Chapter 12Chapter 12Nuclear EnergyNuclear Energy

Overview of Chapter 12*Overview of Chapter 12*

o Introduction to Nuclear Power• Atoms and radioactivity

o Nuclear Fissiono Pros and Cons of Nuclear Energy

• Cost of Nuclear Power

o Safety Issues at Power Plants• Three Mile Island & Chornobyl• Nuclear Weapons

o Radioactive Wasteo Future of Nuclear Power

How do we make Electricity?How do we make Electricity?

o Need fuel source to …

How do we make Electricity?How do we make Electricity?o Need fuel source –

• to boil water• to make steam• to turn a turbine• to convert mechanical energy into electrical

energyo Fuel sources = fossil fuels, nuclear

o Exceptions• solar – converts solar energy into electrical energy• wind – turns turbine itself

How Burning Coal Produces ElectricityHow Burning Coal Produces Electricity

How Nuclear Fission ProducesHow Nuclear Fission ProducesElectricityElectricity

Introduction to Nuclear EnergyIntroduction to Nuclear Energyo Nuclear energy

• Energy released by nuclear fission or fusiono Nuclear fission

• Splitting of an atomic nucleus into two smaller fragments, accompanied by the release of a large amount of energy

• Process used by nuclear power plantso Nuclear fusion

• Joining of two lightweight atomic nuclei into a single, heavier nucleus, accompanied by the release of a large amount of energy

• Process that powers the sun

Atoms and RadioactivityAtoms and Radioactivity

o Nucleus • Comprised of protons

(+) and neutrons (neutral)

o Electrons (-) orbit around nucleus

o Neutral atoms• Same # of protons

and electrons

Atoms and RadioactivityAtoms and Radioactivity

o Atomic mass• Sum of the protons and neutrons in an atom

o Atomic number• Number of protons per atom• Each element has its own atomic number

o Isotope (Greek for “at the same place”)• Different forms of the same element

• have same number of protons• have different number of neutrons

• Some isotopes are radioactive

Examples of IsotopeExamples of Isotopeo Carbon

• Carbon-12: 6 protons & 6 neutrons (stable)• Carbon-14: 6 protons & 8 neutrons (radioactive)

o Uranium• Uranium-235: 92 protons & 143 neutrons

(radioactive)• Uranium-238: 92 protons & 146 neutrons

(radioactive)

Elements which contain at least one stable isotope;Radioactive elements: the most stable isotope is very long-lived, with half-life of over four million years;Radioactive elements: the most stable isotope has half-life between 800 and 34,000 years;Radioactive elements: the most stable isotope has half-life

between one day and 103 years;Highly radioactive elements: the most stable isotope has half-life between one minute and one day;Extremely radioactive elements: the most stable isotope has half-life less than a minute. Very little is known about these elements due to their extreme instability and radioactivity.

Radioactive IsotopeRadioactive IsotopeRadioactive Decay

• Emission of energetic particles or rays from unstable atomic nuclei

o Alpha Decay• Loss of 2 protons and 2 neutrons• Lose four mass units • Lose two atomic numbers – so move to the

left 2 spaces on the periodic table

o Beta Decay• Loss of electron from a neutron• Gain one atomic number - so move right 1

space on the periodic table• Gain no mass units

Half-lifeHalf-lifeo TIME it takes for half of a radioactive element’s atoms to

decay, or change, into a more stable element.o range from a fraction of a second to billions of years –

4.5 billion for uranium 238. o the longer the half-life, the less intense the radiationo each isotope decays based on its own half-lifeo example: Uranium (U-235) decays over time to Lead (Pb-

207)

o Parent Material = original radioactive materialo Daughter Product = new, stable material

Radioactive Isotope Half-livesRadioactive Isotope Half-lives

Calculating Half LivesCalculating Half LivesDRAW PICTURE FIRSTHalf-life l Starting Point ex: 200g of X 1 l 100g 2 l 50g 3 l 25g

Half-life l Starting Point ex: what percent…? 1 l 50% 2 l 25% 3 l 12.5%

Half Life CalculationsHalf Life Calculations

1. How many half-lives will pass by the time a 100g sample of Au-198 to decay to 6.25g?

2. How many half-lives will pass by the time a 60g sample of Co-60 decays to 7.5g?

3. How many half-lives does it take a 180g sample of Au-198 to decay to 1/8 its original mass?

4. If a 700g sample of I-131 undergoes 4 half-lives, how much material remains?

5. What is the half-life of a radioisotope if 1/16 of it remains after 4 days?

6. If 5 half-lives pass, what percent remains of the original radioisotope?

7. What is the half-life of a radioactive isotope if a 500g sample decays to 62.5g in 24.3 hours?

8. How many years would it take for a 1g sample of Krypton-85 with a half-life of 10.4 years to decay to about 31.25mg?

Released Question from ExamReleased Question from ExamUranium-235 has a half-life of 710 million years. If it is determined that a certain amount of stored U-235 will be considered safe only when its radioactivity has dropped to 0.10 percent of the original level, approximately how much time must the U-235 be stored securely to be safe?

A. 7.1 x 106 yearsB. 7.1 x 107 yearsC. 7.1 x 108 yearsD. 7.1 x 109 yearsE. 7.1 x 1010 years

STOP HERE

Nuclear Fuel Cycle

processes involved in:oproducing the fuel used in nuclear reactors andodisposing of radioactive (nuclear) wastes

Pros and Cons of Nuclear EnergyPros and Cons of Nuclear Energy

o ProsPros• Less of an immediate environmental Less of an immediate environmental

impact compared to fossil fuelsimpact compared to fossil fuels

Pros and Cons of Nuclear EnergyPros and Cons of Nuclear Energy

o Pros (continued)Pros (continued)• Carbon-free source of electricity- no Carbon-free source of electricity- no

greenhouse gases emittedgreenhouse gases emitted• May be able to generate H-fuelMay be able to generate H-fuel

o ConsCons• Generates radioactive wasteGenerates radioactive waste• Many steps require fossil fuels (mining and Many steps require fossil fuels (mining and

disposal)disposal)• ExpensiveExpensive

Cost of Electricity from Nuclear Cost of Electricity from Nuclear EnergyEnergy

o Cost is very highCost is very higho 20% of US electricity is from Nuclear 20% of US electricity is from Nuclear

EnergyEnergy• Affordable due to government subsidiesAffordable due to government subsidies

o Expensive to build nuclear power plantsExpensive to build nuclear power plants• Long cost-recovery timeLong cost-recovery time

o Fixing technical and safety issues in Fixing technical and safety issues in existing plants is expensiveexisting plants is expensive

Radioactive WasteRadioactive Wasteo Low-level radioactive waste- Low-level radioactive waste-

• Radioactive solids, liquids, or gasses that give off Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation small amounts of ionizing radiation

o High-level radioactive waste- High-level radioactive waste- • Radioactive solids, liquids, or gasses that give off Radioactive solids, liquids, or gasses that give off

large amounts of ionizing radiation large amounts of ionizing radiation

Radioactive WastesRadioactive Wastes

o Long term solution to wasteLong term solution to waste• Deep geologic burial –Yucca MountainDeep geologic burial –Yucca Mountain• As of 2004, site must meet EPA million year As of 2004, site must meet EPA million year

standard (compared to previous 10,000 standard (compared to previous 10,000 year standard)year standard)

• Possibilities:Possibilities:• Above ground mausoleumsAbove ground mausoleums• Arctic ice sheetsArctic ice sheets• Beneath ocean floorBeneath ocean floor

Radioactive WasteRadioactive Wasteo Temporary storage solutionsTemporary storage solutions

• In nuclear plant facility (require high In nuclear plant facility (require high security)security)

• Under water storageUnder water storage• Above ground concrete and steel casksAbove ground concrete and steel casks

o Need approved permanent options Need approved permanent options soon.soon.

Case-In-Point Yucca Case-In-Point Yucca MountainMountain

o 70,000 tons of high-70,000 tons of high-level radioactive wastelevel radioactive waste

o Tectonic issues have Tectonic issues have been identifiedbeen identified

Types of Waste*Types of Waste*

High-Level Waste•The most dangerous radioactive waste•Spent fuel comes from nuclear reactors (52,000 tons)• liquid and solid waste from plutonium production (91 million gallons).•About 70 percent of the available storage space is now filled with used fuel assemblies at Turkey Point.

Types of Waste*Types of Waste*

Transuranic WasteTransuranic Wasteo Includes clothing, Includes clothing,

tools, and other tools, and other materials materials contaminated with contaminated with plutonium, plutonium, neptunium, and neptunium, and other synthetic other synthetic elements heavier elements heavier than uranium. (11.3 than uranium. (11.3 million cubic feet)million cubic feet)

TypesTypes of Waste* of Waste*

Low and Mixed Low-Level WasteLow and Mixed Low-Level Wasteo Includes radioactive and hazardous wastes Includes radioactive and hazardous wastes

from hospitals, research institutions, and from hospitals, research institutions, and decommissioned power plants (472 million decommissioned power plants (472 million cubic feet)cubic feet)

o Turkey Point produced annually on average Turkey Point produced annually on average about 2,500 cubic feet of low-level waste. This about 2,500 cubic feet of low-level waste. This amount of waste could be contained within an amount of waste could be contained within an area about the size of a 30'x30' room.area about the size of a 30'x30' room.

Uranium Mill Tailings

•Residues left from the extraction of uranium ore (265 million tons).

Types of Waste*