UNITED STATES

NUCLEAR WASTE TECHNICAL REVIEW BOARD

INTERNATIONAL WORKSHOP ON LONG-TERM EXTRAPOLATION

OF PASSIVE BEHAVIOR

Thursday

July 19, 2001

Hilton Arlington & Towers

950 North Stafford Street

Arlington, Virginia 22203

[NWTRB BOARD MEMBERS PRESENT]{.underline}

Dr. Daniel B. Bullen, Chair,

NWTRB Panel on the Repository

Dr. Paul P. Craig

Dr. Alberto A. Sagüés

Dr. Priscilla P. Nelson

[SENIOR PROFESSIONAL STAFF]{.underline}

Dr. Carl Di Bella

Dr. Daniel Fehringer

Dr. Daniel Metlay

Dr. Leon Reiter

Dr. John Pye

[NWTRB STAFF]{.underline}

Dr. William D. Barnard, Executive Director

Paula Alford, International Liaison

Karyn Severson, Director, External Affairs

Linda Hiatt, Management Analyst

Linda Coultry, Staff Assistant

[CONSULTANTS]{.underline}

Ugo Bertocci,

National Institute of Standards and Technology, Retired

Gustavo A. Cragnolino,

Center for Nuclear Waste Regulatory Analyses (SRI)

Alison J. Davenport,

University of Birmingham

Jerome Kruger,

Johns Hopkins University, Emeritus

Digby D. Macdonald,

The Pennsylvania State University

Barry R. MacDougall,

National Research Council Canada

Phillipe Marcus,

L\'Ecole Nationale superieure de Chimie de Paris

Roger Newman,

University of Manchester Institute of Science and Technology

Howard Pickering,

The Pennsylvania State University

Robert A. Rapp,

Ohio State University, Emeritus

Norio Sato,

Hokkaido University, Emeritus

Toshio Shibata,

Osaka University, Emeritus

Susan Smialowska,

Ohio State University, Emeritus

Hans-Henning Strehblow,

Heinrich-Heine University Duesseld

[I N D E X]{.underline}

[PAGE NO]{.underline}.

**Call to Order/Welcome**

Daniel Bullen, Member, Nuclear Waste Technical

Review Board (NWTRB) and Chair of the

NWTRB\'s Panel on the Repository . . . . . . . . . 7

**Introduction of Panelists. Background and**

**Scope of Workshop**

Alberto Sagüés, Member, NWTRB. . . . . . . . . . . 14

**Overview of Proposed Waste Package Designs**

**and Waste Package Environments**

Carl Di Bella, NWTRB Professional Staff . . . . . 27

**Overview of Research on Alloy-22 corrosion**

**Questions 1 and 2**

Alberto Sagüés . . . . . . . . . . . . . . . . . . 37

**Initial Responses to Questions 1 and 2**

(Questions are included at the end of this index.)

Panelists . . . . . . . . . . . . . . . . . . . . 52

**Roundtable Discussion of Question 1**

Panelists . . . . . . . . . . . . . . . . . . . . 73

**Recess** . . . . . . . . . . . . . . . . . . . . . . 246

**Question 1: On the effects of long-term passive dissolution**.

-Since commercial allows are being used to manufacture the waste
packages and due to \"atmospheric\" corrosion conditions in the
repository, it has to be assumed that most of the effects described in
the speculative scenarios (defect sweeping, vacancy build up, debris
accumulation, potential ennoblement) do not necessarily occur uniformly
over the whole passive surface of a WP (Waste Package). Therefore, if
these effects are really occurring during the long-term exposure, and if
these are also effective to promote passive metal dissolution, they will
lead to some degree of inhomogeneous metal loss. In case of oxide
spalling, it is assumed that repassivation occurs fast enough and no
localized corrosion takes place.

-According to our experience from exposure tests in long-range alpine
road tunnels in Switzerland and in France up to 25 years, we never
observed this scenario on passive metal surfaces. Instead, external
debris accumulation from environmental influences occurs much faster and
may lead in case of hindered repassivation to enhanced localized
corrosion processes. These debris accumulations are not necessarily
connected to the passive state of the materials, but are rather caused
by the environment in the repository.

-Our results from the field tests in the Mont-Blanc Tunnel lasting for
approximately 8 years show that the nickel-base alloys (Inconel 2.4856,
Hastelloy C4 2.4610) do not corrode at all in this heavily contaminated
atmosphere of long-range alpine road tunnels, contrary to 304 and 316 SS
which show severe corrosion already after one year. (Pollution:
Chlorides, sulphates, sulfides, nitrates, RL plus or minus 78 percent, T
plus or minus 35 degrees C.)

**Question 2: On the long-term preservation of conditions**

**preventing localized corrosion**.

a\)

-Critical pitting potentials quoted in the literature are usually
threshold potentials at or above which stable pit growth occurs. Pit
initiation processes followed by metastable pitting may already occur at
much lower potentials. This leads to the concept of \"metastable
pitting\". Therefore, Question 2 should be rewritten more precisely:
What is the lowest potential where metastable pits can be transformed
into stable pits under certain given environmental conditions. (In case
of Ni in highly conc. NiCl2 - solutions this potential is approx. -50 -
-100 mV sce at RT)

-If the transformation from metastable to stable pitting is mainly
controlled by the chemical composition of the pit or crevice
electrolyte, the pit or crevice geometry of the initial pits and
crevices, together with the mass transport in the bulk electrolyte are
of decisive importance. High Cl concentrations (saturation) in the water
films strongly promote this transition and decrease the corresponding
critical pitting potential. Therefore, the expected environmental
conditions in the repository, including temperature, play a key role
with respect to the critical pit growth potential. It is important to
consider these surface conditions as function of time. Our experience in
long-range road tunnel investigations indicate that we get a gradual
increase in concentration over the years.

-The open circuit potential is mainly influenced by the oxidizing
conditions in the repository, in the present case probably air or
eventually products from radiation.

b\)

-Transition from metastable to stable pit growth depends on many
parameters, such as potential, pH temperature crevice or pit geometry,
etc. Some of them may not be directly related to Ecrit. Therefore, the
necessary conditions for stable pitting always result from the behavior
of the whole system. It also has to be looked at from a stochastic point
of view.

c\)

-Corrosion tests and surface analytical investigation of worst case
repository conditions.

[P R O C E E D I N G S]{.underline}

(8:30 a.m.)

BULLEN: Good morning. Thank you for your indulgence while we took care
of some technical difficulties up here.

My name is Daniel Bullen. I\'m a member of the U.S. Nuclear Waste
Technical Review Board, and I\'d like to welcome you to this
International Workshop on Long-Term Extrapolation of Passive Behavior.
This workshop is being conducted under the auspices of the Board\'s
Panel on the Repository, which I chair. I will be serving as the
moderator and facilitator for most of the workshop. It\'s my please to
welcome you to a workshop which is a little bit of a departure from the
normal meeting format for the Nuclear Waste Technical Review Board.

First, I\'d like to say a few words about who the Board is and what the
Board does. As you may know, Congress enacted the Nuclear Waste Policy
Act in 1982. The Act made official the policy that the Federal
Government is responsible for permanently disposing of spent nuclear
fuel and high level radioactive waste, and that the owners and
generators of the waste should pay for that disposal.

Among other things, the Act created the office of Civilian Radioactive
Waste Management, or OCRWM, within the U.S. Department of Energy, and
charged it with developing repositories for the disposal of the
nation\'s spent nuclear fuel and high-level wastes for reprocessing.
Five years later, in 1987, Congress amended that law to focus OCRWM\'s
activities on the characterization of a single site for a permanent
repository, Yucca Mountain, on the western edge of the Nevada Test Site,
about 100 miles northwest of Las Vegas, in the State of Nevada.

In those 1987 amendments, Congress created the Nuclear Waste Technical
Review Board as an independent Federal agency to review the technical
and scientific validity of OCRWM\'s activities. The Board is required to
furnish its findings, conclusions, and recommendations to the U.S.
Congress and to the Secretary of the Department of Energy at least twice
a year. We do this in Congressional testimony and through our written
reports. We issued our latest report, a summary of last year\'s
activities, about three months ago.

As specified by the 1987 Act, the President appoints our Board members
from a list of nominees submitted by the National Academy of Sciences.
The Act requires the Board to be a multi-disciplinary group representing
a broad range of scientific and engineering disciplines related to
nuclear waste management. A full-strength Board, which we now have,
consists of eleven members. We meet as a full Board three or four times
a year, usually in the State of Nevada.

I would like to introduce a few Board members and a few of the Board\'s
staff at this time. As I mentioned, my name is Dan Bullen. I\'m a Board
member and a nuclear engineer in the Mechanical Engineering Department
at Iowa State University. My areas of interest include nuclear waste
management, risk modeling, and materials science.

Paul Craig\--Paul, would you raise your hand please\--is professor
emeritus at the University of California at Davis. He is a physicist by
training and has special expertise in energy policy issues related to
global environmental change.

Alberto Sagüés\--Alberto, would you raise your hand, please? Alberto is
Distinguished University Professor in the Department of Civil and
Environmental Engineering at the University of South Florida in Tampa.
He\'s an expert in materials engineering and corrosion, with particular
emphasis on the behavior of steel in concrete and in infrastructure
durability.

We have one more Board member here. This is Priscilla Nelson. Priscilla,
would you raise your hand? Priscilla is Director\--or actually, yeah,
Director in the Directorate of Engineering at the National Science
Foundation, and a civil engineer by training. I want to say geotechnical
engineer by training. Is that not correct? I don\'t have it written
here, Priscilla, so I\'m in trouble. I have to do this from memory.
Priscilla is a Board member and previously served as Chair of the
Repository Panel.

I also have a couple of staff members that I\'d like to acknowledge.
First, I\'d like to introduce Bill Barnard. Bill, will you raise your
hand? He serves as our executive director for the Board. Next to Bill is
Carl Di Bella. Carl, would you raise your hand? He is the staff member
who spent many hours on the phone and on e-mail organizing the many
technical aspects of this workshop and communicating with our experts
internationally.

I\'d also like to introduce Linda Hiatt and Linda Coultry. Linda Coultry
is right there. Is Linda Hiatt outside? The Lindas have been responsible
for many of the logistical aspects of travel arrangements, getting
everybody here, organizing the room, and I\'d like to express our
appreciation for that. Unlike Board members who are part-time, these
staff members serve on a full-time basis.

I\'d like to talk a little bit about the agenda for today and tomorrow.
In a few minutes, I\'m going to turn the meeting over to Alberto Sagüés,
who will introduce our distinguished panelists and explain why the Board
is sponsoring this workshop. Carl Di Bella will then summarize to the
panel the current repository and waste package design and the
environment that the waste package will experience in a repository.
Alberto will provide an overview of research on Alloy 22 related to
nuclear waste disposal, and he will repeat the two questions about
long-term corrosion that were furnished to the panelists about a month
ago.

Each panelist will then give a very brief five to ten minute
presentation on his or her initial response to those questions.
Following the completion of the panelists\' presentation, which should
be around lunchtime, the entire remainder of the workshop, with the
exception of the public comment periods, which I\'ll talk about later,
the entire remainder of the workshop will be devoted to a roundtable
discussion of the question among panelists. So this is going to be like
a brainstorming session. And a little bit of apology to the general
public, because it might get very technical, but that\'s the purpose of
this meeting, for us to understand the technical opinions of the
international community.

As I said before, this is not a typical Board meeting. In a typical
meeting, presentations are made, often by the DOE or its contractors,
and the Board engages in a dialogue with each of the presenters, with
the meeting Chair often leading that dialogue, or at least participating
heavily in it. Here, my role as Chair will be somewhat different. I\'ll
be more of a moderator, facilitator, timekeeper, and maybe even a
referee, should we have some heated exchanged. Rather than ask many
questions of my own during the roundtable discussion, I\'ll be more
concerned about the questions asked of the panelists and questions by
the Board members, Paul Craig and Alberto Sagüés, or the other panelists
themselves.

I need to offer our usual disclaimer that everybody is clear on as we
conduct this workshop. What you are hearing, and its significance, and
the reaction by Board members are spontaneous by design. Those of you
who have attended our meetings before, and I know many of you have, know
that the members of the Board do not hesitate to speak their minds. I\'m
sure that goes for the panelists today, too. But let me emphasize that
Board members and panelists are speaking their minds. They do not speak
on behalf of the Board. They\'re speaking on behalf of themselves. From
the Board\'s perspective, the purpose of this workshop is information
gathering. Any Board position that may develop would be taken only after
the full Board has had a chance to process this information.

Now, let me say a few things about the opportunities we\'ve provided for
public comment and interaction during the workshop. This is something
that is extremely important to the Board. By \"public\" I mean those who
are not Board or staff members, or members of the panel. We try to give
the public as many opportunities as possible to comment during our
meetings. Today\'s public comment period will take place at the end of
the roundtable discussion of Question 1, and tomorrow, at the end of the
roundtable discussion of Question 2.

Board Member Paul Craig will chair the public comment session. Those
wishing to comment should sign the Public Comment Register at the
check-in table where Linda Hiatt and Linda Coultry were sitting on the
way in. So, if you\'re interested in making public comment, please sign
up and we\'ll hear your comments either today or tomorrow. Both of the
Lindas will be glad to help you sign up and be prepared for the public
comment period.

Now, let me point out, and I\'ll remind you again later, that depending
on the number of people who sign up, Professor Craig may have to set a
time limit on the comments that are made.

An additional opportunity for questions or comments, and continuing
something that we\'ve tried pretty successfully before, is you can
submit questions or comments or concerns in writing to either Linda
Hiatt or Linda Coultry during the workshop. If there\'s time and the
question or comment is relevant to the discussion at hand, then I will
read that question to the panel members during the course of the
workshop. If I can\'t get the question or comment worked in during the
workshop, I will hand that question to Paul, who will reserve the right
to read that question, the same question, during the public comment
period.

In addition, we always welcome written comments for the workshop
transcript, and this workshop is being transcribed. Those who prefer not
to make oral comments or ask questions during the workshop may choose
this route at any time. We especially encourage written comments when
your comments are more extensive than our workshop time allows. Please
submit these written comments also to either Linda Coultry or Linda
Hiatt, and they\'ll be happy to help you.

Are there any questions from the panel about how we\'re going to operate
the workshop?

(No response.)

BULLEN: Excellent. Seeing none, I will turn it over to my esteemed
colleague, Dr. Alberto Sagüés to introduce the panelists and begin the
process.

Alberto?

SAGÜÉS: Thank you, Dan.

Good morning. My name is Alberto Sagüés, and as Dan has explained, I\'m
also a member of the Board. I would like to welcome you, the panel,
officially to the workshop, and tell you how absolutely elated I am that
all of you could make it. We have truly work-class panel.

One of the things that pleases me the most is that so many people were
able to accept our invitation to participate, despite the fact that
there was two months or less notice. And several of you have long
distances to travel. I think this testifies to the importance of the
issue we are addressing, as well as its intellectual challenge.

Stating the overall issue is simple. In the United States Repository
Program, and this may be true in some other countries as well, the waste
package, that is the container the waste will in when its placed in the
repository, has come to have a very important long-term role.

The proposed outer layer of the waste package is a two centimeter thick
shell of Alloy 22. Alloy 22 is a very corrosion resistant material that
depends on a nanometer thick passive layer for its corrosion resistance.

Now, mankind\'s experience with Alloy 22 is only a few decades, and
mankind\'s experience with alloys like Alloy 22 spans only a few more
decades. And mankind\'s experience with any metal or alloy that owes its
corrosion resistance to a passive layer is at best not much more than a
century.

By the way, I fully expect to be challenged on this particular issue
during the workshop by members of the panel, and you\'re welcome to do
so.

So if our experience is limited to a century or so, what are the
theories and the assumptions that form the basis for extrapolating for
thousands and thousands of years? In other words, what is the basis for
extrapolating? That\'s what I\'m trying to get at here. Do we really
have one? Why or why not? And in a nutshell, that\'s what the workshop
is all about.

I think everyone on the panel knows each other. But both for the record
and to refresh our memories, I would like to introduce each panelist
briefly, and I would ask you to please raise your hand when I call your
name.

We\'ll start with Dr. Ugo Bertocci. He holds a doctorate in chemistry
from the University of Milan. He worked for the National Institute of
Standards and Technology, NIST, for more than 20 years, and retired
about nine years ago. Now, NIST, of course, used to be the Bureau of
Standards.

More recently, Dr. Bertocci has done research at the Federal Highway
Administration, again at NIST, and he has collaborated extensively with
the French CNRS. His research interests have always been in the field of
electrochemistry.

Dr. Gustavo Cragnolino is a staff scientist in the Center for Nuclear
Waste Regulatory Analyses at Southwest Research Institute in San
Antonio, Texas, where he has been conducting experimental research and
modelling of corrosion and thermal stability of metallic container
materials for high-level radioactive waste disposal since 1990. He holds
a Licenciado and doctorate degrees in chemical sciences from the
University of Buenos Aires in Argentina, and has worked before in the
Argentina Atomic Energy Commission, the Fontana Corrosion Center at Ohio
State, and Brookhaven National Laboratory.

Dr. Alison Davenport is a lecturer at the University of Birmingham in
the School of Metallurgy and Materials. Now, that\'s Birmingham in the
UK and not in Alabama. She has a doctorate in Materials Science and
Metallurgy from the University of Cambridge. Her research interests
include the structure, chemistry and stability of passive oxide films,
and the effect of microstructure and alloying additions on corrosion and
surface treatment of metals. She\'s also a Brookhaven alumna, spending
eight years there as a scientist in the late Eighties and early
Nineties.

Professor Jerome Kruger, Jerry Kruger, received a Ph.D. in physical
chemistry from the University of Virginia, and joined the Naval Research
Laboratory. Three years later, he went to the National Bureau of
Standards, and eventually became Chief of the Corrosion Section. In
1984, he joined the faculty of John Hopkins University in the Materials
Science and Engineering Department, becoming Emeritus in 1999. He\'s a
fellow of NACE, National Association of Corrosion Engineers, the
Electrochemical Society and the Institute of Corrosion in the UK.

Professor Digby Macdonald is a professor of Materials Science and
Engineering, and director of the Center for Electrochemical Science and
Technology at Penn State. He has a Ph.D. in chemistry from the
University of Calgary and BS and MS degrees in Chemistry from the
University of Auckland. His research interests include passivity,
nuclear reactor technology, and high temperature aqueous
electrochemistry. And, of course, he\'s the developer over the past two
decades of the Point Defect Model for the growth and breakdown of
passive films. Dr. Macdonald is a fellow of NACE and the Electrochemical
Society.

Dr. Barry MacDougall leads the Electrochemical Technology Group at the
National Research Council of Canada. He received his doctorate in
electrochemistry from the University of Ottawa. His research interests
include the formation and breakdown of passive oxide films on metals and
alloys, with emphasis on the mechanism of film breakdown leading to
localized pit initiation. His interests also include improving
understanding of fundamentals of corrosion processes of metals and
alloys through the use of surface electron spectroscopies to study the
composition and structure of surface layers. Dr. MacDougall is a fellow
of NACE and the Chemical Institute of Canada.

Professor Philippe Marcus directs the laboratory of physical chemistry
of surfaces, part of the National Center for Scientific Research at the
University of Pierre et Marie Curie in Paris, France. He received his
doctorate in chemistry from the University of Pierre et Marie Curie. His

research interests include the effect of atomic layers of absorbed
sulfur on dissolution and passivation of metallic surfaces, the study of
passivity of metals and alloys, the use of photoelectron spectroscopy
toward the standard relationships between the chemical nature of passive
films and their corrosion resistance, as well. He co-chairs the
Corrosion Electrodeposition and Surface Treatments Division of the
International Society of Electrochemistry, and also chairs the Corrosion
Working Party on Surface Science at the European Federation.

Professor Roger Newman is professor of Corrosion and Protection at
UMIST, which is the University of Manchester Institute of Science and
Technology in the UK. He has a doctorate in metallurgy and materials
science from the University of Cambridge. He\'s been at UMIST for 17
years, but is another of the folks spending time at Brookhaven, in his
case, four years, as a researcher in the early Eighties. He\'s a fellow
of the UK Institute of Materials and of NACE and holds a doctorate
degree from the University of Manchester. His research specialties are
passivity, localized corrosion, and stress corrosion cracking,
especially the formation of oxide films on alloys, mechanisms of growth
of pits and cracks, and prediction of pitting or cracking thresholds.

Professor Howard Pickering is distinguished professor of Materials
Science and Engineering at Penn State University. He has a Ph.D. from
Ohio State University. His research interests include selective element
dissolution from alloys, localized electrochemical degradation
processes, such as crevice, pitting and grain boundary corrosion,
hydrogen evolution and its absorption and diffusion into metals, and
surface reconstruction in metal electrodissolution and electrodeposition
in aqueous solutions using the scanning tunneling microscopy and atomic
force microscopy.

Professor Robert Rapp is distinguished university profession emeritus in
the Department of Materials Science and Engineering at the Ohio State
University. He has a doctorate in metallurgical engineering from the
Carnegie Institute of Technology in Pittsburgh, a predecessor to
Carnegie-Mellon University. By the way, our Board Chairman, Dr. Jared
Cohon, is the president of Carnegie-Mellon these days. Dr. Rapp is well
known in the areas of corrosion mechanisms, coating and protection,
extractive metallurgy, and high temperature materials. He\'s a member of
the National Academy for Engineering, and a fellow of four U.S.
Societies, ASM, TMS, Electrochemical Society, and NACE, as well as two
foreign societies.

Professor Norio Sato is emeritus professor at Hokkaido University. He
received a doctorate in engineering from Hokkaido University in
electrochemistry. He\'s an electrochemical scientist, specializing in
corrosion and fundamental understanding of metallic passivity and its
breakdown. Professor Sato is a fellow of NACE, the Japan Society of
Corrosion Engineering, the Institute of Corrosion in the UK, and the
Electrochemical Society in the US.

Also from Japan we have Dr. Toshio Shibata, who is professor emeritus as
of March of this year in the Department of Materials Science and
Processing of Osaka University. His doctorate is from Hokkaido
University. He has been concerned with the passivity of stainless steel
and its breakdown, including pitting, and stress corrosion cracking.

Professor Susan Smialowska is professor emeritus at Ohio State
University, and also the director emeritus of the Fontana Corrosion
Center there. She earned her doctoral degree in chemical engineering at
the Silesian Technical Institute and University in Poland. Dr.
Smialowska\'s principal research interests have been investigation of
the kinetics of the mechanism of electro processes, pitting corrosion,
stress corrosion cracking, corrosion inhibitors, hydrogen embrittlement,
different types of aqueous corrosion at high temperatures and, of
course, passivity.

Professor Hans-Henning Strehblow is professor of physical chemistry at
the Institute for Physikalische Chemie and Elektrochemie at
Heinrich-Heine University in Duesseldorf. He has a doctorate in physical
chemistry from the Free University of Berlin. His research interests
include electrochemistry, corrosion, surface analyses, and the physical
chemistry of surfaces.

Now, we have one other distinguished panel member who unfortunately will
not be able to be with us today. That was Professor Hans Bohni of the
Swiss Federal Institute of Technology in Zurich, who was to have been a
panelist, and he e-mailed us Monday afternoon that he has come down with
an infectious disease with a fever and, therefore, would not be able to
participate. However, he had gotten started on preparing some notes for
the meeting, and he was kind enough to forward them to us. You should
find them, it is one sheet of paper printed on both sides, in the
package of handouts that Linda Coultry and Linda Hiatt set out for you
this morning.

I have a couple more introductions to make for the benefit of the panel.
And before I make those introductions, I first want to apologize to any
of the other distinguished visitors and friends that may be present in
the audience that I more than likely will be overlooking, but I wanted
to highlight some of our participants that are involved in the project
in one manner or the other.

First of all, Dr. Gerry Gordon, formerly of General Electric, he\'s the
lead materials scientist for the Department of Energy. And he and the
group that he\'s with have kindly volunteered to answer any questions
about the materials DOE program, should they arise during the course of
the workshop. Indeed, the work of that group is going to be discussed in
some detail during this meeting.

We also have Professor Joe Payer. He\'s professor of Materials Science
and Engineering at Case Western Reserve University in Cleveland, and he
directs the Yaeger Center of Electrochemical Sciences at Case Western
Reserve. He\'s chairing a ten month peer review of the DOE Materials
Program, and we have some of the peer review panel members here as well.
The peer review just got started a month ago, and some of you members of
the panel may be serving as subject matter experts for the peer review
as well.

I want to assure you that this workshop and the peer review are
independent efforts. The workshop has a very narrow focus, and is a one
shot affair. The peer review is much, much broader and extends for
nearly a year. Even though the two efforts are independent, they do
overlap, and we hope what comes out of the workshop will be helpful to
the peer review, as well as the Board.

I think that we have Professor Gerry Frankel in the audience as well.
Jerry? He\'s in the Materials Science and Engineering Department of Ohio
State, and is the current director of the Fontana Corrosion Center.
He\'s a member of Dr. Payer\'s panel.

Do we have Professor Kelly as well in the audience today? Maybe later.

Dr. David Shoesmith is in the audience? David Shoesmith originally from
England, he spends most of his time in London, but that is London,
Ontario, where he\'s a professor of chemistry at the University of
Western Ontario. And I know Professor Shoesmith because of his extensive
participation in the DOE effort and as a contributor to a number of
previous discussions concerning materials in the repository.

Let\'s see, we have also Dr. Roger Staehle in the audience. Roger? He\'s
formerly an Ohio State professor, University of Minnesota dean, and he
is also involved in Rickover\'s nuclear navy, and now he\'s associated
with Roger Staehle Consulting, and he\'s also in the audience and he has
been involved also for a long time in these areas.

We have, again, many other friends and distinguished people. Dr. Scully
maybe is in the audience? Well, anyway, and I apologize for those whose
names I may have failed to notice at this moment.

Okay, a couple of housekeeping issues. You might notice that the meeting
is being transcribed, and this is standard practice for all Board public
meetings. The transcript will be kept in our permanent archives and will
be posted on our website.

Scott Ford, who is recording the meeting and his staff back in Denver
have provided transcribing services to the Board for quite a while, and
they\'re good and they\'re familiar with many of our technical terms,
but there is something you can do to help them. Whenever you speak,
members of the panel, please identify yourself, unless someone has just
introduced you, just saying your last name is enough, but that will help
keep the record straight as to who is saying what.

Now, just a couple of very brief comments introducing the next
presentation and the overall orientation of the workshop. Now, the basis
for extrapolating corrosion resistance thousands of years into the
future has been a concern of our Nuclear Waste Technical Review Board
for at least four years. And this is a concern that the Board has
mentioned frequently in its writings.

We have encouraged the Department of Energy to begin some basic research
on the issue, and the DOE has responded by beginning some basic
research, but much of it only recently. You will need to consider that
in detail, and we\'re going to be addressing some of that in some of our
next presentations.

Why are we having the workshop and why are we having it now? Dan Bullen
mentioned the Nuclear Waste Policy Act of 1982. This Act, and its
subsequent amendments, set in place, among other things, a careful and
detailed process involving the Secretary of Energy, the President of the
US, the State of Nevada, the Congress, and other parties, for making the
social decision on whether to proceed with Yucca Mountain.

The Department of Energy plans that the first step of the process, a
decision by the Secretary of Energy whether to recommend the site to the
US President, shall take place late this year. Clearly, the decision
will have a technical component. The Board\'s views will be important
for the decision, and we want to have as complete a basis for our views
as possible.

Hence, this workshop. We are seeking a broad range of diverse opinions
on the matter of extrapolating corrosion resistance far into the future.
We are not seeking consensus, and we are not seeking agreement. We are
seeking opinions.

What transpires during the workshop will form an important part of the
basis for the Board\'s view on the extrapolation issue. And since we
have to express that view before the Secretary\'s decision, you can
understand the timing of the workshop.

Now, finally, the subject of this workshop is the long-term
extrapolation of passive behavior. I know there are many tempting side
topics that this group is eminently qualified to explore, for example,
stress corrosion cracking, or the design of the waste package itself.
But if we get off onto those topics, we risk not fully addressing the
reason we\'re gathering here in the first place. Long-term extrapolation
is our focused interest. Also, we didn\'t furnish you with the
background information to address those other issues.

So, if we travel down the side road, I\'m sure Dr. Bullen will feel
obliged to pull us back before we go too far.

Thank you. And now I would like to turn the floor over to Dr. Carl Di
Bella, who will describe briefly the waste package designs and the range
of chemical, physical and thermal environments that the waste packages
may experience in the repository. Then I will return to summarize Alloy
22 corrosion research, and repeat the questions for the workshop.

Before I turn the meeting over to Dr. Di Bella, do we have any specific
questions on the part of the panel?

(No response.)

SAGÜÉS: If we don\'t, then Dr. Di Bella, please.

DI BELLA: Thank you very much.

Well, Mr. Referee, we\'re running just a bit behind, but I\'m going to
help.

BULLEN: I am keeping score.

DI BELLA: I sent to each of you about a month ago some information about
the waste package design and about the environment that a waste package
at Yucca Mountain would experience. I\'m going to repeat that very
briefly, more for the purpose of you asking questions, if you want to.

I don\'t have copies of my handouts because I\'ve already sent them to
you, and because I got them from the DOE website anyway.

So, first, let me remind you, particularly for visitors from overseas,
where Yucca Mountain is. All right, Yucca Mountain is located in the
State of Nevada about 150 kilometers northwest of Las Vegas. It\'s at
the very western edge of the Nevada Test Site, which is blown up
here\--blow up I guess is a good word for it. Here is the footprint of
the repository located just west of the Test Site on Bureau of Land
Management Land, on Nellis Air Force Range land. That\'s where it\'s
located.

This is a semi-arid location. There are about 17 centimeters of
precipitation a year. Most of that evaporates off or runs off, but some
does filter into the mountain and eventually reaches the water table,
which is about 600 meters below the surface.

The repository would be located above the water table about 300 meters.
So it\'s in the unsaturated zone, the vadose zone, as it\'s known. And
the pressure at that level is essentially the pressure of outside air,
or the atmosphere, and the elevation of the repository is about 1000
meters. So at that elevation, pure water boils at 96 degrees rather than
100 degrees.

The repository would look like this. This is an isometric view of the
repository. I\'ll give you a little closer view in just a moment. The
emplacement drifts are the drifts going east/west where waste packages
would be placed.

This is another view that emphasizes the ventilation aspects of the
repository. I\'m doing that to show you that the repository would not be
closed immediately after waste packages are emplaced, but that some
period of ventilation would take place, and this period of ventilation
could be as short as 25 years, could be as long as 300, or perhaps even
longer.

The waste packages look like this. There\'s a person there shown for
scale. They do vary somewhat in diameter and length, but they\'re
roughly between one and a half meters to two meters maximum in diameter,
and they\'re up to on the order of five meters long, about the size of a
Lincoln limousine, if you happened to see them when you came into the
airport waiting outside for VIPs.

The outer surface of the waste package is C-22, a two centimeter layer
of Alloy 22. The inner layer of the waste package is 316-N stainless
steel, five centimeters thick, and it gives the structural strength, or
a large portion of the structural strength, to the waste package. Then
there is a basket to hold the assemblies. And the entire waste package,
with the exception of the lid, is annealed before waste is put into it.
Then waste would be put into it, and the lids welded on, and then the
lids would be individually treated to put into a compressive state.
There\'s a double lid. One lid gets laser peened in the current concept,
and the other lid weld gets induction annealed, locally induction
annealed to protect the waste.

That\'s the design of the waste package. Let me show you one conceptual
diagram of how the waste would be put into the repository. The diameter
of the emplacement drifts is roughly five and a half meters. The
diameter of waste packages remember is on the order of two meters.
Selection of waste packages are shown here in an emplacement drift, and
you might notice towards the back of the drift, this device, which is
called a drip shield, which would be made out of titanium, and the idea
is to place the drip shield after the ventilation period, just before
closure of the repository. And it would be a continuous drip shield of
segments that are hooked together, overlapped like shingles, so that
they would prevent water from going onto the waste package. That\'s the
concept anyway.

You might think, of course, that besides C-22 outer layer of the waste
package depending on passivity, so does titanium drip shields, so does
the stainless steel inner layer, so does, hence, and we don\'t have a
picture of an assembly here, but so does the zircaloy tubing that
consists the assembly rods. However, we\'re going to talk about Alloy
22, of course, for this workshop. What comes out with regard to that may
well have application to passivity for these other materials, too.

There is water in Yucca Mountain. Even though it\'s above the water
table, water percolates down through Yucca Mountain and there is water
in the pores of the rock at Yucca Mountain. And I have here a very
complicated table, a very data-laden table that has the compositions of
two of the native waters in the Yucca Mountain area.

This column here is the water from the water table, actually several
kilometers away from Yucca Mountain, but it\'s close. This water here is
water that has been squeezed, or centrifuged I think, out of rock pores
at the repository level. They\'re really quite different, and you can
see the difference in when you evaporate the respective waters. This is
an evaporation of this water. This column is an evaporation of this
water right here.

You will notice in evaporating the water below the water table, that you
basically get rid of all of the calcium and the magnesium. What happens
is that they combine with the carbonate, and that it precipitates them
out.

However, in the case of water at the rock level, in the pores, there\'s
much higher concentrations of calcium and magnesium, and when you
evaporate this, you basically get rid of all of your carbonate, but you
still have calcium and magnesium left.

What\'s the significance of that? The significance is that the calcium
and the magnesium, together with the chlorine anion, have very high
boiling points as saturated solutions, or near saturated solutions in
water. Whereas, the salt here that has a combination of cation and anion
that would have the highest boiling point of the saturated mixture here,
is sodium nitrate.

In this case, the boiling point approaches 150 to 160 degrees. In this
point, the boiling point approaches 120 degrees.

Now, why am I bringing that up and what does it have to do with
corrosion? Well, the salts that are deposited on the waste package,
whether they are from ventilation air that comes in, whether they are
from rock dust that comes onto the waste package over this 25, 50, 100
year period, may have some of these salts here in them, some calcium,
magnesium chloride salts in them, or some sodium nitrate salts in them,
which would determine the highest temperature at which is going to be
aqueous condition on the waste package.

If this is typical of the kind of salts that are on the waste package,
then pretty much 120 degrees you can safely say is the highest
temperature that there\'s going to be liquid water on the waste package.
If this does, then maybe 160 degrees is the highest temperature, and
that has something to say about the corrosion.

For the purposes of the workshop, I think we\'re going to have to play
it safe and say it\'s possible that maybe there will be liquid water on
some of the waste packages, or some part of some of the waste packages
as high as 160 degrees.

Now, there are many other trace components. These are just what I call a
major species in the water, and they can be important, particularly if
they find a way to concentrate, and that\'s simply out of the scope of
the workshop, but it\'s an important issue.

Temperatures can be generated at Yucca Mountain. There are basically two
schools of thought for a repository at Yucca Mountain. One is called hot
and one is called cold. And I\'ve tried to represent them both here with
a plot of waste package surface temperature versus time for the hot
case, which is red, for the cold case, which is green. And there are
many, many of these different kinds of cases. This is just meant to be a
representative or a sample case. The actual temperature of a waste
package is going to depend on where it\'s located in the repository, and
what\'s inside that particular waste package.

But let\'s take this. And so in the hot case, ventilation goes on for 50
years. Then the repository is closed. Ventilation is turned off. The
decay heat from the package boosts the temperature up to 160, and
there\'s a slow decay as the heat dissipates from then on.

In the cold case, ventilation is not turned off. The repository is not
closed at 50 years, but instead, natural ventilation is allowed to
occur, and this removes a portion of the heat from the repository,
keeping the temperature below 80 degrees.

Again, this red case here is the DOE base case right now, although they
have studied both cases right here. But I think for the purposes of the
workshop, that it would be wise to consider the DOE base case as being
the base case for the workshop, that is, one where the temperature will
stay above 95, 96 degrees for maybe on the order of 1000 years. It\'s
going to be 500 to 2000, depending on the individual waste package.

Now, I think that\'s really all I wanted to say. Really, I put this up
more to give you an opportunity to ask questions, if you want, about the
environment that the waste package is going to experience. Are there
any?

NEWMAN: I just have a question, which shows my total ignorance of
radiation. Does the stainless steel stop all that?

DI BELLA: Yes. Does the stainless steel?

NEWMAN: Does the stainless steel stop all the radiation?

DI BELLA: No, there is a fairly significant radiation field outside of
the C-22, at least from a personal point of view. From a radiation
damage point of view, I think the consensus is pretty strongly that
radiation damage from the waste, either of the stainless steel or of the
C-22, is not a significant issue.

However, radiolysis, which is ionizing of chemicals in either the water
on the waste package or in the humid air, and then some sort of
concentration of, say, the nitric acid or hydrogen peroxide that you
get, that\'s a potential issue if you can think of a concentration
mechanism.

Dr. Kruger?

KRUGER: Are there any scenarios where the waste package sees only hot
air and steam, and no aqueous environment?

DI BELLA: The proponents of the hot repository hope, of course, in this
period of time that all of the water is driven away, that it will
condense someplace far away from the waste package, and drain in between
the tunnels, and so that it\'s not an issue.

KRUGER; The issue is that the environment at 160 at least, hot metal, in
gaseous environment, which I think is an issue as well.

DI BELLA: There has been a fair amount of study of that. And, indeed,
dry oxidation, or dry air oxidation is what term is used inside the
project, does occur, but the rate is infinitesimal, I am told, so
dwarfed by any aqueous corrosion rate.

KRUGER: Okay.

DI BELLA: Dr. Davenport?

DAVENPORT: I just wondered how much variability there is in the solution
compositions that you quote? Is there a sense that in different parts of
the tunnels, there might be some areas with particular constituents that
go significantly above the amounts that you\'ve indicated?

DI BELLA: In my mind, just speaking for myself, neither the variability
issue nor the uncertainty issue have been sufficiently addressed yet.

Looking at it from an overall point of view, the mountain is a
relatively homogeneous kind of rock called tuff. But looking at it from
an individual waste package point of view, and there\'s going to be more
than 10,000 waste packages, each waste package is going to see different
characteristics of the water around it. And what that spread is, I
don\'t think there\'s enough data yet, particularly of water at the
repository level, to answer the question.

Dr. Strehblow?

STREHBLOW: I wonder why you stopped your concentration of the brine
action? I would guess it\'s some 10 to the minus 2 molar solution.
You\'re talking also about dry situations, and it could be that the
electrolyte is really concentrated, more concentrated, like a Q brine,
or something like that, which is extremely high in concentration. It
might be more corrosive. Is that a realistic situation? We can talk
about that later. But you might give it some thought.

DI BELLA: I think it\'s an absolutely realistic situation. I only put
that chart up because I had something to cite behind it.

And now may I give the floor back to Dr. Sagüés?

SAGÜÉS: Great. Well, we\'re getting closer now to the substance of the
workshop, and what Dr. Di Bella showed you is another introduction of
our mental parameters. By the way, we do have here in the audience Yucca
Mountain Project scientists who might be able to clarify some of these
issues. So I would invite the panel participants that if they have any
additional questions on this, feel free to indeed ask if we can have
some additional clarification. And that applies also to what I\'m going
to mention right now. I\'m just going to highlight a couple of issues,
and I don\'t pretend by any means to make this into an exhaustive
presentation.

And what I wanted to do is to quickly address the question of what kind
of corrosion performance is needed if a repository of this type would be
somewhat successful in doing what it\'s supposed to do. And the first
thing I want to mention is that the performance of the repository has
become increasingly dependent on the integrity of the waste package.

Maybe a decade ago when the initial concepts of the repository were
considered, at that time, the mountain was an extremely, and still is an
extremely important part of the overall equation that would determine
separation between the waste and the public, but the mountain, during
the last decade or so, more evidence began to appear that the mountain
had a lot more water than was initially anticipated. The flow of water,
the flux of water was found to be quite significant. There was
uncertainty as to how slowed down that water motion would be, and so on.

So, as a result, the present performance projections for the repository
are relying strongly on that package being there and staying in very
good shape for a very long time.

Indeed, at this moment, to have a very credible, a very robust
repository concept, really, there shouldn\'t be any widespread
penetration of the Alloy 22 shell during the first 10,000 years of
operation of the repository. And we cannot give any specific time
period, and the like, but indeed, a very robust package, a package that
will stay for a very long time is indeed needed.

Now, things like localized corrosion would be very detrimental to the
anticipated performance of the repository. If there were strong evidence
that localized corrosion, big pits would develop in the system, if those
penetration phenomena are really very fast, to get something that would
be a workable repository concept, so, really, localized corrosion is
something that the concept cannot afford very much.

Now, that leaves, of course, uniform corrosion. Now, uniform corrosion
rate would have to be quite small. To be quite sure that there\'s no
widespread penetration, well, we have to have corrosion rates that have
to be much, much smaller than two micrometers per year. Two micrometers
per year is, of course, the nominal kind of corrosion rate that would
give you two centimeters penetration in 10,000 years.

So, you realize that we are asking here for the kind of performance that
in many industrial operations may be something you could live with, but
in this case, you couldn\'t.

Now, the challenge that we have here is an extrapolation challenge,
because the package corrosion performance relies on passivity. And I\'m
going to show a graph in a second here to dramatize this. The empirical
evidence that we have on the performance of passive materials is very,
very low. We haven\'t used a trick for engineering, as far as I can
think, and as far as from conversations with a number of individuals who
should know, we don\'t have much more than about 100 years, maybe 150
years perhaps, the first applications of some aluminum alloys, and one
could say that, well, yes, maybe steel and concrete, there have been
nails or some small components of steel embedded in mortars and concrete
for a long period of time, and that would be passive. But, again, we are
talking about a fairly short time.

So I put together this graph some time ago, and this graph is simply an
indication of the following. Here, we have, say, assumed uniform
penetration rates in micrometers per year. Here would be the millimeters
per year; here would be the micrometers per year. And here would be the
nanometers per year kind of thing. To penetrate through 20 millimeters,
well, you have this amount of time. So if you have 10 micrometers per
year, then you are talking about a couple thousand years, and so on, and
so on.

Well, the kind of desired performance is something that begins to get
better and better the farther away we are from 10,000 years. So this is
sort of like a desired kind of regime, that cloud of behavior over
there. But the problem is that the actual empirical evidence that we
have on passive materials doing their job is about 100 years.

So, we have here an extrapolation gap, and we have here a heck of an
extrapolation gap. We are talking about one, two, maybe three orders of
magnitude extrapolation gap. And, clearly, we cannot just rely on maybe
ten years test and saying this worked for ten years. We have to have
something to support that, and that something has to come from some
fundamental understanding of the processes that are responsible for this
behavior. And, of course, that\'s why you\'re here.

Let\'s talk a little bit about what is the available evidence on uniform
corrosion. I\'m just going to highlight some of the results that the
Project has produced, and some of the \-- . And, again, as I said
before, feel free to ask some of the Project scientists in the audience,
if you would like, some very specific detail.

The evidence that is available on Alloy 22 comes, quite a bit of the
most detailed evidence comes from gravimetric corrosion tests, coupon
tests, in a fairly large facility that is located at Lawrence Livermore
National Laboratory. Over there, Alloy 22, among other alloys, has been
tested, and in simulated repository environments, the corrosion rates
that are obtained by gravimetric tests are distinctly below the tenth of
a micrometer per year. And I\'m going to show that much of them maybe
show a hundredth of a micrometer per year.

There\'s also electrochemical evidence that provides similar evidence,
and then there is a little bit of evidence on temperature dependence. So
let me show you some of that evidence so you get a flavor of what is
involved.

First of all, about gravimetric corrosion rates, those of you who have
been involved in coupon testing know that when we are talking about
those very low rates, we must be talking about very, very small mass
differentials in coupons that can be quite heavy. And sure enough, when
you have data from the first maybe couple years, or one year, you may
get indications like this.

And, here, we have the evaluated penetration rate for a whole bunch of
coupons, in this case, of Alloy 22 in a number of simulated
environments, and this is the cumulative percentage of it. And, of
course, what you see is that a number of your coupons are going to show
a negative mass loss. They have gained weight during the test, even if
you clean them up, and so on.

So, you realize that right there, you are in a situation in which you
have to start making some assumptions. Maybe we have silica deposition
on the surface of the specimens. Maybe we have to have some controls,
and so on, and so on.

Now, this gets a little bit better when you go over maybe two or three
years, and that is indeed what is happening here, are similar cumulative
distribution curves, in this case, going up to two years, and now a
number of things showing negative rates are becoming a little bit less.
Up here you have your corrosion rates. You have some kind of a median
that is less than a tenth of a micrometer per year, but you have some of
\-- here and there.

And, indeed, this kind of information is being used now for a number of
ways of assessing what may be happening over long periods of time.
Indeed, also what you see is that as the time of exposure increases, the
mean rate of corrosion of these coupons by gravimetric observation is,
indeed, coming down. And, here, we are hitting more like maybe the
hundredth of a micrometer per year. But, of course, you have this
uncertainty that comes from this test, and of course means you\'re going
to have also a spread of values.

So, so much for the kind of gravimetric information that is coming up
for these periods. There aren\'t too many other studies of extremely low
corrosion rates by gravimetric purposes of passive alloys in general.
You do have electrochemical evidence.

For example, in Gustavo\'s group at the Center for Nuclear Waste
Regulatory Analyses, they have produced information like this. I\'m
going now to the Yucca Mountain Project which provides information of
this type. You go ahead and you potentiostat an Alloy 22 specimen, and
then of course you look at the kind of current decay that you get, and
in this particular case, we have, in this example, we have a couple of
weeks worth of testing, and you see that the corrosion rate reaches some
kind of apparent stabilization at the value that is maybe about a tenth
of a micrometer per year kind of information.

Now, as many of you know this, you can get this, you plot a log of
current density as a function of log of time, and in that case, well,
maybe it still has a way to go on this. It may go to much, much lower
value if you extrapolate in that fashion. And I\'m sure that many of you
have other opinions and may have conflicting opinions after having
interpreted this kind of evidence. But this is the kind of evidence,
direct immediate evidence that we have right now, sort of like empirical
observations, that have to be meshed with some basic understanding to be
able to go ahead and extrapolate this orders of magnitude into specific
behavior.

And then, yes, you do have electrochemical, in this case polarization
resistance to the impedance as well, and you see also corrosion rates
approaching a hundred, maybe a tenth and a hundredth of a micrometer per
year, and this is linear polarization. In this case, we\'re talking
about a half a year kind of period of time. And this also indicates
something which seems to be distinctly below the tenth of a micrometer
per year.

So much for rates. This is the kind of information, the immediate
information that is available. A little bit on temperature dependence of
this kind of uniform corrosion.

The first indications of temperature dependence came from gravimetric
tests, and those indications were really not very informative. These are
rates, in this case in nanometers per year, from coupon tests that were
conducted at a couple of temperatures, 90 degrees and 60 degrees
centigrade, and this is the spread of the information. There\'s no
really good indication about what might be the temperature dependence.
Of course, this is a very crude method of trying to obtain that.

But on the other hand, we\'re talking about data that spreads over a
couple of years of time. So you have something in one direction, and you
have some in the other. But this was quite inconclusive. And in the
initial performance assessment exercises that the project carried, it
was assumed that temperature dependence of the uniform corrosion rate of
Alloy 22 in these kinds of environments was not very great.

Now, yes, you can do short-term experiments, and this is an example of
results from short-term experiments that were made at the University of
Virginia by John Scully and his collaborators. And here, you have some
potential scan tests performed in a relatively short time scale. We\'re
talking here in the hours or maybe a day at the most kind of time frame.
And, yes, in this case, you can get some indications of apparent
corrosion rates. This is a natural log, by the way, so it\'s a little
bit\--it\'s not immediately easy to look at.

But nevertheless, yes, there seems to be an indication of an increase.
You can go ahead and do what we\'ll do, just put a range of dependence,
and you end up with about 30 kilojoules per mole kind of activation
energy. It doesn\'t sound too outrageous, but what I want to indicate,
this is very preliminary information. This is just quick kind of
testing. We have some idea of what is happening, as one can speculate,
but that\'s about the kind of bit of information that is available for
this particular issue at this moment. More is coming, but we are not
quite there to the point where we have very nice data after several
years of exposure with different temperatures and very low margins, and
so on.

So, I\'m showing this primarily to give you a flavor of the kind of
information that exists. And, again, I apologize to the Project if I am
short-changing some of the information that is available. I\'m sure
they\'ll be glad to supplement some of it.

Now, I\'m just going to say a couple of words about localized corrosion,
and the kind of information that is available at this time. And I should
say that at this moment, the Project approach to performance analysis,
which is sort of like an extremely sophisticated overall durability
projection type of model, and that approach uses a critical potential
criterion. And that is, of course, to measure ranges of open circuit
potentials, to measure ranges of repassivation potentials. If your open
circuit potential is below the repassivation potential, well, you should
be fine. If it is above, you\'re in trouble.

A lot of this information comes from cyclic polarization tests, and some
additional information is now emerging, but again, we have to deal with
what is available at this time. And the overall conclusion of what has
been observed is that crevice corrosion will not sustain the
temperatures on the order of 100 degrees centigrade, and at the kind of
expected open circuit potentials, if you are balancing the chloride ion
content of the solutions with a comparable concentration of beneficial
ion, such as nitrate, for example, things of that order, if you put just
sodium chloride at those temperatures, and it\'s highly concentrated
sodium chloride, several molars, and so on, yes, you may develop
localized corrosion even in Alloy 22.

But when you have the kind of balances that Dr. Di Bella showed earlier,
then the localized corrosion doesn\'t seem to develop, at least within
the time frame and within the limits of the information available to
date.

There is concern, and Dr. Staehle has pointed out this, that there may
be other substances, say, trace elements of lead in the rock, and the
like, that may lead to surprises in not only the localized corrosion,
but also perhaps uniform corrosion of these materials.

But what I want to do is I want to close this review of the highlights
of what is know about corrosion of these materials by emphasizing
something in here. A, we have a very long time frame. We mentioned this.
10,000 years, we want to get farther ahead than that. The other thing is
something that I\'m sure Dr. Shibata has sensitized many of us of that,
and that is that each one of these packages, oh, has about some 20 to 40
square meters of surface, say 30 square meters of surface. There\'s
about 10,000 packages, or so, depending on what kind of a concept we
have. So, you can have 30 times 10,000, have 300,000 square meters of
passive alloy here to deal with. And there\'s a little bit of an
extrapolation from tests that you perform with 10 square meter specimens
when you\'re going to 300,000 square meters of surface.

The other thing is welding. These things have welds that have been
annealed, and then there\'s finally a closure weld at the end of the
package. Well, each one of these packages will have at least some 6
meters, or so, of closure weld at one end. So you have 6 meters times
10,000 packages, minimal, so you\'re talking about some 60,000\--about
some 60 kilometers of weld to consider in here. We are talking a long
time, and we\'re talking about a lot of material to consider. All of it
has to stay\--you want for it to be passive, and you certainly don\'t
want widespread failures of that material.

So, having said all that, we went ahead and we submitted to this
distinguished panel a couple of questions. And you have the text of the
questions. I\'m just going to show this to remind everyone of what is
the general flavor of the questions. And the first question was can you
propose a mechanism or mechanisms that would after a long service time
substantially increase the passive corrosion rate of all the presently
expected values.

You saw that if we go to \-- in the micrometer per year, we are likely
to have some kind of a very important question as to whether these
packages will do the job that the repository would need to have done.

And the idea was, of course, that maybe we do have these very low
corrosion rates, maybe a tenth or a hundredth of a micrometer per year.
This is happening for a while. But then maybe there is some kind of an
aging process that we don\'t know about. And, again, we\'re bringing you
here to speculate as to what processes might occur, and \-- may kick in
after 100 years or 1000 years or 5000 years. And if at that moment we
get something that starts boiling quickly through the container, we want
to have an idea, we collectively, not just the Board, but the community,
we would like to have some idea as to whether that might or might not be
happening. And the best thing that we thought of was to bring you all
here and ask you directly that question.

And then, of course, the other is let\'s suppose that we lay uniform
corrosion to rest, well, could something be happening at the localized
corrosion end? Is this open circuit potential, critical potential
criterion, that works so well when you\'re designing a refinery for a
chemical processing plant, will that work also for something that has
such a huge time designed service life, if you want to put it in those
terms, and also such a large opportunity for damage to develop from a
surface area standpoint.

And, of course, if you come up with ideas of things that could happen,
you thought about this or this, how could this be tested in a reasonable
time frame? As you heard today, our society is getting very close to
making some kind of a decision. Our representatives will make that
decision. We\'re not going to make that decision. But they are going to
have to be informed as to what may be happening, what may not be
happening, what may go wrong, and also, of course, what can go right
with the present concept.

I would like to finish this by pointing out a couple of questions which
are a little bit broader, but have to do with this as well, and they
have been posed by Dr. Paul Craig. And I\'m just going to flash them
here. We may put them back later. And I guess that someone decided to
call these philosophical questions. That was not my choice, but we\'ll
leave it with that name, and I think philosophical is a good idea.

And I think that the number one, this is addressed to the members of the
panel, and this is more of a general flavor kind of idea, and that is
what is, you know, when I think about this, what is the most significant
unexpected result or surprise that you have experienced personally in
the physical, chemical, materials science area. And then given this
experience, why do you or don\'t you believe that unexpected results or
surprises concerning Alloy 22 corrosion behavior will or will not occur
over very long periods of time. I think that that\'s a very good point
that Dr. Craig has made, because this is going to be a humbling
experience of going through observations in this area.

And, now, number two, which is again a little bit more general, is what
is your level of confidence in this kind of extrapolation that one would
be doing. And then how far out in time would you feel confident
extrapolating the corrosion behavior of Alloy 22. And, again, how far in
time are the operational works in here? Because that is what makes this
problem quite unique.

And I think those two particular issues are of quite significant
importance, and we\'re going to have to be looking at them. And there
may be one or two other questions that will be brought out that we can
discuss later.

So, this is really the overall kind of introduction that I wanted to
give you. And before we go into the individual presentations, do we have
any questions or comments that you would like to bring up based on what
I have shown up to now?

(No response.)

SAGÜÉS: Well, I think that you will have plenty to say on your own
presentations, so I\'m going to now pass the meeting to Dr. Bullen.

BULLEN: Thank you, Professor Sagüés. I appreciate you getting us right
back on schedule. We are at 9:55, and that\'s the beginning of the
individual responses.

Fortunately, I had a volunteer approach and volunteer before the meeting
started to be the first participant, and that is Dr. Gustavo Cragnolino
from the Center for Nuclear Waste Regulatory Analyses. And so I\'d like
to ask Gustavo to give us a five to ten minute overview presentation of
the response to the two questions.

So, Gustavo, would you please kick us off?

CRAGNOLINO: I want to start raising the same slide that you have seen
that Alberto placed here, and these are the results of our work, only to
emphasize that in this type of extrapolation that was done on the basis
of electrochemical measurements of passive current density over the
period in which steady state conditions are very well attained, we are
using Faraday\'s laws to extrapolate time of this nature.

However, these are the main issues that we have to confront, that we
don\'t have any way to estimate defect generation or accumulation of
metastable events that may lead to higher corrosion rates at longer
times.

And at some point that he touched on at the very end on how this could
be impacted by the effect of fabrication processes that we need to
consider.

These concerns about the validity of these long-term extrapolations,
either from the experiments that I mentioned as electrochemical or
gravimetric - we believe they need a critical assessment of mechanistic
models that could provide us a framework to try to understand new
methods or approaches that can be used for the purpose of experimental
verification.

And we have used this modified point defect model as a starting point,
but we have to keep in mind consideration of other type of passivity
models that should be placed in the perspective of providing us a way to
find an experiment that can in some way test, within the limitation of
time, the results.

And I will talk on one issue that we have to deal with very clearly is
there is validity for high temperature experiments as accelerated tests
for extrapolations to the low temperature regime. This is a question
that has been posed for many systems. It\'s possible that we are
confronting here times that are much longer than the time of the
engineering experience. And there is another factor that can be used to
accelerate this.

I\'m not going to go into details because I can cover this later on, but
to give you an idea, we started working with the idea of the modified
point defect model to try to develop a concept about the stability of
the passive film, and we came to the conclusion that by using this
model, the only thing that can explain seeing that would lead to
eventual failure of the passive film is the process of film spalling at
irregular locations. And we propose an heuristic model to account for
this process.

But the final conclusion by analyzing the process through this type of
model is that the steady state passive dissolution of this film is
stoichiometric in nature, even though initially, it would be a
preferential dissolution of the most easy to dissolve species like the
nickel in this particular case of the nickel chromium based alloy.

The important thing is that as we mentioned here, in this family of the
Hastalloy alloy that may contribute to passivity of the chromium rich
oxide type of film in which we can have a double layer in the interface
with the aqueous solution that is essentially more of a hydroxide type
of effect.

We went through this type of exercise using this theoristic model to
consider the process of film spalling and the alloy at different
thickness, and we can work with this, in which situation with
particularly this type of thickness of this flat, thin material in the
calculation, and the lifetime of the container will be a function of the
critical vacancy concentration fraction. This fraction is the
concentration of vacancy over the concentration of the other species
present in the interface. And film spalling is assumed to have occurred
under this condition.

We can come out with prediction in life that lead us to very long times,
except for critical vacancy concentrations that are relatively long.
This puts in question obviously to our thinking, that for one side, this
is valued as a concept, or there are some essential flaws that we have
to find out.

Our approach by using this model, and for that reason I emphasize the
model as a good way to design the experiment, but as critical responses.
If the model will not agree with the response that we are expecting, we
have to change the model. But this is the only way that we can come out
with an approach to predict this type of long, long time decay.

And we are doing an experiment in which we measure solution composition,
you\'ve seen capillary electrophoresis, to really evaluate if this
concept of stoichiometry in the long term is maintained, or we have
preferential dissolution of the alloying elements, and this is the type
of cell that were used for electrochemical purposes. I\'m not going to
go into details. We can discuss it later.

We need to grow to have very high resolution of the passive corrosion
density measurement over an extended period of time, because in my first
failure, you see that even though the current density is steady there is
a lot of fluctuation, indication that they are processes of film
breakdown and repair, and in order to evaluate the possibility of metal
vacancy accumulation, we consider the use of resistivity measurements in
thin foils.

To complete my point, we have to consider any other possible processes
leading to small increases of passive current density. That could be a
superposition of cumulative metastable passive film breakdown and other
repassivation effects. And another approach is consider other types of
models. I mentioned initially if the modification of the outer deposit
layer is able to create a local, more aggressive environment with time,
that will promote this type of very localized fluctuation in the
concentration of the variables that influence the breakdown and repair
of the films.

Obviously, the possible methodology that we have in mind is this.
Enhanced resolution of long-term either potentiostatic or zero
resistance ammeter measurements. But we have to keep in mind that when
we are using an electrochemical approach, this is a very important
consideration.

The basis of the consideration that was mentioned by Alberto regarding
the probability of events that we cannot capture using the smallest
specimen - tied to this, we have to consider the important role of the
cathodic area when we are talking about a very extended cathodic area,
compared to the situation when we are doing this under potentiostatic
control, in which we have a driving force for the process.

I\'m going to go very, very briefly, and think that is a matter of
further discussion, about certain semi-empirical approach that we have
been using for localized corrosion. And I think that we have to
distinguish very well in this type of approach. Here, we are
representing this dry period that was mentioned before in the
discussion, the situation of the formation of the liquid film that was
the condensed layer, that is many times promoted by the deliquescent
point of salts that have high hydrotropic properties, and the possible
evolution of the corrosion potential or the repassivation potential.

But this critical potential is not the potential that you have for the
initiation of pitting corrosion in the short-term experiment, but it\'s
a potential that you define as the minimum potential at which a surface
can remain active after having grown. And, here, there are some factors
I\'ve included in this, and what we have to consider is the stability of
this type of parameters in the long-term, because, as I mentioned here,
these parameters are environmentally dependent and the environment\'s
change with time.

And to emphasize the point, here are probably the main factors that have
an involvement in the definition of this corrosion potential and
repassivation potential. The temperature of the repository will decrease
with time. The corrosion potential will increase, but at the same time,
will increase the critical potential, decreasing the possibility of
localized corrosion.

But you have other types of events that could have an effect, like the
well-known effect of chloride, or the effect of the aging of the passive
film that will lead to an increase in the corrosion potential and
promote conditions for the initiation of corrosion.

And, finally, two aspects that cannot be neglected, and depending a lot
about the fabrication processes, and in particular, the post-welding
type of treatment either in the stage of fabrication or as was mentioned
by Alberto, in the closure welds, and this has a detrimental effect in
particular on the critical potential. For that reason, I don\'t have a
clear answer to the question in the way that it was formulated, but I
think that I tried to provide the idea that we have to confront this
issue by looking not only in terms of the projection in time and in the
space, but the projection in space has to take into consideration the
important variability in the condition of the material, as they seem to
consider in the long-term.

Finally, I want to acknowledge the people that have helped me in this
endeavor.

BULLEN: Thank you, Gustavo. I appreciate your brevity, and you were done
in twelve minutes. That\'s great. I\'ll try to keep everybody to at
least ten.

Now, at the risk of asking a professor who\'s usually programmed for 50
minutes to talk, because I notice most of you are faculty members, do I
have a volunteer?

Digby Macdonald, I saw him rustling his view graphs there. So, Digby, if
you could do it in ten minutes, that would be great, or less.

MACDONALD: Okay, I want to address this question in a somewhat
philosophical manner by pointing out that repositories are unique. In
fact, we haven\'t actually built one yet. And being unique systems, we
have great difficulty in developing empirical models that are based on a
statistically significant database. It doesn\'t exist.

Furthermore, the horizon is far too distant, 10,000 years, compared with
our experience in any given system where we have a well established
database, far too distant for any effective extrapolation. Accordingly,
empirical models are highly unlikely to succeed in this business. And
what we have got to do is to appeal to determinism as a prediction
philosophy.

And what is determinism? Determinism in this context simply says that
the future may be predicted from the past, provided that, and this is
the caveat, the caveats in this business are very, very important, the
phenomena are described in terms of viable physical mechanisms and
models; that the solutions to the constitutive equations, those are the
equations in a model that tell you how the model works, are constrained
by natural laws that are invariant in space and time; and finally, that
the path to the future state is continuous and can be specified. And
that is part of the\--one of the major problems in this whole business.
Can we accurate predict the path over which one of these canisters is
going to travel for the next 10,000 years.

I\'m going to show you a couple of models just very briefly that meet
these criteria, and the first one is some work that I\'ve been doing for
Gerry Gordon and his colleagues on general corrosion, and it\'s just
essentially a mixed potential model. What it proposes is that any
corrosion process can be broken down, fundamentally down into anodic and
cathodic processes, or oxidation and reduction processes, if you like,
and that the constraining condition is that charge must be conserved at
the surface.

So, the sum of all the partial anodic current densities must be equal to
the sum of all the cathodic current densities. And that condition
defines a very important parameter called the corrosion potential that
Gustavo just talked about.

Without going through all the mathematics, and there are a lot of
mathematics, I\'ll just point out that the model is based upon point
defect model, which I and my colleagues have developed over a couple of
decades, and I should point out that one important reaction, and this
should actually be over here, is the dissolution of the barrier layer,
in this case, chromic oxide, and that establishes a lower limit for the
corrosion rate. The rate of dissolution of the barrier layer represents
a lower limit, not a higher limit and not necessarily the corrosion
rate, because there are parallel reactions that can occur, the
transmission of cations by cation vacancies and the transmission of
cation interstitials through the barrier layer.

Nevertheless, if one goes through the mathematics and carries out the
prediction, you can predict the corrosion potential, which I should add
is in reasonable accord with the experiment, and you get this classical
\"S\" shaped, sigmoid shaped variation with log of the partial pressure
of oxygen. And this is on a standard hydrogen scale, which is not a
scale that is commonly used, but open atmospheric conditions puts the
potential around here.

Now, why is the potential so important? Well, the potential is important
because it determines the likelihood of localized corrosion occurring. I
think as Gustavo has shown, and Alberto showed as well, there\'s a good
argument that can be made that general corrosion probably will not
represent the major threat, unless there\'s some process that is
currently unknown in corrosion science that causes a massive increase in
the corrosion rate.

But that\'s not true with regards to localized corrosion. The problem
with localized corrosion is that we have very, very long periods of time
available for the nucleation of localized corrosion events on the
surface, and yet our experience of course is very, very short.

Just to show you some predicted corrosion current density plots, up to
120 degrees, you\'ll see that the corrosion current density is not a
strong function of the corrosion potential.

But let me move on to localized corrosion damage. Now, the objective in
localized corrosion damage is to calculate the so-called damage function
as a function of time. The damage function represents a histogram of the
number of pits that exist on a surface per unit area as plotted against
the pit depth. The pits that cause the greatest damage and could
ultimately cause failure are, of course, at this upper extreme of that
distribution. The total damage on the surface is the integral of the
distribution.

Now, the reason why the damage function is important is that you can
see\--and these are just schematic ones, but I\'ll show you actual
calculated ones shortly, and by the way, this work was funded by\--this
type of work was funded by the Department of Energy\'s Nuclear Energy
Research Initiative. The reason why this is important is it leads to a
natural definition of failure. If you have a critical dimension, in this
case 2 centimeters of C-22, then what you seek to calculate is the time
at which the upper extreme of this distribution extends past that
critical dimension, and that gives you the time of failure. And what we
want to assure is that the time of failure is greater than 10,000 years.

Now, does C-22 pit? Yes, you can make C-22 pit. Here\'s a pit. C-22,
this happens to in saturated sodium chloride solution at 80 degrees
Centigrade and a pH of 3, and I should point out a very high potential,
about 900 millivolts on the saturated cal/mol electrode scale.

Here\'s another one. This one shows the remnants of the barrier layer on
the surface, and you might also notice here that there\'s some very
small pits associated with crystallographic features on the surface. We
can actually measure the property. For example, we can measure the
apparent breakdown potential as a function of voltage sweep rate, and
the theory predicts that this should be a linear relationship, which it
is. And from this, we can extrapolate to obtain a fairly accurate value
for the breakdown voltage. And that\'s required in order to actually do
the modelling work.

Now, the model assumes that passivity breakdown occurs via the
accumulation of vacancies at the metal film interface, followed by just
dissolution of the film. And I\'ll show you now a series of calculated
damage functions. And I\'ll draw your attention to this parameter gamma.
Gamma is the delayed repassivation rate constant.

What happens, you see, is that pits are like people. They\'re born, they
live, and they die. And this parameter gamma actually describes how
these pits will die after they\'re formed. So if gamma is high, the
population dies very rapidly. If gamma is low, the population doesn\'t
die very rapidly. Gamma being zero, this calculation says none of the
pits die. They live forever.

The reason why you get a distribution is that pits are nucleating at
different times on the surface. Now, if I increase gamma, and I\'ll do
that drastically, let me go to this plot here, we now take gamma as
being equal to ten to the minus 3, year to the minus 1. It\'s the first
order rate constant. You can see that it has a very remarkable effect
upon the shape of the damage function. But most importantly, it has a
tremendous effect upon the population of pits at the upper extreme.

In this case, the pits do not extend to the critical dimension of 2
centimeters. And most of the pits in this distribution are dead.
They\'re ones that have already died. And it\'s only pits here at the
top of the distribution that are still living.

Now, I bring up this whole issue of gamma because it provides an avenue,
I believe, for being able to control the rate at which localized
corrosion accumulates on the surface. If you can devise a means of
controlling the value of gamma, you hold within your grasp a tool for
determining the ultimate amount of damage that will accumulate on the
surface.

With that, I\'ll finish.

BULLEN: Thank you, Digby. Again, twelve minutes. You did a great job.
I\'ll try and be more strict with the rest of you, I guess, otherwise
we\'ll be here all day.

Let me also comment that if you have extra viewgraphs and you want to
talk about them during the discussion period, feel free to bring those
up. We\'d like you to keep your comments to five to ten minutes right
now, and I\'m looking for my next volunteer. Any hands that are going to
shoot up before we have\--we\'ll do one more presentation. Professor
Strehblow? And we will take a break after Professor Strehblow\'s
presentation.

STREHBLOW: Everybody has to come up with ideas, and so I thought I\'d
come earlier so I can relax and listen to the remarks of others.

We have heard about the composition of these films, and I think the
major point is that these films are highly chromium containing, and it
depends on the pH whether there\'s any nickel in there or not. It\'s a
bi-layer film. The nickel is outside the chromium, the oxide is inside.
But in acidic electrolytes, when nickel has a chance to dissolve, we
have a lot of chromium inside. So this is a good idea for the choice of
the material, because chromium and its oxides are very resistant to any
aggressive anions, so it does not dissolve. It does not pit. It has a
slow dissolution rate. And the deeper reason is that the complexing or
the fierce coordination of such an ion is relatively stable, and it
needs a high activation energy to make any changes, let\'s say, to
chromium ion, to transfer the chromium ion from the oxide phase to the
electrolyte phase. So this is a very simple model of a passivated metal
to metal, oxide to the electrolyte.

We discussed about the corrosion rate in the passive state, and this is
the transfer of metal ions from the oxide to the electrolyte.

The potential at that interface is also determining the transfer rate,
because this transfer reaction sees the potential drop at the
oxide/electrolyte interface, which is in the stationary situation,
determined by disequilibrium of O2 minus formation.

And there is a very important point that we can expect that some
aggressive or complexing ions will help the cation to be transferred
into the electrolytes. So this is the case with the nickel. This is the
case with iron, which is not a point of discussion for this material.
But for nickel, it is, and that is the deeper reason that we accumulate
automatically the corrosion resistant chromium oxide which is sitting at
the surface, and once it has a chance to form a continuous film, it will
stop corrosion.

But there is perhaps some other point which we have to mention, and that
is the difficulties which may arise. One thing is the complexing ions
that I said when there\'s a chromium oxide, we have a good situation.
Mostly it\'s anorganic. As we know, the composition of the water in this
repository are \-- and I have seen fluoride and chloride, which is very
important.

Another problem could be the temperature, and the accumulation of
impurities which could also lead to a low local deficiency of chromium.
Once we have not enough chromium, then at some part of the surface, we
might not be able to reform this chromium oxide film once it has been
destroyed by some event, it could be also mechanically, and in this
case, we have perhaps a difficulty to reform this protecting chromium
oxide film. And as Alberto Sagüés has mentioned, we have large surfaces,
and these large surfaces could have also defects in manufacturing, in
welding and preparing the metal, and so forth.

Another point which I would like to mention, which is very important in
the test of corrosion rate, and could be important in the dissolution in
the passive state, could be radiation damage. This has been mentioned
earlier, and I\'m just wondering whether this is a major issue or not.
We have perhaps a difficulty to get alpha radiation through the thick
shell, and we might have difficulty even with the beta radiation, but we
will not have difficulties with the gamma radiation. And this could also
perhaps cause voids and defects. Implantations would be with heavy
metals, but this would be at the opposite side of our material.

And then last but not least, there is radiolysis, which is causing
oxidizing species like the hydrogen peroxide, which could raise the
potential if this is a major problem. But that depends on what is in the
containers and what the situation is there.

We have heard about the composition of the water in the water table \--
and the brines which could be formed. Then there was a relatively modest
concentration of these special aggressive anions, like a 10 to the minus
2 molar for chloride, or four times 10 to the minus 2 for the fluoride,
which I estimated from the amount which is there. And these
concentrations might not be critical for our Alloy 22, or similar
alloys, but we have also the situation, as Carl Di Bella said, there
could be an environment where the concentration could be higher. If we,
for instance, have a higher temperature and we concentrate more and more
of these species, then the concentration could be higher and we could
end up with a Q-brine, which is more or less a concentrated chloride
solution. And that\'s also something that Cragnolino mentioned perhaps.
But I\'m sure that Digby has mentioned that, and he did pitting
experiments with a high concentration of chloride.

And then we end up with a very critical situation. The fluoride is also
very aggressive. We should call that in mind. It\'s very aggressive for
the nickel, but not for the chromium.

Now, just to mention some few experiments which are in this sense and
which could be important, is passivation transients with material which
is relatively similar to the Alloy 22, this is Hastelloy C-4. It has 5
percent less chromium, but it is close to the Alloy 22, and it has a
high chromium content. If we have a 25 centigrade electrolyte, and if we
have this highly concentrated electrolyte, high in chloride, the
Q-brine, then we don\'t see any pitting in these transients. The
potential is just positive enough to have a transpassive situation.

Now, if we raise the temperature, then we end up with pitting
experiments. This is the logarithmic growth of the current density as a
function of the time, and with the preservation change, you should have
a slope of minus 1, which is the case. But then if you have a slope of
plus 2, then you have the typical pitting situation, and then you have a
pit growing, and if this is the case, you can look to the surface and
the pit is growing. So the potential is not very high. This is against a
standard \--. And then you end up here with a potential where nothing is
occurring in this short time scale at 200 milliwatts, but this is 60
degrees. And I have another one which shows the situation for 90
Centigrade, and this is even more dramatic. Then you have already a
beginning of localized corrosion at 200 milliwatts, which is about the
open circuit potential for these conditions, as has been studied.

I also would like to mention that we have breakdown and repair events.
And if we increase the temperature from 50 degrees to 80 degrees, and we
make a temperature transient, then you see a strong increase in these
oscillations, which is breakdown and repair, then breakdown and repair.
And I just estimated if we take this amount of charge and extrapolate
that, we are ending up also with something like a little bit more than a
micrometer. It could be two or three micrometers if these oscillations
remain as large as they are. But they might die out and get smaller, so
I made a factor of .1 in there, but I\'m still ending with 3.5
micrometers per year as a material loss.

And if there\'s a pit and we have a pit within the pit, it will deepen
the defect. And then, finally, we may end up at up to 10,000 years with
a breakdown.

Well, just to illustrate a little bit radiation damage, I brought along
one viewgraph which is showing in principle the possibilities which may
occur. This is the alpha radiation, which is not a big deal, because our
radiation is coming from inside. This is the situation when the solution
is contacting the corroding surface, and there is the oxide film, and
there we have defects which will be formed. And this is something that
goes in the direction of Digby\'s defect model.

You have also the formation of dopings, and then you have\--I think that
is the thing which we should discuss a little bit, whether this is
realistic or not. We might have the formation of very oxidizing species
due to radiolysis. If the gamma radiation is, for instance, getting
through this material, and it will, then there might be a chance that we
have oxidizing species which are increasing the potential, and then it
could get above the pitting potential if the concentration and addition
of the aggressive anion is very high.

Well, I think this should be enough for the viewgraphs, because we would
like to have some little break, and then the others might add something
else.

I just wanted to mention here at the end that the penetration depth for
alpha is definitely too small to get to the other side of the container.
The beta might be good enough if the energy of the radiation is high
enough. The gamma definitely will get through.

Thank you.

BULLEN: Thank you very much, Professor Strehblow.

I\'m going to keep us to a strict time table, so we\'ll take a 15 minute
break, and reconvene at 10:45.

Oh, by the way, could I make the comment to all the presenters if you
have additional transparencies or viewgraphs that we haven\'t made
copies of, would you please make sure the staff gets them so we can get
copies to everybody?

Thank you.

(Whereupon, a brief recess was taken.)

BULLEN: The second part of the presentations by the panel. Our next
presenter will actually be Roger Newman, to be followed shortly by
Alison Davenport. So, Roger, if you\'re ready, we\'ll get you miked up
and ready to go.

NEWMAN: This is the second one of these events that I\'ve been to, and I
was very disappointed that the professor of philosophy wasn\'t here this
time. That was really enjoyable having her here pointing out when we
were talking bunk, which was most of the time. But, anyway, now the
scientists are using the word philosophy.

I\'d like to just say a few very brief words really about, rather
conventional words about this topic. And to some extent, I think I\'ve
addressed the questions, although I must admit to some extent, I\'ve
made up my own questions.

The first question is what is this passive film that we\'re all talking
about? And my view, which I think has been acted by one or two of the
other panelists, is that this is essentially chromium III oxide. You can
find a lot of other things in it if you look hard enough, but to this
day, I don\'t think we have any understanding of whether these other
things have any causal role in the passivation process. We have quite a
lot of evidence that the chromium oxide is the thing that actually
causes the passivity.

The second point, and I certainly would expect a certain amount of
discussion with some of my colleagues on this point, is whether the
molybdenum is good for the passive film. My view, and I think I\'m not
entirely out on a limb here, is no. This molybdenum that we put in this
alloy prompts its resistance to localized corrosion. But I would
certainly argue that that effect takes place when you already have a
small dissolving cavity, in other words, a kind of protopit. It has
absolutely nothing to do with the passive film. And, in fact, quite
often, molybdenum just comes after the passive film. So it\'s really
this chromium oxide film.

The third question, which I think we\'re coming to the actual questions
gradually here, is that how thick does this passive film grow? Well, we
often find this sort of 1/t, in other words, the growth rate of the film
is proportional to time. And if you extrapolate some data that exists,
you find this thing doesn\'t really grow at all. It will never get
further than about six or seven nanometers.

On the other hand, the assumption in this 1/t extrapolation of the
corrosion rate is that the passive film is not dissolving. Well, that\'s
clearly a poor assumption. And I just point it out here. Suppose even
though the film development is limited by some film dissolution process,
and even if this dissolution, the equilibrium solubility, if you like,
is only on the order of 10 to the minus 14 molar, this would still pin
the corrosion rate up at one nanometer per year. And if all this stuff
is re-precipitated, you could build up a layer on top of the film.

Now, so what, you might say. It wouldn\'t be shiny any more, but it
would still be protecting the contents. And, indeed, my general view is
probably the so what is probably right response to that, because I think
this C-22 is pretty good stuff. And most of these discussions on
localized corrosion probably are going to lead to the conclusion that it
will last pretty well, for at least hundreds to thousands of years.

So, how could this mechanism of film growth change with time? Well, one
aspect that\'s already been mentioned is that you have a steady outward
drift in this thing called the corrosion potential. That\'s the steady
state electro potential to metal. And not only do you have oxygen
driving that up, you also have peroxide created by radiolysis on the
surface of the container. And, in fact, this reaches the borderline of
what I\'ve chosen to call transpassivity, especially if the pH is a bit
high. In fact, this transpassive dissolution is worse at high pH values
than it is at neutral pH values.

And in the pulp and paper print industry, for example, when some people
carelessly use peroxide as a bleach without thinking about their
materials, they discover that these nickel based alloys would corrode at
several millimeters a year. That was a lot more peroxide than you have
in this system, obviously.

What is this transpassivity? Well, normally it\'s considered to be this
chromium to chromium VI, and that might be possible, but the main thing
that\'s going to happen is the molybdenum is going to dissolve out. So,
to some extent, you\'re losing the beneficial effects of the molybdenum
in the near surface layer as a result of this dissolution reaction. So,
in other words, the corrosion rate might level out instead of paring off
and falling to 1/t.

Another thing that might do that is fluoride. Henning said that fluoride
doesn\'t complex with chromium. But it certainly is an aggressive anion
and might make the film continue to dissolve.

There are other things. Peroxide itself is a complexant of titanium. The
same people that had the problem with the nickel based alloys in the
pulp and paper industry, some of them replaced the nickel alloys with
titanium, and promptly found that the titanium corroded away at several
millimeters a year as well. And that\'s because the peroxial anion is
actually a complexant of titanium. So there could be other things
floating around in this water that you just have to think about, even
organic materials, which are possible complexants that could make this
corrosion rate level out instead of continuing to fall.

Having said that, I don\'t think that\'s going to make these things fall
apart or leak all over Nevada, or anything like that.

But, can a thicker film be bad? A thicker film seems like it\'s good.
It\'s a protective. Well, this is where we come to the issue of
localized corrosion. And there is a strong possibility, and Professor
Sato was the originator of this kind of idea, is that if you have this
thick sort of nanoporous type corrosion product film that results from
this long-term passive dissolution, it can act like a membrane. Well, in
fact, specifically can act like an anion selective membrane, such that
you will stabilize the pitting process.

So, if we say that pitting is stable at 90 degrees in normal conditions,
over long periods of time, you might find that pitting is just as stable
as crevice corrosion in these containers, because this layer, this
membrane of corrosion product will enable the pitting to survive under
conditions where normally you\'d only get crevice corrosion, essentially
because the chloride ions can get in through the layer, but the metal
ions can\'t get out. You build up the aggressive metal chloride
environment underneath the film.

On the other hand, if by that time the temperatures fall to 60 degrees,
I wouldn\'t anticipate that these containers are going to suffer any
dramatic corrosion. And, in fact, all this discussion neglects the
actual cathodic reaction, in other words, the reduction of oxygen or
peroxide, whatever is the oxidant in the environment. I consider it
perfectly possible that when you build up these thick layers, that in
fact that might shut off the oxygen reduction reaction and make it very
difficult for the process to continue.

However, we should always remember this water is full of nitrate.
Nitrate is also an oxidant. You can say, well, it\'s not very
kinetically oxidizing, but it is there.

With regard to measuring these corrosion rates with electrochemistry,
this water has enough redox activity in it that I would rather doubt the
ability of electrochemistry to measure long-term corrosion rates when
you\'ve got nitrates and other things in the water.

And, finally, just a comment on metallurgy, is that we do have welds in
these things. They have spatial variations in chromium and molybdenum
are less corrosion resistant. I still don\'t understand why Henning\'s
C-4 alloy pitted as easily as it did. It shouldn\'t pit like that at 60
degrees anyway. These large areas of metal will have large inclusions,
fabrication defects, and so forth, in them.

And I\'ll just mention phase transformations because at one time, people
were talking about higher temperatures for these containers. Maybe that
was a long time ago. But I would think that the temperatures that are
being discussed now maybe these transformations are not important.

So, just reverting then to the two main points, I don\'t think these
things are going to fail by passive corrosion, but you will develop
probably thick layers, microns thick layers, and these thick films will
probably adversely affect the localized corrosion resistance, in other
words, pitting resistance, they\'ll act like membranes, and you will, to
some extent, have local, the possibility of local perforation of the
material if it\'s exposed to the appropriate bulk environment. But, you
know, I\'d have one of these in my back yard, and if anybody wants to
pay me to put it there, I\'d be happy to discuss it with them later.

Thank you very much.

BULLEN: Thank you very much, Dr. Newman. We appreciate it.

Next up is Dr. Davenport.

DAVENPORT: Well, I think the issues that I\'ve been considering are in
many cases quite similar to a number of the ones that previous panel
members have come up with. So I\'ll try and keep things fairly brief, so
that it doesn\'t get too repetitive.

I\'d like to start off by thinking about, very briefly, about how
passive films actually form, and in aqueous environments, because
obviously that\'s going to be the conditions where we\'re going to get
the most severe attack, compared with dry conditions.

First of all, we\'re relying on a passive oxide film. The passive oxide
film that does the job, that actually drops the current density down to
a low level so the corrosion resistance is very low is very thin. It\'s
on the order of nanometers. The driving force has to do with the overall
potential drop across the metal environment interface. And we form the
passive film by a solid state process here, and it\'s driven by the
electric field, and then we are going to have dissolution of the film at
the surface. And chances are, over long periods of time, we\'re going to
get to the point where we\'ll get to a limiting thickness of this film,
where when we get to the dissolution, we\'re going to get a bit more
film growth to replace the material that\'s lost.

So, chances are, in terms of the average passive current density, the
average penetration rate of a passive system, is going to be affected by
the solubility of these metal ions into the adjacent environment. Very
much as Roger said before, these dissolved species are going to probably
precipitate with things from the environment, ions from the environment,
and also get involved with dust and scale and any other debris from the
environment, to perform a much thicker external layer.

So, thinking about the factors that could actually make corrosion take
place at a faster rate than we expect, I think the thing that we need to
think about is what the materials are that we\'re dealing with.

Now, the group of people here, I don\'t need to have to say this to, but
to those of you who don\'t study passive films, it\'s very difficult to
study passive films, and one of the first things that we do when we
study passive films is try and work on a very, very well defined
surface. So, a lot of us here spend a lot of time preparing single
crystal surfaces or spotted thin films that are beautifully homogeneous,
so we can test fundamental models.

And so I think there\'s a risk that we might possibly forget that we\'re
dealing with real alloys, and we have to remind ourselves sometimes that
the problem in these systems is going to happen at heterogeneities in
the surface. These alloys have intermetallic particles. They have grain
boundaries and dislocations which are high energy sites, where
impurities can segregate.

When we\'re dealing with very large amounts of alloys, we\'re going to
have big defects introduced from the processing of these alloys, and
then when we have segregation and precipitation processes, we\'re going
to get regions that are depleted in beneficial areas.

So, I think we have to remember that whatever theories that we\'re using
to test these ideas, to test passivation processes, we have to remember
what metallurgical heterogeneity will do to this.

So, being a little bit more specific, what are the factors that could
increase dissolution of passive films? We\'ve got the possibility of
impurities in the alloy, and over long periods of time, perhaps with
elevated temperature, perhaps with the effect of vacancies introduced by
radiation, is there a possibility that elements that we know are
damaging to passive film stability, for example, sulfur and phosphorous,
these will increase the dissolution of the passive film, is it possible
that these, over long periods of time, can segregate to high energy
sites such as grain boundaries or dislocations, so that we get a local
enhancement in the rate of passivation?

Similarly, as I mentioned before, could we have the formation of
intermetallic phases or solute-depleted regions? Again, could these
happen over the very long periods of time that we\'re concerned about
here?

To reiterate what Roger said further, other issues we have to consider
are the possibility of transpassive dissolution. And this, for
transpassive dissolution to take place in the system, we have to have a
somewhat elevated potential compared with the open circuit potentials
that people expect for this material in the environments that we\'re
considering.

So, I think we have to think about what sort of factors might increase
the open circuit potential, and those are going to be things that affect
the cathodic reaction. And in worrying about anodic dissolution, I think
it\'s very important that we don\'t forget the importance of the
cathodic reaction.

Again, people have already talked about radiolysis. Are there some sites
on the surface which could end up being catalytic for oxygen reduction,
for whatever reason? Is there a possibility of microbial effects that
could do that?

And then, finally, my comment earlier, what is the variation in the
water chemistry across the repository? Is it a possibility that there
are some regions in the repository where we might have particularly
elevated concentrations of some adverse species? For example, sulfur
oxyanions are known to be very detrimental in affecting the reaction of
nickel based alloys.

The factors that affect localized corrosion are in some ways going to be
quite similar to the factors that affect passivation. Again, we\'re
concerned about the open circuit potential, so we\'re concerned about
the cathodic reaction driving up the potential. Segregation of
impurities or loss of beneficial elements is also going to affect
localized corrosion, as well as passivation processes.

And, again, we have to think about the effects of these thick scale-like
deposits. Roger has already mentioned these two factors, the idea that
could we get crevice-like behavior underneath these deposits, and some
issues such as ion-selective action of the deposits.

So I think the two main areas that I\'d like to highlight are the
metallurgy of the alloy and how the heterogeneities in the alloy that
could lead to sites that actually behave worse than the bulk matrix of
the alloy and, secondly, to think a lot more carefully about the
cathodic reaction and things that could influence the cathodic reaction,
and take the open circuit potential rather higher than we would perhaps
normally expect.

BULLEN: Thank you very much. I appreciate your succinctness. That\'s
great. It keeps us on schedule.

Our next presenter who had volunteered is Jerry Kruger. Dr. Kruger?

KRUGER: I\'m going to restate the issue as I see it, and that is that
even though the test facility results are a rather narrow range of
conditions, show\--and I\'m quoting from it\--no discernable effects of
solution composition, vapor space, or direct emersion of placement, or
temperature, the main issue, as I see it, is can long-term changes in
these conditions completely overturn this result.

And, being an old time government worker, I\'m going to follow very
precisely the kind of instructions that we were given.

BULLEN: Thank you.

KRUGER: Including using the plausible mechanisms that were suggested.
And it was said that we could use the ones, and I\'ll one of my own.
First of all, is the defect sweeping, and that\'s described in the
attachment, and I won\'t describe it. But, anyway, what happens is that
the passive film becomes a film with high vacant densities and leads to
enhanced ionic transport.

And then we were asked is this plausible? And I say, well, possibly
plausible when conditions change over time.

The second one is vacancy build-up. And what we have is different rates
of dissolution alloy components, and that, as has been pointed out by
the last two or three speakers, is certainly a possibility when the
potential brings you into the transpassive region. So, these different
rates of dissolution yield to vacancies at alloy passive film interface,
causing film disruption, the kind of point defect model that Digby
Macdonald, for example, has worked on. And this is more likely to occur
at discrete sites because of the metallurgy and impurities and various
variations. And so this would lead to localized corrosion.

So, in terms of uniform corrosion, perhaps not. But in terms of
localized corrosion, certainly. It would lead to uniform corrosion if
the disruption or the spalling of the film, which was mentioned, would
remove large parts of the film, which I think is quite unlikely.

The third one of these speculative mechanisms is debris accumulation.
And, here, the passive film is transformed into a film composed of
corrosion products of hydrated metal ions. Henning Strehblow mentioned
these. And the film is probably, again, the result of chrome depletion.

And as the work of, for example, Norio Sato showed, such films may be
anion selective, thereby again promoting localized attack. So this is
plausible for failure by localized attack. Again, the question number
two. I looks like localized attack, is going to be a much bigger
problem, of course. And as Roger Newman pointed out, the passive film is
pretty darned good.

Incipient transpassive behavior. And this I think is maybe the biggest
problem, because thermodynamics would predict that if the potentials
become transpassive, you would get dissolution of molybdenum and
chromium. They oxidize to soluble species, and this leads to an
unprotective film, and the process is promoted at high pH, as Roger
Newman mentioned.

So, this is plausible if conditions change that lead to transpassive
potentials, and we don\'t really know. We really need more research to
determine whether this indeed could happen.

And, finally, one of my own additions on mechanism, and one that has
generally been ignored, and that is gaseous oxidation. And, here, we
form thicker layers by oxidation mechanisms that would occur when the
system is dry and contains steam and/or air. Now, these layers, it\'s
found in the research that has been going on that Dr. Sagüés mentioned,
that this is a minor effect.

Sure, I agree, but over 1000 years, it may not be, and the films would
grow very, very slowly, but they would grow, and they may not be as
protective as the original passive film. So you could result, once the
environment becomes wet again, and that could go between dry and wet a
number of times, you have aqueous solutions with chloride ions, and
these films may lead to localized corrosion.

So, this is plausible when conditions change from gaseous to aqueous
solution environments.

Now, the next thing we were asked to do was experiments and/or theory to
assess the validity of mechanisms, and I would suggest the follow two.
One, experiments and theories on the effects of environmental changes on
the increase of potentials to transpassive values, leading again to the
dissolution of the alloy components in the passive layer.

And, finally, the gaseous oxidation that I mentioned earlier in steam
and/or air at temperatures, and we go to high temperatures just to speed
things up a bit, 100 to 250 degrees C. to determine the nature of the
film produced over long times, and whether these films can resist
localized attack in aqueous solutions containing aggressive anions, as
the solution goes from dry to wet.

Now we get to question number two. We had a choice of 2A or 2B, or both,
and I chose 2B, because 2A is more difficult. And this question 2B is
localized corrosion mechanism for the initiation and propagation not
dependent on the critical potential. And it has been suggested that if
you are below the critical potential, you get metastable pitting, and
many, many experiments have shown that this is so, and this is
considered by many workers, for example, Tim Burstein from Cambridge, to
be the kinetic precursor to stable pit growth.

And it especially can happen, I think, for long times. So one of a
number of proposed ways in which these events of metastable pitting
leading to stable pit growth can be described is as follows.

One, the anion, probably chloride anion, moves through the passive film
at local sites under the influence of an electric field, as Alison
mentioned just a few moments ago.

We have the formation then of metal chlorides at discrete sites at the
passive film-alloy interface. And the with the point vacancy model for
pitting that Digby Macdonald has mentioned, we have initiation upon
rupture of the film at the metal-chloride sites.

Then you get pit growth at the exposed sites sustained when chloride
ions under diffusion control can prevent repassivation. And this would
occur for the very large areas and below Ecrit. And our absent panel
member, Hans Bohni, has also shown that crevice corrosion is considered
by some to also be dependent on metastable initiation r-passivation
events to sustain growth.

Now, finally, question 2C, experiments and theories to investigate the
issues of 2B. And first of all, we need more experimental studies of
metastable pitting by, for example, using things like Dr. Bertocci has
done, electrochemical noise at environmental extremes that may develop
in the repository.

We need theoretical treatment of the effects of environment on the
chloride ion transport through the passive layer under an electric field
to examine the build-up of metal chloride at sites of local film
distribution.

And, finally, we need theoretical treatment of such events as those in
air and steam for long periods of time.

BULLEN: Thank you, Dr. Kruger. I appreciate your brevity. Dr. Rapp\--oh,
I have one more, and then I\'ll go to you.

Dr. Marcus has volunteered to go next, and then, Dr. Rapp, if you\'re
interested? Okay, we\'ll go around the table. That would be great. Thank
you.

MARCUS: Okay, we\'ve been asked to answer some precise questions in a
very concise manner, and although I don\'t work for the U.S. Government,
I also tried to do it in a concise manner. So I have written down a
number of phenomena which I believe could be important in terms of
mechanisms that may cause the long-term corrosion rate to increase. So
that was question number one.

And the proposed mechanisms I have indicated here four possibilities,
which I think should be taken into account. I think we have to consider
the increase or at least the change in the surface and interface
roughness during dissolution in the passive states. Usually when a
smooth surface is passivated, there is an increase of the roughness, and
I\'m talking about roughness on the thermic scale, and this increase of
the roughness is caused by competition between the dissolution of the
metal and the formation of the oxide. So, there is a marked initial
increase of the roughness.

Whether this roughness will continue to increase on the very long-term
experiments, that is not known. Usually the roughness increases very
much at the beginning, and then it does not increase very significantly
over a time period of hours or tenths of hours, but over 10,000 years, I
think we don\'t know.

And I think that this is an important issue, because there is no such
thing as uniform dissolution in the passive states. In fact, dissolution
of the passivated metal or alloys takes place at preferential sites,
even without localized corrosion, on the atomic level, and any increase
of the surface roughness will correspond to an increase of the number of
defects. And, obviously, the dissolution current is proportional to the
number of defects, and that could increase the dissolution in the
passive states.

Now, similar reasoning leads to the consideration also of the roughness
at the interface between the metal and the oxides, because that may be
more important even for localized corrosion, because the dissolution of
the cations from the interface through the film to the electrolyte takes
place essentially at defects located under the passive layer. So that\'s
important both for general corrosion in the passive states, and also for
the possible initiation of localized corrosion.

Another point which has already been mentioned previously is the
accumulation of vacancies below the passive film, which may result from
the injection of vacancies during dissolution of the oxides, at the
surface of the oxide, as Digby proposed. But that would also be due just
to the fact that in the passive state, dissolution involves the
transport of metals from the interface to the surface of the oxide, and
of course that leaves the vacancy behind, and if the vacancy cannot be
annealated, then there might be correlations, and that can lead to the
formation of cavities on long-term time periods.

Another aspect is, in my view, the segregation of impurities. Any alloy
contains impurities, and these impurities can segregate at the interface
and weaken the chemical balance between the substrate and the oxides.
And there are two mechanisms of segregation of impurities in aqueous
corrosion. One is the anodic process by which an impurity, this is
illustrated here, an impurity even with a very, very small
concentration, which is in the material can accumulate at the surface,
or at the interface with the oxide film while the metal is being
dissolved.

So, even impurity levels of the order of the ppm, parts per million, can
result over a long time period in the formation of very significant
amounts of these impurities at the surface, or at the interface. This
was found many years ago and called anodic segregation. This was found
for sulfur on nickel and nickel based alloys. But this can also exist
for other impurities, not only for sulfur.

Now, another, say, more classical process for surface segregation is, of
course, the thermal segregation by diffusion, and perhaps we cannot
exclude that if the temperature goes up to, say, 160 degrees, and that
is an average temperature, I don\'t know what is the variability, and
maybe in some local area that could even be higher. So if we reach
temperatures of the order of 200 degrees Celcius, I don\'t think that we
can exclude the possibility also to have segregation, interfacial
segregation, under the effects of temperature, just by, in that case,
with diffusion.

In the first case, there is no transport through the solid state which
can take place at room temperature. Of course, in the second case, it
would take place only in the case where the temperature becomes higher.

And the fourth mechanism which I think should be taken into account is
that the composition of the alloy near the interface can change. It\'s
known that just under passive layers, alloys have a different
composition than the nominal composition. Usually, the area of the
thickness in which this composition is modified is very small. It\'s on
the order of a few atomic planes. But, again, that\'s for experiments
that last just some hours or tenths of hours. And over 10,000 years, I
think we have to worry about the composition of the alloy under the
oxides.

I have indicated here just the chromium depletion, but other elements,
they can also become enriched or depleted in the zone which is under the
oxide surface.

So, here, the emphasis that you see is maybe more on the interface
between the oxide and the substrate than just on the surface, but I
think issue is on the interface, the oxide alloy interface, can be
important.

We were also asked to suggest some experiments of theoretical treatments
to assess the validity of these proposed mechanisms. So this is only
some general ideas. I think that there is correspondence between the
colors in these dots. I think surface roughness which definitely needs
at least some short-term measurements. We don\'t know at this stage, at
least I don\'t know whether the roughness will increase or not, and that
can be important. And then, of course, we need to use simulation.

But I think that I don\'t necessarily agree with what Digby said
earlier, that for any simulation or modelling, we need really to know
the mechanisms. It has to be based on deterministic or mechanistic
approach. So I think it\'s necessary to know the evolution of the
surface and interface roughness, and then use the data in simulation.

The same would apply to the investigation of vacancies. We have been
talking already a lot about vacancies under the film, but there are very
few, and I think there is a real lack of data. There are now techniques
capable of detecting vacancies under thin oxide layers, and I think
experiments should be conducted, and then again the data should be used
for simulation on long-term evolution.

Regarding the segregation of impurities, one way could be to produce
alloy with increasing amounts of impurities, including sulfur, and then
look at the behavior of some sort of accelerated tests on the effect of
impurities. And I think we also need data on changes of composition for
this particular alloy, changes of composition under the oxide layer, and
again, data which could be used if they are based on a mechanism which
could be used in simulation.

Now, about question number two, in fact, there are many similarities
between phenomena that can increase the corrosion in the passive state
and those that can lead to localized corrosion. It\'s not two separate
worlds. And I have mentioned here the passive film breakdown which can
be caused also by segregation of impurities at the interface. So this is
very similar to the mechanism I have shown before for anodic segregation
on surfaces. But this time, we have the passive film, and this
interface, and this is mentioned in one of the scenarios, the interface
here is just sweeping the alloy with time because of the dissolution,
and then we can have the accumulation of any impurity that cannot
diffuse through the oxide layer.

And, for example, it\'s the case of sulfur, which does not diffuse even
under the electric field through the oxide layers, and will accumulate
here. But in that case, we usually have fluctuations of the
concentration, with higher concentrations at the defects, so the
vacancies are also important for this mechanism. And that can lead to
localized breakdown of the film, and that breakdown is not really well
described by just using the concept of critical potential, critical
pitting potential.

Another aspect is the local depassivation by aggressive ions other than
the chloride ions. This has been mentioned already I think by Henning
Strehblow earlier. I think we have to maybe worry about other anions
than chloride, which can complex the surface. So, fluoride usually is
not a complexing agent for chromium oxide, at least if we look at the
general surface, but the question remains on whether maybe fluoride
could have some effects on localized area over a very long time period.

So I don\'t want to say that it\'s only fluoride that should be
considered, but say a number of anions present in the environment.

And now for the suggested experiments. I think that I have here brief
suggestions. The answer is the same as for question number one. I think
that for the localized breakdown of the film caused by progressive
accumulation of impurity at the interface between the oxide and the
metal where we could do some measurements with increasing amounts of
impurities that could be considered as potentially detrimental, like
sulfur, and that we\'d also need some maybe more work on the mechanism
of local depassivation by anions other than chloride ions which have
already been studied a lot. Probably we need even more work on that, but
we definitely need more information on the effects of anions other than
chlorides in the perspective of long-term extrapolation of passive
behavior.

Thank you.

BULLEN: Thank you, Dr. Marcus. Dr. Rapp?

RAPP: The panel members are well aware that I\'m not an expert in
aqueous corrosion, but I have studied for a while scaling and high
temperature dry oxidation. And about four years ago, with Sylvain
Larose, we prepared a review of low temperature oxidation of carbon
steels, and low alloy steels for high level radioactive waste packages.

At one time, as I understand it, a thick steel, cheap steel container
was considered, and they wanted to know what would be the corrosion
prediction for 1000 years. And so I will make some comments concerning
the growth of dry scales on steels, but you can generalize the comments
to other alloys, for example, C-22, eventually. At least for these
steels below 550 C., you only make magnetite and hematite, and the
proportion of the two scales is something like three to one. Cations are
the migrating species in each scale layer, and by vacancy migration in
hematite, but both interstitials and vacancy diffusion in magnetite.

Well, the oxidation of pure iron had been studied very nicely by Caplan
and Cohon, who\'s a world-class outfit for such studies, and they
showed\--this is a parabolic rates constant, Kp, this is the\--the
equation is the weight change squared is equal to Kpt. So the Kp is
shown to be dependent upon the initial surface preparation, which has
not been mentioned once here today, I don\'t think, and they found that
here for temperatures down even 400 C., that there\'s about an order of
magnitude faster oxidation when a metal is electropolished, pure iron is
electropolished\--excuse me\--lower when it\'s electropolished, and
reasonably defect free, compared to a surface which has been cold worked
and deformed.

So, I think in these canisters that will eventually be made, if they
are, we should certainly have some specific initial surface treatment,
and I would recommend electropolishing if that\'s possible.

Now, these are the results of a study, a very nice study by Runk and Kim
on the oxidation of iron chromium alloys. They used mechanically
polished surface, which would not be the best. They had three kinds of
high purity alloys, .2, .4, .8 carbon. In other words, these were not
commercial alloys. They had three kinds of microstructures, fine
pearlite, coarse pearlite, sparidized structure, and at low temperature,
at really low temperatures, 200 C., they did get logarithmic kinetics,
but only for a matter of hours, or a day or so.

After that, everything became parabolic. And so this is what I would
call low temperatures of interest to this canister, and these are our
extrapolations of the parabolic rate constants for a steel with .8
percent carbon to 1000 years.

Now, I\'ll tell you, by the way, if you look at this kinetic curve, this
is the weight gain squared per unit area versus time, and this is the
classic way that everybody gets a parabolic rate constant. They say when
that becomes linear, that is an incorrect calculation, and we have
corrected all of these.

You see, it is not parabolic unless this curve goes through zero. Then
it is parabolic. Here, you see there\'s some initial rapid weight gain
in both of these, and when you take the total weight gain squared, you
have some initial, plus the time dependent W and you square it, there\'s
always a middle term of 2W initial times W, which never is terribly
small.

So, if you instead analyze the weight change in such an experiment as
the linear weight change versus the square root of time, you will get a
true parabolic rate constant, and you will find out when it is
established. So, we have done that, and these are corrected weight
constants.

And the important point is after 1000 years, for .8 carbon steel, these
are all negligible. This is the weight gain, this is the thickness of
the scale, and this is the recession of the alloy. These are all
negligible, in my opinion, for 1000 years. And because it\'s a
parabolic, if you want 10,000 years, just take a ratio of times, square
root of a ratio of times, and it will still be negligible. So, even
carbon steel looks perfectly all right in a dry environment for the
protection at these temperatures.

We also examined the oxidation of a two and a quarter Chrome-1 moly
steel. And these, again, were abraded surfaces. The only studies
available were hot temperatures, 550 to 700, but it allowed us to get a
corrected parabolic rate constant again, and look at its temperature
dependence. And so we have extrapolated these high temperature data to
low temperatures, and this is sort of a nice plot. It has three ordinate
scales. One ordinate is the gravimetric parabolic rate constant. This is
the recession parabolic rate constant. And this is the scale thickness
parabolic rate constant. So, all of the data are on one plot.

But if you use that extrapolation, this is for a two and a quarter
Chrome-1 moly steel, temperatures from 100 to 100 C., once more, 1000
years of oxidation. These are all about a half as much as plain carbon
steels, and they\'re all negligible. And if you take a parabolic ratio,
a square ratio of the times, they\'re still negligible after 10,000
years.

Now, there\'s been a lot of talk today about vacancy and diffusion and
annihilate at the metal scale interface and accumulation, and I just
want to point out for high temperature scales where you have a
crystalline scale and a crystalline metal, the metal scale interface is
a site where you have epitaxial relationship obeyed. And if you look at
a really simple one, for example, for nickel/nickel oxide where you have
a parallel arrangement, the FCC planes of the metal are carried into the
FCC cation planes of the oxide, which is the dominant parallel
relationship, you have what are called misfit dislocations, a grid of
misfit dislocations.

The difference in lattice parameter between, for example Ni and NiO, is
about 14 percent, or so. Therefore, you have one of these misfit
dislocations which amounts to an edged dislocation in the metal reaching
the interface, about every seven or eight lattice spacings. They are all
over the place.

On the other hand, any place where a slip plane intersects the metal
scale interface, there, dislocations of the opposite verterspecter can
become part of the interface, and those are called misorientation
dislocations, and they are equivalent to a minor tilt away from this
ideal epitaxial relation. You could look at these misorientation
dislocations as little steps, if you like, or otherwise just squeeze it
down and then you\'ve got a dislocation in the interface. And, in fact,
these steps are also created whenever a, for example, a screw
dislocation in the metal goes right through the epitaxial relation, into
the oxide, and it sets up a spiral staircase of these monatomic steps.

In any case, the way in high temperature oxidation, and I\'m sure it
also happens in aqueous solutions if you have a scale that is at all
crystalline and epitaxial, the way vacancies are annihilated is that
vacancies arriving through the corrosion product climbs these
dislocations. The misorientation dislocations climb in the plane of the
interface. The misfit dislocations would have to climb, leave the
interface and climb into the metal. But these dislocations are all over
the place, and when I hear about vacancy injection into the metal as the
way of getting rid of vacancies, I don\'t believe it and I don\'t\--I
just don\'t believe it.

So, now, what good can we make out of this\--two more minutes, good. In
high temperature scaling reactions, we have something called a reactive
element effect. The reactive element effect says the following. For
certain very large, highly charged cations, we observe a drastic drop in
parabolic rate constant, very much better adherence, and the mechanism
changes from cation diffusion out to anion diffusion in a fantastic
triple positive effect, and this is the mechanism by which this works.

You see, if the scale can only grow by vacancy diffusion and
annihilation here, it can\'t grow if you pin the dislocations so they
won\'t climb. And this is what cerium and yttrium do in an alloy
chromium interface, for example. These wrong sized cations, like yttrium
and cerium, which are 45 percent too big, simply pin these dislocations.

If cation vacancies cannot be annihilated, then the scale grows by anion
diffusion, which is the only alternative. Anion diffusion is very much
slower. It makes a very nice adherent scale, and it\'s an excellent
idea.

Here\'s an example for nickel oxide growing on nickel at a hot
temperature. If you put 250 angstroms of calcium on the surface, just I
mean spray it on the surface externally, the scaling kinetics go from
this one to this one, and if you plot the weight gain versus the square
root of time, you see you have reduced the scaling rate by a factor,
parabolic rate constant, by a factor of 20. And this is extremely
adherent.

And the same kinetics more relevant to the alloy 22, here is an alloy,
iron 25 chromium, which grows a chromium layer. If you add only 40
angstroms of ceria to the surface by sputtering, you can reduce the
scaling kinetics from this one to this one, and the adherence is great.

Another example, this is for a nickel 30 chromium alloy, getting pretty
close to C-22. These are the ordinary scaling kinetics at a hot
temperature, agreed, but if you will ion implant 10 to the 16th cerium
ions into the metal, you will drop the oxidation kinetics like that.

And, finally, this is a cobalt chromium alloy. So I just want to show
you the generality of this mechanism. Unimplanted oxidation to form
chromium oxide follows these kinetics. If you will ion implant yttrium
into the metal, you can drop the scaling rate by several orders of
magnitude, and the scale adherence is excellent. I think that this sort
of a doping mechanism should be considered in aqueous solution.

BULLEN: Thank you, Dr. Rapp. I appreciate\--well, actually, Dr.
Smialowska is next, and then Dr. Bertocci.

SMIALOWSKA: What I would like to do is to say a few words concerning the
property of the passive film which are of interest and importance for my
further discussion.

So, what we know is that during the film growth, you have logarithmic
growth of passive film. In fact, logarithmic growth of the thin films
are always logarithmic. And initially, what you have is you have quite
high current, and during these currents, you produce, you grow fast the
film, and at the same time, you dissolve metal or alloys. So this is a
non-stationary state when you have selective dissolution of alloy, and
at the same time, passive film growth.

We know later on in stationary conditions, that the whole current in the
passive range is going for dissolution of film, not film, but passive
dissolution.

So, the passive film is, as everybody knows, not\--the bi-layer films.
There are two layers, an inner layer, which is oxide film, and an outer
layer, which is hydroxide film. And, for me, the most important is the
hydroxide, because hydroxide films stabilize the passive film.

Another very important phenomena is the aging effect. During the aging,
you have improved the property, corrosion property of the film, and
decreased the number of defects. I am not talking about this phenomena
when we have increase of the corrosion potential and we reach the
localized corrosion. I am talking about the general corrosion.

So, now what we have in the corrosion in the repository, so the people
did a lot of measurements trying to find the corrosion rate, and these
experiments were done usually by immersing the specimens into the bulk
of the solution. There are some data also in vapor phase, but mostly
there are these experiments by immersion in the solution.

In fact, in repository conditions, we do not have this kind of
corrosion. We have the corrosion in very thin layers on the metal
surface. And this surface, liquid layer, has no constant composition.
The thickness also is not the same, because of different phenomena which
can occur in the repository, like changing of humidity, changing of flow
of air, changing of temperature, salt precipitation, and so on.

So, therefore, the corrosion in bulk solution do not necessarily
represent the corrosion rate on the waste package. And we can
differentiate two extreme cases. One, we have on this layer of fluid on
the metal surface, we have solution, dilute solution, and we have
precipitated salt film, which would be soluble in water, or insoluble in
water. And, in fact, we\'re not\--this would be dry corrosion. It means
the water will be absent.

So, now, one, if you will do the experiments, the experiments in some
kind of periodic way, one to have wet conditions and another time you
have the dry conditions, then we will be much more closer to a real
situation.

But what will happen during this time when we have dry conditions on the
metal surface? We will have for sure some interaction between salt and
oxide film, and between salt and this outer layer of the film when we
have hydroxides. So we will have the degradation of oxide film, and we
will produce in fact oxide film. And it is also quite known from the
experiments that oxide film is much more susceptible to corrosion
without this hydroxide film.

So, in fact, we will have destabilization of the passive film. And when
we have this situation, we will change the \-- wet corrosion, when we
have electrochemical corrosion, to these dry conditions, then we
destabilize this film very much, and we will have, in fact, a result of
this procedure will be that the corrosion rate will be probably much
higher.

So, I think that it would be very useful to do these kind of
experiments, it\'s much more real in thin film of solution, and taking
into consideration that we can have this situation when we will not have
on the metal surface water.

Now, I have some kind of remarks concerning the increase of corrosion
after long time by vacancy and defect accumulations. So, there are two
propositions that we can have vacancy accumulation, either in the metal
phase, either on the interface on the metal, either in the passive
layer. So everything would be fine, even if I will accept another model.
It seems to me that these models do not apply to the situation when we
are doing the experiments for this very long time of exposure, because
during the aging, what we know from the short time, we have improvement
of corrosion resistance, and not increasing of the corrosion resistance.

So it is difficult to accept that during the long time of aging, there
is different mechanism than in the short time of aging. If it would be
like this, we should have some kind of changing of mechanism that is
going on in short term, and long term. You can, of course, find some
mechanism which would be okay, or relevant or not relevant to what we
have. For example, we can assume that after this short aging time, the
film is much more perfect.

But at the same time, you will produce in the passive film, some
stresses, stresses and cracks which destabilize the film, and you will
return to this condition which you have during the short time of aging.

So there is also a proposition that you can have during the longer
period, longer time, you can have selective dissolution of the alloys.
Again, if we will assume that the same mechanism is varied for short
times and long times, you should not have, of course, selective
dissolution, because selective dissolution occurs only in initial times
of passive film formation.

These are my remarks concerning the general corrosion during the longer
period of times. And now I would like to say only a few words about
localized corrosion, which I think that the repassivation potential for
crevice and repassivation potential criterion for pitting are valid to
determine whether localized corrosion will or will not occur. But,
again, only when you have defined conditions. But when the conditions
are changing, that you have destabilization of the oxide film, then of
course you will not be able to use this kind of criteria.

So, that is all.

BULLEN: Thank you very much, Dr. Smialowska.

Our next presentation is Dr. Bertocci.

BERTOCCI: All the previous panelists have already presented, I think,
all the possible mechanisms, and so forth. So I hope to do it in much
less than the five minutes that I have.

The short answer for the first question, if I look at that report, which
is the one that Professor Sagüés showed at the beginning, the short
answer is no, I don\'t really see how it could corrode. One could even
say that maybe the thickness will increase, since there is certain
probability that the weight increases according to the data.

But I would like to stress a certain point. Maybe I\'m flogging a dead
horse. And it\'s radiation damage. This thing is sitting in a gamma
field for a long time, and there is also a neutron field that comes
about, and I\'m not an expert, but I would wonder whether this will
affect the behavior of the material. After all, it\'s a metastable alloy
on the things, and who knows what happens. Maybe there is \-- inhibition
of corrosion, as somebody has found, in certain cases, but who knows.

This vapor is not important in any way, but it\'s the case where the
nickel passivity, here we deal actually more with the chromium layer,
but it\'s reduced by foreign element. Do the neutrons create enough
impurities in a certain time to cause problems? This is what I would
like to hear.

The second, also the short answer is no. But, again, one is worried
about the radiolysis field. We have a gamma field for years and years,
which would create hydrogen peroxide and nitrous oxide, and apparently
there will be ventilation for a long time, so part of these products
might be carried away, but where? They might end up in the rocks and
come back 5000 years later as nitric acid, or something like that.

Probably this is a crazy idea, but I\'d like to mention it. And I think
the main point, in conclusion, is that I would like to see models
describing the behavior of the passive film, rather than counting on
some parts which have been kept in solution for years. And in a certain
sense, Gustavo in the beginning, and of course Digby have addressed this
point, so there is no point in continuing talking about that.

But from the reports that you find on Yucca Mountain, you don\'t find
any other information, except weight losses and maybe a little bit of
elementary electrochemistry. I mention some of the things that could be
desirable. Impedance measurements, and Gustavo is doing that. Noise,
just to make a little bit of noise. The kinetics of the redox reactions
on the passive layer, transports, and so forth. And we have now
specimens which have been sitting there for a year. Do they behave
differently if you take them and you do the electrochemistry on them?

I mention here an example of Schultze\'s laboratory, in which they look
at the gamma radiation on titanium, which is probably not relevant here,
but it would be nice to see their work done on these materials.

Thank you.

BULLEN: Thank you very much, Dr. Bertocci.

Our next presenter is Dr. MacDougall.

MACDOUGALL: It\'s certainly difficult to be as brief as Ugo. I will try
to be a little bit brief, if possible.

This alloy, Alloy 22, is one I haven\'t worked on at all. But I have
worked on other systems that I think have relevance in fact. I think
everybody here today has talked about the fact that it has a thin oxide
film, which confers passivity, and you have to maintain that thin oxide
film on the surface.

I have a little bit of a cartoon at the bottom there showing, in fact, a
metal or alloy with a very thin oxide film and defects associated with
that particular oxide film, breakdown of the oxide occurring at the
defects, most probably some chemical dissolution, or something like
that, and some repair mechanism, and the current efficiency for that
depends on how much of this parallel metal or alloy dissolution reaction
there is, in fact, going to be.

I\'ve done a lot of work with nickel and iron over the years, and I want
to say one of the things that probably troubles me about this particular
system, although I certainly hear that Alloy 22 is an outstanding
candidate, and one of the things that I think has to be looked at a bit
for that, and this, again, just simply shows rather the cartoon of a
very thin passive oxide film on some metal or alloy, a breakdown, and
then chloride migration interfering with the repair, an attack and the
pits developing on that particular surface. And most of us are, I think,
aware of that sort of thing.

In the case of nickel and iron, I did a lot of work years ago with my
own hands looking at chloride induced pitting of nickel after I
pre-passivated the sample, added the chloride at a certain period of
time, and found there was a certain induction time for pitting. And this
is in chloride.

In fluoride solutions, different, I pre-passivated in a non-fluoride
containing solution, and then I added fluoride at time zero, and the
current behavior is absolutely different in fluoride containing
solutions. The pH, the composition, I won\'t get into at the moment, but
there is a slow gradual increase of a current. This is a depassivation
which is occurring, and the chloride and fluoride were quite different
in terms of their breakdown modes, depassivation modes, in fact, this
thing leading to one or two pits on the surface, this thing leading to
massive depassivation and a very, very rough surface.

What I found was, in fact, that the worst combination that you could
have for the nickel and the iron\--I investigated this in iron,
too\--was a combination of fluoride and chloride in solution. There
seemed to be some sort of synergism between the two of them where the
total was more than the sum of both parts.

I\'m showing here again chloride. What I\'m doing here is in the case of
nickel, stepping the potential from some oxide free region into the
passive region, and monitoring the response of the current with time.
This is in a sulfate solution, a background solution.

Chloride, you have an increase in the charge because the chloride
competitively absorbs, interferes with passivation in the short term.
Bromide is here also. Fluoride doesn\'t give that much of an
interference initially in terms of the charge. But what fluoride is able
to do is it interferes longer term. The current will not fall by this
time, in point of fact, the seconds here, I guess, or whatever it is.
The current, in the case of chloride and bromide, would have been down
here if pitting had not in fact occurred.

So, the fluoride incorporation into the passive oxide film, I measured
the amounts of fluoride I was getting in my NiO films. They could be as
much as 15 and 20 percent in those films. Chloride, I never got those
amounts. I got 2 to 3 percent.

Reasons for that complexation, but also the F-minus anion, in fact, has
a radius which is comparable to that, an ionic radius of 02 minus at 1.3
angstroms. Chloride is, Cl minus is 1.8 angstroms. So you could get
that. So what you have is in a case of a system where you have both
fluoride and chloride simultaneously in the solution, you have the worst
of all worlds. You have the short-term interference and long-term. If
you could possibly do things in the short-term, the fluoride was still
there to cause, in fact, the interference, and held that thing up so the
chloride had a lot longer to work its nasty business.

And when we used to have people visiting from time to time, we would
have senior officials come by, and if I wanted to pit a sample in a
swiss cheese mode, it would be nickel and iron, not Alloy 22, obviously,
but it would be in that particular concoction, that particular solution,
a combined solution of chloride and fluoride.

So, I think it\'s very important for the people who are doing these
experiments with the Alloy 22, which may indeed be resistant to many of
these things, to work in solutions which contain simultaneously the
fluoride and the chloride.

The question, and I\'m not going to go into all the parts of this
question number two, which I tried to address, in fact, but I would just
concentrate on this part here, which is one of the complexation, the
ability, and I\'m using cyanide\--thank God there\'s no cyanide in this
particular system\--but this is a very, very famous cathodic reaction,
and I think that most of us know it, in fact. We may have forgotten it.
And it\'s the stability complexes of the ferree (sic) versus the ferro
cyanide.

And you can see by complexing with cyanide, you move the potential
something like 400 millivolts, in fact, in the wrong direction in this
particular system. You made iron dissolution that much easier, so you
don\'t have to change the open circuit potential. In fact, in a case
like that, the driving force has gone up for that particular reaction,
the anodic iron dissolution reaction, by an amount of 400 millivolts.
And, in fact, we have lots of complexing ions in this particular system,
so that\'s something that should be taken into consideration.

And I would finish off by saying just there was a question asked about
was there a result that you ever obtained which was a bit shocking,
unexpected, or something like that. And I guess the biggest one that I
had was quite a few years ago when I did work with nickel, and I was
looking at pitting of nickel in chloride containing solutions, no
fluoride, here just chloride. And I was measuring the induction times,
and I pre-passivated a sample and then I looked at different potentials,
and really what one has is a critical pitting potential range, I
suppose, with sort of an exponential increase of the induction time.
Obviously, as you go to more anodic potentials, the pitting is going to
occur more and more rapidly.

This was the one done in a standard mode, pre-passivating in a
non-chloride containing solution. This was the one where I
pre-passivated in a chloride containing solution. I notice chloride in
the film. It didn\'t pit, but I got chloride in the passive oxide film.
And the trouble was this particular curve should have been down here,
obviously, if all of the theories were correct, because chloride is a
precursor to pit initiation. And because I obtained this result, I had
to do literally hundreds and hundreds and hundreds of experiments,
because people in the lab did not believe it, and it kept on coming up
this way.

I think I have the explanation for it. I think I have one. I know others
have others. But that result is true. So we have shifted the pitting
potential range to more anoded values, making it more difficult for the
nickel to pit, by incorporating chloride into that passive film before
we did the pitting experiment. It was done in a sequence or series of
steps there. And, as I say, if this result had been down here, it would
have been a nice easy simple sort of experiment.

So, there can be times when you predict something and you\'re certain
that chloride is a precursor, and maybe in some state it is a precursor
to pit initiation. In this case here, the chloride in the film made the
nickel metal more resistant to pit initiation.

I\'d just like to emphasize again that I think it\'s extremely
important, in fact, that one do these experiments in combined solutions,
so the amounts of fluoride you have in those solutions is not small, the
amounts of chloride is not small in those dried, evaporated modes. And
in the case of nickel, I could get pitting with 100 or 1000 times less
chloride/fluoride than what we have here. Of course, Alloy 22 is going
to be a lot more resistant, but then one has an awful lot more time to
do these things.

BULLEN: Thank you, Dr. MacDougall. Do you have a question, Gustavo?

CRAGNOLINO: Yes. The purpose of clarification of that plot, when you
pre-passivate in a chloride containment solution, this will then have a
potential obviously lower than 50 millivolts.

MACDOUGALL: Yes.

CRAGNOLINO: I mean, as you age the film, even in the presence of
chlorides, but in a regime in which pitting cannot be induced.

MACDOUGALL: Cannot be induced. That\'s right. That\'s right. If there
was any pitting, it would simply be null and void, and the result
wouldn\'t be worth commenting on.

BULLEN: Next is Professor Shibata.

SHIBATA: When I received this agenda, I\'m finding the premise that
fundamental knowledge suggests that the passive layer on such material
is thermodynamically stable. So, I think that this system is
thermodynamically not stable. So, I think increasing the long term
passive dissolution of alloy seems not to be expected, but still no
definite evidence exists because this system is thermodynamically a very
open system and there is a free exchange of matter and energy. Then, the
system is not at equilibrium.

There are many explanations already presented. So, I\'d just like to
point out one factor. The alloy and the environment system is a very
complicated, large component system which is difficult to reach a simple
equilibrium state. An important point is the selective dissolution or
selective enrichment of a specific element. And, Roger Newman said that
the main point of this passive term is chromium oxide is a main player.
So, I\'d like to know about this process. Selective enrichment of
chromium is very important, I think.

Unfortunately, we know the very short time enrichment process and we
know the exact analysis over such kind of enrichment process, but know
it\'s a long time or a long time exposure and its (inaudible) density is
known. So, the compositional change will continue for a long time. So,
we like to get definite evidence for this change.

Unfortunately, you know, the natural analog studies are done on the
carbon steel and copper alloys, but still do not exist for the stainless
steel. So, I hope the long term selective enrichment evidence will be
accumulated.

So, I\'d like to focus on the localized corrosion. In the document, I
stated this condition is deciding the localized corrosion occurrence.
So, it is well-accepted that the possibility of the initiation and
development of a local corrosion could be judged by just comparing the
open circuit potential with the critical potential here. But, of course,
the open circuit potential is quite easy to measure. But, standardized
method has have been known for measuring critical potential of pitting.
But, still many discussions on the definition of the initiation and
repassivation of crevice are discussed in the Report. In Japan, the same
situation existed through 1980 to \'90. But, this year, a method
proposed by Professor Tsujikawa is standardized in Japanese Industry
Standard.

This method for measuring the critical potential for repassivation of
crevice is standardized in Japanese Industry Standard. The basic concept
of this method is specimen with crevice former is used and preliminary
existence of the crevice produced by the constant anodic current is
necessary to measure or define the crevice repassivation potential.

The critical potential for stopping the growth of a crevice, we call
this one E~R,CRV~ and it was decided by the potentiostatically step down
method. The anodic current decreases at the constant potential after
step down and again increases if the potential is over E~R,CRV~. When
the potential is equal to E~R,CRV~, the anodic current stops to
increase. So, we can easily define E~R,CRV~.

Here is a specimen with crevice former. We have some crevice here. The
main point is that initially we increase the potential by
potentiodynamic method, and if the current leads to the 200
microamperes, we kept it constant at the galvanic constant techniques.
So, this corresponding to the potential decrease back here. After enough
crevice is formed, the potentiostatically step down here just 10mV. So,
if you measure the anodic current, anodic current decreases fast and
again increases because this crevice is active. So, the anodic current
increases. At this point, we again step down potentiostatically so the
anodic current decreases, again increasing if this crevice is active.
This process is repeated. Several step changes, the current decreases,
and no increase is observed here. So, we can decide the E~R,CRV~
potential here. This procedure precisely decided the crevice
repassivation potential for the crevice. And, also, the method that is
required to confirm the existence of 40 micrometer depth crevice after
the measurement.

When we use this kind of method, we can decide the E~R,CRV~. This is the
dependent of the other function of chloride concentration. If you use
the potentiodynamic method, you can decide such kind of crevice
potential. But, this kind of crevice potential is much lower here. But,
if you use the potentiostatic step down method or long time step down
method, we can decide, like this one. But, if you use the higher speed
of potential, a much lower value is obtained.

So, the criterion use that\--if the natural corrosion open such
potential here, then lower concentration can be a load for this kind of
initiation or stopping the growth here. But, if the natural corrosion
potential around here are much higher chloride concentration is allowed.
So, this is a very good criterion.

But, why such method is not the standardized in our business\--? Because
industry people they just use such kind of idea because this barrier is
so much severe, so ordinary stainless steels\--like 304, 316 cannot be
used if this kind of criterion used in the ordinary environment. But, a
designer or a user still can safely use this kind of material, even if
the E~R,CRV~ is much lower, because the designer avoid to make a crevice
condition and a user, of course, usually cleaning and avoids a crevice
formation. So, in that case, we can use even with such kind of
conditions.

So, I think that this E~R,CRV~ measurement value is very suitable for
the long time protection of the crevice formation for this kind of
material. I don\'t know that Alloy-22 can be measured by this kind of
method. But, this is a very\-- a reproducible result can be obtained.
And, also, this procedure can be the program by using the computer. So,
this is a very good method to decide the E~R,CRV~.

I\'d like to add some comment to the distribution of natural corrosion
potential or on the also critical potential. Of course, the natural
corrosion potential, also distribution like this one, and the
E~critical~ is also distribution. This area can be pitting or crevice
possible here. So, this is very important to decide what kind of
distribution function can be observed for this alloy in the environment
of a combination.

And, the probability density function of pitting potential, the
experimental data on this pdf, many data is accumulated. And, normal
distribution is observed for pitting potential. A general trend is
observed at the higher pitting potential and seems to show a wider
scattering, but, of course, some exception exists. Of course, just
depending on the material, environment, or combination. But, the general
trend, the higher pitting potential seems to show wider scattering. So,
this material, Alloy-22, is a very high (inaudible) material. So, I
think such kind of behavior will be expected.

And then, how the E~R,CRV\--~the probability density function, not so
many data is accumulated of this E~R,CRV~. But, normal distribution can
be fitted for also. A more narrow distribution is observed for E~R,CRV~
than pitting potential. This is possibly caused by the measuring method
itself because a slower stepping method is used.

So, now I conclude that increasing the long term passive dissolution of
alloy seems not to be certain, but still no definite thinking has
existed. Changing the composition of the passive film including the
subsurface due to selective enrichment should be clarified.

And, criterion of this condition can be used for assessment of
possibility of localized corrosion. More discussion is required to
deciding the critical potential for crevice corrosion.

We propose that the method which was proposed by Tsujikawa will provide
a reliable and a confidential critical potential, E~R,CRV~, for the
repassivation of the crevice which was produced before the measurement.
So, information about probability density function of E~R,CRV~ should be
accumulated.

Thank you.

BULLEN: Thank you, Dr. Shibata.

Could we move on to Dr. Sato now? I\'m going to take some chair\'s
prerogative and we\'re going to go through all the presentations before
lunch. So, we hope to finish and we will give you an hour and 15 minutes
for lunch. It just might be in about 20 minutes from now.

SATO: Thank you. Well, because of the short time, I would like to focus
our attention on the open circuit potential, particularly. During
long-term storage, it may happen for some reason that semiconducting
oxides are formed and brought into contact with the alloy surfaces. The
open circuit potential of the alloy depends not only on the aqueous
environment, but also the semiconducting oxide present on the alloy
surface. Here, two pieces of solid electrode. One is a metal and the
other is the oxide. An isolated metal electrode sets its electrode
potential at the so-called corrosion potential while the oxide electrode
stands at its\-- flat band potential. If you get in contact these two
electrodes, then the mixed electrode potential come to somewhere between
the corrosion potential and the flat band potential. And, when the oxide
is excited by radiation or photo illumination, so that you have quite a
concentration of excited holes and electrons, then the mixed electrode
potential usually come to very close to the flat band potential.

Under illumination, as you see here, semiconducting oxide in contact
with metal surface affects the open circuit potential of the metal. The
oxide potential comes across to the flat band potential reaching usually
more positive in the case of p-type oxide or n-type oxide. In the case
of n-type oxide, the flat band potential is more negative than the
potential of the passive metals. The oxide metal mixed electrode
potential thereby shifts the potential in the positive direction. In the
case of p-type oxide, while n-type oxide shifts the open circuit
potential in the negative direction.

Here is the electronic level diagram for metal and p-type oxides. When
being excited by radiation, in particular, p-type oxides may elevate the
electrode potential. It opens up the potential (open circuit potential
of the passive metals). And it may happen the electrode potential gets
up to the point more than the passivity breakdown potential. We have two
kinds of critical passivity breakdown potential. One is for pitting
initiation potential and the other is the crevice corrosion. Usually,
the pitting initiation potential is more anodic, more positive, than the
crevice prediction potential. So that crevice corrosion really is more
likely to occur when the electrode potential is going up.

Here is the schematic representation. When you have no oxide on the
passive metal surface, your electrode potential is rather narrative.
But, if you have p-type oxide on the metal surface, the electrode
potential is going up then. If the electrode potential becomes beyond
the certain critical potential, you have passivity breakdown. And, here,
the localized type of corrosion occurs.

In addition, under the illumination, the excited electrons in the
conduction bundle of the oxide are now incapable of reducing water
molecule to produce hydrogen on the oxide surfaces. So that you have
hydrogen evolution, cathodic hydrogen evolution, taking place on the
metal electrodes which can be coupled with the anodic metal dissolution
at the passivity breakdown sites. Therefore, you have a local corrosion
cell, anodic metal dissolution, coupled with the cathodic hydrogen
evolution on the oxide surface. So, it means this type of local
corrosion is taking place even in the absence of oxygen. Of course, in
the presence of oxygen, the local dissolution current is very much
faster.

In the case of n-type oxide, you have the situation exactly the reverse
to the case of p-type oxides. The n-type oxides shifts the open circuit
potential in the cathodic direction. If your electrode potential gets
down below the hydrogen electrode potential, then you have a higher
evolution on the metal side, on the metal surfaces.

In addition, on the n-type oxides, excited holes in the valence band of
the oxide are now capable of oxidizing the water molecule to produce
oxygen gas on the n-type oxide surfaces. So, this oxygen evolution may
be coupled with the hydrogen evolution on the metal side. So, you have
oxygen, hydrogen, local cell, oxygen evolution on the oxide surface and
the hydrogen evolution on the metal side. This type of local cell gives
us a possibility of hydrogen damage in the metal electrodes.

This gives us the conclusion, p-type oxide may cause the passivity
breakdown leading to a localized mode of corrosion. N-type oxide
inhibits the passivity breakdown though increasing the probability of
hydrogen damage. In order to prevent the p-type oxide induced passivity
breakdown, the coating of n-type oxide layers on the metal surface will
be effective.

Now, the suggestion I have made in this presentation is based only on
the thermodynamic estimation at the present time, but any direct
experimental evidence except that n-type titanium oxide was found to
inhibit the metallic corrosion in a number of cases.

Thank you.

BULLEN: Thank you very much, Dr. Sato.

I have a little apology to the audience, but we\'re going to finish with
Dr. Pickering\'s presentation. His transparencies are being duplicated
as we speak, but he does have a duplicate of his conclusion slide. So,
he has agreed to go ahead and speak before lunch and we\'ll give him the
option of first refusal after lunch if he wants to follow up on his
presentation.

Dr. Pickering?

PICKERING: Well, I have this duplicate of kind of a summary outline, so
to speak. And, what I will focus on is the crevice corrosion, #2, here;
crevice corrosion rather than passive film breakdown and pitting which
you\'ve heard a good bit about already. I\'ll look at two things that I
think are questions I would want to know about Alloy-22. And, mind you,
these are now questions that pertain to the conditions inside the
crevice, not the conditions outside the crevice that we\'ve been talking
about. I\'d like to know, too, what the repassivation potential is, but
I\'m with the understanding of what the repassivation potential is, but
right now, I\'m going to talk about the conditions that we\'ve measured
and so forth inside the crevice and how they lead to criterions to
susceptibility of a particular crevice in a particular metal electrode
system.

And, there are two things that I want to say then about that, as far as
characterizations, that I would want to know about. The potential
distribution on the crevice wall, that is the electropotential, how it
varies and how big the variation is as you go into the crevice? That\'s
this on the left here. The potential is here at the outer surface. It
could be applied potential or the actual corrosion potential. Then, as
you go into the crevice in this direction, you find that the potential
goes negative. And, the question is how much of the polarization curve
do you have on the crevice wall? That depends on how big the IR drop is
that is generated by the current from the inside of the crevice flowing
through the electrolyte to the outside cathodic site or to a counter
electrode if you\'re using a polarization technique. So, that\'s one
question. How big is this potential drop under passive conditions on
Alloy-22 in a given size crevice?

Okay. And, the other question is that alone will not produce crevice
corrosion, but if you add the second condition, does the possibility
exist that the passive condition shown here at times zero, just a
straight passive, whatever it is for Alloy-22\--10 to minus 8 amps per
square centimeter, I\'ve been told and we heard about that this morning,
too\--does the possibility exist as stagnation occurs in the crevice for
an active peak to form at the lower potential region? And, if it does,
then we know from those studies now\--I don\'t have these documentations
with me, but maybe this afternoon, I\'ll have them\--that that peak can
grow in some other systems like nickel and stainless steel, that peak
can grow with time if the right buildup of concentration in the crevice
occurs. And, when it reaches this criteria here where the IR drop is
greater than this defined quantity right here of the voltage drop
between the applied potential or the corrosion potential at the outer
surface and the passivation\--what I call the passivation potential,
reactive passive potential of the system, that\'s when then crevice
corrosion would start and that would be at the end of the induction
period. That is a little bit beyond what we\'ve done experimentally,
this last statement about, but we have seen passive films grow in
crevices, get larger, and kick off the crevice corrosion process.

So, as a result of criteria that evolves out of that\--and this is
essentially the criteria\--the IR drop generated in the crevice, be it
due to a passive condition or an active peak already in the system,
we\'ve studied mostly the active passive alloy electrolyte systems and
we are starting now to study these (inaudible) passive systems, as well,
like Alloy-22 is. But, that\'s for later.

Now, the next point to comment on is how big can this IR be in, say,
Alloy-22? There are two factors I want to point out as I see are
important. There are several factors that go into how big this IR drop
is. I won\'t mention them all, but the one I want to comment on here is
what\'s the size of the opening? And, we know we have to have a tight
crevice to get crevice corrosion in all these corrosion-resistant
alloys. So, that size opening, the generality is that the tighter it is,
the bigger the IR drop will be. And so, how big can it be?

Well, these are two factors here that I would bring up. You certainly
have the situation where one surface might be very smooth, but the other
surface forming the crevice is rough. And so, the roughness determines
the average opening of that crevice. The other case\--and a big question
for Alloy-22\--is does hydrogen evolution occur inside the crevice
because, if it does, then you form hydrogen bubbles. And, a bubble has
the unique property, of course, of filling the space. So, now, we ask,
well, what\'s the space between the bubble and the wall? Of course, you
might say is it molecular dimensions? So, you what you can have actually
when you have crevice\--and we\'ve seen this and I\'ll you some later
this afternoon maybe. When we have relatively large openings, we still
end up with a gap opening between the bubble and the wall which is very
small and we can\'t measure conditions in there. But, we see crevice
corrosion occurring in the center of the bubble on that passive wall.

So, that\'s where I\'ll stop and, as I say, we can kind of show you
examples of all three of these things; of potential drop here; of the
buildup with time as the acidification occurs or whatever; and, also, a
lot of gas bubbles forming in, say, stainless less, not so many in
nickel. That\'s interesting, isn\'t it, from a point of view of
Alloy-22.

BULLEN: Thank you, Dr. Pickering. I guess we did find out how to limit
the speakers to five minutes. We just take away their slides and it will
get done.

Right now, I would like to recess the meeting for an hour and 15
minutes. We will reconvene at 2:00 o\'clock and Dr. Pickering has first
right of refusal.

Thank you very much.

(Whereupon, a luncheon recess was taken.)

[A F T E R N O O N S E S S I O N]{.underline}

BULLEN: We are going to digress a little bit from the written agenda. We
have had one of our distinguished materials scientists who is interested
was interested in making a comment, but cannot stay until the 5 o\'clock
hour. And, as such, we\'re going to allow him the microphone.

So Roger Staehle, who is working his way to the front of the room, would
like to make a few comments for the benefit of the workshop panel. And,
with that, I give you Roger. Keep it to less than three hours. Is that
okay, Roger? How about ten minutes, just like everybody else?

Thank you, Roger.

STAEHLE: That\'s pretty restrictive. This will just take about five
minutes.

I first discussed this meeting with Alberto maybe a month or two ago
when he had suggested the idea of bringing a group together to look very
carefully and thoughtfully at what innovative ideas there might be in
developing loss of passive films. And my concern then is more now that
one of the things we know about passivity is that it\'s very
environmentally dependent, and so what the passivity is in a lead
solution isn\'t the same as passivity in a sulfur solution, is not the
same passivity, and so on and so on.

And zirconium, which is very good in some environments, when you add
fluorine to it, it\'s not. And so the first point I want to make is that
the passivity, the protective quality of the film is very
environmentally dependent, which is something most of you know
certainly.

But the second point I want to make is that the chemical situation on
the metal surface is an absolutely unbounded chemical situation. And
what you have to realize here is that the unboundability is related to
the fact that you have a super-heated surface. And in nuclear steam
generators, the super-heat, even in a very controlled bulk environment,
produces environments locally which are virtually unboundable. And
that\'s for a very controlled external environment.

Now, in this situation where the external environment is not controlled,
but we don\'t know what\'s going to drip out of the mountain, except
some part of the periodic table, and where we don\'t know what the
composition of the deposits is on the fractures, which is quite
different from the average composition, that means that the chemical
composition on the surface will be an absolutely unbounded condition.
And, so to make a prediction based on an unbounded environment is an
impossible problem.

Now, the third point I want to make is that virtually all the work that
has been done so far has been done in the general range less than 100
degrees Centigrade, like 95 Centigrade, or thereabouts. I think it was
mentioned this morning possibly looking at 160 centigrade on the
surface.

But let me back off a little bit and say that a lot of the low
temperatures that people are thinking about today is based on the
assumption that ventilation will be used. In fact, I think the
assumption that ventilation is going to be used may be a very bad
assumption, because the idea of ventilation means that if there\'s a
leak, it will spread whatever the leak is around the countryside, and
the chance of anybody putting up with spreading the results of a leak
around the countryside I think is zero.

And so I think the possibility of using ventilation for a variety of
reasons, not the least of which is lowering the temperature and lowering
the humidity, is a very strained assumption. Therefore, the surface
temperature will be at least 160 centigrade, and more, and that means
the super-heat in the concentration process, and the environments that
are there will be soupy saturated\--this is soupy, not super\--soupy
saturated environments of undefined compositions. And, therefore, to
conduct experiments in that kind of environment, or in something like
that, seems to me a very difficult challenge.

And then on top of that, in this 160 centigrade plus range, the concept
of modes of corrosion changes. Up to this point, as Gustavo mentioned
this morning, and others have, that they\'re primarily thinking about
pitting. In fact, in this range, I don\'t think pitting is an issue. I
think we\'re looking at either major generalized corrosion, or extensive
stress corrosion cracking. And I think the stresses will come from a lot
of places. I think the idea that they can be eliminated or lowered is
just a fantasy.

So, those are my concerns about making predictions, and sort of from the
perspective of thinking about passivity, it seems to me the central
question in making predictions is not to detail passivity, but rather
how do we come to grips with an unboundable environment.

BULLEN: Thank you, Dr. Staehle.

Actually, before you leave, I have a question for you. One of the issues
that the Board has raised is that cooler and drier and simpler might be
better. Not regarding ventilation as the mechanism that you get cooler,
would you agree that a cooler repository would be better or maybe easier
to bound or to calculate?

STAEHLE: Well, I\'d have to separate this question, because cooler and
drier is better. But the question is whether cooler and drier is
achievable.

BULLEN: Okay. Well, actually, let\'s start with the first part. If it is
achievable, is it better?

STAEHLE: Well, any time you can lower the temperature, and the corrosion
process in general, that\'s a good thing. So that\'s a good step. And if
you can make it very dry and cool, that\'s a good thing.

BULLEN: But the concern is not to be able\--if it gets cool, it may not
be dry, is the comment you\'re going to follow up with?

STAEHLE: Well, you know, I have a hard time understanding how a person
could achieve coolness in a situation where you have a super-heated
possibility, because what\'s going to happen is you will very quickly
start putting dust on the surface, and that dust will create an
insulating layer, which will immediately lead you to a super-heated
condition. And I was in that tunnel a couple months ago, and just my
note pad ended up with a bunch of dust on the top of it, a couple
microns of dust probably. So I think that the conceptual framework which
is interesting has to be very carefully thought out in terms of whether
it\'s achievable.

BULLEN: Thank you, Roger.

As Chairman\'s prerogative, I\'m going to give, maybe with a little
trepidation, Professor Pickering the opportunity to do an encore
presentation, which he tells me is not 50 minutes. So we will let him
have his viewgraphs and present\--how about ten, is that okay? Ten
minutes?

PICKERING: I could easily do it in ten. Okay, so I\'ll build on this
dust, and consider those dust particles the start of a crevice, because
I don\'t think there will be crevices deliberately built into the
system.

So, if we have crevices, then just to illustrate quickly three things
that I mentioned earlier, the distribution of the electropotential along
the wall of the crevice, and if it falls\--this is for the bigger peak I
showed you here. If it\'s a smaller peak that you\'re dealing with, then
this would be much more gradual, and it won\'t fall below the
passivation potential and, ergo, you don\'t get crevice corrosion until
that peak gets bigger to this point. So, this line here is for the\--by
the way, the viewgraphs are a little bit\--or your hard copy is a little
bit mixed up. But the top viewgraph goes at the bottom. I\'ll get to
that last, and they\'re mostly in order after that.

Okay, then I\'ll show you this process taking place, and I\'ll show you
the effects of this gas, and then I\'ll make a calculation to see how
big the IR drop is.

Here you have the results, and this is typical now. These are stainless
steel actually in an acid chloride solution, which is a spontaneously
active system, meaning it has an active and a passive region. And you
can see at the beginning here, in both cases at the time, this is
different times here, the profile of the potential distribution going
into the crevice here is steeper as time goes on, because the current,
you measure the current increasing. So the crevicing current is going
up, so the IR drop per unit is going up. So at the end of the experiment
here, the red curve, you can see the position.

Now, here\'s the active/passive transition measured on the crevice wall,
the potential, and that means that the position of the passive region is
going to be closer to the opening than that, and the position of the
active region on that crevice wall is to your right of that, and the
biggest penetration, corrosion penetration, is going to be where the
peak currents are, which would be right to the right of this 3
millimeters.

We obtain these data by simply putting a microprobe into a relatively
open crevice of .1 or .2 millimeters, which you can do for this duplex
stainless. Here\'s just an example then of afterwards, a cross-section,
and you can see that 3 millimeters down is where you get the attack.
Okay? Just as you would expect, and as are indicated from the potential
measurements.

Well, if we didn\'t have a lot of chloride in there, we\'d have an all
passive condition, like we do in Alloy 22. This is just sulfuric acid of
two concentrations, A and B, and you can see there\'s no active peak
whatsoever. It\'s a spontaneously passive system. If you add the
chloride to the system, then you get the buildup of the passive peak,
and the A curve is the lowest chloride concentration, the next highest,
and finally the one that we used there to get the data I just showed
you.

Now, when you use this active/passive situation with this chloride
concentration, you get instantaneous crevice corrosion as soon as you
polarize into the passive region for the conditions we used there,
because that IR drop was larger right from time zero than the delta phi
star value I showed you earlier is a criterion.

So that\'s the sort of thing with the buildup then. After you have the
potential drop, you need to get the active peak to form. And you need to
now also know how to measure the chloride concentration in the cavity.
I\'ll just show you these data. These are the only data, and I\'m just
pointing out the blue curve here, because the red curve is actually the
potential distribution as measured for now. This is iron in a pH 5
solution. It\'s an active/passive system. But the blue curve is\--and
these are the only data of the blue curve that are not\--they\'re our
new data and I didn\'t even want to present them on hard copy because I
don\'t know if they\'re right. You know, they\'ve haven\'t been
reproduced.

But it looks like they\'re going to have a peak chloride concentration
an order of magnitude higher\--these numbers have to be reproduced
also\--an order of magnitude higher than the region where the metal
dissolution rate is the highest. That\'s where the X pass position is,
and the active peak is right here. And so you\'re seeing that the
measured, using again a microprobe now for chloride going into the
crevice, it\'s maximized there and it falls off to some value that\'s
just a little bit higher than the bulk solution of 2 millimolar
concentration.

Now, here is some data\--all the rest of this data, this appeared ten
years ago on the Electrochemistry Society, and it just shows now a
passive situation where it has a small active peak in this system. It\'s
iron in the pH 10 solution. A small active peak, but the IR drop wasn\'t
big enough to push the electropotential down into the peak. So you
didn\'t see anything but a passive current at time equals zero, and
it\'s about 10 to the minus 6 amps per square centimeter here read on
this axis here. We have it in milliamps here, so it\'s 10 to the minus 3
on milliamps. But 10 to the minus 6, and for this relatively open
crevice, the IR drop is pretty small. Like I said before, you have to
have a tight\--or if you tighten the crevice up, the IR gets much bigger
for the given current that\'s flowing.

And so the applied potential was this dash line, 200 millivolts on this
scale, and the measured potential halfway into the crevice now, that\'s
what we\'re measuring on this axis, is only 25 millivolts below the
outer surface potential. But notice what happens with time. Up to 14
hours, the passive current is gradually increasing, and of course then
the IR drop is increasing, and you\'ll see the measured current halfway
in coming down.

At about 14 hours, suddenly, the current increases quite steeply, and
we\'re getting up into the milliamp current range now, or the actual
crevice corrosion. The potential drops way low. I didn\'t show you where
the passive age potential is. It\'s right in here somewhere. It drops
way below into the\--below that boundary into the active peak region.
And, of course, you have stable crevice corrosion indicated by the
potential, and indicated by these high currents. So, there it took 14
hours to do that, and the reason for that we don\'t know, because we
didn\'t have the chloride and pH that we do now, so we don\'t know what
was causing the passive current here to increase with time. It might had
been a pH decrease, or something of that sort.

And then the gas bubbles is the third item I told you I\'d show you
about. Here\'s a gas bubble, hydrogen gas bubble, formed in an iron
crevice wall. By the way, we\'re looking through transparent plexiglass.
And while we\'re doing these in situ probe measurements, we also monitor
the appearance of the crevice surface with some necrolenses and a
camera, and so forth. And then in this case, the wall was all passive in
this region, but there was a hydrogen gas bubble that had formed there
and lodged in place.

And knowledge you have after some time is very strong crevice corrosion
at the middle part of the bubble. What you see here is grain boundary
effect, which we also saw on the polarization curve when we did
experiments at different potentials, getting close to the active peak.
And here you see it blown up. You can see as you go in, you get slight
intergranular effect. As the potential drops closer to the active peak,
you get heavier intergranular effect, and then you have a boundary here
where now you\'re in the active peak and you get an attrition.

So, that\'s the importance of the bubble, and that\'s why, you know, we
would like to know whether hydrogen gas bubbles can form. Dynamically,
they can form of course in any base metal, so also in C-22. We don\'t
know, though, whether they form in there.

And the final question was how big of an IR might you get if you had
really a low passive current, like C-22 has, and so I just made\--I
tried to make a calculation here using numbers we knew about. This is
for one of our nickel systems. We had a pH 2 solution which was
saturated with nickel sulfate in the crevice. And that has a measured
resistivity of 23 ohms per centimeter, which is not a real high
resistivity. You can get much higher resistivities in solutions that are
more dilute, and so forth.

And we then had the relationship, a simple relationship where the IR
drop, or the delta phi here to the bottom of the crevice, going from
here to the bottom, is going to be just the average current flowing out
of the crevice\--I assume the average current. I assume the current was
linear going, with increasing depth in, just to make a calculation,
we\'re seeing results of the average value, and multiply that by the
resistivity, times the depth, L, which we assume to be just 1
centimeter, and the cross-sectional area here of the opening, and
that\'s A times W, divided by A times W, and you see that here.

So, that\'s just IR, of course, where R is L over AW. And so now we
assume that 10 to the minus 8 amps per square centimeter of passive
current on that wall, and there we chose not molecular dimensions. If we
had gas in there, I don\'t know how big the crevice would be, but it
wouldn\'t be very big. We took an order of magnitude higher than that,
10 to the minus 6 centimeters, and we end up calculating, if you plug
the numbers in then into this equation right here, you end up
calculating 230 millivolts, so a sizeable potential drop. You can\'t
really rule it out just because you have 10 to the minus 8 amps per
square centimeter.

So, I\'ll stop there.

BULLEN: Thank you, Dr. Pickering.

PICKERING: You\'re welcome.

BULLEN: Actually, I\'m going to ask Professor Sagüés if he\'s going to
help me out.

In your presentation this morning, you had a viewgraph of the first
question. Could you dig that out?

SAGÜÉS: I don\'t have it. I have a summary of the question.

BULLEN: The summary is fine. I just wanted a talking point to put up
there. And then as we dictate the procedure for the roundtable
discussion that\'s going to occur this afternoon, I thought maybe we
could start off by just asking each individual as we go around the table
to make a few comments about what they\'ve heard, what they haven\'t
heard, but specific to question one. And I was trying to decide which
side of the table to start with, and Dr. Davenport on the way in said
she\'d solved all the problems over lunch. So, obviously, we have to
start over there, but I can\'t start with her, because she\'s not in the
first position.

So, Dr. Kruger, because Dr. Davenport has already solved these problems,
gets to actually take the first shot at question number one, which
essentially deals with mechanisms\--well, let me read the question
specifically from the handout.

Question one basically states that can you propose any plausible
mechanisms that would cause a long-term corrosion rate to increase once
penetration under passive conditions reaches significant values, so that
sustained corrosion rates may be no longer uniform, extend sort of
greater than a micrometer per year?

And so specifically to that, we\'d like to ask you to just say a few
sentences, maybe a few words about what you learned this morning, if you
think there are mechanisms that exist, if so, what? If you don\'t think
they exist, that\'s fine, too.

So, we\'ll start with Dr. Kruger and just work our way around the table.
That\'s a good way to start.

KRUGER: Well, since Alison has already solved all these problems\--

BULLEN: That never seemed to stop you before, though.

KRUGER: Right, and it won\'t this time. But I was tempted.

Well, I think the thing that I heard, not this morning, but this
afternoon, the things that Roger Staehle said is to me the most
significant thing that you can say about question one. And that is that
under the conditions that exist, you would really expect an increase in
the passive current. Plus the fact that, and a number of people
mentioned this, if the potential goes to the transpassive region, you
dissolve a lot of the constituents of the passive film creating an
unstable condition, and a large increase in the passive current density.

So, I\'m not as sanguine as I was when I first came here that at least
from a uniform corrosion standpoint, we really wouldn\'t expect any
problems. I think we could expect some serious problems.

BULLEN: Bullen, Board. Actually, I\'ll follow up with the same kind of
question that I asked Roger with respect to temperature dependencies of
what you see, if you stayed away from the 160 degrees C. temperature
regime, for example, would you find more confidence or less confidence
in your expected performance for the long-term stability of the passive
film?

KRUGER: You mean you were able to keep the temperature below 160?

BULLEN: Yes. Well, we saw two curves this morning that one was like kind
of 80 degrees, 90 degrees C. maximum temperature. Do you have a little
more confidence in that?

KRUGER: Yes, you would. But even under those circumstances, with the
environment changing in very many possible ways, even at the lower
temperatures, you could expect especially localized corrosion problems
to exist even at those lower temperatures, which we have little
experience with as well.

BULLEN: Thank you. Any other comments you\'d like to make, or do you
want to pass the baton to Alison next to you? You yield your three
minutes?

KRUGER: Yes, I yield my three minutes to the lady from Birmingham.

BULLEN: Dr. Davenport?

DAVENPORT: I had a very interesting conversation with Gustavo Cragnolino
over lunch, and this very much reinforced my view of the importance of
metallurgical features, and in particular, what can happen along weld
lines with thousands of meters of weld. It\'s not inconceivable that
some of it may not be done perhaps as well as it could be, things may go
wrong with the heat treatment somewhere, and I\'m very much convinced
that that is the most likely source of problems in terms of both local
increase in passive behavior, and also in the risk of localized
corrosion. But I think Gustavo can probably give more details about what
the particular problems might be around welds. But I\'m very firmly
convinced that that\'s quite important.

Another couple of things following up on that that come to mind, and
that is when people are doing measurements on pitting corrosion, any
kind of measurements, and you have a hundred results and you look at the
range, the spread, including some negative corrosion rates, or whatever
that appears to be on that, I think the interesting ones are the
outlyers where there are particularly high corrosion rates. And this
again follows up with my interest in metallurgical features. When there
are outlyers, is it worth taking a much more careful forensic look at
the ones that seem to have corroded particularly strongly? Are there
some features in the alloy, common or less common faults or defects or
impurities in the alloy that can give sites where there\'s localized
attack?

Again, we come to a size issue, and is a corrosion coupon of very
limited size a very good analog for the canister itself?
Metallurgically, they receive very different treatments. And also
you\'re sampling a much larger area, and so rare defects can then come
on and become a problem. So those are the features that I think have
struck me going through today\'s proceedings, including lunch.

BULLEN: Bullen, Board. I actually had a couple of follow on questions
that I had written down during the course of your presentation.

You mentioned that, you know, as a metallurgist and as a corrosion
scientist, you try to prepare those perfect surfaces of single crystals,
and then understand the fundamental mechanisms. How difficult do you
perceive the ability to model the heterogeneities, to model the real
world, to model the defects that you\'d expect to see? And is it a
realistic assertion that that can be done? Or is it an intractable type
problem?

DAVENPORT: I\'m not quite sure what you mean by model. I mean, I would
say that the first thing to do is to actually have a look at the
failures and see if we can identify particular problems. I mean, we\'re
all very well familiar with the fact that pits in stainless steel
initiate in manganese sulfide inclusions, but we don\'t have the same
sort of common knowledge that, oh, failures always initiate at whatever
kind of a particular in this particular case. So, I think a bit of
forensics is needed first if we can go on to model anything.

I must say the other thing that very much struck me was actually in Bob
Rapp\'s presentation when he talked about the importance of surface
finish. And, again, the idea of electropolishing all these canisters is
quite an interesting but probably rather impractical one. But there\'s
an enormous effect of surface finish on corrosion behavior, because if
you have a very rough machined surface, you\'ve got deformed layers and
bits where the metal is folded over on itself, and you\'ve got automatic
little crevices on the surface, not just with dust as well, so I think
that\'s a very important feature, too.

BULLEN: Thank you. Actually, my emphasis in modelling stems from the
fact that I\'m a performance assessment modeler, so I was thinking
extrapolation beyond 10,000 years and how well you do it, not the lab
scale models, although those are the fundamental mechanistic models that
we\'d like to understand.

Anyway, thank you very much. You had a good intro for Dr. Rapp. Dr.
Rapp, would you like to say a few words? Or do you just want to say
ditto?

RAPP: It\'s a lot more complicated than that. This matter of surface
finish I do think is important, and I don\'t know why these canisters
can\'t be polished up before they are loaded up, you know. They
don\'t\--loading them up shouldn\'t make that much difference to the
surface finish. So I think it could be done. I don\'t know why not.

KRUGER: They don\'t have to be electropolished. There\'s chemical
polish.

RAPP: Chemical polish. And, in fact, I think you could dope up the
surface with some cerium while you\'re at it. An anodic oxide on the
surface with a little cerium doped in would be a nice idea.

Other than that, it seems to me like the most dangerous part of this
service is the deposition and drying, and deposition\--wetting and
drying, and wetting a drying, which concentrates the salts. That\'s the
critical thing. And if you do permit ventilation on occasion, you might
use it as an engineering variable. You might let the stuff get hot, as
long as it\'s not going to have any deposition to keep the water away
from it until, by some monitoring system, you see that that period is
over with. Then you might cool it down and let the water deposit on it,
but not cycle evaporation deposition. Just either have it hot or else
have it cooler, and you could use your ventilation system as the
engineering variable to do that. I\'m just dreaming here, of course.

But the other thing is, as was mentioned, no matter how this would be
started out, it would be growing a little minor air formed product scale
in dry oxidation at the very start, and I think that should be taken
seriously, and experiments should use something like that, or simulated
scale, as the initial condition for electrochemical aqueous
experimentation.

And as Susan said, and I thought about anyway from my own experience,
there\'s a big difference between atmospheric corrosion in an aerated
film and deep solution in a vat of aqueous solution. And as I have
heard, experiments are not being done in the atmospheric mode today, but
they certainly should be.

BULLEN: Thank you. Professor Craig, did you want to make a comment, or
do you want to just listen for a while and go around the table? Okay.
Dr. Newman?

NEWMAN: Well, I don\'t have any particular qualms about the 90 degrees,
or whatever it was, the lower of the two temperatures that we discussed.
I don\'t think this stuff is suddenly going to start corroding
generally, although I definitely hear what Roger Staehle says about the
deposition and the evaporation issue. And I think 160 is kind of the
minimum temperature where I would really start to be concerned about
that.

So if somebody says, well, these things are not going to be ventilated
and the temperature is going to go up to 220, I\'m still a little bit
puzzled as to what Roger thinks is the uniform corrosion mechanism that
can operate there. But definitely in terms of promoting various kinds of
localized corrosion, that then becomes a rather different kettle of fish
then.

You know, quite clearly, if you have some conditions that persistently
generate a highly alkaline environment full of peroxide from radiolysis,
then you\'re going to corrode stuff at a significant rate. You know,
whether it\'s a micron a year or ten microns a year, I don\'t know. But
I think those mechanisms, I would say 150 or 160 is the threshold for
what I would call a steam generator heat transfer mechanisms to really
start switching on.

And you do see all kinds of stuff. I mean, just the other day, I was at
a lab where they were using a new surface analytical tool to look at
some alloys that have been exposed to these kinds of environments, and
they were finding all kinds of stuff in the grain boundaries down to
quite large depths, 100 microns, or so, lead, that kind of thing. And
those mechanisms seem to be specific to these concentrated, I would
going to say alkaline environments, maybe Roger can correct me here, but
probably alkaline environments at temperatures in the 200 range and
above. You can certainly get a lot of things happening to these nickel
alloys that I wouldn\'t particularly want to be\--I wouldn\'t
particularly want to be associated with predicting that they were going
to last for 10,000 years under those conditions.

BULLEN: Bullen, Board. Actually, you led into something that I was going
to ask a little later. But Alberto mentioned this morning that the minor
constituents in the groundwater, such as lead, or maybe mercury, or
arsenic, or some of the other bad actors, could play a role in the
passive film stability. And so I guess what I\'d be interested in is
maybe your interpretation of the importance of that role, and whether or
not you would see it as more significant in a hot 160 to 200 degrees\--

NEWMAN: Well, definitely the lead.

BULLEN: \--versus the 60 to 80? Yeah, could you comment a little bit on
that?

NEWMAN: The lead phenomenon, I mean it can be demonstrated at
temperatures like 100 if you use the right kind of hydrochloric acid,
and so forth. But as something that destroys materials, I\'m not aware
of any reports at temperatures, you know, in the 100\'s. But then on the
other hand, the time factor always has to be taken into consideration.

STAEHLE: There\'s a lot of work on lead, as you probably know, up to
about 300 centigrade.

NEWMAN: Yeah.

STAEHLE: Killian\'s work and Wong\'s work, it\'s pretty extensive. And
the one thing that\'s of interest in the lead in a way is, you know,
lead forms a lot of insoluble compounds. These compounds turn out to be
very temperature dependent in terms of their solubility. And so you
could have a compound which is quite stable at 100 centigrade, and at
200 centigrade, it\'s totally soluble. And so there\'s that kind of
thing going on, without belaboring it.

NEWMAN: My concern would be intergranular corrosion. I guess if I have
to summarize, if the conditions are what Roger says they\'re going to
be, and they\'re going to close it up and forget about it, the
temperature is going to go up to 200 and something degrees, I think one
could have localized corrosion of the pitting type, but I think what
Roger calls general corrosion, I think it would be more likely what you
would get is this intergranular attack, or intergranular corrosion, and
I would be concerned about that at a high temperature.

STAEHLE: Well, just to continue a point, we all work on different kinds
of consulting problems here and there, and I\'m working on a problem at
the moment, a thing in Venezuela where the temperature is around 250
centigrade in a potassium carbonate heat transfer crevice. So, potassium
carbonate is filling up in the crevice. It\'s corroding generally like
made in this heat transfer crevice.

NEWMAN: The material being?

STAEHLE: Stainless.

NEWMAN: Stainless steel.

STAEHLE: So, you know, I\'m not so sure the detail of the mechanism, but
there\'s no question about what\'s happening.

NEWMAN: Well, you can get high corrosion rates in carbonate for
well-known reasons, I think. I mean, it\'s a complexant, so, I mean, you
don\'t need the very high or very low pH. But, yeah, I agree that
that\'s the sort of thing that could happen. Carbonate is something that
I think is not so aggressive to nickel, so that\'s not something to be
so bothered about. I mean, you say 200 degrees. I\'ll jump to the other
side of the fence.

BULLEN: Okay, thank you. Actually, Rob, before you sit down, I have a
request for you. We had some questions about the testing program and the
experiments that were being done, and Professor Rapp basically asked
about the high temperature oxidation. Could you address maybe just a
little bit of some of the experimental program that\'s on. Is that a
fair question to ask you, or do you want to defer to somebody else?

HOWARD: Rob Howard, Integration Manager for Bechtel SAIC. I would like
Greg Gdowski, who is one of the PIs involved in our experimental
program, to just clarify a few things about what the testing program
involves. And we do do testing in humid air environments. It\'s not just
vat solution.

BULLEN: Okay, thanks, Rob. Dr. Gdowski?

GDOWSKI: Greg Gdowski, Livermore.

A few things about the environment that are probably not apparent
initially is that we are bounded by atmospheric pressure. So you\'re not
going to get super-heated steam there. You\'re not going to raise the
environment about one atmospheric pressure.

The reason you can go to high temperatures with the aqueous solution is
because of the forming of the saturated aqueous solutions with mag
chloride.

NEWMAN: The temperature of water is higher?

GDOWSKI: Yes. I\'m not denying that. Other concerns that we are testing
atmospherically, we do have a series of tests to address atmospheric
corrosion. We are doing periodic wet and dry type experiments under high
relative humidity conditions, where we\'re dripping saturated aqueous
solution salts on the specimens, letting them evaporate, trying to
characterize those environments.

We\'ve also done a series of evaporative concentration experiments where
we evolve these brines to very high concentrations. We\'re not, as Carl
put it, they were at much higher concentration aqueous brine solutions.
We\'re not at the .05 molar solutions. We\'re in the molar solution
range on these salts.

I guess that\'s about it, unless you have some other questions.

RAPP: With what observations then? What are your results?

BULLEN: Identify yourself, Professor Rapp, and ask.

RAPP: Rapp is asking what results have you observed then under these
test conditions?

GDOWSKI: Which tests?

RAPP: Well, any of them. Choose one.

GDOWSKI: Choose one. I could talk mostly about the evaporative
concentration experiments. What we have seen under the wet and dry
dripping is primarily the formation of the scale on the surface, with
very little oxidation of the underlying metal. We\'ve done these tests
at around 90 and 100 degrees C. at this point.

Under the carbonate base waters, high silica, high carbonate, you form a
very tenacious scale on these materials.

RAPP: As a deposit; right?

GDOWSKI: Yes, that\'s right, with very little indication of any
corrosion underneath these deposits at this point.

NEWMAN: May I ask a question. This is Roger Newman.

Can somebody tell me what, given the constituents of the water, what is
the highest temperature that you can conceive of maintaining a liquid
environment on the surface?

GDOWSKI: It would have to be the magnesium chloride or the calcium
chloride type brines. Calcium chloride boils at about 164 degrees C.

NEWMAN: Okay. Zinc chloride boils at a higher temperature than that. You
don\'t have any zinc chloride.

GDOWSKI: Well, I mean, from the constituents at Yucca Mountain, from the
groundwater constituents.

NEWMAN: Right.

STAEHLE: This bounding condition that Greg mentions of atmospheric
pressure is certainly an important one. The question I was just asking
him was whether or not in thinking about maximum temperature, you\'ve
got to think about some kind of a deposit build-up on the surface that
has some dimensional substance to it, and maybe some capillary structure
to it. And that may not change the temperature a lot, but it probably
would be somewhat higher than 160.

GDOWSKI: Agreed. Agreed. It will raise it, but you have to, at these
elevated temperatures, the size of the pores that you have to bring
about a very large elevation in temperature are very, very small.
You\'re talking sub-micron levels at these temperatures.

BULLEN: Thanks to both of you. I guess this maybe is a very good lead-in
to the brine question that\--oh, Alberto, do you want to say something?

SAGÜÉS: I have a couple of questions for Roger.

BULLEN: Go right ahead.

SAGÜÉS: Now, depending on what we get into, we may go into this later
with some of the other participants.

BULLEN: Okay, feel free.

SAGÜÉS: You made a very quick estimate, Roger, in assuming a certain
chromium solubility, and from there, you went ahead to try to obtain a
guesstimate of the corrosion rate. Now, I assume that in doing that, you
must have assumed that you were at some kind of a pH in the system, and
you looked at how much the chromium oxide line interfaced in the\--shift
in the equilibrium, something like that?

NEWMAN: It\'s something like that, yes. In fact, I was just pointing out
that you could have very low equilibrium solubility of the stuff, and
yet over a period of hundreds to thousands of years, build up a layer of
porous oxide, which a lot of people would probably agree might have some
effect on the stability of corrosion. I wasn\'t really picking a
particular point, but I mean, if you want to equate that to a particular
pH, it would probably be anywhere near neutral, you could probably have
10 to the minus 14 molar solubility of something like chrome.

SAGÜÉS: And, from there, how did you work it out into a rate of
dissolution?

NEWMAN: Just Pick\'s law, yes, Pick\'s first law. I mean, it\'s just a
factor of the envelope diffusion.

SAGÜÉS: So, do I understand then that what you are suggesting with that
kind of thinking, without making a very precise statement, of course,
would be that that would be one way of having a non-conservative passive
layer dissolution process at the passive layer solution interface.

NEWMAN: No, I don\'t associate that with some kind of accelerated
general corrosion at all. I associate that membrane like layer with an
increased probability of localized corrosion.

SAGÜÉS: Localized corrosion?

NEWMAN: So, over a long period of time, it seems reasonable to suggest
that you would build up a thick, as to say microns thick, oxidized layer
on the surface, which would be mainly a product of a re-precipitation
process, simply arising from the passive current. And that that layer
could promote a localized corrosion process.

SAGÜÉS: Okay, yeah, that I have followed. I guess another question, and
this applies to you and then maybe as other members of the panel get
through it, I think that one of the questions would be what is the
thickest, maybe not the barrier layer, but the thickest passive debris
layer that anyone may have seen anywhere that one can ascribe to a
process like the processes we\'re talking about in here? Is there such a
thing, or are we talking\--what I\'m trying to establish is are we
talking about something that is totally, absolutely fictional, or are
there any examples\--

NEWMAN: Science fiction.

SAGÜÉS: \--that we can look at?

NEWMAN: Well, I think the problem was that most of the practical cases
where those happen at ambient temperatures have been where you are on
the borderline of the transpassive dissolution. I once had to deal with
a problem where industrial dishwashers were going blue. They actually
looked much nicer when they were blue than they did before. This turned
out to be due to peroxide in the detergent materials causing a kind of
transpassive dissolution on the material. All the material was dissolved
and then redeposited and it gave this blue film.

I don\'t know of any example, if you like, in the middle of the passive
region where anyone has seen a similar thing. The best chance to get
something like that would probably be at high temperature where the
process is faster, the passive dissolution process. But, I do know that
in acid environments, of course, you can see something like that. If you
were at pH 1 and you passivate stainless steel, then the passive current
is higher so it doesn\'t take so long to build up such a layer, and you
could perhaps learn something by artificially growing such layers at low
pH or something like that.

In fact, you know, you can actually make stainless steel go blue by
cycling the potential. There\'s lots of ways to make stainless steel go
blue and you cycle between active and passive. So, you\'re producing
this sort of very finely divided re-precipitated type of material. That
certainly makes pitting much easier. I\'ve seen in lab tests that when
you have that deposit, that blue material on the surface, it always pits
prematurely at very low potential.

SAGÜÉS: I would like to ask the remaining members of the panel when it
is their turn, if they know of any blue stainless experience or
sighting, and I would like to hear that and it certainly would be very
instructive to have some blue C-22.

NEWMAN: Well, I can supply it in different colors.

BULLEN: Then, we don\'t have to polish the containers. We could just
have different color containers.

Go ahead, Professor Bertocci?

BERTOCCI: Is it then interference color?

NEWMAN: Yes, but it\'s always blue. So, it\'s something more than
just\--you know, you\'d expect to get rainbow colors if it was\--but
it\'s definitely an interference effect, but sometimes you do see the
rainbow colors. But, when you don\'t see the colors, it\'s always blue.

BULLEN: Gustavo, go ahead? Do you have a question?

CRAGNOLINO: Well, talking about colors, you produced this precisely for
Alloy-22 when you go to the transpassive regime?

NEWMAN: It goes blue, yeah.

CRAGNOLINO: Goes to yellowish-blue type of color and this is associated
with the transformation of the film under certain conditions, but we are
talking a very high potential. So, I don\'t see that that\'s attainable
by any means. You can obtain this potential in reprocessing units, but
not in the condition of the repository.

NEWMAN: Well, I think, Alberto was just asking is it possible to speed
it up so that you can do some experiments\--was that the\--

SMIALOWSKA: (Inaudible).

BULLEN: Please use your microphone, Susan.

STREHBLOW: Could I give a comment on that?

BULLEN: Oh, Dr. Strehblow, go right ahead?

STREHBLOW: Okay, sorry. If you have these interference colors, is it
that you just dissolve the iron and you have the iron 2, and if you\'re
back in the passive range, then you oxidize it to iron 3 oxide? I think
that is the reaction which is occurring. So, if you by intention would
like to have this layer, you also could add iron 2 salts to the
solution, just oxidize it up and then at moderate pH it could be, let\'s
say, 6 or 7, so that the iron 2 is still soluble. Then, you get this
nice film and then you can study it in detail what it is doing to
localized corrosion.

NEWMAN: Well, if there\'s any iron in the water in this mountain, it
will certainly oxidize onto the surface of the alloy and produce a layer
like that anyway, as indeed could one or two other elements. Any
corrosion process that you propose here is going to be occurring under a
membrane-like layer of something. And, you know, I think these, in
general, would be just as aggressive as physical crevices for the
corrosion, but not necessarily very aggressive. It depends on the
temperature and so on and so on. Anyway, I took too much time there.

BULLEN: Thank you. Bullen, Board. Professor Strehblow, did you want to
make any comments about Question 1 as we go around since we\'re
returning to that?

STREHBLOW: Yeah, I just wanted to repeat also that\--and support what
the previous speakers have said\--the higher concentration of the
electrolyte is a very big danger and these wetting and drying periods
which might concentrate the electrolyte. And this, in combination with a
depletion of the chromium and the material by some wrong treatment,
welding and whatever, you might also remember that you have chromium
depletion at the grain boundaries for stainless steel by chromium
carbide precipitation. And, things of that kind which might happen and
which could lead to a local depletion of chromium is a source of danger
because then the passivation mechanism by chromium oxide formation could
be hindered because there is not enough locally, not enough chromium
oxide. As Carl De Bella said, we have huge surfaces which have to be
treated. There could be a weak point where this might occur. This is the
first remark I would like to make.

The second, we heard something by Bob Rapp about high temperature
corrosion and I would like to add some little remark which I didn\'t
include in my short presentation because I didn\'t want to overload it.
But, there is existing the possibility that also chlorides and high
temperature corrosion could give a big danger of film breakdown and
corrosion if the temperature is sufficiently high. When you have, for
instance, HCl oxygen mixtures at 700 Centigrade, then you easily will
corrode the metals and also the nickel- based alloys. We did a couple of
these studies in the past. This will break down the material with a high
velocity. Now, we have lower temperatures. So, it might on the
long-term, there might be some mechanism of this kind. You might not
have the HCl, but you might have the chloride sitting on the surface as
a little crystal and then something of a similar kind may start and, as
you have a long time, this may also cause some corrosion phenomenon in
the dry at high temperature. This was the second remark.

And, the third remark was about radiolysis which somebody in the
audience asked me or gave a remark at the end of the session and he told
me that especially in the first time you have a danger of formation of
high oxidants and electrolyte because then you have the high radiation.
But, when it slows down, then this danger will be over. So, one has to
discuss this in detail and there has been some work on it, as he said. I
don\'t remember the name of the person.

BULLEN: Bullen, Board. Actually, with respect to the radiation field,
and we started talking about point defect production, I wanted to sort
of follow up on that. I know that a scientist named Rich Von Konynenburg
at Lawrence Livermore National Laboratory had done in the late \'80s an
analysis of alpha, beta, gamma neutron damage, and, basically, same
conclusions that were reached this morning. Alpha is not a problem
because it\'s inside the waste package. The betas may or may not be a
problem, but usually aren\'t significant. The gammas can cause some
local ionization, but usually don\'t cause displacement damage. The only
displacement damage you\'d get would be from the neutrons. But, the
conclusion from the Von Konynenburg paper is that the neutron flux is so
low compared to the similar flux that you have in a nuclear reactor that
in the 10,000 year kind of time frame, you may end up with sort of the
equivalent of one or two reactor days of equivalent operation or
radiation damage. And so, the kinds of point defect production rates
would be, you know, maybe 8 or 10 orders of magnitude less than what
you\'d see in a reactor.

So, you\'d ask yourself, you know, even though I have a factor of 5
increase in time, I\'m still a factor of 10^8^\--or excuse me, a factor
of 10^5^ increase in time, I have an effect of 10^8^ decrease in rates.
And so, is that going to be significant? I guess, I don\'t know the ins
and outs of point defect production and its impact\--maybe Digby could
comment on this\--its impact on the stability of the oxide films. But, I
would venture to guess that the neutron damage would not be a real big
precursor to those kinds of issues. And, maybe, I should defer to Digby
about that.

MACDONALD: No, you\'re right. Neutron damage isn\'t significant. About
the only way that you could have a deleterious effect is if something
like hydrogen peroxide kept building up, but, of course, the hydrogen
peroxide decomposition is catalyzed by transition metals. Okay? So,
it\'s a little far-fetched to see a massive buildup in hydrogen
peroxide.

Just to put this radiation situation in perspective, a number of years
ago, we did some modeling work on copper canisters and, of course, the
wall thickness of copper canisters, much, much greater than the wall
thickness of the C-22. The conclusion then was that there might be a
very small shift, positive shift, in the ECP corrosion potential due to
radiolysis. Now, of course, with the thinner C-22 wall, I believe that
the dose rate of the surface is now about 2400 rad per hour, okay,
compared within a nuclear reactor of maybe 1000 times that. But,
nevertheless, it may be significant and that issue possibly should be
looked at again.

BULLEN: Professor Strehblow, did that answer your question with respect
to radiation?

STREHBLOW: Yes.

BULLEN: Dr. Rapp?

RAPP: May I comment on one of your comments, please? Relative to
something like chloride cracking an oxide at a hot temperature, there
were very nice experiments by Peter Hancock a long time ago where he
took a metal wire and vibrated it to its resonant frequency and then put
a drop of sodium chloride on it and it immediately cracked, but this was
at a very high temperature, maybe 800 Celsius. But, the experiments are
so easy to do that. I mean, if you want to try this at 300C, I think it
only takes 10 minutes to find out whether sodium chloride will crack a
film. So, that sort of experiment would certainly be reasonable, I
think.

STREHBLOW: But, I think it is also very important in the context of the
stability of a passive film because you are reaching perhaps 160
Centigrade or somebody told something about 220. So, we are approaching
some temperature where this could be a danger.

BULLEN: Thank you. Dr. MacDougall, would you like to make a few comments
about Question 1? You can show whatever you like because now we don\'t
have a time limit. Well, maybe as a professor, you have a 50 minute time
limit, but that\'s it.

MACDOUGALL: I\'m not a professor.

BULLEN: Oh, well, we could promote you. Could you put the microphone on,
please? Right there. It\'s right next to you.

MACDOUGALL: Well, it\'s about the passive current, in fact, and the
nature of the question. I\'m not again talking about Alloy C-22; I\'m
talking about nickel. I spent a good part of my life years ago
decorating defects on passive films that were formed on nickel in
sulfate solutions over various pHs and breaking those films down and
open circuit. This is the nickel single crystal work that we talked
about and it\'s a one-one-one. You have little arrowheads, and in point
of fact, you can see them here. They\'re beautiful crystallographic etch
pits which are developed, I believe, and I\'m absolutely convinced, in
defects within the passive film that are frozen in once you open the
circuit you take the driving force away. There\'s a large number of them
there. That was formed on a film that wasn\'t formed very long or it has
low potential or something like that. You had fewer of them when the
conditions of formation of the film, passivation conditions, were, in
fact, longer or at higher potential. In this case, I believe it\'s
longer. Then, when you went to very long periods of time, you had fewer
defects still. You only had a few on the surface. In fact, it was 70
hours at 0.0 volts. You only had a couple.

Now, the passive current is obviously going to be lower here than it is
for that, than it is for that one, but I don\'t necessarily agree that
we\'re better off with this than we are with those ones because it\'s
something that Susan alluded to this morning. In fact, I\'ve had the
feeling and qualitatively I believe that I\'ve pretty much proven it
qualitatively is a different story. This was done some years ago, many
years ago now.

But, I think what happens is that the number of defects going from 100
to 10 to 1, the current doesn\'t go for 100i to 10i to 1i; it goes from,
exaggerate, perhaps 100i to 30 or 40i to 10 or something of this nature.
What I\'m saying is that each of the defects here has to handle
more\--not more strain, but has to handle more activity because the
strain of the film is not going down accordingly. So, the passive
current that you see is going down. You\'d say that\'s very good in
point of fact. But, the activity associated with that defect, which was
caused because of breakdown and repair, these defects are not static,
they\'re mobile over the entire surface. They will eventually, when you
have the potential applied, encompass the entire surface. The oxygen 16,
18 SIMS work proved that, in fact.

But, what I\'m saying is that you would say, look, if a very low passive
current here, but that doesn\'t necessarily mean, in fact, that you have
a better scenario for localized corrosion which depends upon the current
efficiency for the repair of any of those breakdown events. When you\'re
on open circuit, it could be even worse because you have a larger
cathodic area, in fact, involved in this particular case here.

So, I think just to say what of the passive current, the implication of
the question is that it goes down, you\'re better off. That\'s not
necessarily true. If it was up, you may be better off in some cases.
I\'m not sure. I think with this alloy, C-22, it may have such a
frightfully resistant passive film\--and I don\'t know firsthand\--but
you may have to mechanically disrupt it or remove it in some sort of way
like that which is perhaps not out of the realm of possibility. But,
this is 70 hours and, as I say, the film, in point of fact, the defects
in the film, I think, are getting, if anything, more prone to supporting
some kind of a localized attack in that particular system that I was
investigating. So, I think one has to be terribly careful of just
looking to the passive current. It\'s an overall thing, I realize, but
it has other things encompassed in it, in terms of the current
efficiency for the repair of those events.

BULLEN: Bullen, Board. Just a follow up question. Because one of the
things you look at is the drift in that current, do you think that it\'s
the increase in the population of those types of sites in C-22 that
makes that happen?

MACDOUGALL: This was nickel here in point of fact.

BULLEN: Right.

MACDOUGALL: It was decreased and the density was decreased in point of
fact. But, certainly, yeah. Yeah. There are fewer defects in that, and I
counted them up, you could count them. I\'m sure today, if people were
doing it today, they could do it much better. The ultimate would be, I
guess, if one had, I suppose, only one defect. It may be so active that
it would drill a hole in something in no time flat. So, maybe there\'s
an optimum number of them or something of this nature in a system like
this.

C-22, I certainly don\'t know, but I\'ve used the analogy and again I
have to be cautious because I don\'t know if this is applicable to this
particular system here, but I think that one should, at least, consider
it, the analogy with people. Some people have heard me say this before.
Human beings, in point of fact, are those human beings who have lots of
small defects, well, it\'s okay, I think they can get by in life and not
do themselves or society any great injury. But, if a person
has\--perhaps, he\'s perfect, but he has one defect, it would be one
deuce of a defect.

So, you perhaps, have to be careful that you reduce things\--something
to almost nothing. It\'s the strain in the film and, again, I mean,
there were people at the University of Virginia years ago that looked at
this Gwalfney and his group and people. It\'s a very difficult problem
to look at, but just how is the strain decreasing within these films as
time, in fact, goes on and the propensity towards this sort of localized
corrosion.

And, I would agree that, in point of fact, if you have some kind of a
porous deposit on a surface that Roger is talking about and others, then
you could be in a bit of trouble, in fact. I mean, that\'s pretty nasty
thing because the stews, the environments, the crevice situation, all of
these places where you can have these occluded cells, that\'s something
that could make things certainly much worse if they were to happen.

BULLEN: Thank you, Dr. MacDougall. It makes me happy for my small
defects and hopefully not one big one that I seem to have. We\'re not
all as well-engendered as you are, Dr. Kruger. So, we all have a few of
these.

Dr. Smialowska, would you? Please, right to the microphone.

SMIALOWSKA: I would like to emphasize again the differences that can
occur during these short time aging and long time aging because, in
fact, we don\'t know nothing about what happens during the longer period
of time. If you would take into consideration the mechanism of aging in
this short period of time, you know that the corrosion properties are
better which means resistance to corrosion increases. At the same time,
there are a lot of mechanisms which showed that during the longer period
of time, you should have rather higher corrosion than lower. According
to what we know from short time of aging, it should be very small
corrosion. But, we cannot say that after a certain period of time you
have some changing in the mechanism of corrosion because some other
phenomena appears.

This phenomena which I think could be, it is that after some time, we
have this very small defect in passive film. Passive film is much more
resistant, much more stiff, much more rigid, and what we will have then,
we will have mechanical breakdown of the film which will be\--first of
all, we will have stresses in the passive film and later on cracks. And
then, you will have destabilization of the film and it might be you
start again to have high corrosion and then going up to the lower
corrosion again.

So, I think that it is, of course, very difficult to model the aging
after longer period of time, but it can be done some experiments which
can show you that after special treatment, you have decrease of this
defect, and later on, you might probably see this mechanical breakdown.
I think that I know these kind of experiments.

Concerning other things, the surface preparation, of course, surface
preparation is very important, but again this is very important in
initial period of time. Initial period of time, I am saying about this
100 years or something like this. Later on when the corrosion starts,
then the preparation of specimens will not play very much role, very big
role. But, what I think it would be important, it is agglomeration of
corrosion products of salt, salts films different which were these salts
especially which are not dissolved in water and you have this calcium
salt, and magnesium, also, not dissolved, and then you will have some
specimen which is not uniformly covered by this debris and by this
corrosion. Then, you will have non-uniform general corrosion which is
some kind of localized corrosion.

So, it seems to me that quite a lot should be done to be able to model
what is going on after longer periods of time. We don\'t know. For
example, we don\'t know if the composition of film is changing and how
much it\'s changing. Composition like you have at the beginning,
everybody knows that it\'s agglomeration of chromium oxide on the film,
but if it change during aging or not, we don\'t know nothing about this.
We don\'t know also nothing about the physical property of the film.

SAGÜÉS: I would like to make a comment on a question. The first comment
is that, indeed, the kind of things that you mentioned that we don\'t
know about, the makeup of the film after long periods of time. It is
part of the reason why we are here talking about this. One thing that
you didn\'t mention and interestingly I haven\'t heard anyone mention,
so far. It\'s sort of like the sore subject, sometimes, is whether the
film starts as a crystalline and then goes into amorphous or it\'s
amorphous and then goes into crystalline or where is it in this area?
And, I wanted to ask what you may have to say about that particular
aspect? Then, I have something else I wanted to ask you.

SMIALOWSKA: If I would know, it would be nice. Concerning the amorphous
film and crystalline films, then when I know, it is all old work of
Jurry who showed that when you have higher concentration of chromium in
the film, you have much more\--the film is much more amorphous. Is that
right?

SPEAKER: That\'s controversial, but that\'s right, yes.

SMIALOWSKA: Yes. And so, however, after some time, maybe the
crystallization can occur, but I don\'t know. It might be. It might be
yes, it might be not. But, it would be some kind of the cyclic changes
of property, I believe, in this. That it is not constant.

SAGÜÉS: Thanks for your answer. Before I ask you the other question, Dr.
Strehblow had a comment, I guess.

STREHBLOW: To your aging aspects, I don\'t have experience with the
Alloy-22, but with many other binary alloys. The chemical composition of
these films is changing from\--in many cases, we followed that from
milliseconds to a week about. Even in the long-term, you may accumulate
those species which are not dissolving. So, even after a week, we have
still an increase, for instance, in chromium and iron chromium alloys.
This is the chemical aspect. The other aspect is the question
crystalline or amorphous and I think Phillipe can add many further
arguments to that. We\'ve studied together the situation on copper and
you have a certain sequence. In a very short period of time, you see
amorphous films forming at the very beginning, and then later on, at
least in the case of copper where we have experience, it turns to a
crystalline form when you see the crystalline structure with STM. There
are changes and you can follow them with these methods you have today
and this is giving us the idea that in many cases the crystalline film
is not a bad film; it\'s a very good film and protective film.

SMIALOWSKA: Okay. I am glad that I was thinking in the right direction.

KRUGER: Copper is quite different from chromium, though.

SPEAKER: Of course, of course.

BULLEN: Okay. Dr. MacDougall?

MACDOUGALL: May I add just one caveat here in terms of the crystal
nature of these films? The one on nickel, I certainly know rather well.
On the Nickel 1-1-1 crystal, one has a film. The passive film is a
particle size approaching, I think its about 10 angstroms, which is a
pretty small particle size, in fact. But, it\'s perfectly epitaxed. If
you look at the diffraction patterns, it\'s 1-1-1 on 1-1-1, the
directions in the two major directions. What you have are very small
angle boundaries. It\'s a mosaic. The boundaries between these particles
are certainly less than a degree, much less. So, we\'re into a bit of a
gray area what these things mean in terms of dislocations and that sort
of thing. Are they sweeping the surface? And, we have very small
particle sizes which indicate a lot of disorder. But, diffraction
patterns indicate (coughing) tremendous order. So, you have to interpret
these things in a special way, especially when you\'re dealing with
films that are 10 or 12 angstroms thick. I mean, they aren\'t like bulk
phases or anything like that.

BULLEN: Dr. Smialowska, did you have another comment?

SMIALOWSKA: No, I have\--no, but I wanted to say something about the
passive film.

BULLEN: Oh, please do?

SMIALOWSKA: Concerning the effect of potential on the passive film, in
fact, you grow the passive film with potential, but this growth is not
very substantial. It means you will have at the most 14 angstroms thick
film and less. And, I think that if you will do some kind of experiments
to keep the passive matter at potential which will be below the
transpassive potential\--so you have to be sure that you are indeed
below this transpassive potential and keep it for long period of
time\--you might be able to see this mechanical breakdown. And, if it
would be like this, it means that during the long period of time, you
will have the same situation in your case.

BULLEN: Thank you. That\'s a very good suggestion.

I\'m going to take some chairman\'s prerogative. I would like to ask Dr.
Sato to make a few comments and then we\'re going to take the break that
was scheduled for 15 or 20 minutes ago and I\'ll do that in just a
second.

So, Dr. Sato, would you, please, make your comments on Question 1,
please?

SATO: And, for uniform passive film dissolution is concerned, the
accepted knowledge indicated that the passive film dissolution was
controlled by the interfacial potential difference between the film and
dissolution. So that anything that changed the interfacial potential
will change the dissolution rate. For instance, aqueous environment, a
different kind of composition, and also the absorption of hydrated
anions. But, I don\'t think such a arrangement, the absorption gives us
a dangerous increase of the dissolution current. I don\'t think so. So
that I cannot see any specific mechanism that causes a great deal of
increase of dissolution current.

Well, in addition, I think that the most important thing is that we have
to keep the open circuit potential in the certain limit range where the
passivity is maintained. If your open circuit potential goes outside the
safety regime, you will get into trouble. For instance, going up,
potential going up so you have transpassive dissolution region which you
have a great deal of dissolution rate compared with the passive state.
And, also, if you go down the potential, you will probably get into the
active state. I\'m not quite sure, your Alloy-22, how the active
dissolution regime is\-- .

BULLEN: That\'s a little difficult.

SATO: Except for hydrogen.

Well, I would like to add one more thing. That is the radiation effect.
So far, we have been thinking only the electrolysis, radiolysis, which
produced, for instance, oxidizing substances, such as hydrogen peroxide,
which is one of the candidates which increases the electrode potential
so that you get into trouble.

But, besides this electrolysis, we have to pay attention. The low energy
radiation produces excited electrons and holes, as I told you in the
morning. This excitation in the solid state\--for instance, the electron
and hole has an energy of the same order of magnitude, same order of the
electron volt, similar electron volt, with the action of corrosion. So,
it means this is direct effect to the corrosion process itself. But, we
have quite a different kind of solid, you see, mostly probably the salt
or oxide which are probably semiconducting oxide materials. So, it has,
you see, band gaps so that the low energy radiation excites these
solids. You have excited electrons and holes which have relatively high
reducing and oxidizing capacity which affects the growth process itself.

BULLEN: Bullen, Board. I actually had a follow up question on the
presentation you made this morning with regard to the radiation and
radiolysis effects. This may be an inverse argument for temperature
because do you expect the stability of the electron/hole pairs produced
by radiation or radiolysis to be greater at lower temperature\--and I\'m
showing you my ignorance of solid state physics now by asking this
question\--versus higher temperature?

SATO: I am not quite sure, but you see the high energy radiation with
the energy median electron volt at the\--not directly affected the
corrosion process, itself.

BULLEN: Right.

SATO: Of course, you have radiation damage producing lattice defects or
something like that. But, these point defect affects indirectly to the
corrosion processes, but not directly.

BULLEN: Okay.

SATO: But, in the case of excited electrons in the hole, because the
energy lengths, you see, similar electron volts so this is able, you
see, to change the corrosion process itself.

BULLEN: Okay.

MACDONALD: Can I just make a comment on this?

BULLEN: Yeah, go ahead, Digby?

MACDONALD: You know, it has been found that irradiation of passive
stainless steel surfaces inhibits pitting corrosion, inhibits the
nucleation of the pits. Now, we\'ve done that work, Professor Shibata
has done that work. It does that by producing electron/hole pairs\--at
least, this is my interpretation\--producing electron/hole pairs which
essentially quench the electric field within the passive film, the
barrier layer and, hence, reduces the driving force for the movement of
vacancies across the layer. So, you have go to a higher potential on the
metal in order to compensate for that effect. Okay? So, what would be
interesting to do would be to find out whether that same phenomenon
occurs in C-22, firstly. Secondly, if it can be induced with gamma
radiation\--I don\'t see any reason why it couldn\'t be induced with
gamma radiation\--and whether the shift in the breakdown voltage is
comparable to the shift in the corrosion potential produced by
radiolysis of water. I think if you were able to do those three things,
you might be able to sort out that issue quite nicely.

BULLEN: Thank you. Actually, we are a little more than halfway through
the panel roundtable type discussion of Question 1, but I want to
introduce a break. I would like to take 10 minutes which means I know
you\'ll be back in 15, but 10 minute break so everybody is back here at
3:35.

Before you leave, I\'d like a couple people from Livermore or the
project who have access to C-22 results to come talk to me, please? I
think that may be Jerry Gordon or maybe Greg Gdowski or maybe even David
Shoesmith who looks like he\'s a culpable individual there. So, I\'d
like to talk to them during break, please. 10 minutes.

(Whereupon, a brief recess was taken.)

BULLEN: We had a request from a panel member for some additional
information. And so being as responsive as possible, the Department of
Energy has identified Gerry Gordon as the opportune one who gets to come
up here and give us a brief description of some of the results of the
C-22 work that has been done to date. And, so I\'m going to give Gerry
the onerous task of going six to ten minutes max, and giving a quick
overview of some of the general, or maybe even localized corrosion
issues associated with C-22. And then I\'ll ask a couple of the
questions of some other members of the audience. But, Gerry, you\'ve got
about five to ten minutes, please.

SAGÜÉS: Dan, excuse me.

BULLEN: Oh, Alberto, go ahead.

SAGÜÉS: Gerry, would you mind telling the panel members what is your
exact capacity within the Yucca Mountain Program, and what are your
technical responsibilities? Because I think that that may\--

GORDON: Yeah.

SAGÜÉS: Thank you.

GORDON: I am the materials team lead in Las Vegas on the Yucca Mountain
Project, with Bechtel SAIC BSC Company. That\'s primarily what I am.

This is just some of the environments that we are doing tests in. They
represent concentrated salt solutions. This is the so-called J-13
groundwater at the site, concentrated to 10X, 1000X. This is similar,
but with the pH adjusted to 2.8. This is about 50,000X concentration of
the groundwater. It\'s fairly high in chloride. And this is a
non-carbonate nitrate, sodium potassium nitrate chloride. This is wrong.
It can\'t be more than a million parts per million, but it\'s very high
in nitrate.

I think a key observation is that the molar ratio of chloride to some of
the buffer or more beneficial ions is listed down below. It\'s on the
order of one. If you go to pure sodium chloride, the environment becomes
significantly more aggressive.

You saw a version of this earlier. These are the data based on descaled
weight loss from the long-term corrosion test facility, and they covered
the first three environments on the left that I showed on the previous
slide over a limited range of temperature from 60 to 90 centigrade. And
what\'s on here is the uncertainty band due to the very low corrosion
rates. At two years, a mean rate is 100 angstroms per year. And so when
you\'re doing descaled weight loss, the total weight loss is very low,
and the air and the microbalance that does the measurement, and the
dimensions of the sample, the descaling process, and so on, leads to
this type of uncertainty, which with time is decreasing because of the
total metal loss is increasing.

You saw some of these earlier, but they do represent independent
confirmation of the magnitude of the general corrosion rate, the mean
rate being on the order of .01 microns per year, and being relatively
insensitive to temperature. I think that shows up on a later slide. And
these are some potentiostatic tests and unbuffered, so it should be
.028, I think, molar-sodium chloride that show a similar kind of fairly
low rate.

This is the surface from a specimen in atomic force microscopy after one
year\'s exposure at 90 centigrade in simulated concentrated water. In
this case, it was exposed in the vapor phase. There are also samples at
the water line, and submerged. And this one had relatively little
surface deposit. In many cases, you see silicate and some sodium
chloride sometimes deposits when you examine the surface. This is a
control sample, and this is a sample after one year\'s exposure. And you
can see very little rounding of the sharp edges. These are 600 grid, I
think, polished initially, and you can still see the polishing marks.
And it\'s obvious the corrosion rate is very low.

Initially, the waste package will be exposed to dry air at maybe 160
centigrade. It depends on the final temperature mode that is selected.
So, we\'ve started to study the growth kinetics using the tunneling
atomic force microscope. these are some results at Lawrence Livermore.

This is a surface. In this case, it\'s an atomic force microscope in
which you\'re applying a bias potential and you\'re measuring the
current that results, and it\'s a function of the oxide thickness. There
are some calibration constants that need to get established for a given
alloy system and oxide. This is conventional atomic force microscope.
This is the electron current density map, if you will. It shows
scratches, polishing scratches on the surface. This is after 45 days at
200 centigrade.

On the left here is the current versus the bias potential that\'s
applied. These are calculated lines at one, two, three and four
nanometers. The points are experimental data. The passive film, the air
form film at the start was about 2 microns. After 28 days, it went up to
something like 2.8\--I\'m sorry\--nanometers. After 45 days, about 3.2
nanometers. And recently, they\'re 210 day data, and it\'s up to about
3.3. It\'s essentially leveled off to a constant thickness.

These are some data from the University of Western Ontario using time of
flight secondary ion mass spectrometry. And, again, we\'re looking
at\--these are sputtered off and analyzed in a mass spectrometer, and
you can see that for Alloy C-22 in the air grown films, it\'s rich in
chromium oxide and molybdenum. At 200 millivolts, I think this was about
12 hours at 200 millivolts, and 1 molar pH 1 sodium chloride at 85
centigrade, similar to the air form film.

In contrast to Alloy C-4, which contains something like 15 or 16 percent
chromium instead of 23, and somewhat higher molybdenum, you see the film
is rich in molybdenum, and because of the lower chromium content, a lot
lower chromium. But in Alloy 22, chromium, and in this case, molybdenum
are present in the film.

At 500 millivolts, you\'re starting to get transpassive dissolution, and
the chromium is dropping out. It\'s dissolving. The chrome 3, which is
insoluble, is going to soluble chrome 6. So the ratio of chrome to
molybdenum is decreasing.

In terms of localized corrosion, there have been a lot of tests and
they\'re described in a lot of documentation, primarily done with cyclic
polarization in a range of environments with and without these nitrate,
sulfate, silicate, carbonate type buffer ions that are always present at
least in all the waters that have been examined at the site. The
groundwaters, the percolating waters, the pore waters all have roughly
that one-to-one ratio of chloride to nitrate. You can get localized
corrosion in Alloy 22 in pure sodium chloride at high enough potentials,
especially if you crevice it.

This is an example of probably, along with magnesium chloride, the most
aggressive postulated environment, and this shows the cyclic
polarization curve with and without nitrate present. And it has a very
marked effect. In this case, this is at 120 C., with near saturated
calcium chloride and calcium nitrate. There are a lot of other data that
show similar effects, that ratio of chloride to nitrate, plus sulfate,
as it approaches one. There have been data done at 10 to 1, 100 to 1,
and 1 to 1, and there\'s a very marked benefit of all of these oxyanions
that are present in the water. So that needs to be considered.

These are some data generated again at the University of Western Ontario
very recently, where these are potentiostatically polarized samples, and
the current density after I believe it was 12 hours exposure over a
range of temperatures from room temperature to, I think, 85 centigrade,
and it\'s a comparison of a range of nickel based alloys. And at 200
millivolts, the corrosion potential is approximately that, so a little
above the corrosion potential. There\'s very little temperature
dependency over this range. There\'s some, but it\'s very small.

At 500 millivolts, it\'s somewhat higher. These vertical lines on some
of these alloys, these were samples mounted in a plastic mount, and
there was a crevice at the edge of the sample. In some of these samples,
you could see crevice corrosion occurring. Alloy 22, at least under
these conditions up to this 85 centigrade, didn\'t suffer crevice
corrosion. Again, this is in one molar sodium chloride, pH 1.

BULLEN: Thank you, Gerry. I appreciate that.

Were there any specific questions on these types of results, or other
questions from the workshop panel members?

Roger, go right ahead.

NEWMAN: I guess in terms of transpassivity, that\'s much less likely in
acid than in alkali, I think. Is that you\'re experience?

GORDON: Because of chromium solubility; that\'s right.

NEWMAN: Yes. So I just wonder if the use of the pH 1 solution there
might be deemphasizing the transpassive phenomenon quite a bit.

GORDON: Well, if you look at that very first table on the range of
environments that have been tested, we\'ve tested up to pH 13, and a
very, very concentrated J-13. Can you go back to that table a second?

NEWMAN: Okay. You don\'t claim any credit for the OH minus ions there in
that solution, that pH 12. You say that the inhibition is due to the
nitrates and the sulfate. But I guess if you\'re at pH
12-point-something, are you also getting some inhibition of localized
corrosion from the hydroxide ions?

GORDON: You likely are. You can postulate neutral or closer to acid
environments that could exist. But the nitrates are always present, at
least in all the waters that have been identified.

BULLEN: Bullen, Board. Any other questions from the panel?

MACDOUGALL: Could you leave on the conclusions for a moment?

GORDON: Okay. I didn\'t go through all the charts that led to them. But
I certainly can.

I also didn\'t go into the path forward, the test program that\'s
underway. There\'s a lot more experimental effort, modeling effort
underway now.

BULLEN: Professor Davenport?

DAVENPORT: Just a quick question. In the absence of Professor Bohni, I
guess somebody should ask is there much work being done on metastable
activity in this system?

GORDON: Metastable pitting?

DAVENPORT: Yes.

GORDON: At the University of Virginia, Dr. Scully, under project
funding, has done a fairly extensive study of metastable pitting over a
range of these oxyanion to chloride ratios. And under potentiostatic,
long-term potentiostatic tests, you do see a small amount of what could
be metastable pitting that dies off with time and potential. It\'s
pretty resistant to it.

KRUGER: Even at elevated temperatures?

GORDON: These were up to 100 centigrade.

BULLEN: Any other questions? Roger, I\'m going to defer\--I think I\'m
going to try and get around the table before we finish up.

So, thank you, Gerry. In fact, I\'ll apologize to David Shoesmith right
now. He may want to make a comment in the public comment period, but I
would like to get the rest of the way around the table on question one,
and we still have six panel members left. So, if we could move to Dr.
Bertocci? Please identify yourself.

BERTOCCI: The question is whether we can imagine mechanisms whereby the
corrosion rate is higher than the expected one. And I think all day
long, we have heard of possible mechanisms. I think that most of us
would agree that if the conditions used for the test can be maintained
for the whole time, probably the corrosion rate would be what the data
said. But I think that we question, or a lot of people here have
questioned the possibility of keeping these conditions, instead of
having small samples which have been cleaned and so forth, we have these
huge things which have been transported inside the tunnels, presumably
not in a condition like the electronic industry, so we have dust
depositing, we have the formation of films and scales, and what not.

And so the real point is how can\--most of us I think are very doubtful
that the conditions which have been used to do the measurements will be
maintained in time and space.

BULLEN: Alberto, did you have any specific questions you wanted to ask?
Or do you want to finish the rest of the way around the table?

SAGÜÉS: I would like to say something that pertains to what Dr. Bertocci
was saying that may be for the other participants to keep in mind, and
that is that maybe since we\'re going to be getting to the end of the
day pretty soon, I really would like to hear an answer to the question
that Dr. Craig formulated. And that is can we extrapolate over 10,000
years? And more importantly, say why we can extrapolate over 10,000
years. As a technical community or as a scientific group, and the like,
do we feel that there is enough here to make a reasonable extrapolation?
Or perhaps maybe the other way to say it would be how uncertain or how
certain you will be that this extrapolation is in order? And, again,
we\'re looking here for opinions, and maybe to frame your answer, so
your comments perhaps around that kind of a question.

BULLEN: Do you want Dr. Bertocci to answer, or do you want to go on to
Dr. Pickering? Dr. Bertocci?

BERTOCCI: I think that we have, a number of us have proposed quite a
number of possible mechanisms which would be active if the conditions
are not the ones that have been used. So, I suppose all of us would
propose tests in conditions which were outside the range which has been
used so far in order to have a better idea of what would happen if the
conditions are not maintained.

A question I would like to ask also is what do we expect? That all the
canisters will resist 10,000 years, or would be satisfied to have a few
failures? I think that this would become an important point to decide
whether or not the conditions and the materials in so far are sufficient
or not.

BULLEN: Bullen, Board.

I\'d actually like to address that one, because we really have a very
focused nature for this workshop, which is how well do the waste
packages work, and what mechanisms are going to operate over the 10,000
year time frame. But in the grand scheme of things, the project and the
decision-makers who have to decide whether or not the site is suitable
have to look at the legal criteria which are the EPA standard for
performance, which is a dose based standard, or a risk based standard,
for a population of people living down gradient from the mountain 10,000
years from now.

And, so to be perfectly honest, and this is a terrible way to put it,
the solution to pollution is dilution, and so you would want to fail one
can every ten years or so, and have a very slow release, and that would
be the best. But that\'s obviously not a very licensable approach.

And, so in answer to your question, you know, we want to do the best we
can in understanding the performance of the repository. But the actual
performance itself isn\'t the waste package only; it\'s the waste
package in conjunction with the natural system. And so we\'re asking you
to focus very, very narrowly here, and we kind of apologize for that,
but in a certain sense, no, because we want to get your expert opinion.

But, in answer to your question, sure, it doesn\'t have to last for
10,000 years. I mean, if one can fails, does the entire repository fail?
No, that depends on how it fails and what time it fails and the release
rates and the mechanisms, and all that. So, that\'s kind of beyond the
scope of this. And I hope I didn\'t confuse the issue too much, but we
are very focused here on passive layer stability, and long-term
extrapolation. And, so that\'s kind of the focus here, and I hope I
answered your question.

Did I raise any more that the rest of the panel have? Digby, go right
ahead.

MACDONALD: If you ask the question can we predict, it begs the following
question. To what accuracy? Now, there\'s another aspect of accuracy,
and that is that if you were to build the canister with too thin a wall,
of course, you couldn\'t ensure reliability. If you say, well, I\'ll go
the opposite direction and build with a very thick wall, you may not be
able to afford it. So what we haven\'t discussed here and defined is the
accuracy with which we need to make these predictions. Is it a factor of
ten? A factor of 100? It makes a big difference. Roger is going to say
something.

BULLEN: Bullen, Board.

Actually, you get beyond the realm of science, into policy issues, with
respect to certainty of performance and those types of issues.

MACDONALD: Right. But it\'s absolutely vital that somebody give us
guidance as to what accuracy these predictions need to be made to.

BULLEN: I\'m looking at Alberto now.

SAGÜÉS: Well, what I\'m saying is the following. Suppose that you have
this same group, and you say we\'re going to build this\--or, rather,
the Yucca Mountain Project is proposing to build a canister out of 1
millimeter thick 1020 carbon steel, and nothing else in between that and
the waste, I have the feeling that we would be hearing some opinions
saying this can never make it, impossible. It makes no sense to even
think about it, et cetera, et cetera. That would be one extreme
attitude.

The other would be to say we\'re going to build this out of a very thick
and internally strengthened precious metal alloy, and I have a feeling
that we may be hearing most people on this panel saying that, well, that
is pretty much guaranteed as far as we know with all of our knowledge to
last for a period of time that would be extremely long, and I would say
exceeding, with a good degree of certainty, 10,000 years, if not maybe a
much greater amount of time. And you get now into having analogs and all
that that can show that. Evidently, we have something in between.

And what I would like to see, to hear a little bit more when you have an
idea of the kind of evidence that exist, the direct evidence, empirical
evidence, and so on, and of course this group has an extremely good idea
of what is the present status of fundamental knowledge in the area of
passivity. And what I would like to hear is maybe not a yes or no, and
indeed we don\'t want to do that with this kind of a group, and maybe
we\'d like to hear a little bit more of how your answers are colored by
this overall question. Are we having a reasonable chance of predicting
durability over 10,000 years using our present empirical knowledge, and
the knowledge that the scientific community has on the phenomenon of
passivity and its stability?

BULLEN: Can I hand that one right to Professor Pickering as he sits
here? You\'re on the spot. Dr. Pickering?

PICKERING: Well, I think I came in here with the feeling that we
couldn\'t trust the passive current density to remain at the low level
for many reasons, and we\'ve heard many mechanisms. Certainly the one
that seems to come out, at least to my ears, from many members of the
panel is this deposition of debris, or reaction products, other things
that might form this film.

Immediately, then I, you know, you see the possibility of composition of
the electrolyte changing at the base of that film. And, you know,
whether it\'s sulfur species or chloride or whatever that might
accumulate, it\'s going to raise, you can visualize it raising the
passive current density. And if you need 10 to the minus 8 amps per
square centimeter to last ten years, then if you raise it only to 10 to
the minus 7 amps per square centimeter, you\'re only going to last a
thousand years, if my simple minded calculation is right.

So, yeah, I think it would be hard for me to say that we can extrapolate
comfortably from what we know at this time.

That\'s all.

BULLEN: Okay. Dr. Cragnolino?

CRAGNOLINO: Yes, I have a comment, and I would try to concentrate
essentially on question number one. I\'ll leave some of the issues
related to number two in some way connected with what Alison mentioned
before for tomorrow.

In some ways, even though I respect the opinion of Roger, I have to
disagree in the sense that I believe that the environments are much more
bounded than we tried to demonstrate. I learned not a long time ago that
as a chemist, you do something called chemical divide, and allow then to
discriminate what is the tendency of the environment and the condition
of evaporation. What salt could precipitate and what you can expect as
evolution, and we have two possibilities that were mentioned by Carl
this morning in some way, but was not paid enough attention. One, is an
evolution towards\--an environment that is more acidic, or you could say
it\'s slightly neutral, in which is magnesium chloride or calcium
chloride, no zinc\--chloride because it\'s not there, could predominate.
And the temperatures\--in this case, assuming that we have contact with
air, because this mountain breathes, is going to be about 160 degrees C.

On the other side, we have the possibility of much more alkaline type
environment, and this is a situation\--in which we move\--. Now, if we
use short-term measurements of passive corrosion rate that are not in a
steady state condition, we can demonstrate that this rate measured by
electrochemical methods are almost independent upon the concentration of
the chloride, and upon the pH, from a wide range of pH. And this is
because chromium dominate the composition of the passive film under
steady state conditions.

Now, this is telling us what happens under what we can consider a steady
state condition that for nickel chromium alloys, contrary to
iron\--chromium alloys, you can get a steady condition in a couple of
days at most. For nickel based alloys of this type, you need much more
time.

However, you establish this condition, and you get films, as was
mentioned some time, of the order of two nanometers, 3 nanometers,
something like this, that I believe that is the real barrier film
controlling rate of dissolution.

Now, we have these two problems. One, this possibility that was
mentioned recently by Howard Pickering, and is connected with the idea
of Professor Sato, of a membraine mentioned by Roger Newman, the
possibility of having a membrane formed by corrosion deposition of
products of the dissolution. And this is an issue that we have to deal
with. But the main implication that I see is in relation to localized
corrosion.

NEWMAN: May I just butt in there one second? I think when Susan before,
or somebody referred to localized general corrosion, I think it could
also be that.

CRAGNOLINO: Oh, okay.

NEWMAN: But it\'s a chemistry change type of corrosion. It\'s the type
of corrosion where the anodic side becomes acid.

CRAGNOLINO: Exactly. I agree and I think that\'s an important
consideration.

KRUGER: What about the potential going into the transpassive region?

CRAGNOLINO: I will touch up on that point later.

I\'m going to bring up another point that Phillipe called to my
attention, and was the point that was raised by Phillipe Marcus before,
regarding impurities in the metal. And I think that this is important.
This material has a specification has a sulfur content of .02 percent.
But a good manufacturer of Alloy 22 will try to decrease significantly
the number. It\'s one order of magnitude lower. It\'s 20 ppm. This is my
question. Assuming this process that you mentioned of anodic
accumulation of impurities due to the process of dissolution, do we have
a risk that the stability of the passive film cannot be maintained. Not
over a distributed interface, but at grain boundaries at a specific
location. And this could lead to a form of attack that we didn\'t
mention, for instance, localized corrosion in the form of intergranular
corrosion that will lead to other processes that is not the issue here,
but would be stress corrosion cracking, and so on. These are my
concerns.

Coming to the corrosion potential, we have done experiment, obviously
short-term experiment. We have done long-term experiment for Alloy 825.
We have experiment for five year in Alloy 825, and the corrosion
potential doesn\'t evolve beyond the 200 millivolts, in the calomel
scale, that is in the passive regime of Alloy 22.

The addition of hydrogen peroxide can produce an increase, but is not
substantial. And we are in that situation. A transpassive dissolution
over a wide range of pH, and I forget the value but we can look later in
my hotel room\--, for Alloy 22 takes place at about 400 millivolts
calomel scale, unless, unless, and here there are problems with the
fabrication process, and the alloy has precipitation, modification in
the microstructure, that would be possible, and will lead to problems.

That means that in dealing with the issue of passivity, I think that
this is one thing that we have to consider as a possibility, and this is
the process of accumulation of more information regarding factors, as
was mentioned by Professor Sato, that could alter the corrosion
potential for reasons that we cannot anticipate very well.

Now, responding to the philosophical question, I have one experience.
The experience is an unanticipated process of irradiation growth of
zircaloy. It\'s an alloy that is used in fuel elements as a cladding,
but is not used very common as a structural material in the core of
nuclear reactors. Well, nobody anticipated there was going to be a
break-out rate in the kinetics of irradiation growth, and in the country
I was working at that time, Argentina, a nuclear power plant was out of
operation for six months because fuel channel broke down due to this
that nobody was able to anticipate. This is regarding things that show
that to have limit in our knowledge as you confront issues that could be
catastrophic.

BULLEN: Thank you, Gustavo. Any comments from the panel on what Gustavo
just said?

Seeing none, I will move on to Dr. Marcus.

MARCUS: As most or all of the panelists, I have proposed this morning a
number of mechanisms that would or that could\--I should say that may
after long service times modify the passive currents, I think I proposed
four mechanisms, and one of them was reemphasized by Gustavo, which is
the segregation of impurities, including sulfur, at the surface or at
the interface between the passive film and the metal. So I\'m not going
to repeat that.

Instead, I may make one or two comments. There was a comment this
morning, I think it was Ugo Bertocci who said that, and I\'ll read my
notes, that only weight loss and elementary\--electrochemistry are
available. Okay, we\'ve heard a little more later this afternoon on the
thickness and composition, but my concern is that we know really very
little on the specific passive film which is formed on this specific
alloy. We, around this table and the audience, know a lot about passive
films on many metals and alloys, but not specifically on this alloy.

So I think it\'s quite hard to predict the behavior of something that
you don\'t really know the nature of. We know very little on the
thickness. We\'ve had just a few data this afternoon. We don\'t really
know the composition. Of course, everybody agrees that it\'s going to be
largely enriched with chromium oxide because this is a general finding
on chromium containing alloys in potential and pH conditions where
chromium oxide is stable. But how much nickel do we have in the passive
film? I think what we saw this afternoon with the SEM\--data, in fact I
was a little surprised. I saw that there seems to be a lot of nickel
oxides in these. So it\'s far from being really a chromium oxide passive
layer. I saw a huge signal which was assigned to nickel oxide, and I
doubt that nickel oxide would behave very well under the expected
environments.

Another point which has been raised I think by Alberto Sagüés earlier is
the structure. We know absolutely nothing on the structure of these
films. And to answer this question, I think this is something we must
know, because the current in the passive state is largely determined by
the defects, the structural defects which are present on the surface of
the oxide film. In fact, most of the oxide films dissolved at specific
sites, where the cations have low coordination, and that\'s of course
directly related to the structure.

What we know from other metals and alloys in terms of structure is that
for short-term passivation, as was shown a long time ago by Jerry
Kruger, these films are amorphous. But what we have learned more
recently is that aging of these films in the electrolytes will lead to
partial or complete crystallization\--, giving some long-range
periodicity\--with the structural defects, as was stated with these
structures. And I think we definitely need to know the structure to
really\--predict the integrity of the passive films.

So, I think it\'s hard to conclude on that result, I mean, predicting
the behavior of something that you don\'t really know the exact nature
of.

Now, maybe a more general issue is to predict, what we have to do is to
extrapolate on the long-term. But what do we have really to extrapolate?
We have to extrapolate in time and space. So, what I have learned at
school is that to extrapolate something, I need to have a plot of
something as a function of time. And then if I know the mathematical
law, I can extrapolate. And I have to do the same in space. But I have
seen very little data of that type that would give some important
parameters for the integrity of the passive films that would vary with
time and that would vary with space derived from experimental data.

So, I\'m not sure what exactly we can extrapolate. Okay, if we
extrapolate the weight loss measurements, it seems to be that we can be
rather confident that the passive dissolution would be low enough. But
to my knowledge, I think it\'s the only curve where we have something as
a function of time on which we can really apply mathematical
extrapolation.

So, now, maybe another comment is that there seems to be a consensus
around this table, and I would like to also share this consensus, that
there\'s a risk related to the concentration of salts in the
electrolyte. I think that seems to be an important issue.

And, also I would like to reemphasize the effects or the possible
effects of wet to dry, and to wet transitions, in particular on the
composition and structure of the film. It may well be that the film will
have a different composition, under dry as compared to wet conditions,
and that even the structure may be different. And when we will have this
transition, I think it will be important to know what changes we can
expect during these transitions.

That\'s all I wanted to say.

BULLEN: Thank you.

SHIBATA: I\'ll just make comment on the effect of temperature on the
kinetics of the passive film growth. I have done it using the
electroscanning electrode and I follow the kinetics of the film growth
from room temperature to 250. Of course, I used the oldgrave (phonetic)
system\--and I found\--and then, there are the materials, iron, iron
nickel and iron chromium, binary alloy, and a series of materials are
used. And, I found the logarithmic or inverse logarithmic type of film
growth is observed from room temperature to the 150. Above the 150, the
kinetics change to the usual\--type parabolic law is observed. So, this
is quite similar to the dry oxidation type. But, below 150, the inverse
logarithmic type prevails. This is typically observed for iron system.
Of course, iron chromium and iron- nickel is also the similar behavior.
So, I think that in dry case also, the iron shows inverse logarithmic
type near room temperature. If you increase the temperature, of course,
these kinetics change to parabolic. I don\'t know exactly what
temperature is changing the kinetics.

But, in the aqueous systems, I think that 150 is some critical
temperature because the stress corrosion cracking or corrosion fatigues
also very, very susceptible at 150. So, I think that this is connected
to the nature of the passive film formed on the surface. So, recovery of
the repassivation is some effect of such kinds of cracking behavior. So,
I believe that below 150, the extension of the room temperature behavior
might be expected, but I\'m not sure in the instance of Alloy-22. This
is my comment on the effect of the temperature on the kinetics.

BULLEN: Thank you. Bullen, Board. Go right ahead?

STREHBLOW: I wanted to say some remark to the outlines of Phillipe
Marcus.

BULLEN: Oh, go right ahead, Professor Strehblow.

STREHBLOW: Is that too late or\--

BULLEN: No, no. This is a roundtable discussion and we can all speak at
any time. So, go right ahead?

STREHBLOW: Okay. I agree that we don\'t know anything about the
structure because it has not been studied; for instance, with STM or AFM
or whatever it is. But, the chemical composition of the films on, let\'s
say, nickel at\--20 chromium and nickel 34 chromium has been studied
very intensively as a function of the potential, pH and time and these
data are known from surface analysis, XPS studies. I didn\'t go into
these data because that it is a whole story and I\'m not prepared. But,
roughly speaking, what you said, there is nickel in the film or not and
how much and what is the film composition? Of course, it depends on the
pH. If you are in a strongly acidic electrolyte, then the nickel is
almost not there at the lower potentials and it enters at the higher
potentials to some extent because then you have also the dissolution of
chromium and you can play these games and you can follow that from a
millisecond\--we did studies from a milliseconds up to an hour
passivation time. And, we know also the changes in that time range, not
about years or something like that. But, in that time range and pH and
potential, we know what the film is and its structure of the hydroxide
composition and the oxide underneath.

MARCUS: Yeah, Marcus. That\'s right, but in this alloy, in addition, we
have molybdenum and tungsten. So, we would like to know how much. As we
saw earlier this afternoon that according to the SSIMS data that there
is molybdenum in the film, but these are not quantitative data. We
don\'t know really the composition of the film. We know what is in and
what is not in. But, I don\'t remember if there was some tungsten in it
or not.

STREHBLOW: There is molybdenum in the film. That\'s what I have seen.
But, these are data of Schultzigan (phonetic) \-- on hastaelloy C-4, but
it\'s also not exactly the same alloy. If you are talking about Alloy-22
and nothing else, then you are right. But, if we are talking about
nickel 20 chromium which is very close to that composition, then we know
what the film is.

BULLEN: Alberto?

SAGÜÉS: Yes, a comment on Dr. Strehblow. I have no doubt that there are
investigations that have looked at this in some detail, but I think that
I\'m correct in assuming that those are investigations that looked at
relatively young films, maybe things that have been exposed to the
environments for intervals of hours to days maybe. But, I would be
surprised if this knowledge extends to mature films that have been in
situations resembling service for many years or is there some\--

STREHBLOW: These are basic studies, of course, and these are specially
prepared alloys which have been subjected to special conditions and not
to service or to field-like conditions.

SAGÜÉS: One of the things that the project, the Yucca Mountain Project,
is generating is now relatively well-characterized, specimens have been
exposed for periods of years to relatively well-characterized
environments. Of course, they have a different kind of finish and
they\'re not single crystals. But, there may be an opportunity there to
learn things that couldn\'t be found otherwise.

BULLEN: Bullen, Board. I had a follow up to Professor Shibata\'s
comments and maybe they tie in again to what Susan Smialowska had said
about the structure and the kinetics of the film and its mechanical
properties. You mentioned that you saw sort of different kinetics that
occurred below 150 degrees C and you were concerned specifically about
mechanical properties associated with the film as it grows. Would you
have more confidence in a lower temperature if you never went above 80
degrees C during the operating phase of this? Would you expect to see
perhaps better performance or perhaps better understanding or more
confidence in the understanding that you\'d see, as opposed to going to
160 to 220 degrees C? I\'ll ask Professor Shibata first, and then,
Susan, if you could follow up, that would be great.

SHIBATA: This kind of technique, it just took a very, very short time
and you cannot extend over this kind of behavior to the long-terms
because of the very, very short time. But, even that kind of conditions,
the kinetics changes at the critical temperature, so that I just
confidence that the film growth kinetics is almost controlled by the
passivity-like behavior below 150. And, of course, this is very much
related to the mechanical behavior suggested by Ms. Smialowska. So, I
think that the understandings of the amorphous nature or crystal nature
of the structure of passive film as it depends on temperature is very
important, I think.

BULLEN: Okay. Bullen, Board. Just to follow up on that. So, I guess the
kinetics issue with respect to temperature is important, but if you had
a longer period of time, would you expect to see similar types of
changes in the mechanisms at lower temperature or you think it\'s actual
fundamental mechanistic change? Susan, do you want to try that one?

SMIALOWSKA: Can you tell me what kind of material did you study because
it\'s, I guess\--because it is very\--this 150 threshold, it is the
change of the iron oxide from magnetite to hematite. So, of course, this
might be because this, you have\--

SHIBATA: Yes, I think that it\'s mainly the ion system. Yes.

SMIALOWSKA: Mainly this is because you change from one oxide film to
another. So, it is nothing\--

BULLEN: Not a good comparison?

SMIALOWSKA: Yeah.

BULLEN: Okay, thank you. But, with respect to your mechanical changes in
the film, would you expect to see differences at different temperatures?

SMIALOWSKA: Let me think. Yes, I will. But, this is not how you can
prove that you have mechanical changes. You can prove only when you keep
the condition constant. It means rather high potential because, another
way, you will not see nothing.

BULLEN: You won\'t see anything.

SMIALOWSKA: But, below this transpassive potential\--so you have to do
the experiments this way, that you have to be sure that you do
experiments also to find what elements you have in the solution. Okay?
To be sure that you have no transpassive dissolution. And, if you will
take this kind of potential, then, of course, the time of aging should
be much more shorter. And, if you will keep this for a long time, I
expect that you will see some differences in the property of the passive
film. Maybe, I am wrong, but I think you will.

BULLEN: Okay. Thanks. Dr. Kruger?

KRUGER: I have a question about these mechanical effects and I don\'t
know the answer, but in these very thin films, you know, we\'re talking
about 10 to, say, 20, 30 nanometers. I\'ve always thought that
developing stresses in such thin films is a very difficult thing to do.
That you really can\'t talk about mechanical effects in such thin films.
I may be wrong, but certainly with thicker films\--

SHIBATA: I think that such thin films, of course, some stresses are
generated and, of course, if you increase the temperatures, there is
more thick film, thicker films\--

KRUGER: Thick films, yes, absolutely. But, thin films, I don\'t know.
Maybe you can, but it seems to me that it\'s very difficult to develop
stresses in such thin films.

SMIALOWSKA: It will be difficult, but not impossible. Let\'s put it this
way. The film which is flexible and not very\--which will not go to very
easy mechanical breakdown, there will be film which is hydrated. If you
have this other, this hydrite layer on the oxide film\--it would be
double layer\--then it will be much more difficult. But, when you are
doing the experiments at a higher potential, the hydration is much
less\--and you will have just oxide only. And, in oxide, this mechanical
breakdown could go much easier. So, if you will prepare, for example,
oxide film using just high temperature oxidation. Yes? And then, put to
the solution, then you have breakdown of the film, at once. Very easy.

KRUGER: Well, easy to get stresses and\--

SMIALOWSKA: Yes. But, it is not necessary to have very \--thick oxide
film.

KRUGER: But, oxide films formed in aqueous solutions by electrochemical
means are different than\--

SMIALOWSKA: Yeah, it\'s completely different. I think it is possible to
check this, you know. It might be just that nothing would happen, but
this a rather easy experiment and so why not check?

KRUGER: Some experiments have been done, incidentally, many, many years
ago by Vermillier, but looking at rather thicker film.

SMIALOWSKA: I don\'t remember Vermillier, but he did experiments\--

KRUGER: And, Leach also did some.

SMIALOWSKA: Yeah, but he make experiments on the passive film, anodic
films.

KRUGER: Thick films, yes, yes, anodic films on aluminum, titanium,
things like that.

BULLEN: Okay. Dr. Strehblow?

STREHBLOW: It seems to me that this discussion is also showing the two
opinions of a more simpler homogeneous film concept which has been used
up to, let\'s say, five years ago and the further information about
atomic resolution methods which show the details of such a film. Very
often, you have stresses, let\'s say, between crystalline film and its
substrate because the fit is not, at all, good and then the system
reacts by faceting. We have studied this with Phillipe Marcus on the
oxide film on copper, but he has also studied this with other systems.
The situation was such that, let\'s say, in the case of the copper
oxide, the epitaxial relationship between the copper 1 oxide and the
copper metal substrate on a 1-1-1 orientation of a single crystal was
not, at all, perfect. And then, the system reacts by a very interesting
and nice-looking efaceting and so it overcomes this stress. If you have
a stress, then perhaps you have faceting or slipping steps and so forth.
And, if you study these systems and if this has been perhaps done with
these methods for all these various systems which are of interest to
this audience, then you might get an answer and further insight.

SMIALOWSKA: But, you know, I do not think that it is such a big
difference between these different points of view how to study because,
of course, when you are studying something in atomistic scale, then
it\'s fine. You\'ll know what is going on exactly. Then, when you are
doing these in microscopic scale, then you have many of these events on
the forces and you measure some kind of film. Okay?

STREHBLOW: I didn\'t want to say that you should do one thing and not do
the other. You should both and both concepts are not wrong, they are
constructive to each other. That\'s what I wanted to say.

SMIALOWSKA: That\'s okay.

BULLEN: Thank you. Gustavo, did you have a comment?

CRAGNOLINO: It was only a clarification to the comment of Jerry Kruger.
The experiment that he was referring to was Bupar (phonetic) and
Vermillier was experiments done with films of the order of few
nanometers in aluminum and other metals and tantalum\--to try to
discover what of the film were brittle or ductile, but subject to
microscopic deformations. I mean, I think that the regime that we have
to discuss here, in some way, is a different type of regime, a much more
lower stress level and other \--.

KRUGER: That\'s my point actually. I wasn\'t saying there were not
stresses. I was just posing the question.

NEWMAN: May I just say something?

BULLEN: Roger, go right ahead?

NEWMAN: Roger Newman. Also in that Bupar and Vermillier (phonetic)
paper, they found that when you anodize tantalum and you pull it, the
film changes color (laughter) and it goes thinner. Remember that?
That\'s one of the observations that have never been explained by
anybody.

BULLEN: Bullen, Board. Does it turn blue?

NEWMAN: It depends.

BULLEN: Oh, okay. Thank you.

We still have one member of the panel to hear from and that\'s Digby
MacDonald. He sat at the wrong end of the table after lunch. So, he gets
the final say of the go-around. You can take out your viewgraphs now.
So, Digby, can you give us your summary?

MACDONALD: I want to address the first question because I knew it was an
important question. I actually did some calculations on it.

I showed you this morning by using a point defect model and a mixed
potential model, you can predict the corrosion potential. So, the
question is then what can I do to the oxygen reduction reaction in order
to get the corrosion potential to exceed the potential for transpassive
dissolution? Is there anything I can do?

Well, I can change the partial pressure of oxygen that will change the
concentration of oxygen. And, by the way, this model assumes a very thin
electrolyte film of saturated sodium chloride on the surface and it
takes into account salting in and salting out and all those nice
effects.

Well, the model also predicts the transpassive dissolution behavior. Let
me just show you this one which I calculated current voltage curves as a
function of pH. This branch up here is hydrogen evolution. This branch
down here is oxygen reduction. Here is the passive current, here. Then,
the model predicts that there\'s a sudden jump at this potential here
which corresponds to the potential at which the oxidation state of
chromium changes from 3 to 6, corresponding to dissolution as the
chromate species. So, the question then is what can I do to the oxygen
reduction reaction that will displace the potential of the \-- ?

And, the origin of that effect also comes out of the point defect model.
What happens when you change the oxidation state from 3 to 6, the model
literally predicts the film disappears or becomes very thin. Okay?
There\'s a sudden decrease in the thickness of the film. So, now, the
potential just below that which is distributed across the film now
becomes distributed across the interface where it affects a dissolution
reaction. That\'s why there\'s a sudden increase in the rate of the
dissolution reaction.

Well, it turns out that in order to displace the potential above the
transition to the transpassive state, you need a partial pressure of
oxygen somewhere between 100 and 1,000 atmospheres. That\'s the
prediction. Okay? And, obviously, you\'re not going to have that. Okay?
So, that doesn\'t seem to be likely.

There is, however, another possible way of doing this and that is what
if you introduce something to the exchange current density? Is it
possible to do that? And, unfortunately, I didn\'t bring those
calculations with me. But, the answer to that question is no. There\'s
nothing that I can conceive of doing to the exchange current density
that would raise the exchange current density by the many orders of
magnitude necessary in order to displace the potential above that
transpassive potential. You have to go up 6, 7, 8 orders of magnitude.
And so, I did those calculations for the specific reason that there are
small concentrations of lead and mercury, but in particular lead, in
this water. And, it\'s well-known in electro catalysis, that small
crystallites of lead oxide on a surface is a quite good electro catalyst
for the oxygen reduction reaction. But, even recognizing that, you\'d
have to move the exchange current density for oxygen reduction too much
in order to get the potential above.

So, my personal opinion is that transition to the transpassive state is
probably highly unlikely.

BULLEN: Allison?

DAVENPORT: Davenport. Digby, did you consider the transpassive
dissolution of molybdenum?

MACDONALD: No. No, this is just purely chromium.

DAVENPORT: How much lower might that be? Do you have any feel for that?

MACDONALD: That\'s a good question and, in fact, I could put that in. In
calculating the potential at which the transpassive dissolution process
starts, I assume that chromate is in equilibrium with chromic oxide.
Because you need a chromate activity in the thin oxide\--in the thin
liquid film in order to calculate the equilibrium potential. So, I
assumed that there is equilibrium between chromate species and chromic
oxide and oxygen in the air. From that, I can calculate the equilibrium
potential and then applying the second law of thermodynamics, of course,
potential has to be above that equilibrium potential in order to get
dissolution.

And, one last thing, if I can, Allison, before I\--this plot here, we
have good reason to believe that the calculated thickness of the barrier
layer should extrapolate back to the equilibrium potential; in this case
the chromium/ chromic oxide equilibrium potential for the prevailing
conditions. We found that that holds true for zinc and it appears to
hold true for iron. In other words, for iron, if you measure the
thickness of the passive film, it seems to extrapolate back to something
that\'s close to the equilibrium potential for iron magnetite. And,
certainly, zinc, that works very well. It extrapolates back to zinc,
zinc oxide. Oh, and also for tungsten.

KRUGER: Looking at the Pourbaix diagram for chromium and molybdenum, you
find that the potential where molybdenum becomes soluble is much, much
lower.

MACDONALD: Is much lower, right. Right.

DAVENPORT: And, the other comment following up on that is you can also
get transpassive dissolution of chromium when you\'ve just got a little
bit of band bending at the surface to produce just a little bit of
chrome 6 actually at the surface layer.

MACDONALD: Yeah. Yeah, you know, this is sort of a semi-equilibrium
argument. And, you could also argue that because you\'ve got an
inhomogeneous surface, there might be parts of the surface that have a
different equilibrium potential for the chromic-oxide-chromate reaction
than other parts of the surface. So, you know, this is a first order
approach to that.

BULLEN: Roger and then Susan, please?

NEWMAN: Roger Newman. I guess, you weren\'t considering peroxide, right,
because that would completely change the picture?

MACDONALD: Well, you could put peroxide\--in fact, this model, its
genesis goes all the way back to the model developed for calculating
corrosion potentials in nuclear reactors, where, in fact, you do have
hydrogen peroxide and the whole slew of radiolysis products. And, yeah,
you know, the hydrogen peroxide question is a very interesting one,
although I haven\'t done the calculation. Hydrogen peroxide being a much
stronger oxidizing agent than oxygen, having a much more positive
standard potential. It conceivably could shift the potential up. The
only problem I have with it is that the decomposition of hydrogen
peroxide is catalyzed by transition metal ions and it\'s catalyized very
strongly. So, you know, whether you could get a significant
concentration of hydrogen peroxide in that thin liquid film is
problematic

\--

NEWMAN: Some of the transition metal ions, because they would be
complexed by fluoride in this environment, I think would be inactive
for\--I think fluoride is a stabilizer of peroxide.

MACDONALD: It could very well be. I think you\'d need to get the
concentration of\--I\'m just guessing at this point because I haven\'t
done the calculation\--but, I think you\'d need to get the concentration
of hydrogen peroxide up to well-above one molar.

NEWMAN: Well, I can tell you that at pH 11 and with 200 parts per
million peroxide, stainless steel goes blue (laughter).

MACDONALD: Okay.

BULLEN: Susan, do you have a comment?

SMIALOWSKA: I wanted to ask you did you measure the exchange current
density for all your experiments?

MACDONALD: No, we\'ve taken values that we had measured previously on
stainless steels. However, I do have in that pile of slides\--and I\'m
sure you don\'t want to see it\--data from Moscow. Part of the
program\--this is the NERI program, the Nuclear Energy Research
Initiative program which is the other half of what I did. This model
here was developed for Jerry Gordon and his folks. But, the NERI program
is a joint effort between SRI International, me, and George Engelhard
who is now at OLI Systems and also the Frumkin Institute of the Russian
Academy of Sciences. A lot of experimental data are being measured in
Moscow on C-22 and we actually have now quite a body of data on the
kinetics of oxygen reduction, hydrogen evolution, and\--

SMIALOWSKA: They measured the exchange current density for all these
temperatures and\--at partial pressure of oxygen?

MACDONALD: Right. And, hopefully, by the end of that program, you know,
we\'ll have a significant database for that.

BULLEN: Gustavo?

CRAGNOLINO: Could you put back the plot that you have the thickness of
the barrier layer?

MACDONALD: Thickness of the barrier layer?

CRAGNOLINO: Yes. I was surprised about the number, but I don\'t see well
from here.

MACDONALD: Okay. This is 20 angstroms here.

SMIALOWSKA: 20 to 50.

BULLEN: Digby, before you leave, I actually have to call upon someone in
the audience. Somebody from the University of Western Ontario, please,
stand up back there, David Shoesmith, and maybe address a couple of
issues. First, maybe the hydrogen peroxide issue, and secondly, maybe
you could resolve some of the issues with respect to the ions that were
identified in the Simms work? I mean, that was one of the questions that
was raised.

SHOESMITH: Okay, yeah, sure.

BULLEN: Go ahead and address both, please. Identify yourself, too.

SHOESMITH: Yeah, I\'m Dave Shoesmith from the University of Western
Ontario, but I should confess also that I\'m a consultant to the Yucca
Mountain program so that you know where I\'m coming from.

I just wanted to address the issue that\'s come up over radiolysis or
radiation effects. We have reviewed that. It\'s been studied well on
many materials in many different countries; Germany, Canada,
Switzerland, Sweden, and the United States. It\'s not proven to be a
particularly large effect. The dose rate level at which it was found to
be effective on a reactive material like carbon steel was about 300 rad
an hour and that was George Marsh in England. The present expected dose
rate on the waste container for Yucca Mountain is about 1400 rad an hour
at which level you should see no effect on passive materials based on
the evidence from stainless steel, titanium, and some nickel alloys. The
approximate half life is roughly about 50 to 75 years which means it
should go down by a factor of 2 in less than 100 years. So, over a few
hundred years, this should decay to effectively an insignificant level.

To put that into context with hydrogen peroxide, a dose rate of 10^4^
rad an hour, which is approximately what you expect on this container,
the models would predict about 10^-5^ or less moles per liter of
hydrogen peroxide. So, it should go down from that level even if you wet
the waste container in the beginning. Now, people have tried to simulate
the radiation effect by adding hydrogen peroxide to experiments with
passive materials and the only time they could find a shift in the
corrosion potential to a more positive value is if they went to 10^-1^
moles per liter which is somewhere between 10^6^ and 10^7^ rad per hour
equivalent dose rate. So, I don\'t think that there is a reason to
believe that there will be significant hydrogen peroxide concentrations
from radiation dose fields.

MACDONALD: If for some reason you had a G value, radiolytic yield value,
that could give you a high concentration, I think the decomposition
reaction would\--

SHOESMITH: That\'s a good point. We studied in real detail on fuel
because when you get inside the waste container, the radiation effect
becomes more important. Where we\'re having a real problem is the models
predict if you take a G value of 1, which is what the model would give
you, all our experiments will tell us that all we can measure is
something which is 2 orders of magnitude less than that. We attribute
most of that to a decomposition process which may be catalyzed by all
the impurities which exist in your solution by glass surfaces, by all
the properties of the surface itself. So, I\'m having a real problem
finding that the radiation dose rate effect is significant even at the
model prediction level. It appears to be well-below that.

BULLEN: Roger Newman, go ahead?

NEWMAN: I\'m sure your numbers were correct there, but I can certainly
assert, if that\'s the right word, that one part per million hydrogen
peroxide will significantly ennoble the open circuit potential of
stainless steel in a whole variety of oxygenated solutions. So, I\'m not
sure where that 10^-1^ moles per liter comes from. That doesn\'t sound
right to me.

SHOESMITH: Well, this comes from work by George Marsh and Bob Glass,
both on stainless steel, who saw no effect on the corrosion potential at
those high concentrations.

NEWMAN: Well, I mean, it\'s well-known in a variety of industrial
contexts that once the hydrogen peroxide concentration gets to a few
parts per million that it will dominate oxygen as the main thing
determining the corrosion potential. Now, whether it goes transpassive,
I\--

SHOESMITH: Well, I have to argue with you, Roger, because we see exactly
the opposite effect on uranium dioxide where the decomposition of the
hydrogen peroxide leads to oxygen being the oxidant, not hydrogen
peroxide. The oxidant dominates in that particular case. Now, that is a
catalytic surface for decomposition of peroxide.

I just wanted to also address the point about the blue film. You can see
that on titanium in hydrogen peroxide roughly around the 200ppm that you
mentioned and there is an enhancement of corrosion rate which is roughly
a factor of 2 to 3 in that particular case over the short term. In the
long term, they tended to accumulate salts in the porous deposits which
tended to block the corrosion of the titanium.

NEWMAN: Well, the reason is completely different in that case. In the
case of titanium, the peroxile, if that\'s the right word, the hydrogen
peroxide anion, HO~2~ minus, is complexant. It forms a stable, soluble
complex with titanium. So, that\'s a different effect from something
which is due to the peroxide acting as an oxidant on the corrosion
process. But, I guess I\'ll just have to agree to disagree with you and
suggest that we go and do the experiment because I think my colleagues
in a certain large British-Dutch company that makes soap powder would
strongly disagree with any assertion that low levels of peroxide don\'t
affect the corrosion potential.

SHOESMITH: Is the difference between us the pH? Are you talking
extremely alkaline solution?

NEWMAN: This is mainly in the high pH environments, yeah.

SHOESMITH: Okay.

NEWMAN: And the blue stainless steel is\--that only happens in high pH
environment.

SHOESMITH: Yeah. Most of these observations are from pH 10 down that
I\'m talking about.

NEWMAN: Well, yeah, it could be quite critical as to what the pH is, but
I think a little competitive experiment would be in order there
(laughter).

SHOESMITH: I just wanted to address also the issue of the deposition of
radiation energy directly in the oxide film. There is a difference
between light and gamma radiation. It\'s about three orders of magnitude
difference in energy. So that the efficiency you get for depositing the
energy from light to form hole-electron pairs is quite efficient. For
gamma radiation, it\'s orders of magnitude less efficient because the
energy is too high to deposit as it goes through the thin film. We think
we see this on uranium dioxide. We can\'t be certain. Which means that
you need a much higher gamma dose rate to see the production of
hole-electron pairs than you do a light intensity.

BULLEN: Thank you, David. Gustavo had a question or a comment. Go ahead?

CRAGNOLINO: I have a comment on the dilution data that is reported by
precisely the DOE regarding this issue of the additional hydrogen
peroxide. In what is called in the table that Jerry Gordon presented
before, the saturated, no, the simulated concentrated water at 25
degree, the corrosion potential increased from -230 to -40 millivolt in
the silver silver chloride scale is -275 to -85 in calomel with the
addition of 72 part per million of hydrogen peroxide.

SHOESMITH: I was unaware of that result.

CRAGNOLINO: And, in the acidified condition, that is because there was
this question of low pH, they increased from -80 to 150. In the silver
silver chloride\-- means -125 to 105 in the calomel that we are more
familiar with. 345 millivolt difference in between the two scales with
the same addition of 72ppm. We have measured these using precisely long
ago the effect on Alloy-825 by using 5ppm. That was the number that came
from the Glass and Konynenbeurg calculation, and we got increase of
about 200 millivolt, roughly, of these.

SHOESMITH: That\'s really at odds with other published numbers.

CRAGNOLINO: Yeah. This is what\--to put in context this, the problem is
that is it going to be a stable hydrogen peroxide peroxide system or, as
Digby suggests, is it going to decompose? And I think that this is what
we never able to sustain this value for a long period of time.

NEWMAN: \--oxide by decomposition. I remember there was something about
one of those studies. I don\'t remember whether it was the Marsh one or
the Glass one, which was a little fishy, and I would have to look that
up. Am I allowed to use the word \"fishy\" in this?

SHOESMITH: Ariani\'s data showed that the effect of 10 to the 6th rad an
hour improved the passivity on titanium.

BULLEN: Thank you, Dr. Shoesmith.

Alberto, did you have a few questions?

SAGÜÉS: I have a question, two questions for Digby. The second one
applies to just about everyone. The first one is specific to the point
defect model projections, which by the way, some of us are very glad to
see that the project indeed is making attempts to obtain quantitative
treatment, although we all know like in any other model, there are items
open to discussion and interpretation. But, Digby, in the most recent
calculations that you showed, what kind of steady state passive current
densities is the model predicting? Like in this one, they were using it
to look at the transition.

MACDONALD: Well, I actually fit the current density to experimental
values\--

SAGÜÉS: I guess they cannot hear you.

MACDONALD: I actually fit the model to the current density. So, you
know, it\'s not fair to use the model to predict the current density.

SAGÜÉS: Okay. So then you\'re taking experimentally\--

MACDONALD: Even I\'m not that blatant.

SAGÜÉS: So you\'re assuming then current densities. Of which order are
those?

MACDONALD: 10 to the minus 8 amps per centimeter squared at room
temperature.

SAGÜÉS: Okay.

MACDONALD: About 5 times 10 to the minus 8 at 120 C.

SAGÜÉS: So those are fairly high passive current densities compared to
the ones that may an order of magnitude greater.

MACDONALD: Well, this is pH 3. But pH doesn\'t seem to make a heck of
lot of difference.

SAGÜÉS: pH doesn\'t seem to make too much of a difference. What I\'m
saying is that that may pull down your open circuit potential, and I\'m
wondering if that would affect the point at which your transpassivity
would kick in. Because if you have a much leaner passive current, that
would work together with the oxygen couple and send the potential higher
up; right?

MACDONALD: If it\'s much lower, it will cause a small, relatively small
shift in the corrosion potential in the positive direction.

SAGÜÉS: Okay. The second question is something that you and I have
discussed on a one on one basis like a couple of years ago. But I think
that it is very important to the overall question of long-term
extrapolation. And I don\'t know, my personal impression is that if
someone would tell me, would show me a piece of naturally existing
material from a meteorite or maybe an artifact where someone, say, 5000
years ago by mistake cast a chromium iron alloy and it would show us
this shiny piece of material that happened to have been exposed to a
moist environment, not in an Egyptian tomb where everything is nice and
dry, and say, hey, this thing is passive, look, we\'re looking at it
and, darn it, here is a 5000 year old or a 50,000 year old or a 5
million year old passive layer, and this is what has been, you know, on
top of it we have some blue stuff, and so on and so on. Well, I think
that that would change, at least for some of us, that would change
dramatically the nature of the question of using a passive material for
very long-term engineering applications.

And the question that I\'m asking you is can you think of anything that
has been passive for a very long period of time, beyond the 100 years or
so time frame that we could use? And I think that a couple of years ago,
you mentioned something that many people wouldn\'t think that was
perhaps passive material. We\'re talking about, for example, iron
corroding in a regular moist environment.

MACDONALD: Well, I mean, there\'s that famous needle structure in India;
right? What\'s that called? That has an exceptionally low corrosion
rate. I would say that\'s\--and that\'s been around for a few hundred
years.

SAGÜÉS: Although one could argue that that\'s actually very slow active
corrosion in the active regime, and not necessarily passive.

MACDONALD: One could maybe debate that point. You know, unfortunately,
we don\'t have native chromium around. Chromium is too active. I\'m not
even sure where there\'s any native nickel. Is there native nickel
around?

SAGÜÉS: There are iron/nickel alloys naturally occurring. It\'s called
Josephinite. And that material is available as the native alloy. Whether
that is present in the natural environment in a passive state, or it has
been in a state of very low active dissolution, is another question. And
that\'s something that is being investigated by a number of \-- or by a
few people right now.

But what I wanted to ask you specifically, and also I would like to ask
if there is any member of the panel here who may have an inkling of
something that may have remained passive for extremely long periods of
time.

MACDONALD: Okay, let me see if I can answer that as follows. In many
situations, the passive film on a metal is in a metastable state. And
you can see that from the Pourbaix diagram. In fact, it\'s in your
explanation of Faraday\'s famous experiment. In about 1830, or sometime,
Faraday carried out his famous experiment of placing a piece of iron in
nitric acid and finding that it didn\'t dissolve, and then\--in
concentrated nitric acid\--, repeated the experiment, and I actually
looked it up in an encyclopedia, by the way, and he put the same piece
of iron in dilute nitric acid, and it dissolved.

And, of course, the concept of acids had only recently have been
developed, and he didn\'t have a pH meter or didn\'t have a reference
electrode or anything like that, so he made a guess that the surface had
been oxidized. Okay? But what he didn\'t know, and of course this had to
wait until Marcelle Pourbaix created his potential pH diagrams, and
I\'ll draw it for iron, we commonly label this as the stability region
of iron, and this as the stability region of magnetite, Fe2O3, and even
now you\'ll see people saying, aha, this is the potential, this is the
pH. Aha, we\'ve got a point here, it\'s active dissolution. Well, that,
of course, is not true, because Faraday was actually up here somewhere
in the concentrated nitric acid, and it didn\'t dissolve.

And the reason for that is that if you extrapolate this line here, that
extrapolation of the iron/magnetite line into this stability region
gives you the condition for the formation of magnetite as a metastable
phase on the surface. Provided you\'re at a potential above this dotted
line, magnetite can form as a metastable phase. Okay? Whether it does
form or not depends upon the kinetics; the rate of formation versus the
rate of dissolution. And that\'s where a lot of our passive materials
operate. They operate with metastable passive film.

So, you know, passivity is a somewhat tenuous phenomenon, looked at that
way, but nevertheless, it appears to be quite effective for many
systems.

NEWMAN: You\'re sure it\'s not the second line?

MACDONALD: I\'m sorry?

STREHBLOW: Shouldn\'t it be the stability between the formation of iron
3 oxide gamma Fe2O3 from magnetite, which is then causing the metastable
situation?

MACDONALD: Yeah, if I extrapolate this line here\--

STREHBLOW: I think the Pourbaix diagrams in this regard are even
misleading, because, Digby, because it is a question of kinetic
stability, and not of thermodynamic stability.

MACDONALD: Oh, no, it\'s metastability.

STREHBLOW: You call it metastable. I would call it kinetic stability
because of dissolution rate or transfer rate of cations into the
electrolyte is so extremely slow.

MACDONALD: The correct term is metastability. It\'s a metastable film.
Okay? And if the rate of dissolution is high enough the phase
disappears, passivity disappears.

STREHBLOW: Magnetite will dissolve immediately, and I think this goes
back way in the Fifties, that Fetta (phonetic) tried to find even the
magnetite formation by transient measurements, and he was not successful
because FE304 is dissolving immediately.

MACDONALD: The rate of dissolution of magnetite has been measured under
these circumstances, and it\'s on the order of about .01 angstroms per
hour. And at the same time, of course, you\'re forming magnetite at the
metal/film interface. And so the magnetite layer moves into the metal.

STREHBLOW: It is there, and then FE304, you have to\--you need it,
otherwise you would dissolve the whole thing, and then you have active
dissolution.

MACDONALD: No, it\'s a metastable film.

BULLEN: Bullen, Board. We could actually\--Susan, do you want to
comment?

SMIALOWSKA: I would like to say that if you would like to have the metal
with good oxide film take tantalum. You will not have dissolution in
acid, not dissolution in neutral, not dissolution in alkaline.

BULLEN: Okay.

MACDONALD: But the point I want to make is that, you know, this is the
region where the film is thermodynamically stable. It doesn\'t
necessarily mean it will produce a passive surface, because passivity is
a kinetic term. Okay? It describes a kinetic situation. It doesn\'t
describe a thermodynamic situation.

And, of course, you are able to use iron based alloys, chromium based
alloys under conditions where the oxide is not thermodynamically stable,
because it forms as a metastable phase. And that led to my remark that
passivity is a somewhat tenuous phenomenon, but it seems to be very
effective. After all, we have a metals based civilization.

SAGÜÉS: Yes. Well, the society is going to have to make the decision as
to how tenuous this type of phenomenon is, because it\'s a tremendously
important decision that would affect our energy future. And one of the
reasons we\'re having this meeting is partly to establish how tenuous
and how useful, even if it is tenuous, it may be. I appreciate your
comments.

BULLEN: Dr. Davenport had one small one she said, small.

DAVENPORT: I just don\'t think we should get too carried away with
Pourbaix diagrams and thermodynamics here, because if we look at the
passive film on iron, the stuff that we\'ve done show that it isn\'t,
you know, hematite or magnetite, as you\'ve shown there, it\'s a
different phase. So I think we should take all of this with a bit of a
pinch of salt, and I think we should\--

MACDONALD: But the principle is correct.

DAVENPORT: Yeah. But I think that what\'s going to really affect things
is the dissolution of the films. We do have to look very carefully at
the kinetics there.

MACDONALD: Yeah, but the principle is correct. Passivity is not a
thermodynamic term. It\'s a kinetic term. It can occur because of a
thermodynamically stable film, or a metastable film.

BULLEN: Alberto, did you have a brief comment?

SAGÜÉS: No.

BULLEN: Okay. Well, we may want to continue this over some fermented
beverages a little later on this evening.

But I would like to turn the microphone over to Professor Craig. And
even though we have no one signed up for public comment, we still have
to ask on the record if we have public comment. And you can do it from
your seat, or you can go to the podium, whichever you\'d like. Paul?

CRAIG: There\'s something else I can do, however, prior to doing that.

BULLEN: Oh, go right ahead. I gave the meeting to you, Paul.

CRAIG: Since my hand was up, albeit not very far, a moment ago. By the
way, do we have people who want to speak? Let\'s do that. Are there
members of the public here who wish to speak?

(No response.)

CRAIG: All right. The formal part of the public is now completed. There
are none. This means we have another 15 minutes, so I\'ll make my\--so
we have 15 minutes to talk before we break.

BULLEN: You get ten.

CRAIG: And I want two of them.

I\'ve been listening to this discussion all day, and I\'m absolutely
fascinated, and I perhaps understood 10 percent, although in an
examination, perhaps it would turn out to be only 5 percent.
Nevertheless, I did have some impressions, and I want to express those
impressions in the form of what will become a hypothesis, which perhaps
you will challenge.

Dr. Sagüés gave two examples where he thought people would probably
agree. One was on steel, and the other was on a noble metal in a Yucca
Mountain type of oxidizing environment.

We\'ve also heard from time to time about copper in a reducing
environment, which is being proposed in Sweden, for example. And a nice
thing about copper is it\'s thermodynamically stable and it exists in
nature for periods in excess of a billion years.

During the conversation today, many, many questions and issues were
raised about C-22. I did not see that there was a strong consensus that
this is a material that passes a test as easily as the iron, noble metal
and copper tests just mentioned. That didn\'t seem to be the case. Nor
did I see clear guidelines for extrapolation. The kind of theoretical
underpinnings that apply in copper didn\'t seem to emerge in the course
of the conversation.

What did emerge was that issues, a number of, many different mechanisms,
some proposed previously, some new ones that could cause problems, a
clear statement that the chemical environment matters enormously, and
the kinds of things that might build up on the surface might matter
enormously. The cycling of various sorts might matter, and that there is
an absolute necessity for consistent and superb manufacturing, both of
the material itself and for the fabrication of the welds.

Now, scientists will, of course, disagree about almost anything. That\'s
one of the things that makes science fun. What we\'re concerned about is
when the differences really matter. And the hypothesis that I want to
lay out is the differences that we heard about today are at a level of
significance that it\'s not clear to me that the optimistic conclusions
that Gerry Gordon laid out in the slide that he showed you, which was
from a presentation to this Board a couple of months ago, that those
observations and the confidence associated with those observations is
consistent with the message which I\'m hearing from this panel. My
hypothesis is that in fact those conclusions are not consistent with the
message that\'s coming out of this panel.

Perhaps I\'m wrong in this, but in any event, this is a hypothesis that
we can perhaps discuss at some point.

BULLEN: Thank you, Paul.

Any members of the panel want to respond to Paul\'s comments? Dr.
Davenport?

DAVENPORT: Yes, you may be getting an overly pessimistic view from
today\'s discussions, because effectively, what we\'ve been charged with
is coming up with possible ideas to suggest what could conceivably go
wrong. And so I think we\'re not\--I mean, I think Roger made the point
that he wouldn\'t mind having one in his back yard, but here are a few
things that might go wrong. And I think that may sum up a lot of our
attitudes here. So you may be getting an overly pessimistic view,
because we\'re trying to be a bit creative in coming up with ideas about
what might go wrong.

MACDONALD: And I\'d just like to add that I think the prediction
business is in better shape than what you probably would have concluded
from today\'s discussion. I mean, we have been able to predict, you
know, corrosion damage in nuclear reactors and the heat transport
circuits quite accurately.

CRAIG: There have also been quite a few surprises in the nuclear reactor
metals business.

MACDONALD: Yeah, that\'s because they don\'t use our methods.

BULLEN: Alberto, do you have a comment?

SAGÜÉS: Digby, I think that your statement that you have been able to
predict the damage quite accurately is well substantiated. You have a
verified prediction. What you indicated about being able to predict
quite accurately the damage evolution in nuclear reactors is well
substantiated. The difference between that and the task that we have,
that the project has at hand, is I think one of time frames. We are
talking in your case about predictions in a time frame which is in the
order of years or decades, and a time frame that permits verification of
the prediction, contrasting the predictions. We\'re talking here,
however, about a time frame of unprecedented magnitude, and that I think
is the part that demands more caution.

MACDONALD: Let me just put that up again. Okay? Where I see the
greatest, probably the greatest problem at the moment, is specifying the
future conditions.

I went out to Livermore and listened to some very fine scientists,
geologists and geochemists talking about the conditions that will exist
within Yucca Mountain. And, you know, those conditions are calculated on
the basis of very large models, very sophisticated and complex models.
But I\'m just unsure as to how accurately you can actually predict the
conditions.

Now, what is heartening in this whole thing is that the corrosion rate
is only weakly dependent upon a number of parameters. Okay? Potential
and pH, in particular, and temperature. So, provided that weakness in
those dependencies remains, then we can probably withstand considerable
uncertainty in the exact path that the repository is going to evolve
along, and come out with a reasonable prediction.

So, that\'s where I see one of the major problems. It\'s in this one,
the last bullet here, that the path to the future state is continuous
and can be specified. That\'s an absolutely essential caveat on
deterministic prediction of anything.

BULLEN: Roger?

NEWMAN: Are you sure you meant that corrosion is weakly dependent on
different parameters? You\'re talking about general corrosion then?

MACDONALD: Yes, I\'m sorry, I\'m talking about general corrosion.

NEWMAN: Okay.

MACDONALD: But it\'s not even clear, and in fact in the NERI program,
you know, we\'ve been wrestling with the question how do we actually
predict what form of corrosion is going to occur. And it\'s conceivable
that over the lifetime of this repository, there might be various forms
of corrosion occur at different times. And the question is how do you
predict that path? That\'s a pretty tough thing to predict.

BULLEN: Do we have any more comments from the panel? And having no
questions from the audience, I\'d like to, before we close, express my
appreciation to all the panel members for their patience and their
preparation for this meeting. Some of you traveled great distances to
get here, and I realize that we\'re in a time zone that\'s probably put
you at about 3:00 in the morning, and I do appreciate your ability to
stay focused and to address the issues.

We will reconvene. We\'re going to recess right now. We will reconvene
tomorrow morning at 8:30 to address question number two.

I want to tell the panel members that we are going to reconvene our
panel at the same room we had breakfast this morning at 6 o\'clock
tonight. So, the panel has about 40 minutes, and we will reconvene in
the room we had breakfast this morning.

Thank you very much, and we\'ll see you tomorrow morning.

(Whereupon, the meeting was adjourned, to be reconvened at 8:30 a.m. on
July 20, 2001.)