Nuclear Waste Panel Warns of Hot Storage at Yucca Mountain
WASHINGTON, DC, June 16, 2004 (ENS) - Plans to store high-level nuclear waste deep under Yucca Mountain at temperatures greater than the boiling point of water have caused the scientific group charged with reviewing the repository's development to raise red flags.
In its latest report to Congress, made public on June 8, the Nuclear Waste Technical Review Board warns that if the Department of Energy (DOE) implements its current high temperature repository design, the waste packages will corrode and release radiation into the environment.
"Because of the seriousness of these corrosion concerns, the Board strongly urges the DOE to reexamine the current repository design and proposed operation," the group states. "The Board believes that the high temperatures of the current design and operation will result in perforation of the waste packages, with possible release of radionuclides."
During the time covered in this report, January through December 2003, the Board was chaired by Dr. Michael Corradini, who also chairs the Department of Nuclear Engineering and Engineering Physics at the University of Wisconsin. Dr. Corradini resigned on January 12, 2004, leaving the Board without a chairman until a replacement is appointed by the President.
Dr. Mark Abkowitz at Vanderbilt University, Dr. Daniel Bullen of Iowa State University, Dr. Thure Cerling of the University of Utah, Dr. Norman L. Christensen, Jr. of Duke University, Dr. Paul Craig of the University of California-Davis, Dr. David Duquette of Rensselaer Polytechnic Institute, Dr. Debra Knopman of the RAND Corporation, Dr. Ronald Latanision of the Massachusetts Institute of Technology, Dr. Priscilla Nelson of the National Science Foundation, and Dr. Richard Parizek of Pennsylvania State University were all members of the Board at some time during 2003 and their names are on the report.
In its latest report to Congress, the Board says that in the year following Congress’s approval of the Yucca Mountain site for development of a repository in July 2002, the Board focused on evaluating the DOE’s analysis of how corrosion-resistant its Alloy 22 waste package was likely to be.
Alloy 22 contains chromium, molybdenum, and tungsten and controlled iron, and is resistant to both oxidizing and reducing acid environments as well as those containing mixed acids. It is used in the chemical processing, pollution control, flue gas desulfurization, waste incineration, and pulp and paper processing industries.
But the Board expressed detailed concerns about corrosion of the alloy in the high temperature environment proposed for storing the nuclear waste. "Localized corrosion processes are particularly insidious because initiation is difficult to predict and propagation rates can be very rapid," the Board states in its report.
"Data emerging both from the DOE’s Yucca Mountain Project and from the Nuclear Regulatory Commission’s Center for Nuclear Waste Regulatory Analyses (CNWRA) suggest to the Board that crevice corrosion of Alloy 22 is likely to begin during the thermal pulse - the first thousand years after repository closure."
The Board warned that corrosion would form in the crevices of the waste packages even at temperatures below the peak temperatures on the waste package surface expected in the DOE’s proposed repository design.
"Crevice corrosion, a form of localized corrosion, initiated during the thermal pulse is likely to propagate during the remainder of the thermal pulse and also is likely to continue even after the thermal pulse has passed," wrote the Board.
Work at the Center for Nuclear Waste Regulatory Analyses and elsewhere indicates to the Board that welds and thermal treatment - aging - increase susceptibility to crevice corrosion.
The DOE’s modified waste package design has both welded areas, such as closure welds, and many other features that offer opportunities for crevice formation, the Board warned and recommended that the waste packages be redesigned to reduce or eliminate areas of increased susceptibility to localized corrosion.
In its report, the Board noted that the DOE believes that the conditions in the repository would not promote significant corrosion. The DOE points to data, gathered using thermogravimetric apparatus (TGA), to demonstrate that the conditions necessary to initiate localized corrosion will be present only briefly.
But after evaluating these data the Board "found them inadequate to support the DOE’s claim."
The materials used in the DOE corrosion tests were not representative of those that would actually be present in the repository, and the tests were run only over narrow ranges of temperature and relative humidity, the Board complained.
The Board said that it "believes that total system performance assessment should not be used to dismiss these corrosion concerns."
The report repeatedly advises the Energy Department to rethink its high temperature repository design, relying in part on visits made by Board members to Belgium, France, Switzerland, and Britain in October 2003.
"Of the countries visited by the Board that have looked at repository design issues, none proposes keeping temperatures at or above boiling for as long as the DOE proposes," the report states.
The Board pointed out that Belgium changed its repository design to avoid keeping the waste at such high temperatures. "In changing its reference design from a high to a low temperature, the Belgian program noted that, if temperatures are kept below boiling, it will be simpler, easier, and less complicated to understand natural processes and the behavior of materials and to make predictions."
"The experience of the Belgians illustrates that repository designs and operations can and will evolve. Such evolution is to be expected. Because pressure to build a repository is not strong in this country, the changes do not appear to be viewed as a failure of or a roadblock to the program. Rather, the changes seem to be part of an incremental learning process of developing a design that is both safe and implementable," the Board wrote.
During 2003, the Board also examined the DOE’s efforts to increase confidence in its estimates of repository performance, the DOE’s plans for developing a system to transport high-level waste and spent nuclear fuel from sites where those materials are currently stored to Yucca Mountain, the DOE’s analysis of seismicity issues associated with repository design, and the DOE’s projections of the consequences for waste isolation and containment of igneous activity at Yucca Mountain.
Read the entire Nuclear Waste Technical Review Board 2003 report online at: http://www.nwtrb.gov