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| Fig. 1: Yucca Mountain (Source: Wikimedia Commons) |
One of the significant challenges of nuclear energy is the disposal of nuclear waste. High-level radioactive waste is mainly uranium fuel that has been used in a nuclear power reactor and is "spent," or no longer usable for producing electricity. Spent fuel is thermally hot as well as highly radioactive and requires remote handling and shielding. [1] Although nuclear technology has been around for 60 years, there is still no universally agreed method of disposal. The federal government voted to develop Yucca Mountain for future nuclear storage. When research for the project started the U.S. had about 5,000 metric tons of spent fuel. Today, the U.S. has approximately 70,000 metric tons of spent fuel awaiting a permanent disposal location. For awhile Yucca Mountain was thought to be the answer to this issue. [2]
Yucca Mountain is a geological disposal site. The process of geological disposal revolves around the burrowing of nuclear waste into the ground out of human reach. The waste has to be strategically protected to keep material from leaking out and contaminating the water table. The waste also needs to be fastened to the burial site and structurally supported in the event of a major seismic event, which could result in land contamination. [3] At the repository, the materials would be sealed underground inside double-walled containers, called waste packages, made of stainless steel and a corrosion- resistant alloy. In addition, corrosion-resistant titanium drip shields would be placed above the sealed containers as an added barrier to the geological water issues of Yucca Mountain. [4]
The advantages of Yucca Mountain are extensive. Yucca Mountain has an arid climate, which is optimal for nuclear waste storage. The repository is approximately 240 meters above the water table, meaning it is in the zone of aeration. Aeration brings water and air in close contact in order to remove dissolved gases. Yucca Mountain, as seen in Figure 1, is in the middle of the desert and is therefore sparsely populated. Moreover, Yucca Mountain's natural barriers of volcanic tuff and their proposed engineered barriers of titanium drip shields support its continuance. [5]
The disadvantages of Yucca Mountain are also extensive and have presented many obstacles for the geological disposal project. Yucca Mountain is located in Nevada, (the fifth highest ranked U.S. state for seismicity,) making it an undesirable location for ensuring the safety of the underground barriers that would be built to house the waste. [5,6] Aside from geological factors, Yucca Mountain has been met with much opposition from Nevadan residents who were not consulted before Yucca Mountain was selected as the government's nuclear waste disposal site. Moreover, the politicization of Yucca Mountain has made it difficult for the project to receive funding to further its construction. [6]
The issue that makes it nearly impossible to assess whether Yucca Mountain could be a permanent location is the long lasting harmful effects of radioactive waste. Radioactive waste contain isotopes that eventually decay, or disintegrate, to harmless materials but this process can take a very long time depending on the half-life of the radioactive element. For example, two radioactive materials that contribute to high-level waste are Pu-239, which has a half-life of 24,000 years. [1] The fact that any location in America could undergo several monumental environmental changes during the time it takes for these radioactive elements to decay makes it very difficult to both select a permanent disposal location and to build a structure that could withstand such a large time span.
© Ramona Greene. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Backgrounder on Radioactive Waste," United States Regulatory Commission, April 2015.
[2] J. Werner, "U.S. Spent Nuclear Fuel Storage," Congressional Research Service, R42513, May 2012.
[3] S. Ali, "Nuclear Waste Disposal Methods," Physics 241, Stanford University, Winter 2011.
[4] L. J. Carter and T. H. Pigford, "Proof of Safety at Yucca Mountain," Science 310, 447 (2005).
[5] R. P. Rechard, G. A. Freeze, and F. V. Perry, "Hazards and Scenarios Examined for the Yucca Mountain Disposal System for Spent Nuclear Fuel and High-Level Radioactive Waste," Reliab. Eng. Syst. Safe. 122, 74 (2014).
[6] T. Gomez-Franco, "Yucca Mountain," Physics 241, Stanford University, Winter 2017.
