Chapter 12Nuclear Energy

Overview of Chapter 12*

• Introduction to Nuclear Power– Atoms and radioactivity

• Nuclear Fission• Pros and Cons of Nuclear Energy– Cost of Nuclear Power

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

• Radioactive Waste• Future of Nuclear Power

How do we make Electricity?• Need fuel source – – to boil water– to make steam– to turn a turbine– to convert mechanical energy into electrical energy

• Fuel sources = fossil fuels, nuclear

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

How Burning Coal Produces Electricity

How Nuclear Fission ProducesElectricity

How much energy is produced?

• Nuclear power is an extremely rich energy source.

• One gram of Uranium-235 delivers as much energy as 3.5 metric tons of coal!!!

• One in every 5 houses in the U.S. is supplied with nuclear energy.– So what percentage of US

electricity comes from nuclear?

Pollution: nuclear vs. coalPollution Type Nuclear Power

PlantCoal Fired Power Plant

CO2

SOx & NOx

Mercury

Particulates

Thermal

Pollution: nuclear vs. coalPollution Type Nuclear Power

PlantCoal Fired Power Plant

CO2 No YesSOx & NOx No YesMercury No YesParticulates No YesThermal Yes No

Where are Nuclear Power Plants located?

Energy Information Administration

Where are Nuclear Power Plants located?

http://insideclimatenews.org/news/20130924/first-us-nuclear-power-closures-15-years-signal-wider-problems-industry

Introduction to Nuclear Energy• Nuclear energy– Energy released by nuclear fission or fusion

• 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 plants• 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 Radioactivity

• Nucleus – Comprised of protons (+)

and neutrons (neutral)

• Electrons (-) orbit around nucleus

• Neutral atoms– Same # of protons and

electrons

Atoms and Radioactivity

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

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

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

• 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• 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• 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-life• TIME it takes for half of a radioactive element’s atoms to decay,

or change, into a more stable element.• range from a fraction of a second to billions of years – 4.5

billion for uranium 238. • the longer the half-life, the less intense the radiation• each isotope decays based on its own half-life• example: Uranium (U-235) decays over time to Lead (Pb-207)

• Parent Material = original radioactive material• Daughter Product = new, stable material

Radioactive Isotope Half-lives

Calculating 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 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 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:•producing the fuel used in nuclear reactors and•disposing of radioactive (nuclear) wastes

Pros and Cons of Nuclear Energy• Pros– Less of an immediate environmental impact

compared to fossil fuels

Pros and Cons of Nuclear Energy

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

gases emitted– May be able to generate H-fuel

• Cons– Generates radioactive waste– Many steps require fossil fuels (mining and

disposal)– Expensive

Cost of Electricity from Nuclear Energy

• Cost is very high• Expensive to build nuclear power plants– Long cost-recovery time

• Fixing technical and safety issues in existing plants is expensive

• 20% of US electricity is from Nuclear Energy– Affordable due to government subsidies

Radioactive Waste• Low-level radioactive waste-

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

• High-level radioactive waste- – Radioactive solids, liquids, or gasses that give off large amounts

of ionizing radiation

Radioactive Wastes

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

standard (compared to previous 10,000 year standard)

– Possibilities:• Above ground mausoleums• Arctic ice sheets• Beneath ocean floor