NUCLEAR ENERGY

CHAPTER 12

NUCLEAR POWER PLANT SALEM, NEW JERSEY

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

NUCLEAR ENERGYNUCLEAR ENERGY

Introduction to nuclear energy

• It is the energy released by nuclear fission or fusion.

• Fission: the splitting of atomic nucleus into two smaller fragments, accompanied by the release of large amounts of energy.

• Fusion: the joining of two lightweight atomic nuclei into a single heavier nucleus, accompanied by the release of a large amount of energy.

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– Usually an atom has an equal number of neutrons

and protons– If the number of neutrons is greater than the

number of protons = isotope

Radioactive decay

• The emission of energetic particles or rays from unstable atomic nuclei; includes positively charged alpha particles, negatively charged beta particles, and high-energy, electromagnetic gamma rays.

• Forms of a single element that differ in atomic mass are known as isotopes. The unstable isotopes are called radioisotopes.

Contd..

• Radioisotopes are radioactive because they spontaneously emit radiation, a form of energy consisting of particles. As a radioactive element emits radiation, its nucleus changes into the nucleus of a different, more stable element. This process is called radioactive decay.

• For example, the radioactive nucleus of one isotope of uranium, U-235, decays over time into lead (Pb-207).

• The time taken required for one half of the total amount of a radioactive substance to change into a different material is called its radioactive half-life.

• Each isotope decays based on its own half-life years, days, hours, minutes

Radioactive Isotope Half-lives

Uranium Ore

• Non renewable resource found in limited amounts in sedimentary rocks in Earth’s crust.

• The processes involved in producing the fuels used in nuclear reactors and in disposing of radioactive (nuclear) wastes is known as nuclear fuel cycle.

• In the United States uranium is found in Wyoming, Texas, Colorado, New Mexico, and Utah.

Uranium

CANADA

Australia

South Africa

Nuclear Fuel cycle

Deep geologic disposal of spent fuel is currently under study in several countries including the United States.

• Nuclear Fuel Cycle– processes involved

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

* Enriched Uranium

Enrichment

• The process by which uranium ore is refined after mining to increase the concentration of fissionable U-235 is called enrichment.

• After enrichment, the uranium ore is processed into small pellets of uranium dioxide, each pellet contains the energy equivalent of a ton of coal.

• Nuclear Reactor: A device that initiates and maintains a controlled nuclear fission chain reaction to produce energy for electricity

Which country generates the highest % of its electricity from nuclear power plants?

• France 79%• Lithuania 70%• Slovakia 56%• Belgium 56%• Ukraine 49%• Sweden 47%• S Korea, Bulgaria, Slovenia, Finland, Hungary all above

33%• Nuclear Power: Second largest source of USA electricity,

what % does it supply? 20% of USA Electricity

Nuclear Fission

The fission of U-235 releases an enormous amount of heat, used to transform water into steam, the steam is used to generate electricity. Production of electricity is possible because the fission reaction is controlled.Nuclear bombs make use of uncontrolled fission reactions.

If the control mechanism in a nuclear power plant were to fail, will a bomb like explosion take place?

• It will not take place because nuclear fuel only has 3-5% U-235, whereas bomb grade material contains at least 20% and is usually about 85 to 90% U-235.

• In the highly unlikely event of an uncontrolled fission reaction, an immense amount of heat could be generated. However, the reactor vessel and massive concrete containment building are designed to contain the heat along with the attendant radioactivity.

NUCLEAR FISSION REACTORSPellets placed inside 12’ Fuel RodsThe fuel rods are then grouped into square fuel assemblies. (200)

Can be 50,000+ fuel rods per Nuclear Rector

Fuel Rods

Replaced every 3 years

103 Nuclear Power Plants

103 x 50000 rods

5, 000,000 spent fuel rods produced every 3 years.

How Electricity is Produced

REACTOR CORE

STEAM GENERATOR

TURBINE

CONDENSOR

PARTS

ENERGY vid

How electricity is produced from conventional Nuclear Fission

• Four main parts of a typical nuclear power plant• The reactor core (fission occurs here)• The steam generator(heat produced by fission is

used to produce steam from liquid water in the steam generator)

• The turbine (uses the steam to generate electricity• The condenser – cools the steam and converts it

back to liquid.

Role of control rods in the nuclear reactor

• The reactor core contains the fuel assemblies. Above each assembly is a control rod, made of a special metal alloy that absorbs neutrons.

• The plant operator signals the control rod to move up or down into the fuel assembly.

• If the control rod is out of the fuel assembly, free neutrons collide with uranium atoms in the fuel rods, and fission takes place. If the control rod is completely lowered into the fuel assembly, it absorbs the free neutrons, and fission of uranium no longer occurs.

Refer to page numbers 263 and 264 to know more about water circuit in the nuclear reactor.

How Electricity is Produced

REACTOR CORE

STEAM GENERATOR

TURBINE

CONDENSOR

PARTS

ENERGY vid

kWh

A 100 watt light bulb left on continuously for an entire year consumes 876 kWh.

To produce 876 kWh requires

lbs. of COAL876

lbs. of natural gas377

lbs. of oil508

lbs. of enriched Uranium0.0007

Breeder Nuclear Fission• A type of nuclear fission in which non-

fissionable U-238 is converted into fissionable Pu-239

Because it can use U-238, plutonium based breeder fission can generate much larger quantities of energy from uranium ore than nuclear fission using U-235

Risk involvedRefer page 264,265

Mixed oxide fuel (MOX) and Spent fuel

• MOX: a reactor fuel that contains a combination of uranium oxide and plutonium oxide. The plutonium can come from reprocessed spent fuel or from other plutonium stockpiles, including dismantled weapons.

• Spent fuels: the used fuel elements that were irradiated in a nuclear reactor.

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(spent fuel, radioactive

coolant fluids and other gases in the reactor which are radioactive)

– Many steps require fossil fuels (mining and disposal)– Expensive

Cost of Electricity from Nuclear Energy

• Cost is very high……….• 20% of US electricity is from Nuclear Energy– Affordable due to government subsidies

• Expensive to build nuclear power plants– Long cost-recovery time

• Fixing technical and safety issues in existing plants is expensive

Safety Issues in Nuclear Power Plants

At high temperatures the metal encasing the uranium fuel melts, releasing radiation; this is known as a meltdown.The water used in a nuclear reactor to transfer heat can boil away during an accident, contaminating the atmosphere with radioactivity.

Probability of meltdown or other accident is lowPublic perception is that nuclear power is not safeSites of major accidents:

Three Mile IslandChernobyl (Ukraine)

NUCLEAR POWER PLANT SAFETY

Three mile island Chernobyl

Three-Mile Island

• 1979- most serious reactor accident in US• 50% meltdown of reactor core– Containment building kept radiation from escaping– No substantial environmental damage– No human casualties

• Elevated public apprehension of nuclear energy– Led to cancellation of many new plants in US

http://video.google.com/videoplay?docid=-251372048648239449

Chernobyl

• 1986- worst accident in history

• 1 or 2 explosions destroyed the nuclear reactor– Large amounts of

radiation escaped into atmosphere

• Spread across large portions of Europe

Chernobyl

• Radiation spread was unpredictable

• Radiation fallout was dumped unevenly

• Death toll is 10,000-100,000

Video clip

http://www.youtube.com/watch?v=bSRC1_OZPIg Chernobyl disaster.

Nuclear Energy and Nuclear Weapons• 31 countries use nuclear energy to create

electricity• These countries have access to spent fuel

needed to make nuclear weapons• Safe storage and handling of these weapons is

a concernThe bomb of about 50 megatons was code named Ivan by its developers. This bomb is tested in Novaya Zemlya an island in the Arctic Sea on October 30, 1961

IVAN

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

Nuclear waste/Radioactive waste

• 1982 Nuclear Waste Safety Act• Find a site to store waste and make

operational by 1998.• The Low Level Radioactive Waste Policy Act,

passed in 1980, specified that all states are responsible for the waste they generate, and it encouraged states to develop facilities to handle low-level wastes by 1996.

Read public and expert attitude towrd nuclear energy Page number 274

Case-In-Point Yucca Mountain• In 1987 Congress identified

Yucca Mountain in Nevada.• 70,000 tons of high-level

radioactive waste• Tectonic issues have been

identified

WHY YUCCA MOUNTAIN

Radioactive Waste• Temporary storage solutions– In nuclear plant facility (require high security)• Under water storage• Above ground concrete and steel casks

• Need approved permanent options soon.

Decommissioning Nuclear Power Plants

• Three options exist when a nuclear power plant is closed: a) storage, b) entombment, and c) decomissioning.

• If an old plant is put into storage, the utility company guards it for 50 to 100 years, while some of the radioactive materials decay.

• Permanently encasing the entire power plant in concrete, a viable option, a the tomb would have to remain intact for at least 1000 years.

• To dismantle an old nuclear power plant after it closes is called decommission.

MEDICINE largest man-made source of radiation is medical diagnosis and treatment

(includes X-rays, nuclear medicine and cancer treatment)

More than 28,000 American doctors use radiation

virtually every U.S. hospital has some form of nuclear medicine unit

10 million nuclear medicine patient procedures each year

One radioactive isotope, molybdenum-99, is used about 40,000 times each day, to diagnose cancer and illnesses

Food Processing and Preservation

Irradiation kills bacteria, parasites and insects in food—including listeria, salmonella and potentially deadly E. coli—and retards non-microbial spoilage of certain foods, increasing their shelf life. The World Health Organization in 1992 called food irradiation a "perfectly sound food-preservation technology."

The head of the group's food safety unit said irradiation is "badly needed in a world where food-borne diseases are on the increase and where between one-quarter and one-third of the global food supply is lost post-harvest." The United States is among more than 35 countries that permit irradiation of certain foods. Since the 1960s, NASA has included irradiated food on its space flights. In 1963, the U.S. Food and Drug Administration approved the irradiation of wheat, flour and potatoes; in 1983, spices and seasonings; in 1985, pork; in 1986, fruits and vegetables; in 1990, poultry; and in 1997, red meat.

Industrial Applications

Most Common Human Exposure to Radiation??

Terrestrial Radiation

Carbon -14

Thorium-223

Uranium-238

Polonium-218

Radon-222

Cosmic Radiation

High energy photons

Higher the altitude the Higher the exposure

Other Exposures: bricks, stones, cement,(all sources of radon and uranium ores) then there is tobacco….

Fusion• Fuel= isotopes of hydrogen

Fusion

• Way of the future??– Produces no high-level waste– Fuel is hydrogen (plenty of it!)

• Problems– It takes very high temperatures (millions of degrees) to make

atoms fuse– Confining the plasma after it is formed. At extremely high

temperatures, a gas separates into negative electrons and positive nuclei. This superheated, ionized gas, called plasma.

• Scientists have yet to be able to create energy from fusion