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Conclusion
Concluding observations
Based on the viability assessment, DOE believes that Yucca Mountain
remains a promising site for a geOlogic
repository
and that work should
years, exten-
proceed to support a decision in 2001 on whether to recommend the site
to the President for development as a repository. . Over 15
sive research has validated many of the expectations of the scientists who first suggested that remote, desert regions of the Southwest are
well-suited for a geologic repository.
Engineered barrier~can be designed
to contain waste for thousands of years, and the natural barriers can delay and dilute any radioactive material that migrates from the waste packages. Current models indicate that the possible radiation 'exposure to future populations living nearby could be comparable to present- day exposure levels from natural background radiation. Design alternatives that may improve performance and reduce remaining uncertainties are
now being evaluated.
The performance of a geologic repository over such long time periodslonger than recorded human history-cannot be proven beyond all doubt. Forecasts about future geologic and climatic co'nd~tions and engineering estimates of how long the waste packages will remain intact cannot be directly validated. The mathematical models us~ in the performance
assessment are subject to uncertainties that can be reduced but never
completely eliminated.
The Nuclear Regulatory Commission s general standard for meeting geo. !logic repository regulatory criteria and objectives is reasonable assuri ance. While considerable uncertainties remain today, DOE believes that
I reasonable assurance should be achievable in the licensing process after
the planned work is completed. The DOE believe~, therefore, that ongo-
ing work at Yucca Mountain should proceed as planned.
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Endnotes
0,," '
Endnotes
The numbers at the end of each reference are
Office of Civilian Radioactive Waste Manage-
8 Nuclear Waste Policy Act of 1982. Public Law 97- 425. 222165. .
9 10 CFR (Code of Federal R(!gulations) 60.
ment accession numbers. See the inside front
cover of this document for whom to contact regarding more information.
1 Energy and Water Development Appropria-
Energy: Disposal of High-Level
10
Radioactive
Waste in Geologic RepositoJ'ies. 239474.
tions Act , 1997. Public Law 104- 206. 238115.
2 For a desc,'iption and discussion of radioac-
Nuclear Waste Policy Amendments Act of 1987. Public Law 100. 203. 223717.
60. Energy: Disposal of High. Level
Radioactive Wastes in Geologic Repositories. 239474.
tive waste and its management , see The The Nuclear League of Women Voters 1993.
New Waste Primer: AHandbook for Citizens. York: League of Women Voters Education Jt' und. 2lO(i97.
;j U. S. District Court, Utah 1995. Joint Motion
11 10 CFR
12 Energy
Policy Act of 1992. Public Law 102486. 233191.
for Entry of Consent Order Based on Settlement. Ag,' eement and Consent Order in the Case of Public Service Co. of Colorado v. Batt, October 17, 1995. Civil Case No. 91- 0054-8- . l';JL (Legal Pleadings). U. S. District Court for the District of Idaho. 240346.
4 U. 8.
13 National
Technical Research Council 1995. Bases for Yucca Mountain Standards. Washington , D. : National Academy Press.
104723.
14
Interagency Review Group on Nuclear Waste
Management 1979.
Report to the President by
Linking Legacies: Connecting the Cold War Nuclear Produ.ctioll Processes to Their Environmental
Department of Energy 1997.
the Interagency Review Group on Nuclear Waste Management. TID- 29442 , p. 37. Washington, D. : DOE. MOL. 19980625. 0169.
16
CO1tSeqllcnces. DOE/EM- 0319,
pp. 34. 38.
Washington , D. : DOE. 241255.
5 National Academy of Sciences/National
Uesearch Council 1957. Radioactive Waste on Land.
Letter from Dr. Vincent McKelvey to Richard W. Roberts , Assistant Administrator for
The Disposal of
p. 4. WaRhington , D. Press. 241256.
Publication 519 : National Academy
li'inal
Nuclear Energy, U. S. Energy Research and Development Administration , Washington C. July 9, 1976. 238792.
16 Winograd , I.J. 1981. "Radioactive Waste
6 U. S.
Department of Energy 1980.
Disposal in Thick Unsaturated Zones. Science 212, pp. 1457- 1464. Washington
: American Association for the Advance.
Environmental/mpact Stateme'tt, Manageme" t of Commercially Generated Radioactive
Waste. J)O)4~/E18. 0046F.
ment of Science. 217258.
17
National Research Council 1990.
Washington, D.
DOK 205022.
'j National Research Council 1990.
Rethinking High-J.evel Radioactive Waste Disposal , A Positio" Stateme,it of the &ard on Radioactive Waste Management p. vii. Washington : National Academy Press. 241259.
Rethinking High- Level Radioactive Disposal, A Position Statement of the Board on Radioactive Waste Management, pp. 5-6. Washington , D. National Academy Press. 241260.
Science, Society, and America~ Teacher Guide. DOEI
: DOE.
16 DOE 1992.
Nuclear Waste, Unit
RW- O361 TO. Washington, D.
214909.
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Endnotes
......m ...,
U'Lcaguc of Women Voters
1993.
The Nuclear
p. 12.
Waste Primer: A Handbook for Citizens,
New York: League of Women Voters Education ).'und. 210697.
20 National
Technical Research Council 1995. 12. Bases for Yucca Mountain Standards, Washington , D. : National Academy Press.
104273.
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Glossary
-- --_'n .
Glossary
Adsorb
Backgrou nd
To transfer dissolved materials, including radionuclides, in groundwater to the
solid geologic surfaces with which they come in contact.
Radiation arising from natural radioactive material always present in the
radiation
Cladding
environment, including solar and cosmic radiation , and radiation from radon gas, soil and rocks , and the human body.
The metallic outer sheath of a nuclear reactor fuel element, generally made of a
zirconium alloy. It is intended to isolate the fuel element from the external
environment.
Colloid
Small particles in the size range of 10. 9 to 10-
meters that are suspended in a
solvent. Naturally occurring colloids in groundwater arise from clay minerals.
Defense in depth
A strategy based on a system of multiple , independent, and redundant barriers, designed to ensure that failure in anyone barrier does not result in failure of the entire system.
Margin of safety in specifications for engineered components to account for uncertainty in the conditions to which the components will be subjected and for variability in the properties of component materials.
Design margin
Dose
A quantity of radiation or energy absorbed by any material; measured in rads. Equivalent dose measures the amount of damage to human tissues from a radiation dose; equivalent dose is measured in rems.
From mining terminology, a horizontal underground passage.
A movable crane carried on a four- legged portal frame that runs along rails.
Drift
Gantry
High-level radioactive waste
Highly radioactive material resulting from the reprocessing of spent nuclear fuel. Original1y produced in liquid form, high-level radioactive waste must be solidified before disposal.
(1) The low point of something such as a tunnel , drift , or drainage channel. (2) An engineered structure or material placed on excavated drift floors (the low points) to serve as structural support for drift transportation or emplacement systems.
Invert
Isotope
One of two or more atomic nuclei with the same number of Pl' otons (i. , the
same atomic number) but with a different number of neutrons (i.e., a different atomic weight). For example, uranium- 235 and uranium- 238 are both isotopes
of uranium.
Metric ton
In this document, metric ton means a metric ton of heavy metal.
A metric ton is
a unit of mass equal to 1, 000 kg (about 2 atomic masses greater than 230. Examples include thorium , uranium , plutonium , and neptunium.
205 lb). HeaVy metals are those with
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G/OSSBIY
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Millircm
A millirem is one one. thousandth of a rem , which is the unit of equivalent dose. Equivalent dose is a measure of the effect that radiation has on humans. The equivalent dose takes into account the type of radiation and the absorbed dose. Rem is an initialism for Roentgen equivalent man.
Natural geologic systems that parallel situations that can develop in man-made systems. An example of a natural analog is the natural nuclear reactor at the
Natural analog
Oklo uranium deposit in Gabon, Mrica, which can be used as a source of analog data for conceptual models of nuclear criticality.
Non.w~lded
See
Tllff.
tuff
Percolate
Referring to the movement of water downward through soil and rock.
Performance assessment
An analysis that predicts the behavior of a system or system component
and modeling.
under
a given set of constant and/or transient conditions. Repository performance
assessments wil1 include estimates of the effects of uncertainties in both data
Radioactive waste
Radionuclide
Saturated zone
For the purpose of this document, spent nuclear fuel or high- level radioactive waste.
A radioactive isotope.
The region below the water table where rock pores and fractures are completely saturated with groundwater
Spent nuclear
Fuel that has been withdrawn from a nuclear reactor following irradiation , the
constituent elements of which have not been separated by reprocessing.
fuel
Transurani(: waste
Tuff
Waste contaminated with uranium. 233 or with radionuclides having atomic
numbers greater than that of uranium.
Rock derived from volcanic ash. Welded tllf! results when the volcanic ash is hot enough to melt together and is further compressed by the weight of overlying materials. Non-welded tIlt/results when volcanic ash cools in the air sufficiently that it doesn t melt together, yet later becomes rock through compres-
sion,
Unsaturated
zone
The zone of soil and rock between the land surface and the water table.
Water table
Welded tuff
The upper limit of the portion of the ground wholly saturated with water.
See
Tuff.
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Acronyms
DOE
EPA
Dt' pal'tment of gnol'A'Y
Ellvit' onnwntaJ Protection Agency
Ni\S
NHC
National Academy of Sciences
Nuclear Heglllatol')' Commission
NWPJ\. NlIeJt!f1.1' Wal"tc Policy Ad of 1982
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The following number is for Office of Civilian Radioactive Waste Management Records Management purposes only and should not be used when ordering this publication. Accession No. MOL.l9981O07. 0027
0091
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Viability Assessment of a Repository at Yucca Mountain
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