Environmental Geology
Geol 406/506

Module 10
Radioactive Waste Management

Reading Assignment:  Read Chp.15, Section 15.3 (pp. 429-433) in Keller and Chapter 12, Section 12.5

E-mail your three tasks to:  hughscot@isu.edu

I. INTRODUCTION TO RADIATION

Radiation is everywhere. It is a form of energy. Radiation is produced when the nucleus of an atom is broken apart. Huge amounts of energy are stored in the nucleus. When it splits (called fission) it produces heat and radiation. Nuclear power plants use the heat to turn water into steam and produce electricity. The radiation, and any radioactive materials generated are considered to be waste products. More than four-fifths of the radiation we receive comes from natural sources. This is called background radiation because it is present everywhere, all the time.   Radioactive atoms are often called radionuclides.

A QUICK FACT: Water acts as a natural barrier to radiation and can be used to isolate radioactive spent nuclear fuel assemblies at nuclear power stations.

Half-life diagram showing the decay equation

When atoms split apart naturally it is called decay.  Decay happens because certain elements have unstable nuclei - a situation occurring because they have a whole lot of neutrons and so the nuclear forces are not balanced.  When an atom decays it can form a different isotope of the same element (i.e. it loses neutrons) or it can become a new element (i.e. it loses protons). It is important to realize that, just because atoms have experienced one decay, it does not mean that they are no longer radioactive.  Some elements decay multiple times and go through a series of elements that are all radioactive.  Eventually though, enough time will pass and a stable elemental form will be reached. 

An example of this is the decay series of which Radon Gas is an intermediate.  This series has multiple decay steps from the original Uranium atoms to final, stable lead isotopes. (this is discussed in detail in Module 11 - Environmental Health).

One important property of radioactive elements is half-life.  Half-life is defined as the amount of time it takes for one half of all of the atoms of that element to experience a decay.  Because you are halving the number of atoms each time, the amount of atoms of a particular element (and so the total number of decays) decrease exponentially!  N is the number of decays/second (or atoms) at a particular time t. No is the initial amount.  Lambda is a decay constant. 

As an example, lets say you start with 1000 atoms of a radioactive element that has a half-life of 10 years.  In 10 years you will have 500 atoms; in 20 years you will have 250 atoms; in 30 years you will have 125 atoms and so on...until they have all decayed.

Half-life is an extremely important property of radiation.  It is used to determine how long a particular radioactive species will remain radioactive.  That is, it tells how long that species may present a danger to human health and the environment. 

Half-life varies widely from element to element.   For example Uranium-235 has a half-life of 704 million years while Oxygen-9 has a half-life of only 26.9 seconds! Half-life is an important consideration when attempting to determine how to dispose of a particular radioactive waste.  This is because the waste must be contained for as much time as it takes to render it harmless.  In general, a radioactive species is considered to be harmless when it reaches background levels - usually after about 10 half-lives.

A thought: based on the extremely long half-lives of certain elements, will it ever be possible to store them long enough to prevent them from causing harm?

Radiation is a natural part of our every day lives. There are all kinds of sources of radiation.  Some of these are:

• RADON GAS - this is a significant natural source.
• COSMIC RAYS - can act on nuclei in the atmosphere to produce radionuclides.
• COMBUSTION OF FOSSIL FUELS - fly ash, produced during the combustion of coal, contains a significant amount of radionuclides, even more than an equivalent nuclear power plant!
• NUCLEAR REACTORS/REPROCESSING SPENT FUEL - this is a significant source of Krypton-85 in the atmosphere.
• NUCLEAR WEAPONS - the above ground detonation of nuclear weapons releases tremendous amounts of radionuclides into the atmosphere.

• In addition, people are exposed to radiation from manufactured sources such as color televisions and smoke detectors.

Radiation can occur either as high speed particles or as waves. Non-ionizing radiation is low energy radiation and cannot alter atoms. Examples of non-ionizing radiation are microwaves, infrared, and visible light. Ionizing radiation is high energy radiation that is capable of altering atoms.

There are several forms of ionizing radiation.

• ALPHA PARTICLES (a)
  The slowest, least energetic type. They do not travel far, and can be blocked by almost anything. In general alpha particles cause damage only if inhaled or swallowed.
• BETA PARTICLES (b)
  Are more energetic. Beta particles can pass through cloth or paper, but can be stopped by a sheet of foil, or glass. Like alpha particles, beta particles generally are harmful only if inhaled or swallowed. For example, Radon gas emits beta particles, and is harmful because it is inhaled.
• GAMMA RAYS (g)
  Are the most energetic, and dangerous. These are rays, not particles and they can pass through almost anything. It takes very, very thick concrete, lead or steel to block gamma rays. This type of radiation is dangerous and damaging.

Each radioactive element
emits its own characteristic
form of radiation.

How is Radiation measured?

Radiation is measured in a number of ways, all of which are based on how much damage is done
to living organisms:

• ROENTGEN - a measure of the amount of radiation in the environment.
• RAD - a measure of the amount of radiation absorbed by something (such as human tissue).
• REM - a measure of the actual biological effect of absorbed radiation. REMs are usually reported as millirems which is 1/1,000 of a REM. Some common dosages are:
  Chest X-ray = 10 millirems
  Mammogram = 30 millirems
  Household Radon gas = 200 millirems/year (average)
• CURIE - a measure of radioactivity. This means that it measures how fast a substance is decaying (emitting radiation). One millicurie = 37,000,000decays/second

An average American's exposure to radiation is about 360 millirems per year. Roughly 300 millirems come from natural sources of radiation; 60 millirems come from man-made sources, primarily medical procedures.  People frequently receive far more than the average of 360 millirem per year due to a variety of other exposures such airplane travel, dental and medical x-rays, and occupational exposure. Geography is important in determining how much radiation a person receives. Background radiation varies from state to state.

Less than one millirem per year comes from the use of nuclear power!

Exposure limits are set by the U.S. National Council on Radiation Protection and Measurement, the International
Commission on Radiation Protection, and the International Atomic Energy Agency. The maximum acceptable exposure level per year has been set at 2 REMS (2,000millirems) at work and 0.1 REMS (100millirems) for the general public.

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II. TYPES OF
RADIOACTIVE WASTE

There are four general categories of radioactive wastes: low level, high level, transuranic and mixed.

• LOW LEVEL WASTES - do not present a significant hazard.  They emit low levels of radiation, usually in the form of alpha particles, and generally have short half-lives.  These wastes tend to be suitable for burial given a 500 year containment.  Some examples of low level waste are solution residuals from processing operations, contaminated equipment, contaminated clothing etc.  The historically preferred method for disposing of low level waste s was dilute and disperse.  This is no longer an acceptable practice.
• HIGH LEVEL WASTES - These wastes are very radioactive and present a real threat to human health and the environment. They tend to be beta or gamma (or both) emitters. High level wastes are problematic to store, contain and dispose of.  Examples of high level wastes are the fission byproducts in spent fuel rods and fuel assemblies from nuclear reactors such as Krypton-85 (gamma and beta emitter;half-life=10.72 years), Strontium-90 (beta emitter;half-life=29.1 years) and Cesium-137 (gamma emitter;half-life=30.17 years).
• TRANSURANIC WASTE - Transuranic wastes can be low level, high level or both, and consist of radioactive materials with atomic numbers greater than 92 (they have greater than 92 protons).
• MIXED WASTE is another type of radioactive waste. It is a combination of radioactive and hazardous waste (for regulatory purposes these are taken as two different things).

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III.  LEGISLATIVE HISTORY OF RADIOACTIVE WASTE MANAGEMENT

In 1954 Congress passed the Atomic Energy Act. The purpose of this act was to ensure the proper management of source, special nuclear and byproduct radioactive materials.  The Act also created an oversight committee called the Atomic Energy Commission (AEC) that has jurisdiction over these materials.

• SOURCE - U, Th, or any other material that is determined by the AEC to be a significant source of radioactivity.   In particular, they regulate ores containing U, Th or other radioactive species in concentrations high enough to be useful for the manufacture of nuclear power or nuclear weapons
• SPECIAL - any radioactive material that the AEC designates as significant enough to regulate, but that is not source material
• BYPRODUCT - any other naturally radioactive material , or material made radioactive via exposure to a radiation incident produced during such processes as the manufacturing of weapons, reactors, mining source material etc.

In 1974 the Energy Reorganization Act separated the AEC into the Nuclear Regulatory Commission (NRC) and a committee which evolved into the Department of Energy (DOE) under the Department of Energy Organization Act of 1977.  The growing problem of what to do with radioactive wastes led to the Nuclear Waste Policy Act of 1982.  This Act provided for development of long term waste storage/disposal facilities (see below).

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IV. DISPOSAL OF
RADIOACTIVE WASTES

Radioactive wastes are being generated daily.  The problem of what to do with these wastes has yet to be solved.  As such most of the waste is being stored on-site until some kind of permanent disposal facilities can be constructed. Look at a figure that shows a partial distribution of interim storage facilities in the United States.

For a good overview of some disposal possibilities being considered for low level wastes CLICK HERE!

A wide range of factors must be considered when evaluating an area for a potential radioactive waste disposal site.  Geology and hydrogeology must all be studied just as with hazardous waste disposal.  The following steps must be taken during the evaluation process:

1. Identify potential sites
2. Exploration phase - surface and subsurface mapping (check for faults, bed forms, layers and so on).   What is there that could be problematic or useful?
3. Predict the future behavior of the site (what indications are there of recent seismicity, etc.?)
4. Evaluate risks - what would happen if the waste got free?
5. Make a final decision - this is the political aspect!

Characteristics of a potentially useable site

Here are some characteristics of a potentially useable site:

1. Low precipitation
2. Deep water table
3. Modest soil hydraulic conductivity
4. Slow moving groundwater
5. High ion absorption potential.  For example, zeolites have a very high cation exchange capacity.
6. Homogeneous geology
7. Topography/Soils that minimize erosion
8. Absence, or near absence, of exploitable resources in the area
9. Absence of surface waters
10. Low possibility of tectonic movement
11. Adequate buffer zone ( in case the waste gets loose).

In 1982, the United States Congress established the Nuclear Waste Policy Act to address the problem of nuclear waste management and long-term disposal of wastes. The Act committed the Department of Energy (DOE) to finding sites that could safely store nuclear wastes for at least 10,000 years.  Potential sites were examined in 36 states. Of these only a handful were selected for consideration, and of these only two were selected for intensive study: one at Yucca Mountain, Nevada and one near Carlsbad, New Mexico.  The Yucca Mountain site is being studied as a potential storage/disposal facility for high level wastes.  The site near Carlsbad is already being developed to store low level wastes. The facility being constructed is called WIPP - the Waste Isolation Pilot Plant.

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V. YUCCA MOUNTAIN

For the most current
Yucca Mt. information GO TO:
DOE's Yucca Mountain web site

Yucca Mountain is located in southwestern Nevada, northwest of Las Vegas and not too far from the Nevada Test Site. The area is being considered as a possible repository for two types of high level radioactive waste:

1. Waste from nuclear power plants

2. Any other high level waste suitable for vitrification (vitification means to turn it into glass).

Before Yucca Mountain can become a nuclear waste repository, a facility operation license must be issued to DOE by the Nuclear Regulatory Commission. DOE is expected to apply for this license by 2001. The evaluation of the site for long-term isolation of radioactive wastes is an intensive, multi-disciplinary process. Extensive investigations are required to develop hydrogeologic, tectonic, thermo/mechanical, and geochemical models. These models provide data by which the future performance of the repository can be assessed. Natural events and processes that might occur thousands of years into the future must be predicted, account must be made of the inherent uncertainties involved, and all these studies must be done within a highly controlled regulatory environment. 

AS YOU CAN GUESS
THIS IS A SLOW PROCESS!

VIEW A LIST OF USEFUL WEB SITES ON THE YUCCA MOUNTAIN NUCLEAR WASTE REPOSITORY

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VI. WIPP

For an outstanding overview
of WIPP visit the:
Environmental Health
Center WIPP Web Site

For the most current
WIPP information GO TO:
DOE's WIPP web site

The Waste Isolation Pilot Plant is being constructed in a salt bed formation.  It is 650meters deep, and has about 56 storage rooms each of which is about 100meters long. 

The advantages to using a salt bed formation as a disposal site for low level radioactive wastes are as follows:

1. Layers are bound in definite, confined strata.

2. The salt layers are generally very dry, and when dry are highly impermeable. 

3. Fractures that may develop are self-healing.

4. High compressive strength and ability to resist deformation.

5. High shielding capacity for radiation (like concrete or lead).

6. Generally located in areas of low seismicity.

7. Are relatively abundant .   

Disadvantages include:

1. A low capacity to absorb radionuclides.
   
2. May contain liquid brine pockets.
   
3. Over time, salt flows (this is called rheology).

Why not use a salt dome? Because they move! Salt domes are continually rising and migrating because they are less dense then the rocks surrounding them.

ADDITIONAL WEB SITES
OF INTEREST

Bikini Atoll Homepage
http://www.bikiniatoll.com/

Department of Defense
http://www.defenselink.mil/

Department of Energy
http://www.energy.gov/

Facts about Chernobyl
http://www.belarusguide.com/chernobyl1/chfacts.htm

Hiroshima: the atomic bomb decision
http://www.dannen.com/decision/index.html

INEEL
http://www.inel.gov/

Meltdown at Three Mile Island
http://www.pbs.org/wgbh/amex/three/

Nuclear Regulatory Commission
http://www.nrc.gov/

Radiation Reassessed: health effects learned from Chernobyl and Three Mile Island
http://whyfiles.news.wisc.edu/020radiation/index.html

Remembering Nagasaki
http://www.exploratorium.edu/nagasaki/

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VII.FOCUS IN ON THE
Idaho National Engineering
and Environmental Laboratory (INEEL)

READING ASSIGNMENT: The textbook Rocks, Rails and Trails found on the Digital Atlas of Idaho Web Site has great information about Southern Idaho. Focus in on INEEL by reading Rocks, Rails and Trails see pp. 30a-31 and chapter 20.

Visit the Idaho National Engineering
and Environmental Laboratory  HOMEPAGE

THE INEEL CITIZEN'S INFORMATION HOTLINE NUMBER IS: 1-800-708-2680

Facilities at the INEEL are used in the development of peacetime atomic-energy applications, nuclear safety research, defense programs, and advanced energy concepts. Liquid radionuclide and chemical wastes generated at these facilities have been discharged to onsite infiltration ponds and disposal wells since 1952; use of disposal wells was discontinued in 1984.

• WHAT KIND OF IMPACTS DOES THE INEEL HAVE ON THE SNAKE RIVER PLAIN AQUIFER?
• WHAT KIND OF GEOLOGIC HAZARDS EXIST THAT MAY POSE A THREAT TO SAFETY AT THE INEEL?

MODULE OVERVIEW

See Module Preview for initial information and a Powerpoint Presentation.

Explore the differences between fission and fusion! Read Chp.15, Section 15.3 (pp. 429-433) in Keller & visit these sites: The Energy Story: fission and fusion General Atomics nuclear fusion educational site United States Fusion Energy Science Program

Terms for Understanding

alpha particle atom background radiation beta particle cosmic ray curie decay disposal well element fission gamma ray ionizing radiation half-life high level waste low level waste mixed waste non-ionizing radiation nuclear reactor nuclear waste RAD radioactive radiation radionuclide radon gas REM roentgen transuranic waste

Required Tasks (tasks are found throughout module)

TASK 1: Sodium-24 has a half-life of 15 hours.   If you start with 10,000 Sodium-24 atoms, how many will you have after 75 hours? TASK 2: First visit the Hanford Site D.O.E. website and review the overall programs and activities. Next, compare and contrast the two different web sites shown below about radioactive waste. Read through some of their materials, and try to determine what activities they concentrate on or promote within the organization. The Hanford Site -- Environmental Management EPA Radiation Protection Briefly, state why their activities are so different. Who is the responsible agency and who is the enforcing agency? TASK 3: Select three site characteristics that indicate a favorable radioactive waste disposal site, and briefly describe why you think they are beneficial. E-mail your tasks to:  hughscot@isu.edu

Referenced Web Sites

http://www.em.doe.gov/em94/nwhanf.html http://www.epa.gov/radiation/ http://www.ag.ohio-state.edu/~rer/rerhtml/rer_42.html http://www.nsc.org/ehc/guidebks/wipptoc.htm http://www.defenselink.mil/ http://www.energy.gov/ http://www.nrc.gov/ http://www.inel.gov/ http://www.ymp.gov/ http://www.wipp.carlsbad.nm.us/ http://www.bikiniatoll.com/ http://www.belarusguide.com/chernobyl1/chfacts.htm http://www.dannen.com/decision/index.html http://www.pbs.org/wgbh/amex/three/ http://whyfiles.news.wisc.edu/020radiation/index.html http://www.exploratorium.edu/nagasaki/

END OF MODULE 10

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