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| Table 1: Historical and Projected Spent Nuclear Fuel Discharges from US Commercial Reactors. [2]. |
The United States is currently the world leader in electricity generation from nuclear energy with its 104 reactors being the global high for a single country. [1] Nuclear energy has a minimal contribution to greenhouse gas emissions and global warming while providing consistent energy, day and night, rain or shine, for the lifespan of the nuclear power plant. This consistency carries tremendous value that renewable energy systems like photovoltaic arrays and wind farms cannot match. An unanticipated consequence of the U.S.'s successful nuclear power program has been the accumulation of spent nuclear fuel that sits on site, in storage, all around the nation. [2] Table 1 shows the cumulative spent nuclear fuel discharges up until 2002, and discharge projections up until 2035. Even though controversy involving high level waste always surrounds nuclear energy programs, nuclear energy will be needed by many countries for the foreseeable future. [3]
Nuclear reactors produce high level radioactive wastes which present a variety of problems that must be considered for safe disposal. [4] Some waste products will generate considerable heat as they decay while others will remain intensely radioactive for very long time periods. Because of these hazards, disposal regulations require isolation of the wastes from the public and the environment for tens of thousands of years. Some of the most concerning byproducts from spent fuel are Plutonium-239 (half-life 24,000 years), Technetium-99 (half-life 220,000 years), and Iodine-129 (half-life 15.7 million years). [4] Without a permanently safe location for these byproducts, society will have to carry the burden of storing and guarding nuclear wastes for many centuries. This turns the nuclear energy process into a moral issue involving sustainability and the fact that the power consumed today will leave radioactive garbage for future generations. [5] While the nuclear fuel cycle hardly exacerbates global warming, nuclear power still poses globally significant risks. Two that dominate the discussion are the vulnerability of spent nuclear fuel in storage pools to terrorist attack and leakage from geologic repositories that are designed to isolate high level waste from the natural environment. [3] The biggest problem is how to keep radioactive waste in storage when there is nothing that could be built that would be definitively safe until the waste becomes benign after hundreds of thousands of years. A final high level waste deposit must be absolutely reliable, because the quantities of poison are tremendous, and it must be permanently guarded which requires a society with stability that has not yet been demonstrated by humankind. [5]
Spent nuclear fuel was only intended to be stored at the reactor site for 3-5 years while it was cooled in storage pools. The U.S. follows a "once-through" nuclear fuel cycle strategy which creates a constantly increasing inventory of spent nuclear fuel in wet storage at reactor sites. [2] As time passes and no solutions for high level waste are found, it appears as though storage pools are the current and permanent location for nuclear waste. As this has become commonly accepted, high density fuel racks have been implemented in storage pools to increase the total amount of waste they can hold. Never the less, onsite storage pools are filling up because nuclear waste continues to be produced without a location to transfer it to. To help alleviate the space issue, older spent nuclear fuel is being dry stored in casks in independent spent fuel storage installations. [2] Dry storage casks can be vertical or horizontal in alignment, with the vertical casks more commonly used because they are standalone units that come with their own shielding. Horizontal casks do not have the same amount of protection and must be placed in steel lined concrete bunkers for proper safety measures. [2] The average storage time is 8-12 years for dry casks. There have not been any reported problems with this method of containing and storing spent nuclear fuel, although to determine if any degradation has occurred it would require opening sealed casks and inspecting the fuel. [2]
Neither onsite storage pools nor dry casks are sustainable high level waste disposal techniques, and because of this many alternative concepts have been studied and proposed. Some alternatives include burial in the sub seabed, launching the waste into outer space, and partitioning and transmutation. [4] Although each of these alternatives has benefits, the consensus is that the best and safest long term option for high level waste disposal is geological isolation. The U.S. Department of Energy has studied a site at Yucca Mountain, Nevada, to determine if it could serve as a geologic repository for spent nuclear fuel and high level radioactive waste. At Yucca Mountain, the repository would have the advantage of being in the desert environment where natural geologic features in tandem with engineered barriers could keep water away from the waste for thousands of years. [4] But, as it currently stands, Yucca Mountain would not be able to store all of the U.S.'s spent fuel and radioactive military waste. In 2006 in the United States, the inventory of spent fuel was approximately 62,000 metric tons, and the projected spent fuel from currently operating nuclear power plants will be at least twice this amount over their lifespans. [6] Just the current amount of spent nuclear fuel would put Yucca Mountain almost to its capacity. This means that either Yucca Mountain will have to be expanded or a second permanent storage facility will be necessary to help store the growing quantities of nuclear waste. Table 1 shows that by 2035, the total amount of nuclear waste in the U.S. is expected to increase to an estimated 104,000 tons. [2] Given the success of dry cask storage and the uncertainties around geologic repositories the Yucca Mountain Repository has been temporarily removed as a solution for high level waste. Even though there are uncertainties involved in geologic isolation, the U.S. will almost certainly need at least one in the future to store high level waste. [7] As of 2010, there is not a single geologic repository in operation anywhere in the world.
Nuclear materials generate high level waste that is extremely hazardous and capable of harming living organisms and the environment. While low and intermediate level radioactive wastes are being appropriately disposed, high level radioactive waste is still stored at temporary locations awaiting disposal at permanent facilities. [8] And still, there are no permanent facilities, even though approximately 270,000 metric tons of high level radioactive waste has accumulated in 30 countries and an additional 9,000 metric tons are being added annually. [8] Despite being in the title of this paper, high level nuclear waste "disposal" is a misnomer. [5] Even the strongest promoters of nuclear energy will not claim that ultimate disposal methods are yet achievable. Any idea conceived will have to solve problems regarding storage, guardianship, and management of the waste. [5] Without a known solution to the nuclear energy waste problem, and with continued electricity production from reactors, high level waste will continue to build up around the world. And as debates over this controversial issue continue, the waste will patiently decay as its gets passed from generation to generation for hundreds of thousands of years.
© Brett Madres. 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] A. McDonald, "Nuclear Power Global Status," International Atomic Energy Agency, IAEA Bull. 49-2, 45 (2008).
[2] E. D. Federovich, "Technical Issues of Wet and Dry Storage Facilities for Spend Nuclear Fuel," in Safety Related Issues of Spent Nuclear Fuel Storage, ed. by J. D. B. Lambert and K. K. Kadyrzhanov (Springer, 2007).
[3] "Energy Statistics of OECD Countries 2010," (OECD Press, 2010).
[4] "Radioactive Waste Disposal," in Encyclopedia of Physical Science and Technology, ed. by R. A. Meyers (Academic Press, 2001), p. 633.
[5] J. Abbotts, " Radioactive Waste: a Technical Solution?" Bull. Atomic Scientists 35, No. 8, 12 (1979).
[6] J. Bruno and R. C. Ewing. "Spent Nuclear Fuel," Elements 2, 343 (2006).
[7] "Nuclear Fuel Management and Disposal Act," S.2589, 109th Congress, 2005-2006.
[8] S. E. Hasan, "International Practice in High-level Nuclear Waste Management," in Concepts and Applications in Environmental Geochemistry, ed. by D. Sarkar, R. Datta and R. Hannigan (Elsevier, 2007).