Nuclear Energy

Isotopes Isotopes = 2 atoms of the

same element (same # of protons / atomic # ) that have different numbers of__________.

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Since the number of _________ is different, the isotopes have different __________.

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The number given after the element symbol is the atomic mass.

Examples:

• 3 isotopes of H2O

• Carbon-12 & Carbon-14 (12C & 14C)

• U-235 & U-238

Nuclear Fissionnuclear fission: (fission = to split) a nuclear change in which certain unstable isotopes of high mass numbers split into lighter nuclei & ______________ in the process.

Fission of a uranium–235 nucleus, initiated by a neutron.

Half-Life: The amount of time that it takes half of a radioactive sample to decay.

Determining amount of radioactive isotope remaining

1 half-life ½ (1/21)

2 half- lives ___ (1/22)

3 half-lives ___ (1/23)

4 half-lives ___ (1/24)

Formula: N = No (0.5)t

t= number of half-lives

N = amount left No = original amount

Half-life Comparisons

Radioisotope Half-life

Berillyium-11 13.81 seconds

Iodine-131 8 days

Stronium-85 11 years

Tritium (Hydrogen-3) 12 years

Uranium-235 700 million years

Uranium-238 4.5 billion years

Radioactive DecayUnstable isotopes undergo decay to form other isotopes, & in the process energy is emitted in three forms:

•alpha particles: fast–moving, _______________(= Helium nucleus)

•beta particles: fast–moving, ________________•gamma rays: high–energy__________________

Alpha Decay

Alpha particles can be blocked most easily, since they are _________ than beta particles.

Gamma rays are the most difficult form of radiation to block, since they are not composed of matter, but rather are high frequency electron radiation.

Alpha Decay Animation

Nuclear Fission Video

2 Types of Beta Decay

Beta minus decay: A neutron decays into a __________________ with the electron emitted.

Beta plus decay: A proton decays into a ______ ______________with the positron emitted. (Like an electron, a positron has no significant mass.)

Beta Minus Decay Beta Plus Decay

Discuss with your table partner:

Review the type of particles released in alpha, beta minus and beta plus decay (and what particles breakdown for beta decay). Determine what new isotope would be produced in each of the examples of radioactive decay on the next three slides.

Plutonium-236 (atomic number 94) undergoes alpha decay.

What is the atomic number of the new isotope?

What is atomic mass of the new isotope?

New isotope:

____

____

_________________

Magnesium-23 (atomic # 12) undergoes beta plus decay.

What is the atomic number of the new isotope?

Why?

What is atomic mass of the new isotope?

New isotope:

___

_______________________

___

___________

Carbon-14 (atomic number 6) undergoes beta minus decay.

What is the atomic number of the new isotope?

Why?

What is atomic mass of the new isotope?

New isotope:

__

__

______________________

______________

Radioactive Pathway:

A radioactive isotope can undergo a series of radioactive decay, until a stable isotope is reached.

Increasing wavelength

Increasing frequency and energy

Gamma Rays are very high energy waves with a short wavelength

Radiation Intensity is inversely related to the distance from the source:

Intensity α 1/r2 (r = radial distance from source)

Radioactivity UnitsRadioactivity Absorbed

Dose

Dose Equivalent

Exposure

Common

Units

Curie (Ci) rad rem Roentgen (R)

SI Units Bequerel

(Bq)

Gray (Gy)

Sievert (Sv)

Coulomb/

Kilogram (C/kg)

• Some conversions: 1 Curie = 3.7 x 1010 disintegrations/sec

1 millicurie = 37 megabequerel (1 Bq = 1 disintegration/sec)

1 coulomb/kg = 3880 Roentgen

• Average dose per person/year (US) = 360 mrem/yr (millirem/yr)

• International Standard for safe yearly dose = 5,000 mrem/yr =

5 rem/yr (for people who work around radioactivity)

Sources of Radiation:•Cosmic: from sun and other stars•Terrestrial: decay of radioactive elements in ground. Common decay product is radioactive radon gas

• Food has Carbon 14•Medical: X-rays, CT scans…•Coal plants release some radioactivity

A nuclear chain reaction leads to major release of energy in the form of heat (and light).

Nuclear Chain Reactionsnuclear chain reaction: multiple fissions resulting from a _________ feedback loop in which each fission releases neutrons that cause more fissions to occur.

Nuclear Fission Chain Reaction Video

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Nuclear Energy

Nuclear fission reactors produce electricity from heat released by the fission of uranium–235 or plutonium–239.

• controlled rate of fission by absorbing excess neutrons with _________ & surrounding the reaction core with_______;

•built–in safety features are supposed to minimize the risk of release of radioactive substances or an out-of-control fission reaction.

•Small amounts of radioactive gases

•Uranium •fuel input •(reactor core)

•Control rods•Containment shell

•Waste heat•Heat exchanger

•Steam•Turbine •Generator

•Hot coolant

•Useful electrical energy

• 25%–30%

•Hot water output

•Pump•Pump

•Coolant •Pump •Pump

•Moderator•Cool water input

•Waste heat•Shielding

•Pressure vessel•Coolant passage

•Water •Condenser

•Periodic removal and storage of radioactive wastes and spent

fuel assemblies

•Periodic removal and storage of radioactive

liquid wastes

•Water source (river, lake, ocean)

Nuclear Reactor: Light-Water Reactor

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Nuclear Energy UseIn United States, nuclear energy is declining.

•No new plants since ______ . Although, first permits in decades is underway for two plants.

•Existing plants (105) retired by 2030.

Some other countries are investing increasingly in nuclear energy.

• France gets about 78% of its energy from nuclear power plants.

Nuclear Power Plants in 2005

Japan set a policy to phase out nuclear power by 2040.

Nuclear Accidents: Three Mile IslandOn March 29, 1979, reactor at the Three Mile island nuclear plant near Harrisburg, PA, lost its coolant & the core suffered a _________________.

• 50,000 people evacuated & another 50,000 fled area;

• unknown amounts of radioactive materials were released; an estimated 15-24 curies of I-131

•partial cleanup & payment of damage claims cost $1.2 billion so far;•1997 study concluded that increased cancer rates were caused by released radiation.

Nuclear Accidents: ChernobylOn April 26, 1986, Chernobyl disaster in the Ukraine: a series of explosions in a nuclear reactor flung radioactive debris into the atmosphere.

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Chernobyl• About 400,000 people were forced to leave their homes

• According to a UN report, some 160,000 km2 (62,000 mi2) remain contaminated;

• About 35-49 million Curies of I-131 was released

Chernobyl Zone of Exclusion

The zone of exclusion is _________, which is the size of __________________.

Chernobyl

• In 1998 the Ukrainian health ministry reported 3,576 deaths. However, Greenpeace estimates a total death toll of about 32,000;

• Over half a million people were exposed to dangerous levels of radioactivity;

• The cost of the incident is estimated in excess of $358 billion.

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Nuclear Accidents: Fukishima Dai-ichi• On March 11, 2011, a 9.0 earthquake

hit off the coast of Japan, creating a 13-15 m (43-49 foot) tsunami wave.

• Electricity from Japan’s grid was lost, but emergency generators came on-line to power the cooling systems.

• A tsunami flowed over the 5.7 m seawall at the plant ________________________________________.

• The fuel in the reactors began to over-heat.

• 12 mile exclusion zone

• 80,000 people displaced

• Over 1,600 employees exposed to high levels of radiation.

Nuclear Accidents: Fukishima Dai-ichiThe explosions sent large amount of radioactive elements into the atmosphere

http://www.cbsnews.com/8301-18563_162-57395780/a-rare-look-at-the-fukushima-daiichi-no-go-zone/

Nuclear Accidents: Fukishima Dai-ichi

The coolant leaking out of the cores contaminated ground water and ocean water.

The extent of ocean radiation contamination as of Oct., 2011

•Fuel assemblies •Decommissioning of reactor

•Enrichment of UF6 •Reactor•Fuel fabrication

•(conversion of enriched UF6 to UO to UO2 and fabrication of fuel assemblies)

•Temporary storage of spent fuel assemblies underwater

or in dry casks•Conversion of U3O8

•to UF6

•Uranium-235 as UF6 Plutonium-239 as PuO2 •Spent fuel

reprocessing

•Low-level radiation with long half-life

•Geologic disposal of moderate- and high-level radioactive wastes

•Open fuel cycle today •Recycling of nuclear fuel

Nuclear Fuel Cycle

After 3 or 4 Years in a Reactor, Spent Fuel Rods Are Removed and Stored in Water

Long Term Storage Issues

• Storing nuclear waste is the ultimate NIMBY situation (Not In My Back Yard)

• Until a long-term location is opened, nuclear waste remains stored at ___________________

• Short-term storage involves keeping waste submerged in open pools of water for as long as 5 years and then eventually sealing the waste in steel and concrete casks

• In CA, waste is stored near earthquake faults, and most other plants are located near major water sources, due to the large amount of water that is required for keeping the reactor cores cool

• Many feel that it is dangerous to leave the waste ________ _______________ (i.e. it is vulnerable to terrorist attacks,

accidents, or natural disasters)

Storage of Nuclear WasteStorage of Nuclear Waste

Long-Term Storage of Waste: Yucca Mt. Controversy

Yucca Mountain National Nuclear Repository:• 100 miles NW of Las Vegas on

western edge of the Nevada Test Site

• Repository would be 1000 ft below the top of the mountain and 1000 ft above the ground water.

Yucca Mountain

• $10 billion has been spent so far to build a 5 mile long tunnel in the mountain

• 90% of waste from power plants, 10% from defense programs

• Waste is currently stored at facilities in 43 states

Yucca Mountain

Yucca Mountain Lawsuits• There were many law suits against

Yucca Mountain project. Most cases were dismissed except for the EPA lawsuit on the following grounds:

• EPA was required to keep radiation exposure to safe levels for as long as National Academy of Sciences’ scientists determined the site would have unsafe levels of radioactivity

• Scientists determined the site would be highly radioactive for at least 100,000 years

• EPA would only guarantee site for 10,000 years, and argued that nothing could be guaranteed for longer periods.

Yucca Mountain

• In Sept., 2009, the Obama administration withdrew its application to have the facility licensed in a way that would prevent the Yucca Mountain project from being revived in the future

•Many states, including WA, have filed lawsuits in protest since nuclear waste is currently stored on site.

•The energy utilities want their money that they paid to build Yucca Mountain back.

Nuclear EnergyPros:• U.S. has major reserves of uranium;• lower mining impacts than coal;• ____________________________________

(none in nuclear reactor, some in production of fuel);• no air pollution/acid-forming emissions;

Cons:• high cost; some of cost subsidized by government (esp. _________________________________)

• possible major release of radioactive contaminants;• mining & processing impacts;• storage of radioactive wastes;• possible terrorist attacks• thermal pollution.

Nuclear Fusionnuclear fusion: a nuclear change in which two isotopes of light elements are ______________ to form a heavier nucleus, releasing energy in the process.

A nuclear fusion of helium (He) formed by fusion of two hydrogen (H) nuclei is the source of energy of the ________.