Nuclear PowerRobert Mingey

Catherine Perego

Nuclear Power Nuclear power accounts for 16% of the

world’s energy Although it is not a renewable resource, it is

an important source of energy because it has no carbon dioxide emissions◦ Because of this, it is an important bridge between

the coal and gas energy we use today and the completely clean, renewable energy we are working towards

Timeline of Nuclear History 1898 —Marie Curie (France), a two-time Nobel Prize

winner in Chemistry and Physics, discovered the radioactive elements radium and polonium.  

1899 —Ernest Rutherford (Canada) discovered two kinds of rays emitting from radium. He called the first rays, alpha rays; and the more penetrating rays, beta rays. 

1900 —Frederick Soddy (England) observed spontaneous disintegration of radioactive elements into variants.

1919 —Rutherford (United Kingdom) bombarded nitrogen gas with alpha.  The transmutation of nitrogen into oxygen was the first artificially induced nuclear reaction.

Timeline (cont’d) 1934—Enrico Fermi (U.S. immigrant from Italy) irradiated

uranium with neutrons. He had split the atom, thus achieving the world's first nuclear fission.

1940—A new element (atomic number 94), was found and named plutonium. American physicists confirmed that plutonium was fissionable, thus usable for a bomb.

1942—The first self-sustaining, controlled nuclear chain reaction led by Enrico Fermi (U.S. immigrant from Italy) and other scientists at the University of Chicago.

1951—An experimental breeder reactor (EBR Reactor I, or EBR-I) in Idaho produced the first usable electric power from the atom, lighting four light bulbs.

1953 —The first Boiling Reactor Experiment reactor was built in Idaho.

Timeline (cont’d) 1974—Nuclear Regulatory Commission (NRC) was created to regulate

the nuclear industry. 1979—The accident at the Three Mile Island Unit 2 (TMI-2) nuclear

power plant near Middletown, Pennsylvania, on March 28, 1979, was the most serious in the U.S. nuclear power plant industry's operating history.

1980s—For the first time, nuclear energy generated more electricity than oil in the United States. It surpassed hydropower as the second-largest source of electricity in the US, after coal.

1986—The world's worst nuclear power accident happened at the Chernobyl plant in the former USSR (now Ukraine).

1987—Congress selected Yucca Mountain in Nevada for study as the first high-level nuclear waste repository site.

2006—A survey, in the United States, found a high level of support for nuclear energy among the public; with 68% favoring nuclear energy as one way to generate electricity and 49% stating a need to build more nuclear plants.

2010—President Obama discusses the importance of nuclear power at the State of the Union address.

What is a radioactive element? A radioactive element is any isotope of an element that

is not stable. This is due to an imbalance of charges in the nucleus (either too many or too few protons or neutrons).

A radioactive element emits energy from the nucleus to get back down to a more stable energy. This is called radioactive decay.◦ There are 5 types of radioactive decay (α-particles, β-particles,

γ-rays, positron emission, and electron capture) The radioactive elements decay until they reach a more

stable nucleus. The time it takes for half of the sample of the radioactive isotope to decay is called a half-life. If an isotope has a shorter half-life, it is more reactive, thus emitting particles into the atmosphere more frequently. This poses a greater threat to the people around it.

Nuclear Fission Nuclear fission is the process of splitting atoms. Let's discuss

those reactions. In each of the previous reactions, 1 neutron splits the atom.

When the atom is split, 1 additional neutron is released. This is how a chain reaction works. If more U-235 is present, those 2 neutrons can cause 2 more atoms to split. Each of those atoms releases 1 more neutron bringing the total neutrons to 4. Those 4 neutrons can strike 4 more U-235 atoms, releasing even more neutrons. The chain reaction will continue until all the U-235 fuel is spent. This is roughly what happens in an atomic bomb. It is called a runaway nuclear reaction.

In a nuclear power plant, this reaction is controlled using control rods filled with boron and cadmium, two elements that absorb neutrons. They are lowered into the reaction as necessary to maintain a high enough level of neutrons to continue the chain reaction without having them get out of control, causing a runaway nuclear reaction.

Nuclear Fuel Cycle Uranium is collected from mines and mills It is then converted into uranium

hexafluoride—UF₆, which is highly toxic This compound makes it simpler to separate

the uranium isotopes to extract U-235, which is easily fissionable. The concentration of U-235 goes from .4% to 3-5%

This is then transformed into uranium oxide (UO₂), which is used in the fuel rods in the power reactors

How does Nuclear Power Work? The splitting of the atoms, nuclear fission, is

a high energy exothermic process (gives off a lot of heat). This heat is then used to boil water to create steam, which then spins the turbines, which then powers the generator to produce electricity.

Nuclear Reactor Designs

There are two main types of nuclear reactors, boiling water reactors (BWR) and pressurized water reactors.

PWR

PWRs keep water under pressure so that it heats but does not boil. Water from the reactor and the water that is turned into steam are in separate pipes and never mix.

BWR

In BWRs, the water heated by fission actually boils and turns into steam to turn the generator. The rest of the generation process is the same in both types of plants.

Spent Fuel Once the fuel does not contain a high

enough concentration of U-235 to sustain a fission reaction, the fuel rods are replaced. These are called spent fuel.

The spent fuel is still very radioactive, which causes an issue with how to dispose of it.◦ For the first few years after a fuel rod is spent, it is

submerged in a deep pool because the water acts as a barrier to the radiation. Afterwards, it is transferred into special casks made of concrete.

Environmental Issues

Direct nuclear power generation does not emit C02, Sulfur Dioxide, or Nitrogen Oxides.

Wells-to-Wheels approach reveals some greenhouse gas emission.

Air Quality

Nuclear power plants use large quantities of water for steam production and for cooling.

Heavy metal and salts can be found in plant water.

Some pollution results from mining.

Water Pollution

Waste Disposal 2000 Metric tons of

waste created per year in US.

25-30 Tonnes per plant per year

Waste stored on site

Can leak-cause environmental damage

Yucca Mountain Located in Nevada, 80

miles NE of Las Vegas

Set to be national store of radioactive waste

Set to open in 1997 but legal challenges have delayed it to 2020 or beyond

Proven Reserves: 3-4 million tonnes Uranium

Equivalent of 50 years of fuel

Fast breeder reactors might increase efficiency.

Uranium is non-renewable

Sustainablity

Social Consequences

1950’s: Public Expected new Nuclear Age

80’s/90’s: Two accidents change public opinion Three Mile Island Chernobyl

2010: President Obama promises to increase public utilization of nuclear power.

Social Problems

Occurred March 28, 1979

TMI-2 reactor melted down

No deaths directly associated with incident.

Estimates are that the average dose to about 2 million people in the area was only about 1 millirem.

Three Mile Island

Chernobyl Occurred April 26,

1986 Reactor meltdown

leaks massive amounts of radiation

Over 300,000 people evacuated from surrounding area

30 died directly while 4000 more died due to cancer

Fear of terrorist attack

Nuclear proliferation

Other Issues

Nuclear plants have high capital costs compared to other types of plants◦ Nuclear: $0.067 per kWh◦ Coal: $0.042 per kWh

Carbon taxes and rising fuel prices might shift this balance

Economics