality accident: runaway chain reactionmeltdown

– loss of cooling: not runaway, but overheats meltdown

– reactors are incapable of nuclear explosion– steam or chemical explosions are not ruled out meltdown

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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. 70

The Chernobyl Disaster• Blatant disregard for safety plus inherently

unstable design spelled disaster• Chernobyl was a boiling-water, graphite-moderated

design– unlike any in the U.S.A.– used for 239Pu weapons production– frequent exchange of rods to harvest Pu meant

lack of containment vessel like the ones in U.S.– positive-feedback built in: gets too hot, it runs

hotter: runaway possible– once runaway initiated, control rods not

effective

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Chernobyl, continued

• On April 25, 1986, operators decided to do an “experiment” as the reactor was powering down for routine maintenance

– disabled emergency cooling systemblatant violation of safety rules

– 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

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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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Chernobyl’s political fallout

• Stimulated Gorbachev’s glasnost (openness)• Stimulated nationalism in Ukraine, Belarus,

and other republics that lost clean-up workers.

• Growth of environmental opposition• Questioning of the heart of technocratic

power– Soviet leaders were engineers, not

lawyers– USSR collapsed within 5 years.

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Radiation and Health• Health effects as a result of radiation

exposure:-increased likelihood of cancer-birth defects including long limbs, braindamage, conjoined stillborn twins

-reduced immunity-genetic damage

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“It Can’t Happen Here”

• U.S. reaction to Chernobyl, 1986– Blamed on Communism, graphite

reactor• Also Soviet reaction to Three-Mile

Island, 1979– Blamed on Capitalism, pressurized-

water reactor• No technology 100% safe

– Three-Mile Island bubble almost burst78

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 Pualready stockpiled in the U.S. and former U.S.S.R.!!

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Nuclear Waste• Big Problem• Originally unappreciated• Each reactor has storage pool, meant as temporary

holding place– originally thought to be 150 days– 35 years and counting

• Huge variety of radioactive products, with a whole range of half-lives

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

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

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Storage Solutions?

• There are none…yet• EPA demands less than 1000 premature cancer deaths over

10,000 years!!– incredibly hard to design/account

• Proposed site at Yucca Mountain, NV– Very bad choice, geologically: cracks and unstable

• Worldwide, nobody has worked out a storage solution

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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 Mountain

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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.

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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)

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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• 16 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 off starting 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

each– 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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Nasty by-products?• Practically none: not like radioactive fission

products• Building stable nuclei (like 4He)

– maybe our voices would be higher…• 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, then?

• Believe me, we would if we could• It’s a huge technological challenge, always 25

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 man, the 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