The materials used for isolating waste in the proposed repository
are an important component of the overall approach to the design
of the repository system. Opportunities exist to enhance the understanding
of material performance and to probe technical enhancements. These
enhancements may include optimizing the performance of waste packages
and drip shields for increased reliability and cost effectiveness.
Corrosion is a primary determinant of waste package performance
at the proposed Yucca Mountain Repository and will control the delay
time for radionuclide transport from the waste package. Intact waste
packages fully contain and isolate radionuclides at the proposed
repository. Corrosion is the most probable and most likely degradation
process that will determine when packages will be penetrated and
the shape, size, and distribution of those penetrations. The thrust
program strives for increased scientific understanding, enhanced
process models and advanced technologies for long-term corrosion
performance.
Corrosion resistance is important to the long-term performance
of waste packages. The waste packages are manufactured from highly
corrosion-resistant metals, and the surface of these metals is protected
by the formation of a self-healing, passive layer. The metals for
waste packages and drip shields have excellent corrosion resistance
over a wide range of aqueous solution compositions and temperatures.
Based upon measurements of corrosion rates of passive metals, the
waste packages can remain intact with no penetrations due to corrosion
for durations of 10,000’s and even 100,000’s years.
Materials optimization is realized through a coordinated program
of targeted, applied research. The program comprises directed technical
goals and thrusts. A team of leading scientists/engineers from major
universities and national laboratories is working together to meet
the program objectives. This group brings expertise and specialized
facilities in important disciplines including corrosion science,
materials science, electrochemistry, physical chemistry and geochemistry.
The team is organized among collaborative technical thrusts focused
on important topics:
- Long-term behavior of protective, passive films
- Composition and properties of moisture in contact with metal
surfaces
- Rate of penetration and extent of corrosion damage over extremely
long times.
Each technical thrust has a set of coordinated projects. As the
program evolves, there will be additional technical thrusts and
the collaborative effort will be expanded to include others from
national laboratories, academia, and industry. The Materials Performance
Targeted Thrust is coordinated with the Yucca Mountain Project through
cooperative projects, technical exchanges and program reviews.
Corrosion of metal surfaces covered with particulate and
deposits
The waste packages are supported in air, and they will never be
fully immersed in water, rather the metal surfaces may be covered
with dust, particulate and moisture from the surrounding rock and
humidity. This technical thrust examines corrosion in thin moisture
films and layers of particulate and deposits.
Evolution of corrosion damage by localized corrosion
Localized corrosion processes and particularly crevice corrosion
are high priorities.
This technical thrust examines the rate of penetration and extent
of corrosion damage by localized corrosion over extremely long times.
Evolution of environment on metal surfaces
The corrosion performance of a metal is determined by the inherent
corrosion resistance of the metal and the corrosivity of the environment.
The amount, distribution and chemical composition of the moisture
on waste packages are important.
In addition to the multi-investigator projects, there are bridging
projects that coordinate process modeling activities in the Materials
Performance Thrust to those in the Natural Barriers Thrust and the
Source Term Thrust. The Materials Performance Thrust has been an
“incubator” for work that transitioned to full development
projects in the Advanced Materials program, e.g.advanced welding
techniques and high performance amorphous metal coatings.
Leading scientists and engineers from universities form a multi-university
Corrosion Cooperative (CorrCoOp) that works closely with scientists
and engineers at several national laboratories. The CorrCoOp is
based at Case Western Reserve University and other participants
include Arizona State, Ohio State, Pennsylvania State, University
of California-Berkeley, University of Minnesota, University of Toronto,
University of Western Ontario and University of Virginia. National
laboratories include Argonne (ANL) Lawrence Livermore (LLNL), Oak
Ridge (ORNL), Pacific Northwest (PNNL), Lawrence Berkeley (LBNL)
and Atomic Energy of Canada Limited (AECL).
The Director of the Materials Performance Targeted Thrust is Dr.
Joe H. Payer at Case. He is supported by an executive committee,
a technology/research committee comprised of all program principal
investigators, an external review panel and several international
affiliates.
Technical Background and Information Sources
Several sources provide a basis for the selection of high priority,
technical thrusts. Worthy of special note are the Department of
Energy (DOE), Nuclear Regulatory Commission, Center for Nuclear
Waste Regulatory Analyses and others results and analyses for Yucca
Mountain; the DOE Basic Energy Sciences (BES)/OCRWM Corrosion Workshop-July
2003; the DOE Waste Package Peer Review-February 2002; and the Nuclear
Waste Technical Review Board (NWTRB) Workshop on Long-Term
Passivity-July 2001.
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