Institute for Energy and Environmental Research
Yucca Mountain is located in southern Nevada about 100 miles northwest of Las Vegas. It is on the edge of the DOE's nuclear weapons testing site, where about 700 announced underground nuclear test explosions have taken place to date.
The geologic formations beneath Yucca Mountain are made of a material called "volcanic tuff," formed from volcanic eruptions occurring between eight and 16 million years ago. The water table is deep, lying as much as 760 meters (2,500 feet) below the surface. Because the water table is so deep, the repository can be constructed above it, in the "unsaturated zone." The DOE believes that the low rainfall (about six inches per year) and high evaporation rate mean that there would be little percolation of water downward through the rocks to the water table.71
The Yucca Mountain site is slated for a multi-billion dollar site characterization process to collect data and examine whether it is suitable for a repository. After this process, if the DOE believes that the site is suitable, a license will be submitted to the NRC for construction of a repository.
However, a number of factors relating to both technical and managerial aspects of the Yucca Mountain repository program point to problems inherent to the site, as well as to the way the overall program is proceeding.
Three major technical issues raising serious questions about site suitability are geological complexity, the hydrology of the site (i.e. the behavior of water), and mineral resource concerns.
On the subject of geological complexity, there are at least two prominent concerns:
An NRC memo noted that these data "strongly suggest that the various probabilities (and consequences) which have been used for volcanic disruption of a repository at Yucca Mountain may be in error by several orders of magnitude." 73 This is because recent volcanic activity means that future behavior is less predictable, and that there is a greater possibility of a future eruption which would threaten repository integrity.
The hydrology of the site is also an important issue, since the water is a principal potential pathway for the escape of radionuclides. There are at least three aspects to this:
An issue affecting hydrological issues in particular is the prospect of unpredictable but significant climate change. Such change, due either to human activities which contribute to the greenhouse effect or to natural climatic variation over the very long hazard-life of the waste, could significantly alter the characteristics of the ground or surface waters.
A third area of concern is mineral resources in the region. This is because potential mineral, oil, and gas resources near the site could invite future human intrusion affecting repository waste isolation.
Additional technical problems concern interactions between aspects of the Yucca Mountain site and the characteristics of the waste forms which would be emplaced there. For example, there may be problems with the disposal of vitrified high-level wastes (glass) in Yucca Mountain, and there is the possibility that carbon-14 releases from spent fuel would violate environmental standards.
A problem with vitrified glass wastes (the disposal form planned for high-level reprocessing wastes) may arise under conditions of slowly increasing humidity in the unsaturated environment at Yucca Mountain. This could provide just the right conditions for chemical decomposition of the surface of the radioactive glass waste form. Subsequent saturation of the repository (due to a rise in the water table as a result of climate change, for example), could result in rapid transport of radionuclides from the decomposed waste to the accessible environment, allowing the delivery of high doses from groundwater to individuals. 77
Recently there has been growing concern about the ability of a repository in the Yucca Mountain environment to meet the release limits for carbon-14. 78For example, a scientist from Lawrence Livermore has written that:
[I]t is unlikely that waste containers of reasonable cost could meet either the DOE interpretation of `substantially complete containment ...,' or the NRC 10 CFR 60 release rate limit [of 1 part in 100,000 per year] for carbon 14...[I]t is also not possible to give assurance that EPA 40 CFR 191 cumulative release limit of 0.1 curie [of carbon-14 per metric ton] over 10,000 years could be met. 79
This is portrayed, not as a problem for the repository, but as an example of why the current standards are too strict. The author argues that even releases of carbon-14 from the repository far in excess of the current standards would result in doses that are small in comparison to the natural background dose rate which will occur in any case. Therefore, the author writes, "it seems reasonable to conclude that the high level nuclear waste regulations should be changed to allow higher releases of carbon-14 from the repository." 80
The issue is discussed as if it were a generic problem with the high-level waste standards in general. However, it is actually a problem particular to a repository in the unsaturated zone, and in particular to one in a fractured rock zone like that at Yucca Mountain. This is because carbon-14 can most readily be transported when it is exposed to gaseous oxygen, which readily oxidizes it to radioactive carbon dioxide (14CO2), which is easily transported in the gaseous phase, especially through fractures in the rock. Such conditions would be unlikely in a saturated zone repository, where any carbon-14 escaping from the waste packaging would dissolve in the groundwater, where its release would be limited by the much slower rate of groundwater transport.
Because the release of gaseous nuclides is likely to be a broader problem for a Yucca Mountain repository, we may expect to see an increasing amount of pressure on regulatory agencies from the DOE and nuclear industry sources to relax the release limits contained in environmental standards, not only for carbon-14, but for other gaseous radionuclides as well, such as iodine-129.
This growing pressure to relax the standards to accommodate the particular nature of the Yucca Mountain site is instructive, especially in light of ongoing DOE assurances that actual construction of a repository at Yucca Mountain is not foreordained, and that it is just a candidate site that will be selected only if it is suitable. A consistent criticism of the 1987 law which targeted Yucca Mountain as the only site for characterization has been that once billions are invested in the site, the institutional momentum to build a repository there will be enormous, regardless of the outcome.
Apart from the inherent technical difficulties associated with the site, the DOE's management problems are also causing difficulties for the project. DOE management has been so far from exemplary that even the Edison Electric Institute which represents nuclear utilities in Washington, D.C. said in 1989 that "we are very concerned that the DOE has spent $2 billion of our money already and just seems to be getting more and more behind." 81
Recently the NAS Board on Radioactive Waste Management criticized the whole DOE approach at Yucca Mountain, as well as NRC regulations governing characterization and licensing, as overly rigid and inflexible. Although the Board endorsed the concept of deep geologic disposal as "the best option for disposing of high-level radioactive waste," it said that the U.S. was taking an approach that "is poorly matched to the technical task at hand." 82 The Board said that the program as conceived and implemented would be unable to respond to the new information or surprises that were bound to arise from any new technical undertaking of such magnitude. The NAS Board stated that it "is particularly concerned that geological models, and indeed scientific knowledge generally, have been inappropriately applied.... In the face of public concerns about safety... geological models are being asked to predict the detailed structure and behavior of sites over thousands of years. The Board believes that this is scientifically unsound and will lead to bad engineering practice." As the NAS Board wrote:
The U.S. program is unique among those of all nations in its rigid schedule, in its insistence on defining in advance the technical requirements for every part of the multibarrier system, and in its major emphasis on the geological component of the barrier as detailed in 10 CFR 60. In this sense the government's HLW program and its regulation may be a `scientific trap' for DOE and the U.S. public alike, encouraging the public to expect absolute certainty about the safety of the repository for 10,000 years and encouraging DOE program managers to pretend that they can provide it. 83
Much of the Board's criticism was directed at the current program's inability to deal with or even properly recognize the technical uncertainties inherent in building a repository. The Board said that the DOE's presumption behind the use of huge databases and computer simulation models seemed erroneously to be that more information and detail would lead to decreased uncertainty. The Board pointed out that this presumption is in contradiction to experience with how scientific and technical knowledge in general advances:
The studies done over the past two decades have led to the realization that the phenomena are more complicated than had been thought. Rather than decreasing our uncertainty, this line of research has increased the number of ways in which we know we are uncertain. This does not mean that science has failed: we have learned a great deal about these phenomena. But it is a commonplace of human experience that increased knowledge can lead to greater humility about one's ability to fully understand the phenomena involved.84
The NAS Board calls for "major changes in the way Congress, the regulatory agencies, and [the] DOE conduct their business," suggesting an alternative approach that recognized the uncertainties in repository development, and was designed for dealing with them, rather than pretending they can be removed, thereby increasing the likelihood of failure when they are encountered.
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Last Updated October, 1996
71. DOE 1988a, p. 15.
72. As reported by Wald 1989, p. A1.
73. Trapp.
74. Nevada 1989.
75. Szymanski 1987.
76. NAS 1983, pp. 185-186.
77. Makhijani 1990.
78. ADL 1990; DOE 1990e.
79. Van Konynenburg 1991, p. 316.
80. Van Konynenburg 1991, p. 317.
81. As quoted in Warren 1989, p. 32.
82. NAS 1990, p. vii.
83. NAS 1990, p. 1.
84. NAS 1990, p. 4.