Nuclear Energy

“You are meddling with forces you cannot possibly comprehend.”- Marcus, Indiana Jones and the Last Crusade

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Written by James Dauray

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NUCLEAR POWERNuclear technology was developed first as a

weapon.Two atomic bombs were dropped during World War

II – Hiroshima and Nagasaki, Japan. Yields of 15-21 kilotons of TNT.

Additional nuclear tests conducted after World War II were done so at the Bikini Atoll, one of the Marshall Islands in the Pacific Ocean.This was known as “Operation Crossroads”Total of 23 nuclear devices were detonated.The most infamous detonation was code-named

“Castle Bravo”.

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NUCLEAR POWERCastle Bravo was the first test of

a hydrogen bomb. This was the largest nuclear explosion ever set off by the United States, and was much more powerful than expected.Widespread radioactive

contamination was released by this explosion.

Among the contaminated was a 23-man Japanese fishing boat.

The scandal surrounding this test inspired the 1954 movie Godzilla.

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NUCLEAR POWERFollowing the Castle Bravo

detonation, the Partial Test Ban Treaty of 1963 was signed.This banned all nuclear

tests in the atmosphere, underwater, and in space.

Underground testing was still allowed.

The only nuclear powers that did not sign the treaty were China and France.

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NUCLEAR POWERPresident Dwight Eisenhower in 1953, gave a famous speech

to the United Nations entitled “Atoms for Peace”.

“My country wants to be constructive, not destructive.”

“…the United States pledges before you…its determination to help solve the fearful atomic dilemma--to devote its entire heart and mind to find the way by which the miraculous inventiveness of man shall not be dedicated to his death, but consecrated to his life."

The purpose of this speech was to convey that Hiroshima and Nagasaki would not be repeated and that nuclear technology would be used for more peaceful purposes.

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NUCLEAR POWEROptimism for the potential of nuclear

reactors was initially very high. Lewis Strauss, chairman of the Atomic

Energy Commission, predicted that…“Our children will enjoy in their homes

electrical energy too cheap to meter.”

Between 1970-1974, American utilities ordered 140 new reactors.100 subsequently canceled.

Electricity from nuclear power plants was about half the price of coal in 1970, but was twice as much in 1990.

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Most United States nuclear reactors are 20-39 years old, reflecting this initial period of optimism.

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The first nuclear power plant opened in Morris, Illinois in 1960.

Illinois remains the state with the most nuclear reactors.

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How Do Nuclear Reactors WorkMost commonly used fuel is U235, a naturally

occurring radioactive isotope of uranium.Occurs naturally at 0.7% of uranium, but must

be enriched to about of 3% to create a fuel pellet.

Uranium-235

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How Do Nuclear Reactors Work Cont’dFuel pellets are cylinder-shaped (1.5cm

long) stacked in hollow metal rods (4m long).

About 100 fuel rods rods are bundled together to make a fuel assembly.

Thousands of fuel assemblies bundled in reactor core

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• When struck by neutrons, radioactive uranium atoms will temporarily absorb the neutron, then immediately split into two smaller atoms.

• This is nuclear fission, a reaction that releases energy and more neutrons.

• Triggers a nuclear chain reaction, where more and more uranium atoms will split.• This reaction will continue

uncontrolled as long as fuel remains.

Nuclear Fission

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How Do Nuclear Reactors Work Cont’dReaction is moderated in a power plant by

neutron-absorbing solution called a Moderator.

Most reactors use water as a moderator.In addition, Control Rods composed of

neutron-absorbing material are inserted into spaces between fuel assemblies to control reaction rate.

Controlling the Chain Reaction

Control rods

Fuel Assemblies

Withdraw control rods,reaction increases

Insert control rods,reaction decreases

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Pressurized Water Reactors (PWR)Seventy percent of nuclear

power plants are pressurized water reactors.

Water is circulated in a separate line through the core to absorb heat from fuel rods.

Pumped to steam generator where it heats a secondary loop.

Steam from secondary loop drives high-speed turbine producing electricity.

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Kinds of Reactors Cont’dBoth reactor vessel and steam generator are

housed in a special containment building preventing radiation from escaping, and providing extra security in case of accidents.Under normal operating conditions, a PWR

releases very little radioactivity.

Reactor VesselContainment Vessel1.5-inch thick steel

Shield Building Wall3 foot thick reinforced concrete

Dry Well Wall5 foot thick reinforced concrete

Bio Shield4 foot thick leaded concrete with1.5-inch thick steel lining inside and out

Reactor Vessel4 to 8 inches thick steel

Reactor Fuel

Weir Wall1.5 foot thick concrete

Summary: How Nuclear Energy Works

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Radiation dose is measured in a unit called the sievert.

Radiation has both acute and chronic effects.An immediate dose of 1Sv will cause radiation

burns and sickness. More than that can result in death.

Long-term doses can lead to chronic effects such as cancer, sterility, birth detects, etc.

A dental X-ray contains 5 microsieverts.

How is Nuclear Radiation Measured?

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Nuclear AccidentsIn 1979, a movie called “The

China Syndrome” was released.Fictional story about a California

nuclear plant that experienced a near-meltdown of its nuclear core.

The title of the movie is an exaggeration of what happens during a meltdown – the nuclear core becomes so hot that it melts, even melting through the floor of the reactor vessel.

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Nuclear Accidents10 days following the movie’s release, the

Three Mile Island partial meltdown occurred.• Series of failures occurred in the nuclear core.• Relief water valve stuck open, allowing water

(moderator) to escape.• A partial meltdown occurred before the water

was restored.• High amounts of radioactive xenon gas

escaped, mostly went high into atmosphere.

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Nuclear Accidents In April of 1986, a full meltdown occurred at the

Chernobyl nuclear power plant in the U.S.S.R. (now Ukraine).

• The government was concerned over how the reactor would respond to a power failure.

• Backup generators must restore electricity to the pumps.

• Control rods were completely removed to bring the reactor to full capacity.

• At some point, the fission reaction began occurring uncontrollably.

• The control rods were inserted into the reactor core, but a design flaw in the tips lead to a power surge.

• Graphite was used as a moderator. This, when exposed to air, exploded.

Nuclear Disasters

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• 1986: Explosion at Chernobyl Nuclear Plant in Ukraine, U.S.S.R.

• A controlled test of the safety emergency core cooling feature of the reactor was scheduled.

• Concern over what would happen if a power failure occurred – backup generators took ~1 minute to reach full capacity.

• Control rods had been nearly completely removed to put the reactor at full operating power.

• When the test was started, the chain reaction began occurring uncontrollably.

• When this was detected, a shutdown of the reactor was ordered.

• An unknown design flaw in the tips of the control rods caused coolant fluid to be displaced.

• This created an even larger energy spike, overwhelming the reactor containment, causing an explosion and a complete core meltdown.

Chernobyl

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• The design of the Chernobyl plant also did not have an adequate containment building.

• When the graphite moderator exploded, radiation was able to escape directly into the air.

Chernobyl

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• Valery Legasov was in charge of finding out exactly what went wrong and how to deal with the disaster.

• He discovered many unreported flaws in the reactor design, but was pressured not to reveal them.• The workers received

most of the blame.• He committed suicide

on the 2-year anniversary of the disaster.

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AftermathA 30km wide radius surrounding

the reactor is now considered uninhabitable.

Surrounding towns and villages have shown a marked increase in birth defects, and multiple types of cancer, especially thyroid cancer.Most common type of birth defect: Cardiac

degeneration, nicknamed “Chernobyl Heart”

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Radioactive Waste ManagementAbout 100,000 tons of low-level

waste (clothing) and about 15,000 tons of high-level (spent-fuel) waste is stored in the U.S. from reactor usage.

For past 20 years, spent fuel assemblies have been stored in deep water-filled pools at the power plants. (Designed to be temporary)

Many internal pools are now filled and a number plants are storing nuclear waste in metal dry casks outside.

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Radioactive Waste Management Cont’dU.S. Department of Energy

announced plans to build a high-level waste repository near Yucca Mountain, Nevada in 1987.Facility may cost between

$10 and 35 billion; planned to be open in 2010.

Plans to use Yucca have since been halted due to politics and lawsuits.

No long-term storage plan has been accepted by the U.S.