Bulletin of the Atomic Scientists

September/October 2006


Mounting debate

"The decision-making process must be fair, open, and transparent. Yet, the drive for a Yucca Mountain repository has exhibited none of these attributes."

In "Stuck on a Solution" (May/June 2006 Bulletin), Allison MacFarlane provides an insightful and notably clear discussion of the factors contributing to the continued troubled status of the proposed national nuclear waste repository at Yucca Mountain, Nevada. It's always gratifying to those of us in Nevada when someone with a scientific background faithfully researches and reports the policy and technology quagmire that is Yucca Mountain. Unlike our European and Canadian counterparts, the United States has yet to engage in critical reassessments about potential nuclear waste disposal options.

In 1999, as governor-elect, I joined my predecessor, Governor Bob Miller, in reiterating the site's unsafe nature to Energy Secretary Bill Richardson. With the benefit of seven more years of scientific investigation, it remains clear that Yucca Mountain should have been disqualified as a repository under the Energy Department's Site Recommendation Guidelines. Instead, Energy revised the guidelines, eliminating Yucca Mountain's preestablished disqualifying conditions from the site suitability evaluation.

In 2002, Energy Secretary Spencer Abraham recommended Yucca Mountain to President George W. Bush as a suitable repository. Hence, Congress, overriding my statutory Notice of Disapproval, designated the site for a license application to the Nuclear Regulatory Commission.

To succeed in the essential task of protecting people and the environment from the unprecedented dangers of nuclear waste now and in the future, the unqualified safety of a repository is paramount. The decision-making process must be fair, open, and transparent. Yet, for the past 20 years, the drive for a Yucca Mountain repository has exhibited none of these attributes.

Kenny C. Guinn
Governor, State of Nevada

"Stuck on a Solution" gives a thorough analysis of the effort to bury nuclear waste at Yucca Mountain. It identifies many of the problems with the science underpinning the proposed repository— including the impossibility of forecasting geochemical interaction and threats posed by the area's water flow and volcanic activity.

Unfortunately, from the moment my home state of Nevada was designated as the recipient of our nation's nuclear waste, the process has ignored such science. The Energy Department overlooks the science because it wants to open Yucca Mountain at any cost, eschewing all safety and efficiency concerns. In Nevada, we do not take the health and security of our families lightly, and we will not stand silent in this battle.

Nor are we alone in questioning Yucca Mountain's feasibility. Most scientists agree that a viable, safe, and secure alternative to a nuclear waste repository at Yucca Mountain could be a reality within a decade. Already, on-site dry cask storage—one possible alternative—is in use at 34 sites throughout the country. The Nuclear Energy Institute projects that 83 of the 103 active reactors will possess dry cask storage by 2050. With this in mind, I've introduced the Spent Fuel On-Site Storage and Security Act—along with Senate Minority Leader Harry Reid. The act mandates that nuclear waste remain stored at its production facility and requires the federal government to take responsibility for possession, stewardship, maintenance, and monitoring of the waste while searching for a solution predicated on solid science. The choice is clear. We can either spend an additional $60 billion on a mountain filled with unpredictable seismic activity, or we can allocate a fraction of that money to safely store nuclear waste on-site while investing in recycling technology to turn one of the world's most toxic substances into a clean energy alternative.

Sen. John Ensign
Republican, Nevada

Allison Macfarlane misplaces the emphasis in her skepticism about performance assessment modeling at Yucca Mountain. Macfarlane rightly criticizes this repository project; but rather than sweepingly dismiss performance modeling, she should have pointed out the Energy Department's failure to craft a repository design that exploits the site's natural characteristics and employs well-understood diffusion phenomena.

In "Proof of Safety at Yucca Mountain" (October 21, 2005 Science), we addressed Energy's missed opportunity. Since the site resides 200-300 meters above the water table, movement of water in the rock is slight and occurs only through fractures. But the presence of high humidity and oxygen in repository tunnels means waste containers need protection from corrosion.

Modeling the complex corrosion process over many tens of thousands of years as it affects key elements in Energy's most recent designs—a nickel-alloy outer layer for the waste container and a titanium "drip shield" over the container—is not a credible undertaking. We advocate a capillary barrier concept. First, a layer of coarse gravel is placed around waste containers; then a layer of fine sand is draped over the gravel. Strong capillary forces in the sand would seize any water dripping from the tunnel ceiling and move it slowly away. Proof of safety turns on the gravel layer, however, where capillary forces are absent.

Ultimately, the containers fail by corrosion from the omnipresent water vapor and oxygen. But the radioactive elements that emerge to form a thin coating on gravel particles would diffuse so slowly within the gravel that they're effectively trapped. Compared to corrosion chemistry, such diffusion serves as a far simpler physical process that lends itself to laboratory mockups and extrapolations over vast periods of time. Although absolute proof of safety remains beyond reach, the capillary barrier concept deserves urgent attention and testing.

Luther J. Carter
Independent journalist, author
Washington, D.C.

Thomas H. Pigford
Professor emeritus of nuclear engineering
University of California  at Berkeley
Berkeley, California

Allison Macfarlane correctly concludes that a geologic repository at Yucca Mountain serves as "the best solution to the nuclear waste problem." However, Macfarlane errs in arguing that science does not prove Yucca Mountain's viability as a repository. Twenty years of study by more than 2,500 scientists at the most prestigious U.S. national laboratories and at the world's leading universities has overwhelmingly proved its viability.

Macfarlane similarly misses the mark in contending that performance assessment isn't a valid tool for appraising repository safety. For years, scientists have understood that they must account for a wide range of complex factors when considering the long-term isolation of nuclear waste. To do so, they've developed an analytical methodology known as safety assessment, also called performance assessment. These assessment tools include comprehensive models of all repository systems that simulate how these systems interact during a broad range of future scenarios.

The International Atomic Energy Agency, whose work Macfarlane cites to support her assertion that performance assessments don't work, actually reached the opposite conclusion. The agency devoted an entire chapter to the subject in its 2003 report, "Scientific and Technical Basis for the Geological Disposal of Radioactive Wastes," deducing, "Safety can be evaluated ... using Safety Assessment/Performance Assessment as the main tools." Based on this comprehensive scientific research, the nuclear energy industry believes quite confidently that Yucca Mountain meets the requirements for safely disposing of used nuclear fuel.

Rod McCullum
Director for Yucca Mountain Project,
Nuclear Energy Institute
Washington, D.C.


I appreciate Governor Guinn and Senator Ensign's sentiments, but I disagree with Senator Ensign's suggestion that reprocessing solves the nuclear waste problem. Though it might decrease the volume of high-level waste, reprocessing does not decrease its heat production—and therefore the volume required for waste disposal. Reprocessing also creates huge amounts of low- and intermediate-level waste that will require disposal at separate waste sites. Moreover, reprocessing costs more than direct disposal and creates a proliferation threat.

Rod McCullum is incorrect when he writes that I believe Yucca Mountain provides "the best solution to the nuclear waste problem." I stated that a geologic repository is the best solution, not Yucca Mountain. Moreover, his defense of Yucca based on the amount of time and money the Energy Department has spent on the project is specious. Time and money don't necessarily equal meaningful results. McCullum also misunderstands my objections to the use of performance assessment to determine Yucca's compliance with EPA standards. On thermodynamic grounds it's impossible to validate performance assessment models; therefore Energy's case supporting performance assessment results falls apart.

Finally, though interesting, Luther Carter and Thomas Pigford's idea of a capillary barrier reflects another engineered solution for a proposed nuclear waste repository with inadequate geology. Wouldn't it make more sense to select a more suitable site instead?