Submarines and Aircraft Carriers:The Science of Nuclear Power

Science Topic: Physics and Social Science

Matter and Energy: Energy From the Atom

Plot your course to the Arctic Sea!

Use Google Earth or Google Maps to determine the distance in miles from Kitsap Naval Base in Washington state to a secret location in the Arctic Sea.

How long underwater?

• Example calculation:– Assume a cruising speed of 20 knots (23 mph)– If you measured 3,750 miles, the time underwater =

3,750/23 = 163 hours• Most non-nuclear submarines cannot remain

submerged that long!• With nuclear power, a submarine is limited only

by its food supply.

Nuclear power is…

• A method of generating electricity• A means of powering large vessels, such as

submarines and aircraft carriers• Based on a process involving atomic nuclei:

nuclear fission

Matter and Energy: Energy From the Atom

Fission

A loose neutron…

…collides with a uranium atom… …destabilizing it.

Fission splits the atom into two new elements, releasing energy, gamma

rays and additional neutrons.

Chain reaction1. A neutron collides with

a uranium atom.2. The collision releases

energy, and three additional neutrons.

3. Each neutron in turn collides with additional uranium atoms.

Nuclear Fission and Power Plants

Generating Electricity

Labels:•Condenser•Containment structure•Control Rods•Electric Generator•Pressurizer•Reactor Vessel•Steam Generator•Turbine

Containment structure

Pressurizer SteamGenerator

ControlRods

ReactorVessel

Turbine

ElectricGenerator

Condenser

See the reactor in action!

Nuclear reactor safety – explosion?

• Could a nuclear explosion occur?

- critical massThe minimum amount of material needed to sustain an uncontrolled chain reaction, and therefore cause a nuclear explosion.

- purity of U-235Nuclear fuel in a reactor is about 5% U-235. For a weapon, U-235 needs to be about 90% pure.

- an explosion cannot occurThe purity of U-235 in nuclear fuel is too low to sustain an uncontrolled chain reaction

Nuclear reactor safety – waste

• Why is radioactivity dangerous?

- meltdownOverheating of reactor core due to loss of cooling ability or control rod function.

- cell damageRadioactivity causes damages cell components and causes mutations.

- regular operationsAs uranium fuel is used, it and its byproducts are highly radioactive.

To deal with radioactive waste: •Protect workers•Store waste safely

Exponential decay

Negative power relationship

Faster decay

Slowerdecay

Results of half-life activity

• What shape are the observed curves? • Which of the lines, the class average or the group

line, is closest to the theoretical line? Why?• What is the difference in the average time for U-

232 and P-238 groups to use up all their candies? • What does this difference represent?

Radioactive decay

Over each half-life…

…radioactivity is halved…

…then again, and…

…again, and…

Half-life of top 10 fission products

Element Name (symbol) Yield (%)

Half-life

Caesium (Cs 133) 6.8 2.1 years

Iodine (I 135) 6.3 6.6 hours

Zirconium (Zr 93) 6.3 1,530,000 years

Molybdenum (Mo 99) 6.1 65.9 hours

Caesium (Cs 137) 6.1 30.17 years

Technetium (Tc 99) 6.1 211,000 years

Strontium (Sr 90) 5.8 28.9 years

Iodine (I 131) 2.8 8.0 days

Promethium (Pm 147) 2.3 2.6 years

CONCLUSION•Most fission products have relatively short half-lives (< 90 years).

Percent yield is the relative amount of each element resulting from fission of U-235.

BONUS FACT•Seven fission products have very long half-lives. (Only two of those are shown.)

Types of radioactive decay

Type of Decay (symbol)

Cause Particle Emitted Example

Alpha (α) Excess neutrons cause repulsion

Helium nucleus Uranium-238 to Thorium-234

Beta (β) Excess neutrons cause conversion

Electron Hydrogen-3 to Helium-3

Gamma (γ) Nucleus energy too high

Photon Cobalt-60 to Nickel-60

Penetrating power of decay particles

Predicting decay products

• How does alpha decay affect an isotope?

• What is the atomic number and atomic weight of helium?

• What is the new atomic mass and atomic number?

Loss of a helium nucleus

Loss of protons changes the element. Transmutation = change from one element into another

Atomic number = 2 Atomic weight = 2

Subtract 2 protons Subtract 2 neutrons

Predict alpha decay – example

• Problem: an atom of 238U emits an alpha particle, undergoing alpha decay. What is the product of this process?

3. Look up the periodic table.

(In the periodic table, the element with atomic number 90 is thorium.)

2. Subtract values for helium from uranium:Atomic mass = 238 – 4 = 234Atomic number = 92 – 2 = 90

1. Write the equation:

Solution:

Answer: The decay product is thorium-234 (234Th)

Radioactive decay chain

Th Ra Rn Po PbU

Uranium Thorium Radium Radon Polonium Lead

Check the periodic table to find the atomic numbers for each of the elements. Do you see a pattern?

– 1 α particle

How long is radioactive waste dangerous?

• It depends on the half-life of the products of fission and decay

• A few decades to millions of years• It can be made safer if stored properly

Matter and Energy: Energy From the Atom

The Science of Nuclear Power

• Example concepts

alpha particle

chain reaction

critical mass

nuclear fission

gamma rays

half-life

nuclear decay

exponential decay

nucleus

radioactivity

transmutation

nuclear reactor

Copyright© 2013 Discovery Education. All rights reserved. Discovery Education, Inc. is a subsidiary of Discovery Communications, LLC.

Energy yield of nuclear fuel

• Fun factoids! – 1 gram of nuclear fuel provides 1.76 million times

the energy from a gram of gasoline– If your car was nuclear-powered it could travel 5

billion miles to the gallon

Type of Engine

Engine Efficiency

Energy Yield (1g)

Diesel 40 – 50% 5 x 104 J

Nuclear 30 – 40% 9 × 1010 J

At Sea: Submarine Warfare

Essential (Guiding) Questions

• How does a nuclear reactor work?• What are the benefits and risks of nuclear

power?• What are basic terms used in the fields of nuclear

power and nuclear physics?• How are quantitative data related to radioactivity

analyzed?• Can you define the key words?

Key Vocabulary

• alpha particle• chain reaction• critical mass• exponential decay• gamma rays• half-life

• nuclear decay• nuclear fission• nuclear reactor• nucleus• radioactivity• transmutation