Lesson 4 Plan

Radiation Exposures: Sources, Doses, and Protection

Purpose:

Throughout this lesson, students will review some of the basic concepts covered earlier in Unit 2. Students will also learn more details about the pathways of exposure to ionizing radiation. Then they will learn about the standard techniques and practices for protecting human beings from the negative effects of high levels of radiation, particularly radiation from spent nuclear fuel and high-level radioactive waste. Finally, the lesson explains some of the concepts behind the U.S. Department of Energy’s plans to safely dispose of spent nuclear fuel and high-level radioactive waste in the proposed geologic repository at Yucca Mountain, Nevada.

Concepts:

Radiation is everywhere. It is literally impossible to avoid it.
The average annual background radiation for someone living in the United States is 360 millirem, from all sources, both natural and manmade.
An individual’s annual average dose can vary for a number of reasons, including where he or she lives in relation to sea level, the level of radon rising from the ground, exposure to tobacco smoke, and use of radiation in medical and dental diagnostic and treatment procedures.
Nuclear fuel is a valuable source of energy. The United States gets about 20 percent of its electricity from nuclear power, and about 40 percent of the U.S. Navy’s ships and submarines run on nuclear power.
Nuclear power plants have environmental benefits because they do not emit any greenhouse gases, as do other sources of largescale electricity.
With current technology, after nuclear fuel is used or “spent,” it is highly radioactive. If not properly managed, spent nuclear fuel and other highly radioactive materials pose serious potential health hazards.
Worldwide, there is scientific consensus that burying spent nuclear fuel and high-level radioactive waste in deep geologic repositories is the best way to protect human health and safety, and the environment, from the radioactive risks these materials present.

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Duration of Lesson:

One to three 50-minute class sessions

Objectives:

After participating in this lesson, students will be able to

name the major pathways of exposure to radiation for the average person living in the United States;
discuss the percentages of annual average radiation dose that the typical American receives from various sources;
explain that people who smoke are exposing themselves to remarkably more radiation per year than those who don’t;
provide a basic explanation of “nuclear chain reaction” (or “criticality”);
explain what is meant by “enriched uranium”;
give reasons why plutonium must be tightly controlled;
discuss methods for protecting people from high levels of radiation;
supply some key facts about the physical nature of spent nuclear fuel and the high-level radioactive waste that would be emplaced in a geologic repository at Yucca Mountain, Nevada, should one be licensed, constructed, and operated.

Skills:

Inductive reasoning, deductive reasoning, critical thinking, synthesizing facts, hypothesizing arguments, organizing and presenting ideas to a live audience of peers (optional)

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Vocabulary:

background radiation, criticality, curie, decommissioning, enriched uranium, exposure pathways, fuel rods, global warming, greenhouse gases, high-level radioactive waste, nuclear chain reaction, nuclear fuel assembly, radium, radon, reprocessing, shielding, structural radiation, transportation cask, transuranic, vitrification, zircalloy

Materials:

Reading Lesson: “Radiation Exposures: Sources, Doses, and Protection”

Activity Sheet: “Half-Lives and Spent Nuclear Fuel”

Answer Key: “Half-Lives and Spent Nuclear Fuel”

Background Notes:

“The Periodic Table versus the Chart of the Nuclides” (See Lesson 2 of this unit.)

Suggested Procedure:

Have students read the lesson entitled “Radiation Exposures: Sources, Doses, and Protection.”
Lead a discussion on the reading.
Have students visit the Yucca Mountain Project’s Web site — http://www.ocrwm.doe.gov/ymp/index.shtml — and find fact sheets about spent nuclear fuel and high-level radioactive waste, or about the proposed underground repository at Yucca Mountain, Nevada. Then have students give an oral presentation (individually or in groups) to the class about what they learned from the fact sheets.
Assign students in groups to work out the answers for the activity sheet entitled “Half-Lives and Spent Nuclear Fuel.”

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For Class Discussion:

What are some of the sources of exposure to ionizing radiation for human beings?

(Answers will vary. Correct answers include the following: cosmic radiation; radionuclides, such as carbon-14 and potassium-40, in all food; natural radioactivity in all drinking water; radon from the ground; structural radiation, i.e., radionuclides in building materials such as bricks and granite; medical and dental X-rays; nuclear medicine diagnosis and treatment techniques; television sets and computer monitors.)
What is the annual average radiation dose of someone living in the United States?

(360 millirem.)
What percentage of the typical American’s average annual radiation dose comes from natural background radiation? How much comes from inside the person’s own body? How much from medical and dental diagnosis and treatment procedures?

(About 81 to 82 percent. 11 percent. 15 percent.)
Why do living at higher elevations and flying in a jet plane increase a person’s radiation dose?

(The Earth’s atmosphere is thinner at higher elevations, so more cosmic radiation penetrates it at those elevations. Thus, the higher up in the atmosphere a person is, the more radiation the person is exposed to.)
How could you reduce your exposure from a known external source of ionizing radiation?

(Answers may vary but should emphasize shielding, time, distance, and isolation. For example, students may provide answers such as the following: Wear protective clothing. Increase your distance from the source. Stand behind a shield or protective barrier. If you must be near the source, minimize the exposure time. If it’s a highly radioactive source, such as spent nuclear fuel, having it adequately shielded and isolated from people will reduce the exposure to near zero.)
How would exposure to ionizing radiation be reduced by placing spent fuel in underground repositories such as the proposed site at Yucca Mountain, Nevada?

(Answers will vary. Encourage students to consider the concepts they developed in answering the previous question about protection — i.e., shielding, time, distance, and isolation. The appropriate geologic formation has not been disturbed for many years and will continue to be undisturbed. The repository should be placed in an area away from large populations. The repository will be deep underground, distancing it from the surface. The rocks and soil under which the waste is buried also work as a protective barrier shielding the surface from ionizing radiation.)
What are some key facts about spent nuclear fuel and high-level radioactive waste that the Department of Energy is using in its plans to emplace such materials in a deep geologic repository?

(All radioactive waste will be solid — not liquid. Spent nuclear fuel, by its nature, is solid. High-level radioactive waste from defense activities will be solidified through a process called vitrification i.e., melted and colled into a glass form, before being shipped to a repository. All nuclear waste destined for disposal at a repository will be in the form of solid metals, ceramics, and glass. Spent nuclear fuel and high-level radioactive waste are not explosive. Spent nuclear fuel and high-level radioactive waste are not flammable.)

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Teacher Evaluation of Student Understanding:

Student participation in class discussion and completion of activities will indicate understanding.