1. Nuclear Waste Not Mac Os Pro
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Gregory Tuayev-Deane
May 19, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018

Introduction

Fig. 1: The nuclear fuel cycle. [2] The post-reactor process is particularly important. (Courtesy of the NRC)

Nuclear waste refers to the materials derived from nuclear processes that are either innately radioactive themselves or have been contaminated by other radioactive elements. There is much debate over how this waste should be disposed of and this is especially true in the case of high level waste (HLW). The section below gives more detail on classifying nuclear waste.

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  2. When handled properly it doesn't. The small amounts that do reach the environment are insignificant compared to the large amounts of naturally occurring radioactive materials already in the environment: uranium, thorium, potassium-40, carbon-14, r.
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The popular misconception is that because certain parts of nuclear waste remain radioactive for billions of years, then the threat must be sustained for that period. However, this is not the case. Whilst remaining weakly radioactive for a few hundred thousand years, the radioactivity from the main component of the waste which could cause health.

High level waste can be further classified into two categories: the transuranics which result when uranium absorbs one neutron but does not fission and turns into mostly plutonium, americium and curium, and the actual products of fission. [1] The actual fission products tend to decay rapidly after creation and those products that decay slowly do not usually pose much of a hazard. Therefore, the challenge in waste disposal is a result of the creation of the transuranics.

Ways of Classifying Nuclear Waste

  • Low Level Waste is the type of waste generated by hospitals and industry and is comprised of clothing and tools with short-lived radioactivity. Because of the low levels of radiation, special shielding is not required during handling and it can be disposed of in near-surface sites. [2]

  • High Level Waste contains products of fission and transuranic elements generated by the reactor. The heat it produces is significant and so both cooling and shielding are required for its storage. Fission products such as Cs-137 and Sr-90 (with half-lives of roughly 30 years) account for most of the heat and penetrating radiation initially produced. Transuranics, which have longer half lives (24,000 years for Pu- 239), account for most heat produced after 1000 years. Initial cooling is usually achieved by under-water storage on-site at the reactor facility in spent fuel pools with a typical water depth of 40 ft. [2]

    • Current Methods of Handling Waste

    Fig. 2: Deep Borehole. [13] (Courtesy of the DOE)

    When nuclear fuel is removed from a reactor, it has usually undergone only ~6.5% burn-up meaning that only 6.5% of the atomic fuel is 'burned' or converted to fissile plutonium. The reason for the low burn-up rate is that there comes a point when the levels of fission fragments and heavy metals do not allow the reaction to take place as easily (reduced nuclear cross section) as before and it may no longer be economical to continue extracting energy from those fuel rods. [3] At this point energy is still being emitted from the fuel rods both in the form of alpha,beta, and gamma radiation and in the form of heat. Due to the heat produced, the fuel is usually stored temporarily under large water ponds which are cooled by heat exchangers and act to absorb radiation. As spent fuel pools near capacity, older spent fuel is moved into dry cask storage. The industry norm storage time is about 10 years althought the NRC has authorized transfer as early as three years. [2]

    After being stored, the fuel can either be reprocessed which aims to recover and recycle the usable portion of the fuel or it can be stored in a facility designated for long- term disposal. This process is visualized in Fig. 1 in the post-reactor stage of the cycle. [2]

    Used fuel is typically comprised of Uranium, long-lived actinides such as plutonium, and unusable waste. Reprocessing is used to recover much of the useful portion of the spent fuel by separating fission products from residual uranium and plutonium which can be used again as fuel. [4]

    The issue of disposal stems from the 4% waste mentioned above which, after being dissolved in acid is now in liquid form. It can then undergo vitrification where it is heated strongly to produce a powder which can be mixed with Pyrex glass, allowing it to be more safely stored in the event of water intrusion into the repository. [5] However, there are currently no facilities where this waste can be disposed of. It is simply stored in reinforced concrete casks with the hope that it will one day be reprocessed. The need for disposal has also not been very dire yet since only relatively small volumes of waste have been produced.

    Yucca Mountain

    In the USA, one potential site for long-term storage has been identified as a geological repository by the DOE since the 1980's. Yucca Mountain lies on federal land in Nevada, 90 miles northwest of Las Vegas. [6] Currently, a total of 70,000 tons of HLW are scattered across 39 states in cooling ponds, some of which are located near to rivers or on water tables. However, moving it all to a central location at Yucca Mountain has been controversial and met with much opposition from the state. This opposition stems from the fact that between 1 and 7 shipments would be required across the nation's highway/rail system and directly through Las Vegas for the next 24 years. [7]

    Big Thinking Ideas for Disposal

    Reducing Waste in the First Place

    The methods above focus specifically on storing and disposing of waste products of nuclear reactors. However, there has also been significant investment in finding ways of reducing the amount of waste created in the first place.

    There are currently 55 nuclear startups with $1.6 billion in funding. The nuclear sector is very restrictive and presents great barriers to new players because of the history of the NRC (Nuclear Regulatory Comission) as an entity intended to thwart nuclear arms proliferation and not one that is focused on engaging with innovative entrepreneurs. [10] The two companies below have received significant publicity for their novel approaches to producing less waste.

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    Transatomic Power - Founded in 2011, this company aims to use novel designs and materials to improve the molten salt reactor in order to use nuclear waste as a power source. [10] In March 2014, the company published a white paper claiming that their design could generate up to 75 times more electricity per ton of mined uranium than typical LWRs. This claim prompted an analysis by MIT nuclear science professor Kord Smith in which it was later found that the reactor design would improve efficiency by more than a factor of two, which would still be a great accomplishment. Even this would reduce waste by 53% compared to today's LWRs. Other questions have arisen surrounding the technology's ability to sustain a fission chain reaction using only spent fuel but the company has made its technical analysis public information to invite further analysis. [11]

    Terrapower - is pursuing a novel type of reactor the travelling wave reactor which uses nuclear waste as a power source. Molten chloride is used as both the coolant and medium for the fuel. The nuclear reaction moves like a standing wave through the fuel core converting uranium to plutonium. The company found attractiveness in the use of molten salt reactors, such as chloride, due to their innate safety and economic advantages over conventional reactor designs. If a meltdown were to occur, the molten salt fuel could be moved to underground storage without any need for pumping equipment, where it would cool down. Other advantages of chloride salt reactors outlined by Terrapower's Innovation Director include high power density and efficiency, high solubility of uranium in the chloride solution, significantly less waste, and no longer needing ongoing uranium enrichment after startup which reduces concern over proliferation. [12]

    © Gregory Tuayev-Deane. 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.

    References

    [1] W. Hannum, G. E. Marsh, and G. S. Stanford, 'Smarter Use of Nuclear Waste,' Scientific American, 26 Jan 09.

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    [2] 'Radioactive Waste,' U.S. Nuclear Regulatory Commission, April 2015.

    [3] 'Technical and Economic Limits to Fuel Burnup Extension,' International Atomic Energy Agency, IAEA-TECDOC-1299, July 2002.

    [4] P. Wang, 'La Hague Nuclear Recycling and Reprocessing Plant,' Physics 241, Stanford University, Winter 2017.

    [5] I. Chen, 'Nuclear Waste Glasses,' Physics 214, Stanford University, Winter 2011.

    [6] J. Garcia, 'The Yucca Mountain Nuclear Waste Repository,' Physics 241, Stanford University, Winter 2012.

    [7] R. Leung, 'Yucca Mountain: Transporting Nuclear Waste May Put Millions at Risk,' CBS Sixty Minutes, 23 Oct 03.

    [8] S. Ali, 'Nuclear Waste Disposal Methods,' Physics 241, Stanford University, Winter 2011.

    [9] K. Peek, 'Seven Big-Thinking Proposals For Dealing With Nuclear Waste,' Popular Science, 13 Jul 10.

    [10] K. Fehrenbacher, 'How Startups Can Save Nuclear Tech,' Fortune, 6 Jul 15.

    [11] J. Temple, 'Nuclear Energy Startup Transatomic Backtracks on Key Promises,' Technology Review, 24 Feb 17.

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    [12] R. Martin, 'TerraPower Quietly Explores New Nuclear Reactor Strategy,' Technology Review, 21 Oct 15.

    [13] 'Deep Borehole Disposal of High-Level Radioactive Waste,' Sandia National Laboratory, SAND2009-4401, August 2009.

    With the Trump-Kim Summit fresh in our minds, Americans are ready to confront nuclear challenges that have been on hold for decades. What many may not realize is that one of the biggest challenges is on the home front. Since the Manhattan Project officially began in 1942, the United States has faced ever-increasing stores of nuclear waste. Nuclear security expert Rodney C. Ewing, a professor of geological sciences in the School of Earth, Energy & Environmental Sciences (Stanford Earth) discusses how the United States' failure to implement a permanent solution for nuclear waste storage and disposal is costing Americans billions of dollars a year.

    Where does our nuclear waste come from, and what is being done with it?

    Broadly speaking, there are two types of nuclear waste.
    The first is spent fuel from nuclear reactors used to generate electricity. Those reactors have left us with about 80,000 metric tonnes of used spent fuel, and we don’t have a way forward for the disposal of this waste. It’s stored at more than 75 sites in 35 states around the country, so many of us have some in our state, including California.

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    The second category is the waste generated by our nuclear weapons complex. That defense waste has accumulated since the earliest days of the Manhattan Project. The highly-radioactive waste from chemical processing is mainly stored in very large metal tanks. They are located at the Savannah River site in South Carolina, the Hanford site in Washington State, at Idaho National Laboratory in Idaho, and Nuclear Fuel Services site at West Valley in New York State.