Energy and the EnvironmentSecond Edition

Chapter 6:The Promise and Problems of

Nuclear Energy

Copyright © 2006 by John Wiley & Sons, Inc.

Robert A. Ristinen • Jack J. Kraushaar

Introduction

• The terms nuclear energy, radioactivity, radiation, criticality, and meltdown often have a frightening connotation and are not well understood by the general public.

• No new orders have been placed for the construction of reactors in the U.S. since 1978.

• Nuclear reactors are not subject to looking fossil fuel shortages and do not emit CO2, SO2, CO, or particulate matter.

• There are now 104 power reactors operating in the U.S. which produce ~20% of the nation’s electricity.

A Short History of Nuclear Energy

• In the early 1930s, experiments established that the nucleus of the atom was made of neutral neutrons and positively charged protons with negatively charged electrons orbiting around the nucleus.

• In 1938 and 1939, scientists discovered that when bombarded with neutrons, uranium atoms fissioned, or split into two and produced more free neutrons.

• The fission products’ mass is less than the original uranium nucleus. The difference in mass can be related to Einstein’s equation, E = mc2.

A Short History of Nuclear Energy

• The potential for enormous explosive power was realized. Following WWII efforts concentrated on producing nuclear weapons and the first nuclear power reactor was established in 1942 at the University of Chicago.

• The Manhattan Project was centered in labs at Los Alamos, New Mexico; Oak Ridge, Tennessee, and elsewhere and were faced with the task of accumulating the critical mass of 235U needed for a workable bomb.

• The project did eventually produce 3 bombs. One of which was exploded in a test in NM, the other 2 were dropped on Hiroshima and Nagasaki in August 1945.

A Short History of Nuclear Energy

• Following WWII, efforts shifted toward utilizing nuclear reactors for electricity generation and for the propulsion of submarines.

• The first reactor to produce electricity for the general public was constructed in Shippingport, PA in 1957.

• Since 1978, there have been no new orders for the construction of nuclear power plants in the U.S. for various reasons.

Radioactivity

• Uranium and plutonium are the primary radioactive isotopes that are utilized in power plants.

• Beta particle decay involved the emission of an electron.

• Alpha particle emission involves the emission of 2 protons and 2 neutrons (Helium).

• A half-life is the amount of time it takes for the original parent-isotope to decay into its stable daughter-isotope.

Nuclear Reactors

• In a nuclear reactor, the reactor boils water to produce steam to drive a turbine.

• The uranium in the core is usually 3% 235U and 97% 238U.

• Neutron must bombard the uranium at a very low kinetic energy in order to increase the likelihood of fission therefore the neutrons are bounced around in a moderator of water or graphite prior to entering the reactor.

Nuclear Reactors

• Capture of a neutron by 238U results in the formation of 239Pu, another important fissionable nuclear fuel.

• The probability of fission of 239Pu is even greater than that of 235U, therefore as 239Pu builds up in a reactor core, it can contribute to the power of the reactor.

• To control the amount of fission that takes place, control rods often made of boron are used. When fully inserted, the reactor shuts down so as to become subcritical. When extracted, the power level will rise.

The Boiling Water Reactor

• The boiling water reactor (BWR) is the type that is typically used in electricity generating reactors.

• The other type, the pressurized water reactor (PWR) is commonly used in naval propulsion systems such as in submarines.

Uranium Resources

• Most uranium found in the Earth is in the form of U3O8, known as yellowcake.

• At current rates of consumption, the 104 power plants operating in the U.S. will likely use up all uranium resources in about 155 years. However, if all electricity in the U.S. were to be generated using nuclear power that number would be closer to 30 years.

• Breeder power plants make use of the fact that some of the 238U gets converted to 239Pu which can be used as a reactor fuel. This could potentially extend the fuel source to 4200 years.

• In breeder plants, the fission process can occur at high neutron kinetic energies. Molten sodium is commonly used in the moderator.

Environmental and Safety Aspects of Nuclear Energy

• There can be a very small amount of the radioactive materials krypton and xenon into the environment. Radioactive tritium may also be released in small amounts in the discharge water.

• A nuclear power plant can not explode in the way that a nuclear bomb does. However, it is possible for a runaway chain event to produce overheating and meltdown of the core.

• If the cooling system fails, a loss-of-cooling accident (LOCA) can occur. (Three Mile Island) Fukishima

• The release of the movie, “The China Syndrome” was released at about the same time as the incident and helped spark fear of nuclear energy in the minds of the general public.

• Recent studies show that for the 104 plants in operation over 30 years, there is a 1% chance of a large release of radioactive materials.

The Chernobyl Disaster

• On April 26, 1986, an explosion and fire destroyed a reactor of the Chernobyl power plant in the Ukraine.

• The reactor was a boiling-water graphite-moderated reactor, unlike any power reactor in the U.S. The RMBK reactor was designed to produce 239Pu for nuclear weapons as well as electricity generation.

• A combination of design flaws and human error led to the disaster.

Nuclear Weapons

• In order to produce a bomb, the uranium must be highly enriched to about 90% as opposed to 3% with power plants.

• However, highly enriched uranium can be generated in the spent fuel rods of power plants.

• To control the spread of nuclear weapons, a Nuclear Non-Proliferation Treaty was signed by more than 100 countries in 1957-1958.

• Many feel that since nuclear reactors and nuclear weapons started in the U.S. we have a moral obligation to set an example for the rest of the world.

• Nations such as the U.S. and Russia have already stockpiled enough weapons to essentially wipe out civilization as we know it.

The Storage of High-Level Radioactive Waste

• Currently the only feasible method of getting rid of nuclear waste is to place it in deep geological features.

• As of 1999, 40,000 tonnes of spent fuel rods were awaiting disposal.

• In 1982, a Nuclear Waste Policy Act was enacted that called for the disposal of the spent fuel rods. By 1987, a site at Yucca Mt., Nevada was chosen. To this day it has still not been utilized.

Nuclear Fusion as an Energy Source

• Fusion, such as what occurs within the core of the Sun is the opposite process of fission and is the basis for hydrogen bombs.

A Fusion Reactor

• It has not yet been possible to use fusion for practical energy production.

• Theoretical Fusion Reactors