Natural Backgrounds 1 U 238 Decay Chain U 234 U 238 92 92 - - PowerPoint PPT Presentation

SLIDE 1

Natural Backgrounds

1

SLIDE 2

U238 Decay Chain

Protactinium Thorium Actinium Radium Francium Radon Astatine Polonium Bismuth Lead Thallium α α α β⁻ Uranium α β⁻ Mercury β⁻ α α α

Ra

226 1602 Years 88

Th

234 27 Days 90

Pa

234 27 Days 91

Bi

214 20 Minutes 83

Po

218 3.1 Minutes 84

Pb

214 26.8 Minutes 82

Tl

210 1.3 Minutes 81

β⁻

At

218 1.5 85 Seconds

Pb

210 22.3 Years 82

Po

214 0.1643 Seconds 84

Th

230 75,380 90

α α β⁻ β⁻

Years

Rn

222 3.8 Days 86

α

U

238 4.5e9 Years 92

U

234 245,500 Years 92

β⁻

Bi

210 83

Tl

206 4.2 Minutes 81 5 Days

Pb

206 Stable 82

Po

210 138 Days 84

α β⁻

Hg

206 8.1 Minutes 80

α

Actinides Alkali Metals Alkaline Earth Metals Halogens Metalloids Noble Gases Poor Metals Transition Metals

SLIDE 3

TH232 Decay Chain

Thorium Actinium Radium Francium Radon Astatine Polonium Bismuth Lead Thallium α α α α α α

Actinides Alkali Metals Alkaline Earth Metals Halogens Metalloids Noble Gases Poor Metals Transition Metals

α β⁻ β⁻ β⁻

Rn

220

55 Seconds

86

Bi

212

61 Minutes

83

Po

212

3e-07

Seconds

84

Pb

208

Stable

82

Tl

208

3.1 Minutes

81

β⁻

Ac

228

Minutes

6.1

89

Ra

228

5.7 Years

88

Th

228

1.9 Years

90

α β⁻

Ra

224

3.6 Days

88

α

Po

216

0.14

Seconds

84

Pb

212

10.6

Minutes

82

Th

232

1.41e+10

Years

90

SLIDE 4

Radon

4

SLIDE 5

Radon Hot Spots in US

5

SLIDE 6

Radon Hot Spots in NJ

6

SLIDE 7

Radon

7 19

Heavy noble gas By product of uranium decay 200 mrem per year One in a hundred chance of inducing cancer over a person’ s lifetime Largest source of radiation exposure Main cause of lung cancer among nonsmokers

SLIDE 8

Natural Radioactivity

8

Average dose is 300 to 400 mrem (0.3 to 0.4 rem) Dose from living next to a nuclear power plant is 30,000 times less

SLIDE 9

Main Takeaway Points

9

• Microwave radiation does not cause cancer
• Risk from medical x-ray is small
• benefits far out weigh risks
• full body CT scan about 3 times average annual background dose
• Average annual back ground dose about 300 mrem
• Radiation is everywhere
• cosmic rays
• Uranium and Thorium in soil
• Potassium in your body
• About 1% chance of inducing cancer over a lifetime
• Largest exposure for nearly everyone is Radon
• Radioactive gas that can seep into basements from the ground
• Radon levels in northwestern New Jersey higher than average
• If you live there, have your house radon level tested
• If above threshold level, undertake remediation
• What are the benefits and cons of nuclear power

SLIDE 10

Damage to DNA

10

SLIDE 11

Damage to DNA

11

SLIDE 12

Effect on Living Tissue

12

Radiation can ionize (remove electrons from) atoms This breaks molecular bonds The DNA molecules that contain our genetic code are particular susceptible to radiation damage. DNA is a very fragile molecule. Its bonds can easily be broken.

If the gene on the DNA is mutated it can lead to the growth of caner cells

Harmful effects of radiation Cancer Radiation sickness / death

A large enough radiation exposure can cause large amount of cell death leading to sickness and, if enough, death

SLIDE 13

Doses

13

Below 100 rem no short term illness 100 to 200 rem short term illness Whole body doses 300 rem 50% chance of death More than 1000 rem survival unlikely

SLIDE 14

Cancer Dose

14

Whole body dose needed to for near certainty of inducing cancer

2500 rem

This is greater than the lethal dose! Even small doses have some probability of inducing cancer and it is likely cumulative over your lifetime Assume probability risk of cancer linearly proportional to dose Assume no threshold 25 rem exposure would mean a 1% risk of cancer If 100 people are exposed to 25 rem, we expect 1 to get cancer Even with no radiation exposure 20% of people will get cancer

SLIDE 15

Linear Hypothesis

15

SLIDE 16

Summary of Cancer Risks

16

Lifetime total natural exposure 1 in 100 (1.0%) Lifetime radon exposure 1 in 150 (0.7%) One medical x-ray 1 in 60,000 Lifetime self exposure 1 in 100,000 Living 50 years next to nuclear power plant 1 in 500,000 Non radiation causes 1 in 5 (20%)

Radiation from routine operation of a nuclear power plant is not a health issue

SLIDE 17

Atomic Nucleus

17

The nucleus at the center of each atom is made up of protons and neutrons Protons and neutrons have approximately equal masses and each is about 2000 times more massive than an electron. The number of protons in the nucleus is equal to the number of electrons in the electron cloud The atomic number, Z, is the number of protons The atomic weight, A, is the number of protons plus neutrons Nearly all of the mass of an atom is in the nucleus The nucleus is 100,000 times smaller than the atom If an atom were the size of the Rutgers football stadium the nucleus would be the size of a mosquito

SLIDE 18

Chemical (Atomic) Energy

18

In a chemical reaction electron binding energy is converted into kinetic energy Example the burning of ethane (a hydrocarbon) C C H H H H H H O O

+

O O

+

O H H 2 7 4 6 The daughter molecules are more tightly bound together than the parent molecules There is less chemical potential energy in the final state than in the initial. Chemical potential energy is converted to kinetic energy (heat) C2H6

+

O2 CO2

+

H2O

SLIDE 19

Nuclear Binding Energy

19

A nuclear reaction is similar

236U 92Kr

+

141Ba

+

3 neutrons The daughter nuclei are more tightly bound together than the parent nucleus There is less nuclear potential energy in the final state than in the initial. Nuclear potential energy is converted to kinetic energy (heat) Nuclear binding energy is 1 to 10 million time stronger than chemical binding energy

SLIDE 20

Chemical vs. Nuclear Energy

20

Because of the great difference in binding energies, for as given, mass, tremendous amount more energy is released in a nuclear reaction than in a chemical reaction Burning 1 gram of gasoline releases 42 kJ Fissioning 1 gram of Uranium releases 82 GJ In both cases we need a trigger. Ethane won’ t burn

• n it own and uranium won’

t fission on its own In the case of a chemical reaction the trigger is a spark or heat In the case of a nuclear fission reaction the trigger is the nucleus being struck by an energetic neutron

SLIDE 21

Binding Energy of Nuclei

21

Iron (Fe) is the most tightly bound nucleus Nuclei more massive than Fe can release energy by fissioning to lighter nuclei Nuclei less massive than Fe can release energy by fusing to form heavier nuclei

SLIDE 22

Nuclear Fission

22

In a nuclear fission reaction a heavy parent nuclei fissions (or splits) into two or more lighter daughter nuclei. Several neutrons may be released in the process as well In general the heavier nuclei have a greater tendency to fission

SLIDE 23

235U Fission

23

If a neutron hits a 235U nucleus it will form a 236U nucleus that then fissions into lighter nuclei (fragments)

SLIDE 24

Chain Reaction

24

A chain reaction occurs if the fission process releases one or more neutrons that can then initiate addition fission reactions If a fission releases two neutrons after a few generations there will be many fissions. This all happens very rapidly

generation number of fissions 1 21 = 2 2 22 = 4 3 23 = 8 5 25 = 32 10 210 = 1000 20 220 = 106 40 240 = 1012 80 280 = 1024

SLIDE 25

Uncontrolled Chain Reaction

25

If the chain reaction runs its course after 84 generations 10 kg of Uranium will have fissioned. 10 kg of Uranium corresponds to 300 kilotons of TNT Per weight, Uranium releases 30,000,000 times as much energy as TNT.

We have a bomb

In order for this to work two things are necessary. 1) Critical mass. There must be enough Uranium so that the neutrons interact before they escape. 2) Enrichment. There must a large enough fraction of 235U compared to 238U since 238U absorbs the neutrons. Critical mass: 15 kg Enrichment: 90%

SLIDE 26

Controlled Chain Reaction

26

The chain reaction can be controlled by using a material that absorbs neutrons By controlling the amount of absorber, we can arrange so that for every fission there in only

• ne neutron available to trigger another fission.

Then the reaction won’ t run away but will run at constant power. We have a nuclear reactor

SLIDE 27

Neutron Moderation

27

Slow neutrons are much more effective in causing fission than fast neutrons Use a moderator that scatters neutrons but doesn’ t absorb them. An example is water After enough scattering the neutrons will be thermal. They will have energy corresponding to the ambient temperature.

SLIDE 28

Nuclear Reactor

28

SLIDE 29

Light Water Reactor

29

Most reactors are moderated with light (normal) water Two types: pressurizer water (above) or boiling water. They require that the fuel be enriched to 3% to 4% 235U

SLIDE 30

Fuel Rods

30

Compacted fine powder of enriched Uranium oxide sintered into pellets and placed into long zircalloy tubes Fuel enriched to about 3% 235U About 100 tons of fuel per year for 1 GW reactor

SLIDE 31

Control Rods

31

Control rods usually contain boron since it is a very good neutron absorber

SLIDE 32

Enrichment

32

Naturally occurring uranium is only about 0.7% 235U Since the light water moderator also absorbs neutrons need to enrich to about 3% 235U. Heavy water moderator reactor uses unenriched fuel Enrichment needed for bomb is 20% minimum but efficient bomb requires 90% since don’ t want 238U to absorb the neutrons

SLIDE 33

Plutonium

33

Plutonium is the only other element that can undergo chain reaction fission It is more effective because it releases more neutrons per fission than uranium It is the element of choice for bombs Plutonium doesn’ t occur naturally but it is made in a nuclear reactor by absorption of a neutron by 238U

n + 238U --> 239U --> 239Np --> 239Pu

About 30% of the energy in a nuclear power reactor is from fission of plutonium, by the end of the fuel life cycle this becomes about 60%

SLIDE 34

Issues with Nuclear Energy

34

Radiation Safety Waste disposal Cost Resource availability Weapons proliferation

SLIDE 35

Radioactivity

35

SLIDE 36

Issues with Nuclear Energy

36

Radiation Safety Waste disposal Cost Resource availability Weapons proliferation

SLIDE 37

Accidents

37

Three Mile Island Chernobyl Fukushima

SLIDE 38

Three Mile Island

38

1979 Pennsylvania

carelessness

• loss of cooling water
• chain reaction stopped by control rods
• heat from fission fragments melted 1/3 of core
• did not melt through containment vessel
• some radiation escaped from gases dissolved in leaked water

2 million people exposed to 1 mrem = 0.001 rem excess cancer deaths (2 x 106) x (0.001 rem) / (2500 rem) = 0.8

Reactors

SLIDE 39

Fukushima

39

2011 Japan

incompetence

• Earthquake caused reactor shutdown
• Loss of electricity caused shutdown
• f cooling pumps
• Tsunami flooded diesel pumps. Disaster
• Meltdown of cores
• Hydrogen gas explosions
• Backup diesel pumps kicked in. So

far everything fine

• Release of radioactivity from

venting gas and from water leaks

• If pumps had been on hillside above plant

probably things would have been OK

• about 1000 time worse than

Three Mile Island

• estimate 1000 extra cancer

deaths among exposed population of 5 million

SLIDE 40

Chernobyl

40

1986 Ukraine

stupidity

• operators ran experiment to see what

would happen with cooling system disabled and control rods completely removed

• boiling water reactor with graphite moderator
• unlike any outside of former Soviet Union
• used for power and for plutonium production for weapons
• frequent exchange of fuel rods meant no containment vessel
• unstable because of positive feedback: when gets hot water boils off

less coolant

• chain reaction can run on fast neutrons. Then no controlling. Runaway
• steam explosion ripped open reactor
• graphite reactor caught on fire

SLIDE 41

Chernobyl (cont.)

41

5 million people exposed to 100 mrem per year excess cancer deaths (5 x 106) x (5 rem) / (2500 rem) = 10,000 About 30% of core sent up into the atmosphere and spread over a wide area about one third of natural background

SLIDE 42

Paradox of Evacuation

42

In assessing risks it is essential to take into account the number of people exposed Exposure in the Chernobyl closed zone (50 mile radius) is 3 rem per year 10 times normal background If you lived there for ten years you would have a 1% increased cancer risk. This is probably not worth worrying about. If 1,000,000 people lived there for ten years, there would be an additional 10,000 cancer deaths. This would be unacceptable. Bottom line. Exposure limits are set to protect the million. The risks for a single individual like you are very low. Same is of course true for non-radiation related risks

SLIDE 43

Safety Summary

43

Reactors cannot blow up like nuclear bombs Chernobyl is the worst accident imaginable

large fraction of core sent into the atmosphere about 10,000 excess cancer death special to this type unstable flammable reactor

Modern reactors have advanced safety systems

gravity fed cooling works even if pumps shutdown

Accidents are probably unavoidable but we have seen the worst (Chernobyl) and it won’ t happen again

SLIDE 44

Issues with Nuclear Energy

44

Radiation Safety Waste disposal Cost Resource availability Weapons proliferation

SLIDE 45

Three Types of Waste

45

Fission Fragments

• 4% of spent fuel rod
• intensely radioactive
• half lives cover wide range
• radioactivity down by factor
• f 100 after about 1 year
• negligible after 500 years
• storage not a problem

Long-lived Elements (Pu, Am, Np, Cu)

• 1% of spent fuel rod
• moderately radioactivity
• half-lives order of 100,000 years
• this is the problem

How to guarantee safe storage for 100,000 years or more

238U

• 95% of spent fuel rod
• negligible radioactivity
• not an issue
• same as what came out of ground

SLIDE 46

Radioactivity of Waste as Function of Time

46

radioactivity compared to uranium in the ground

1 million times greater when operating 100,000 times greater as soon as turned off 10,000 times greater after 2 months 100 times greater after 100 years < 1 times greater after 10,000 years

Doesn’ t include plutonium

SLIDE 47

What to Do with Long Lived Waste

47

• A 1 GW reactor produces 100 tons of waste per year
• Currently have 60,000 tons of waste from existing plants
• Expect another 100,000 tons over lifetime of current reactors
• Storing the 1% of this that is long-lived is the problem

Two options

• Secure all of it for 100,000 years
• Separate out the long-lived elements, only 1% of the

total, and then secure the rest for a few hundred years.

SLIDE 48

Securing all of it

48

Yucca Mountain was supposed to be the US solution

Deep stable geological repository in a mountain in Nevada remote, favorable climate, deep water table Limited by legislation to 70,000 tons. Could store much more After 20 years of intensive work, fell victim of politics Seems to be no hope for long term storage of this scale in US But need storage for 200,000 tons from current reactors

What do we do!!

This is a political not a technical or engineering problem

SLIDE 49

Yucca Mountain

49

SLIDE 50

Reprocessing

50

Fuel can be reprocessed to remove plutonium and other long-lived element Difficult but well established chemical process Several options after that

• Burn them up in a nuclear reactor
• Transmute them to stable isotopes using accelerator beam
• Bury then in long term storage
• Use the plutonium in a nuclear weapon
• only about 1,000 tons of from current reactors
• not very radioactive

France is committed to this option US abandoned it because of nuclear proliferation issues

SLIDE 51

Issues with Nuclear Energy

51

Radiation Safety Waste disposal Cost Resource availability Weapons proliferation

SLIDE 52

Cost vs. Coal

52

Immediately after Three Mile Island, nuclear power became factor of six more expensive Since then costs have come down dramatically

• standardized design
• modular construction
• higher reliability

Nuclear power is now

• n parity with coal

Example: the AP1000 reactor shown in the Power Surge video

SLIDE 53

Issues with Nuclear Energy

53

Radiation Safety Waste disposal Cost Resource availability Weapons proliferation

SLIDE 54

How Long will Uranium Resource Last

54

Estimated to be 3 million tons of uranium in the US 1 GW reactor uses about 200 tons per year US currently has 100 GW of operating capacity (3 million tons) (200 tons per GW/year) x (100 GW)

= 150 years

Uranium is not a long term solution Similar situation for rest of the world

SLIDE 55

Breeder Reactors

55

n + 238U --> 239U --> 239Np --> 239Pu

Use reactor to breed (produce) plutonium from absorption of neutrons by 238U Effectively uses all of the uranium (including 238U) Extends lifetime of fuel resource by factor of 140

Problems:

• widespread availability of plutonium
• proliferation danger
• reactor based on fast (not thermal) neutrons
• could explode as nuclear bomb
• need coolant with low moderation and high het transfer
• molten sodium coolant

SLIDE 56

Breeder Reactors

56

Only four in the world 2 in France 1 in Kazakhstan 1 in Japan US abandoned this technology in the 1970’ s France plans on this for their energy future

SLIDE 57

Two Issues

57

Uranium enrichment Plutonium reprocessing

SLIDE 58

Uranium Enrichment

58

A nuclear reactor requires enriched uranium Any country that can enriched to reactor grade (3%) can also enrich to weapons grade (90%). Just run centrifuges longer 100 tons of uranium must be enriched for 1 year supply of fuel for a 1 GW reactor Only 1 ton of uranium need to be enriched for a nuclear bomb. If you have 1000 centrifuges for making reactor fuel, need only divert 10 of these for making a weapon

SLIDE 59

Plutonium Reprocessing

59

A nuclear reactor produces plutonium Any country with a nuclear reactor has plutonium A 1 GW reactor produces about 200 kg of 239Pu per year This is enough to produce about 100 plutonium bombs

SLIDE 60

Summary of Proliferation

60

A country with uranium enrichment or plutonium reprocessing capability can readily make nuclear weapons It is clear that these capabilities should not be widespread If uranium is to be enriched or plutonium to be reprocessed should be done in a neutral country under UN supervision. Has to be a reliable service that all countries of the world can trust This is a political, not scientific or technical, problem that the world has to solve if there is to be a future for nuclear energy

SLIDE 61

Summary

61

Radiation: not a health issue Safety: will be accidents but nothing like

what we’ve seen. Politically acceptable?

Waste disposal: issue is storing the 1% of waste that has a

long lifetime. This is a political not a technical

• issue. Likely unsolvable

Cost: not now a problem. comparable to coal Resource availability: if to be long term solution need

breeder reactor technology. Expensive, dangerous, leads to proliferation problems

Weapons proliferation: major and real political problem

SLIDE 62

Fusion

62

SLIDE 63

Isotopes of Hydrogen

63

1H

• proton. Most common isotope of hydrogen

2H

proton bound to one neutron. One part in 6000 of naturally

• ccurring hydrogen. Straight forward to extract from water

3H

proton bound to two neutrons. Unstable.

• Radioactive. Half life of 12 years so rare

2H D 3H T

SLIDE 64

Nuclear Fusion

64

A different approach Instead of fissioning a heavy nucleus into lighter

• nes, fusion two lighter nuclei into a heavier one
• Releases 10 times more energy

per weight than Uranium fission

• Fuel is plentiful and readily accessible

(hydrogen or heavy hydrogen)

SLIDE 65

High Temperature

65

In order to get hydrogen to fuse the nuclei must be at high temperature to overcome the barrier due to electrical repulsion. Kind of like pushing something uphill to get it into a valley

need high temperature to push uphill energy released when fall into valley

Temperature needed is about 100 million degrees. Ten times greater than those in the center of the Sun Fusion is the process that fuels the Sun

SLIDE 66

D-D and D-T Reactions

66

The Sun fuses two protons together. Fusing heavy hydrogen requires somewhat less temperature and is much easier approach for a fusion reactor D-D Reaction D + D 3He + n D-T Reaction D + T 4He + n The D-T reaction is the easiest to achieve and will be the first to be demonstrated in a test fusion reaction Tritium does not occur naturally and is somewhat dangerous. Why? A power plant reactor will have to be based on the D-D reaction

SLIDE 67

Advantages of Fusion

67

• Fuel is plentiful readily available
• The deuterium in the heavy water in the world’

s oceans is enough to supply all of the world’ s energy needs for a billion years

• No nuclear waste. The spent fuel is
• helium. The gas in party balloons
• Some activation of the materials of the reactor but this is

negligible compared to the radioactivity from a fusion reactor

• No weapons proliferation issues

This is all fantastic. Now, how do we get it to work

SLIDE 68

Magnetic Confinement

68

Hydrogen in the from of a plasma (gas of charged particles) Plasma confined by a toroidal (doughnut) magnetic field Plasma can also be heated by magnetic field magnetic field Can’ t let plasma touch anything. It will loose all of its heat and become cold

Problem is instabilities.

After very short time loose control of the plasma Huge engineering problem Might be insoluble

SLIDE 69

Fusion Power Plant

69

SLIDE 70

ITER

70

International Thermonuclear Experimental Reactor

Designed to produce 10 times more power than it consumes But only briefly. 500 MW but only for up to 10 minutes Engineering demonstration. Not a power reactor D-T reaction Cost: about $20 billion

SLIDE 71

Timetable for Fusion

71

Joke is that fusion reactors are a great idea but fusion power is always about fifty years away. I would say now it is more like 100 years away. Maybe by 2100

Timeline Date Event 2006-11-21 Seven participants formally agreed to fund the creation of a nuclear fusion reactor.[9] 2008 Site preparation start, ITER itinerary start.[20] 2009 Site preparation completion.[20] 2010 Tokamak complex excavation start.[21] 2011 Tokamak complex construction start.[21] 2015 Predicted: Tokamak assembly start.[12] 2018 Predicted: Tokamak assembly completion, start torus pumpdown.[12] November 2019 Predicted: Achievement of first plasma.[22] 2026 Predicted: Start of deuterium-tritium operation.[22] 2038 Predicted: End of project. ITER Timeline